56ci OMC realistic power

[filthy phill]

ferdthe4
No it probably was not a 70hp oval port he saw on the dyno in 2004.

read this from Houndog back in just 2016, 12 years after the dyno test was done. it is very interesting and explains why it was not a 70hp..

" The thought it best to start a thread on this topic. I for one of many thought that the 60 hp and 70 hp carbs were all the same smaller size.
When PPR [Professional Powerboat Racing] made a rule change in FV class to allow the 2000 model 56 oval port in the class it had to run with its original carbs.
That same rule still applies in T850 for any oval port. None of the OMC racers back then ever ran the oval port block in the class.
One racer purchased a new set of 2000 model 70 hp