Evinrude 31.8ci Mod Advice

[Emustard]

I posted a form a couple of months ago asking for peoples info on mods to a evinrude 31.8 cubic inch. over the winter we did some modifying, and were a little surprised with our results. we thought we would be in the high 6000rpms with the 10-15 ss and we were not close. what do you think our problem is?? I added some pictures so you can see how our rig is set up. Boat is 14 feet long with one person in it and motor and gas is 600lbs.

NOW
compression 147psi top, 152psi bottom
port and polished intake and exhaust
Wiseco pistons
intake manifold increase in size
boyesen reeds and opened reed stops
tuner shorted an inch
vent exhaust above the water
1.50inch carb 83Main jet 40air jet


BEFOR
before we were running 125psi in both cylinders and the boyesen reeds. that's it
1.50inch carb 77Main jet 40air jet

The props are a stock evinrude 10-13 aluminum and a solas Stainless steel 10-15

OLD TEST
aluminum 10-13 prop @ 32mph at 6150 RPM (1 person)
4people in the boat 100lb of gear 29mph @5800 RPM

stainless steel 10-15 @ 33mph at 5550 RPM (1 person)
3people in the boat 29mph @5200 RPM

NEW TEST
stainless steel 10-15 @ 34 5600 RPM (1 Person)
3 people in the boat and 100lb of gear 31mph @5300RPM

On the new test the engine has all kinds of power getting up and out of the hole, a lot quicker then before also runs the best it has ever but still thought it would have more power at top end.

53910539115391253913539145391553916

[omcstratos]

It looks like you could raise the motor up on the transom at least 2 or 3 inches, That will gain some in the top end.

[Emustard]

I moved the motor up an inch with a block of wood and it would blow out on turns and off the blocks if I full Throttled it quickly, so I removed it. This was with the stainless steel prop.

[omcstratos]

You are reaching a pretty good speed for that motor and boat. You would need to jack the motor up and try a few props with a little more cupping if you are looking for more speed. The more prop out of the water usually will raise rpm's by a few hundred, just be sure you have adequate water pressure.

[TorqueXrpm]

I posted a form a couple of months ago asking for peoples info on mods to a evinrude 31.8 cubic inch. over the winter we did some modifying, and were a little surprised with our results. we thought we would be in the high 6000rpms with the 10-15 ss and we were not close. what do you think our problem is?? I added some pictures so you can see how our rig is set up. Boat is 14 feet long with one person in it and motor and gas is 600lbs.

NOW
compression 147psi top, 152psi bottom
port and polished intake and exhaust
Wiseco pistons
intake manifold increase in size
boyesen reeds and opened reed stops
tuner shorted an inch
vent exhaust above the water
1.50inch carb 83Main jet 40air jet


BEFOR
before we were running 125psi in both cylinders and the boyesen reeds. that's it
1.50inch carb 77Main jet 40air jet

The props are a stock evinrude 10-13 aluminum and a solas Stainless steel 10-15

OLD TEST
aluminum 10-13 prop @ 32mph at 6150 RPM (1 person)
4people in the boat 100lb of gear 29mph @5800 RPM

stainless steel 10-15 @ 33mph at 5550 RPM (1 person)
3people in the boat 29mph @5200 RPM

NEW TEST
stainless steel 10-15 @ 34 5600 RPM (1 Person)
3 people in the boat and 100lb of gear 31mph @5300RPM

On the new test the engine has all kinds of power getting up and out of the hole, a lot quicker then before also runs the best it has ever but still thought it would have more power at top end.

53910539115391253913539145391553916


I've been watching this post in hopes that perhaps someone with more experience would chime in. With that said, I will address a couple of things that you've listed. First and perhaps foremost, excellent work in detail! Whether it runs or not, you've certainly spent some time on it. Very nice!
Now, of the mods you've listed.
The cylinder pressure is a good move that will help in the low to mid rpm range when it comes to needing more available torque to get a big prop to spinning. And if speed is your goal, you will need a bigger prop. But, once up to wot, I doubt the increase in pressure is going to help turn any more rpms. (Curious though, how much did you shave off the head?)
The carb mods sound good but why such a major leap on the main jet? I believe that carb is standard with a 67D jet. My guess is that it's drowning the cylinder. More fuel isn't of much use if more air isn't added to maintain a proper air/fuel ratio.
The tuner. The factory engineers developed the tuner length for good torque at or near 6000rpm. An inch is way up there. I would think trying to smooth and polish a factory tuner would serve you better. Certainly no more than about 3/8ths of an inch if you are looking to move up to the 7k mark.
As far as expectations of high rpms, that motor came from the factory with a power pack with a rev limiter. Since you didn't make mention of any changes to the ignition, I thought I would throw that out there. Most will hold the R's down in the 6000-6200 range.
As stated earlier, you are currently getting pretty good numbers out of that set-up. If speed is the goal, you will need to raise the motor. It's too low. The reason for your "blow-out" issue earlier is due to the type of prop being used. The stock design was never intended to be run at the surface. The motor will run much better if raised. The stock prop won't. Look into one of Ron's cleaver style props to correct the problem.
Well, hopefully this will give you clues as to what areas to address. Perhaps someone with more experience will chime in if my thoughts are off course as well. Good luck with that and remember, more rpm is not always the answer. You may be better off strengthening the torque at 6k and going with a bigger prop.

[Emustard]

Thank you
we shaved 30 thousands of an inch and packed the head to get our compression around 150psi.
To start off we use a blue point timing light to measure our RPMs which is very accurate so that being said the major leap in the main was because we put a 67D in and it ran a 31Mph and was to lean we confirmed this with the (spark Plugs, GPS and RPMs) we put in a 83D and we ran a 33Mph we confirmed this was our best power through (spark Plugs GPS and RPMs) we put a 87D and our speed dropped to an 32Mph, so it was running to rich we confirmed this (spark Plugs GPS and RPMs)
when you talk about the tuner and the 3/8ths of an inch you mean of polishing inside? or do you mean to shorten?
we are unsure if our engine has a rev limiter how do you know and can you remover it?
so we are going to move the engine up more we are just trying to figure out how at the moment with out a jack plate, how far should we bring it up?
we are currently looking for a new prop but are unsure what prop to go with should we go with a thru hub or over hub and if so do you thing we could go with a 16pitch cleaver over hub and keep our RPMs or will we lose More? what prop would you suggest?
do you have any ideas to get more torque? or HP

Thanks

[TorqueXrpm]

Thank you
we shaved 30 thousands of an inch and packed the head to get our compression around 150psi.
To start off we use a blue point timing light to measure our RPMs which is very accurate so that being said the major leap in the main was because we put a 67D in and it ran a 31Mph and was to lean we confirmed this with the (spark Plugs, GPS and RPMs) we put in a 83D and we ran a 33Mph we confirmed this was our best power through (spark Plugs GPS and RPMs) we put a 87D and our speed dropped to an 32Mph, so it was running to rich we confirmed this (spark Plugs GPS and RPMs)
when you talk about the tuner and the 3/8ths of an inch you mean of polishing inside? or do you mean to shorten?
we are unsure if our engine has a rev limiter how do you know and can you remover it?
so we are going to move the engine up more we are just trying to figure out how at the moment with out a jack plate, how far should we bring it up?
we are currently looking for a new prop but are unsure what prop to go with should we go with a thru hub or over hub and if so do you thing we could go with a 16pitch cleaver over hub and keep our RPMs or will we lose More? what prop would you suggest?
do you have any ideas to get more torque? or HP

Thanks

3/8ths on the tuner would be in shortening it. (You're dealing with pressure waves or pulses traveling the speed of sound. So the difference between 3/8ths and one inch can be great in terms of working for you or against.)
The limiter is built into the power pack. You might get the part number off of it and do a quick search. If it's factory original, I would say it's going to have the limiter. As for the tuner, I'd be curious as to how you came up with removing one inch. Did you get a baseline reading before cutting it? You might be better off replacing that one with a stock unit and checking it again. Just be sure not to change or adjust anything else. I have have been told by one of the old omc boys that those cross flows respond well to closing up the relief holes in the tuner. Your idle will be affected and you may end up re-jetting the carb if you go that direction. Perhaps closing all but the top two.?? As for the prop, I would highly recommend saving up for a trim plate first. With what you are reporting now, I would think you will settle in with a 16-18p prop. But only after you get the motor raised and decide between the over or thru hub design. If you are going to use the prop for all out speed with one person, the over the hub will probably be the better choice. If you will be loading the boat down from time to time, the 16 thru hub may be the ticket. Concentrate on twisting the props into the low 6k range and find the one that works. As a side note, what kind if fuel and oil ratio are you running?

[Chairman]

If the power pack is rev limited, you will see the number "6200" printed right on it. And if you do have one of these packs, there is no question about it when you hit that 6200 rpm.

We race these motors in our Mini GT (25hp) and GT Pro (30/35hp) classes. I've never had any trouble getting into the 6500 to 7000 range, and we run bone stock motors, right off the fishing boat so to speak. Ron has been working on some new props for these classes, but meanwhile many have done quite well with OMC props. A little thinning and sharpening, and some added cup will make a big difference.

Our GT Pro boats run at a minimum weight of 650 lbs. (boat, motor and driver) and run in the 45-48 mph range. On a tunnel boat you can jack the motor as high as performance dictates and still get good water pressure. On v-bottoms height is limited -- water pressure drops of very quickly.

[mobil1]

Polishing ports aint gonna do much...
Its the height, shape and angles that make the diffrence.
Calculate your compression ratio, adjust until you reached your desired values. 8.1/1 is good on europe 98 octane pump gas.
Now you shaved the head, how is your squish? 0.9mm is nice and safe.
And did you reworked the chamber of the cilinder head to its original shape?
High exhaust port means more top end but needs rpms, also less torque so you bump the compression to compensate. (Compresion ratio)
More exhaust area needs more flow of fresh gasses...
And so you go on :-) .

But a good prop and boat setup makes also a big diffrence

[Emustard]

Where would you find a non rev limiter powerpack for this engine? Because I think your right, that it won't rev past 6200.
We did not get a base line reading before, might have to get a stock tuner to test with. If we have a chance we will test blocking the relief holes in the tuner. I think we might buy a jack plate in the next week or two. And as you were saying we want a speed prop with one person in the boat so maybe are best bet is the 16pitch over hub cleaver from Ron Hill what do you think? Are his props good? Is there any body else that makes a prop like that? We are running pump has premium and 50-1 oil ratio.

[Emustard]

Thanks for the tips with the prop, I will check the rev limiter tomorrow. Where do you get as non rev limiter?
Is there anything else you do to get your boats into the 40+ mph what prop would you recommend I go with? Thru hub or over hub

[Emustard]

I will check are compression ratio I know it's 147psi top and bottom 153psi. We run premium fuel but it 94octane. We have about 1 millimetre clearance. We did not rock the top of the piston, we just reshaped the head in the chamber it's almost Identical to the high compression head OMC once offered. We are looking at getting a new prop soon.

[Chairman]

"Rapair" makes CDI modules for outboards. Look them up on Google and a number of dealers will come up. Or if looking at used ones, any 2-cylinder OMC pack with connectors compatible with your stator and coils should work. Make sure the wire harness is long enough to reach the coils.

I've had very good luck with my 10x18 Ron Hill chopper on my v-bottoms. That's an overhub prop. Not sure which is better generally, over- or thru. If you do any idling (ie trolling), the overhub will fill with exhaust and have rather little thrust.

I don't know of anyone other than Ron making speed props for these motors.

[sharpeye Mike]

Ron is your best bet and he is dedicated to the sport, go for it and I'm sure the price will be right.

[JohnsonM50]

I'm thinking your on the right track & all the advise given is good. 1 thing I know for sure is it is difficult to get real increase from the 31.8. I would suggest closing off the above water vent & try closed as it was set up for 'open'. Could be the wrong way to go. Its a 1st for me to read of closing the tuner holes too & is something I will try [Thanks]
Some older power packs are not limited, work or not? From what Ive seen they are wired the same, I eliminate plugs & hard wire them because Ive found them to fail under 50-65mph stress, gounds go bad too.
Props.. RPM's, lower pitch & or less dia will raise RPM period. Ive been pleasently surprised to get better acceleration and top speed from a good prop vs a bigger one. Another inportant thing I've learned is never think going the 'other way. on something won't work.
Reeds. On bending the dampers too far the reeds instead of curving out were hinging on the thinnest part of th petal. This experiment made the motor FAST! for about 10-15 minutes. being a metal reed I had to replace a piston. Later I tried Boyesen 2 stage & was disapointed. I removed them while intact.. too expensive for no noticable power.
On the bench & nearly done I have a .030 over 35hp. Its got square topped ports, the discoloring on the rods honed off, the piston assemblies weight balanced [a few grams off is common]. A problem being ring end gaps of .017+ on new rings usually. I bought a pair of .040 overs & cut them to fit for an .008 gap. for each top ring. I bought a set of reeds from Carlson, single stage composite. Hope they're better. The head is cut to the point where it 'touches' w/o the gasket, the gasket is .050 & the resulting squish is about .062. That might need more clearance & I'm going with new gasket [measuring from an old one].
Will it work? I'm hoping to approach if not break 70 with a Yamato hatchet 1:1 on a C hydro but no promises yet LoLs
Another thing that is FOR SURE.. All the motor mods available or inventable will be slighted by a boat not set up for maximum efficiency & a GOOD prop. Keep taking notes & Best of Luck.

[DonChichoJr.]

Good results !!
On my OMC 25 hp . I did all that mods . and found the best reeds is a CCMS with a ported cages and stock reed stoppers ( don´t mod that !!!...cost me a new sleeve!!), Cut & balance the flywheel, CDI Non limiter pack , Champion QL82C ( gapped 0.030") with a Taylor, 8mm ignition cables, exhaust releiving and a Turbo1 SS Prop ( 3 Blade). Stock timing !!! Waohhhhh!!!! and excellent Punch !

[TorqueXrpm]

I'd be interested in seeing how the reed plate was ported. Something that I've not seen mentioned concerning the intake is the two stud "ears" that protrude into the intake. It appears that they would deflect a lot of air from filling the void in the outside areas of both reed blocks. I took the time to smooth both "ears" on the sides nearest the carb and give them a more blended radius. The intake is still on the bench and I'm still getting baselines on the motor so I can't say that it will be of much benefit too me. But for you guys running 7k and above, I can't see where it wouldn't help. Has anyone cut a new blank reed plate and tried a different reed configuration? The stock design should leave a healthy sized low pressure area near the center (right behind the reed attachment screw, or between the heels of the reeds) that I can't see being filled by an incoming charge until the piston stops it's compression stroke or actually begins to compress the primary. Looks like the motor could take a deeper breath if that center area could get part of the incoming charge. .??

[JohnsonM50]

Theres not much room to port the intake, unless you got oversized reeds? The plate is beveled on the outer edge & can be beveled the full perimeter.
http://i35.photobucket.com/albums/d151/mes355/DSCN0091.jpg (http://s35.photobucket.com/user/mes355/media/DSCN0091.jpg.html)
If you look at the blue area, that can be cut back.
http://i35.photobucket.com/albums/d151/mes355/DSCN0088.jpg (http://s35.photobucket.com/user/mes355/media/DSCN0088.jpg.html)
The ears can be cut & do look like a large obstruction but won't make much difference. In fact none of this does, maybe a little but I have no accurate means to measure flow. If you look backwards thru the whole induct system [reeds out] & into the crank case cover you can see that whats going on is a motor designed to run good while capable of idle/ low throttle all day. Opening up the upper crank case window can be done to match the lower but remember increasing crank case volume iisnt good for fuel mix velocity.
http://i35.photobucket.com/albums/d151/mes355/DSCN0108.jpg (http://s35.photobucket.com/user/mes355/media/DSCN0108.jpg.html)
As far as RPM.s Ive run 72-7500 on several motors for extended time no problem, I doubt they.ll last 30 years LoL like a stock can but several no problem. I've heard of 8g's but never saw it.
As with any performance craft or all out race rig, the prop is one of the most important things.

[TorqueXrpm]

JM50, I see by the pics that you are paying attention to detail. Question for you. Looking at your top pic. See how the 3 reeds of each cyl, closest to the center would provide the shortest pathway for air to travel? What do you think would happen if we had a stiffer reed in that area. Along with a moderate reed at 12 & 6 o'clock. And a more flexible reed covering the outside three.??

[JohnsonM50]

JM50, I see by the pics that you are paying attention to detail. Question for you. Looking at your top pic. See how the 3 reeds of each cyl, closest to the center would provide the shortest pathway for air to travel? What do you think would happen if we had a stiffer reed in that area. Along with a moderate reed at 12 & 6 o'clock. And a more flexible reed covering the outside three.??
Thanks, TXR, Been at it a long time. I'm not sure if it would help but aiming to even the flow around the reeds is interesting. I do know that when I broke one it was right in the 'straight in path' & could imply higher pressure. Figuring how to fit V reeds w/o adding crank case volume would be the trick because the v block takes care of that situation by its shape. I looked into a set from the 4o-50 looper OMC. too big dimensionally & too small if cut down I thought.

[TorqueXrpm]

Interesting. If I'm looking at this right, with all reeds being the same, it already has a variable valve of sorts built into the design. The inner reeds being the ones that provide the most flow throughout the rpm. I'm curious as to how the motor's volumemetric efficiency would change if the incoming charge was redirected to the outside reeds at lower rpms and brought inward as the R's increased. There's always the area behind the reed retaining screw that I see as being problematic but with the right velocities, it's possible that you could get a stuffing charge that would be resistant by a millisecond to the pressure signal of the compressing primary charge. I would venture to guess the motor would be very throttle sensitive but I can't say for sure.

[JohnsonM50]

Interesting. If I'm looking at this right, with all reeds being the same, it already has a variable valve of sorts built into the design. The inner reeds being the ones that provide the most flow throughout the rpm. I'm curious as to how the motor's volumemetric efficiency would change if the incoming charge was redirected to the outside reeds at lower rpms and brought inward as the R's increased. There's always the area behind the reed retaining screw that I see as being problematic but with the right velocities, it's possible that you could get a stuffing charge that would be resistant by a millisecond to the pressure signal of the compressing primary charge. I would venture to guess the motor would be very throttle sensitive but I can't say for sure.
An idea to share that I havent tried yet, fill that low at the center with some type shaped solid material, could serve to decrease crank case volume & subsequently increase velocity. So... what shape?, my 1st guess is obviously a cone Next would be some sort of mushroom shape that fills all but the highest pressure areas.

[TorqueXrpm]

I would say a cone similar to the incoming side of the big three cylinder merc. It would fill the void and direct the positive pressure signal outward toward the reeds from heel to toe. The redirected signal "might" allow for a better reed response as it rebounds away from the "toe".

[TorqueXrpm]

You know. Come to think of it. With that pressure signal rebounding off the outter circumference and across the reeds, that compliments my earlier suggestion and could bring a thin reed open sooner as the primary side transitioned from positive to negative pressure. Hmm

[TorqueXrpm]

Does anyone know if there is a rep with CCMS on this site?

[Emustard]

Hey everyone thanks for all your help so far.

So we took the boat out this weekend and raised the motor (almost 4 inches) and added a little more tilt. our best was 37.2 mph GPS with me (130lb) and a 110lb of stuff add another person 200Lb and dropped to 36.3 mph. At 37.2 mph our RPM was 6060. I have a couple of pictures now just for test proposes we just used a peace of wood and some clams, hoping to buy a hydraulic jack plate soon. does anyone Know what would be the best timing to run? do you think we should go with a 16, 17, 18 pitch cleaver or chopper from Ron hill ? and we are looking at a over hub.

54063540645406554066

[TorqueXrpm]

37.2 mph @ 6060rpm? If your info is correct, I'd say you just topped out in terms of a prop. Those figures indicate a near perfect prop.

[JohnsonM50]

That Emustard is a good step forward, when your near potential an mph is hard to find, 3 is grounds for a party. Whatever #'s the prop you got that on are your safest bet on the next, a performance clever of the same hopefully will be a bit better, going up would risk lost gain.
Since as soon as the h20 leaves the transoms edge it rises to seek level at your motors position it would likely be about an inch above your straight edge. If it will cool & the prop will hold 40 might be an inch away. You can run a small hose from the indicater spray up front so you can see it full time looking forward.
All this is proof that props & set up are the things to do & afterwards motor work can be icing on cake. Good Luck.

[Emustard]

That's what our tac and the GPSs said. I was very impressed with our results this weekend now just looking for a new prop and a stock tuner to test.

[TorqueXrpm]

I would hold off on the prop. Get a trim plate and fine tune the set-up. If it remains the same, I would look at more mods for the engine. By my calculations, you will not find as more efficient prop the way it is. Hold off on the prop till another improvement is found elsewhere. That's MHO.

[Emustard]

I agree with you, before we buy a prop we are going to get a jack plate and maybe a trim and tilt, we want to get the best out of this prop before switching props if we hit 6200rpms then that's are limit to switch props because that's when our rev limiter kicks in. I don't really know what else to do to the engine besides the tuner idea I said, cleaning up the lower unit, and timing to maybe 33 degrees. any more ideas??

[Emustard]

we were surprised with the 3mph gain and quite happy. we are always keeping a good eye on our water pressure don't want to over heat the motor, and I agree with you maybe a little more and we will be right on our 40mph but will probably hit the rev limiter before that.
"All this is proof that props & set up are the things to do & afterwards motor work can be icing on cake." very true

[JohnsonM50]

Cleavers tend to run very efficient, in the 90% & better neighborhood, still there's no garantee one will do better than what you have. best to test, only way to know.

[Emustard]

Hey guys sorry it took so long to get back. Just tested the motor with a stock tuner and ran 37.5mph at 6140RPMs not much difference but with the out side air temp only getting warmer the test held up very well. Making a Hydraulic jack plat this week so will have more feed back next week. Any more advice would be great. Any ideas to make the aluminum boat slide over the water smother?

[JohnsonM50]

Hey guys sorry it took so long to get back. Just tested the motor with a stock tuner and ran 37.5mph at 6140RPMs not much difference but with the out side air temp only getting warmer the test held up very well. Making a Hydraulic jack plat this week so will have more feed back next week. Any more advice would be great. Any ideas to make the aluminum boat slide over the water smother?
Sliding over the water smoother.. that is the question that goes way back. We generally sand cross direction with 400 grit on the flat kneeldown race hulls. Thats thought to be better than shiney smooth. If you want to go radical, a coat of west & graphite but it might do nothing for all the effort. The most succesful method besides lotsa horsepower is airing it out, so the jackplate?? Hope it works out.

[Emustard]

hopefully we can finish it this week so we can test it on the weekend, just have a couple of more things to do before we mount it and wire it.
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[MWhite]

hopefully we can finish it this week so we can test it on the weekend, just have a couple of more things to do before we mount it and wire it.
54296542975429854299543005430154302

u can still rise the motor some more and still be safe on your water. we use to river race down here and we ran 25s and 20s on 10ft aluminum boats and we would put the prop shaft about 1inch under the bottom of the boat,,, a cleaver prop are a chopper prop, works the best at this height, if your stock prop is sliping at this height puts some cup on the end of the blades and it should stop. good luck.

[JohnsonM50]

I agree to raise it all you can with the prop you have been testing, when maxed out a determination on a surfaceable prop can be better made. 2 things happen in general, the motor is free to spin more R's & the boat is hopefully aired out a little more.

[Emustard]

We will definitely try raising the motor a little more but im sure we are pushing the limit with that prop right now so your probably right we will start slipping. What kinds of speed were you seeing with with the 25s on 10ft aluminums?

[MWhite]

We will definitely try raising the motor a little more but im sure we are pushing the limit with that prop right now so your probably right we will start slipping. What kinds of speed were you seeing with with the 25s on 10ft aluminums?

anywhere from 52 to 55 with the ole 20 mercury,, i still have my motor, we all had stacks on them, one guy had a ole 25 johnson,same as the 35 and he put the stacks(horn) on it and it would run 60, we couldnt do nothin with him,, it could fly. lol but we had them all jack high with cleave props on them.

[MWhite]

anywhere from 52 to 55 with the ole 20 mercury,, i still have my motor, we all had stacks on them, one guy had a ole 25 johnson,same as the 35 and he put the stacks(horn) on it and it would run 60, we couldnt do nothin with him,, it could fly. lol but we had them all jack high with cleave props on them.
we ran these motors on 10ftx36wide aluminum alweld boats made in the early 80s they were light. im going to try to get some pictures of them so ya'll can see them, ive got some of mind just have to find them.

[Emustard]

That's crazy fast for a 20, did u run low water pickups or just stock lower units? Where did you guys get ur stacks?

[MWhite]

That's crazy fast for a 20, did u run low water pickups or just stock lower units? Where did you guys get ur stacks?

yes them 20mercs would run on the 10ft boats,, my motor has the ole bayer stacks, they still on it. the 25 johnson like u have has the hustler stacks made by bob snider, he built 2 sets for 2 guys down here and they make a big differents, i think bob still buids them, just have to find him and talk to him. the lower unit was a stock unit, i cut some channels in it and made the bottom hole bigger and block off 3or4 at the top.

[Emustard]

I would definitely like to get a set of stack , just to have LOL. Just out of curiosity what props and rpms were you guys running.

[MWhite]

I would definitely like to get a set of stack , just to have LOL. Just out of curiosity what props and rpms were you guys running.

7300 rpms on the 20merc, the motor was all balanced, the props i used was the 3 blade cleaver that mercury made for that motor, they come 10X14 pitch i would have to cut it to 93/4 and pitch it to 13 to 131/2 so i could turn it. the motor i still have will still get it. the 25s they could turn alil bigger wheel than the 20, they had threw the hub cleavers, and there pitch was like 18 to 20 i think theres was around 6500. ill have to ask the guy who run it to see.

[MWhite]

I would definitely like to get a set of stack , just to have LOL. Just out of curiosity what props and rpms were you guys running.

what model is your motor,i think i have found u a set of stacks for that engine

[JohnsonM50]

Stacks will make a difference. MW, would those be with a filler block off the xhaust ports or out of the mid? Best I saw w/a stock [no stack] 31.8 on a non thru hub was 52 gps on a pals wetback hydro. Beyond that I use Yamato gear cases to exceed 60. For the moment my 'practice' hydro/31.8 will outrun my C stock but not for long I hope! LoLs

[MWhite]

Stacks will make a difference. MW, would those be with a filler block off the xhaust ports or out of the mid? Best I saw w/a stock [no stack] 31.8 on a non thru hub was 52 gps on a pals wetback hydro. Beyond that I use Yamato gear cases to exceed 60. For the moment my 'practice' hydro/31.8 will outrun my C stock but not for long I hope! LoLs

yes,,, filler block off the exhaust port,its cutoff from going to midsection.

[Emustard]

My motor is a 1990 evinrude 20hp model# e20cresb

[MWhite]

My motor is a 1990 evinrude 20hp model# e20cresb

i know where some stacks is if u interested. ready to bolt on.

[captbone]

I would be very interested in some stacks if the OP is not.

Thank you

[MWhite]

I would be very interested in some stacks if the OP is not.

Thank you

captbone,,,emustard was the one that was interested in them stacks, i dont if he bought them are not. Bob snider was the builder of them hustler stacks and i think his son has took over his business now.

[Emustard]

Update on how it is going
Got the new prop last week 11x18 over hub cleaver, going to do some runs this weekend hopping for 40mph "so close". running a 5in jack plate really helps any other tips would be great?

Here are some pictures
5474154742 5474354744

[MWhite]

Update on how it is going
Got the new prop last week 11x18 over hub cleaver, going to do some runs this weekend hopping for 40mph "so close". running a 5in jack plate really helps any other tips would be great?

Here are some pictures
5474154742 5474354744

Emustard, did u buy them stacks for that engine???? that prop looks good, u headed in the right direction, but i believe u could stand alittle more pitch,and diameter to at that motor height u running,, the guy thats got the stacks can fill u in on what he had and he may still have that prop he run.

[Emustard]

I did not end up buying the stacks. I wanted to, but I run this motor every weekend and would probably get shot for being to loud LOL people already think I am to loud. on the weekend we did a little bit of running on the weekend and hit 38mph at 5500 into the wind. still had about another 200rpms but ran out of room and waves were to big.

[Ron Saxvik]

Who made the cleaver ?

[Emustard]

Ron Hill made the prop

[Emustard]

Tested the motor this weekend ran a 41.2 mph, had it jacked all the way up and still had great water pressure so maybe put a shim or move the jack plate up an inch. We reached our goal so thanks everyone for helping and giving your input now everything else will be a bonus so maybe 50mph now LOL, will see.

[smitherik33]

Tested the motor this weekend ran a 41.2 mph, had it jacked all the way up and still had great water pressure so maybe put a shim or move the jack plate up an inch. We reached our goal so thanks everyone for helping and giving your input now everything else will be a bonus so maybe 50mph now LOL, will see.

Just curious as to how long that motor lasted with all the mods you listed? Have a ron hill 10.25X16 thru hub semi cleaver on it's way to me. Sure hope I can turn it.

[Emustard]

Motor still runs great, don’t use it as much, but works well during hunting season. As long as you can get the motor up, you should have no problem turning that 16pitch:)

[Powerabout]

Have you tried to add a spacer between the reed plate and the inlet?
I havent tried it but I would if I was experimenting with a 31ci

[Emustard]

Yes we added a 3/8 spacer, to increase the intake side before the reeds and the results did not show any power gain.

[smitherik33]

Has anyone on here ever fabricated a V block reed set-up for the 31.8ci?

[smitherik33]

Motor still runs great, don’t use it as much, but works well during hunting season. As long as you can get the motor up, you should have no problem turning that 16pitch:)

Did your cleaver slip like hell when trying to plane the boat off. All mine does is slip and the motor goes up to like 5000rpms and I've gotta practically run to the front of the boat to get it to finally bite. I've tried it with the motor jacked all the way up and down. Also tried different pin positions. Just wondering if this is normal

[Arltralite111]

Has anyone used a factory test wheel to test their motors after modifying?
I have wiseco 0.030” pistons in mine and a planed head. 30 deg btc and turn the test wheel 6650rpm.
On my boat with a 10-3/8 x 18 mercury chopper, I run 44mph at 6000rpm. Similar results with a signature 10x18 cleaver.
The 5 blade 10x18 cleaver turns 5500 rpm and runs 40mph

Smitherik33, try making a larger cavitation plate like an oz plate.

[PPRINT]

The factory test wheel...

I have an '81 35hp commercial engine that I recently picked up. I can tell the power head has been removed so I have no idea what all has been done to it.

I do know it has the 1-3/8 dia carb that has the 1-1/8 venturi. It also has a power pack with no Rev limiter and very good compression.

I ran it the other day in a 35 gallon barrel full of water with the factory test wheel.

I let off the throttle at 7850 per the tiny tach in the interest of keeping the rods inside the block.

Either I am using the wheel wrong, or it is not meant to hold the engine back much at WOT.

Take that for what it is worth.

Rob


Sent from my SAMSUNG-SM-G900A using Tapatalk

[Arltralite111]

68337Here is a pic of my test wheel. 6650rpm is at the ramp with the cab plate fully submerged.
Running in a small drum may have a different effect. Or maybe you have a very powerful motor.

[PPRINT]

Nothing special about my $100 motor other than cheap.

The picture tells the tale. The wheel I have does not have that tube-like feature.
Mine is what is called for in my service manual though.

When I finish the deck on this boat I will run it on the ramp and see if more water volume helps.

Thanks for the picture.

Rob

Sent from my SAMSUNG-SM-G900A using Tapatalk

[JohnsonM50]

Has anyone on here ever fabricated a V block reed set-up for the 31.8ci?

I have had a V block in one hand & a crank case in the other, looking at the possibilities & intend to do it. I know serious gain can be found there from a failed reed experiment. bending the dampers out too far will result in a broken reed however till then I had the best result I've seen since putting a gear case & prop on. It's there for the taking but the shapes don't cooperate. I think the answer lies in an extended intake but that will increase crank case volume which could result in loss velocity -defeating the purpose. :confused:

[Arltralite111]

Here are a couple of heads I have. The top heade is from a 1982 30hp. The bottom is from a 1988 30hp.
When I started with the 1982 head, I got 115psi compression. The other head had 120psi compression. After planing the 1982 head and making room for the piston, I got 165psi. I got 155psi out of the 1988 head. Another mod I did to the 1988 head was blocking the water off from going on to the exhaust. The epoxy can be seen in the lower water passage.
I put 4 tubes in the water jacket cover to dump the water overboard.
68387
68388

[smitherik33]

Good evening. I have recently acquired a 1982 head as well. I'm wondering if I'll gain any compression just by simply by bolting it on. Did you use a certain head gasket? I've heard of a thinner version but can't find one.

[RaisedByWolves]

The factory test wheel...

I have an '81 35hp commercial engine that I recently picked up. I can tell the power head has been removed so I have no idea what all has been done to it.

I do know it has the 1-3/8 dia carb that has the 1-1/8 venturi. It also has a power pack with no Rev limiter and very good compression.

I ran it the other day in a 35 gallon barrel full of water with the factory test wheel.

I let off the throttle at 7850 per the tiny tach in the interest of keeping the rods inside the block.

Either I am using the wheel wrong, or it is not meant to hold the engine back much at WOT.

Take that for what it is worth.

Rob


Sent from my SAMSUNG-SM-G900A using Tapatalk

Im currently setting up a 25hp Evinrude with this carb and was wondering if you would tell me your jetting so I can have a rough estimate as a starting point for mine?

My carb is off of a 70hp iof it matters.

Thanks!

[PPRINT]

I am running a 59D jet.

Let us know how that carb works out.

Rob

[RaisedByWolves]

Thanks PPrint.

Any idea what your carb is off of?

Do you have an idle jet? If so what size?

[PPRINT]

I purchased this engine used so I am not sure of the lineage of the carb. The motor itself is a 1981 25hp Commercial Engine (mistakenly identified as 35hp above in previous post).

The carb does not have an idle jet. It is the adjustable needle valve style.

Rob

[JohnsonM50]

The factory test wheel...

I have an '81 35hp commercial engine that I recently picked up. I can tell the power head has been removed so I have no idea what all has been done to it.

I do know it has the 1-3/8 dia carb that has the 1-1/8 venturi. It also has a power pack with no Rev limiter and very good compression.

I ran it the other day in a 35 gallon barrel full of water with the factory test wheel.

I let off the throttle at 7850 per the tiny tach in the interest of keeping the rods inside the block.

Either I am using the wheel wrong, or it is not meant to hold the engine back much at WOT.

Take that for what it is worth.

Rob


Sent from my SAMSUNG-SM-G900A using Tapatalk

Generally above 7200 + or - is about it, a bearing cage fail is the likely reason. Not that an engine couldn't be built to go more but the weight balance alone in these stock is not extremely accurate. To move a moderate load at moderate speed and troll alot is the design trend.

[PPRINT]

I will just leave these here for discussion fodder.


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Rob

[PPRINT]

These are the flow numbers of a stock reed plate versus a Yamaha 500CC jetski V reed block shown in the pictures.

71385

Rob

[RaisedByWolves]

That looks like a nice setup, but dual carbs seems like it would be a PITA.


OK, I got my 1 3/8" carb on and it starts and runs but the idle jet is off.


Iw will idle ok with the primer out on the first notch but when I take the primer off of the cold setting (First notch) it slowly revs faster and faster until it sneezes and quits.

I know I need to go down on the idle jet, but how much or how many sizes?

Im currently running a 40 idle jet.

Do I go 39? 38?

It doesnt run terrible but it certainly needs improving.

[JohnsonM50]

I will just leave these here for discussion fodder.


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Rob The Mikuni slide carbs will probably perform better to start with. I made up a manifold to accept a 2 barrel carb from an OMC 85hp. Each barrel the same size as the stock single. Each cylinder draws from one barrel so it won't double the fuel requirement. It draws the same amount of air thru each barrel at half the pulse rate per barrel out of a common float chamber. No need to syncronize. This gave more mid range power but was not faster on top.

[JohnsonM50]

The Mikuni slide carbs will probably perform better to start with. I made up a manifold to accept a 2 barrel carb from an OMC 85hp. Each barrel the same size as the stock single. Each cylinder draws from one barrel so it won't double the fuel requirement. It draws the same amount of air thru each barrel at half the pulse rate per barrel out of a common float chamber. No need to syncronize. This gave more mid range power but was not faster on top.

I also see in the pic that you set this up as a 31.8 manifold. [clever]

[RaisedByWolves]

OK, I got my 1 3/8" carb on and it starts and runs but the idle jet is off.


Iw will idle ok with the primer out on the first notch but when I take the primer off of the cold setting (First notch) it slowly revs faster and faster until it sneezes and quits.

I know I need to go down on the idle jet, but how much or how many sizes?

Im currently running a 40 idle jet.

Do I go 39? 38?

It doesnt run terrible but it certainly needs improving.

Quoting myself here to keep things coherent.


Took the boat out and saw no improvement in speed. I was able to trick it into idling with the primer set on cold start and that worked OK, but the mid range was a total **** show.


I took a pic of the plug but my phone is dead right now, it was a tan chocolaty color. I couldn't run it wide open for long as the boat was hopping too much and actually only had full throttle for 20-30 seconds.

The motor acting strange in the midrange is what has me baffled. It would stumble and or be unresponsive to throttle input, seemingly have no change in power with throttle input or it would lag then seemingly catch up with a decent burst of speed.

Could this be due to the idle circuit running lean?

Could it be a linc/sync issue?

All I did when I swapped the carb was to adjust the two plates on the side of the carb to get the carb to open between the timing marks. Is there more that needs to be done here?(Timing)

Any input greatly appreciated.

[JohnsonM50]

[QUOTE=RaisedByWolves;157157]Quoting myself here to keep things coherent.


Took the boat out and saw no improvement in speed. I was able to trick it into idling with the primer set on cold start and that worked OK, but the mid range was a total **** show.


I took a pic of the plug but my phone is dead right now, it was a tan chocolaty color. I couldn't run it wide open for long as the boat was hopping too much and actually only had full throttle for 20-30 seconds.

The motor acting strange in the midrange is what has me baffled. It would stumble and or be unresponsive to throttle input, seemingly have no change in power with throttle input or it would lag then seemingly catch up with a decent burst of speed.

Could this be due to the idle circuit running lean?

Could it be a linc/sync issue?

All I did when I swapped the carb was to adjust the two plates on the side of the carb to get the carb to open between the timing marks. Is there more that needs to be done here?(Timing)

Any input greatly appreciated.
Hard to put an answer on what you're getting but a couple Ideas: Throttle/timing syncronizing is for acceleration mostly off low throttle, after about a third it goes to full advance and runs the rest of the throttle range there. It could be lacking some but I doubt it's making the motor hesitate or stumble. Secondary air in the float bowl? Needle packing or bowl gasket leak? [be sure the center doughnut gasket is on the pickup stem] Surging is the usual symptom. Be sure the carburator is seated and the mount gasket not leaking. Make sure also that your fuel lines are sealing well and not drawing air. Lack of fuel could be it as far as hesitating goes. With a normal stock motor the speed won't be improved much on engine enhancements beyond proper tuning. The reason is the gearing, if you gain 100 rpm's on the power head, you're subtracting the gear reduction from that. With the non thru hub [older versions] that 100r's would end up 57.1 r's at the prop, less on he thru hubs. To see a real speed increase you'd need alot more. Time invested in getting the boat optimal and a well suited prop in place would go much farther for the effort.

[PPRINT]

These are pictures of the Link&Sync instructions in one of my service manuals. Maybe it will help.

One picture is a factory jet chart.

Rob

P.S.
Carburetors are very sensitive to float level. A low float level will make a motor lean. Too high will make it too rich.

[PPRINT]

Jet chart picture rotated correctly.

Rob

[RaisedByWolves]

Thanks pprint!

Especially for the jet chart, that will give me a better starting point than trying to suss out the info from different threads.

As far as speed, yeah I need to move up to a 10x15 prop, and was hoping the carb swap would give me a better hole shot with the higher pitch prop.

I’m trying to do this on the cheap so I’m just buying what I can find at a good price now in hopes of having it all come together at some point next spring.

Would the 30/35hp intake be of any benefit?

I’m also wondering if I should work on motor height and or tilt before having the correct prop on hand as I really can’t hang on to it going 28mph as it is.

With just me in it(310lbs) it was proposing so bad the prop sucked air and I had to get out of it.

So I guess my question here is get the motor/hull to run correctly now or wait for the right prop?

If I do that work now (have to make/modify things) will I have to again make major changes with a new prop?

[JohnsonM50]

Props are only as good as test results, different per boat or motor Genrelly if you do change a prop it only makes sense to try different settings. The manifolds are not that significant as long as you dont have one of the restricted ones. The port should be no smaller than the carb. You should try to get that porpoising under control. Tucking the motor in and maybe raising it a little would help. Not gonna do much good going faster if it's not controllable. The deeper the motor, the more leverage it has against the bow. Tilted out too much will make that even worse.

[RaisedByWolves]

I’m working up a tapered spacer to tuck the motor in but I had it out for a couple weeks to modify it as it had too much taper originally. This is with the motor on the pin closest to the transom.

I have the motor raised up 3.5” and I’m making a new bracket to go up to 4” currently. It is honestly worse now that it was before I raised it due to the speed increase I got from that and a better prop of the same pitch.

[JohnsonM50]

Sometimes its tuff to tame them and settling for it to smooth down at top speed is the best it will get. Outboard race runabouts are prone to porpoising [not all] but are faster smooth. Seen it many times where a boat starts hopping and it falls right back against others holding smooth. The drivers have to 'work' these boats to keep control. A stationary drive position in a regular boat, that's less of an option. Can you post pics?

[RaisedByWolves]

Boat is currently under construction so pics wouldn't help much.

Its your basic 14' aluminum vee with two pedestal seats and a front deck with trolling motor and battery. I removed the stock bench seats to put in a floor and the pedestals, and both seat positions are forward of where they were stock.

The description I gave of it porpoising was with me in the back and about 150lbs of gear within 2' of the bow.

With the wife in the front (150lbs) it rides fair, but with just me it is a rodeo.

[JohnsonM50]

[QUOTE=RaisedByWolves;157169]Boat is currently under construction so pics wouldn't help much.

Its your basic 14' aluminum vee with two pedestal seats and a front deck with trolling motor and battery. I removed the stock bench seats to put in a floor and the pedestals, and both seat positions are forward of where they were stock.

The description I gave of it porpoising was with me in the back and about 150lbs of gear within 2' of the bow.

With the wife in the front (150lbs) it rides fair, but with just me it is a rodeo.

Weight distribution counts for alot. Funny story, a couple pals and I put a 25 on a beat up light duty 12' aluminum boat and went, 3 of us, near 600 pounds lol. The boat Couldn't stop porpoising bad and the bottom was visibly form rippling in time with the porpoising, it would have just ripped apart if we kept running it but up the river a couple miles to a bar and back after a few beers was enough of that lol. I drove it full power all he way, it was a hoot, we didn't care about a swim.

[smitherik33]

I will just leave these here for discussion fodder.


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Rob

I'm just curious if this can be done with one carburetor? If so, I'm pretty confident that I can design/fabricate a similar v block set up.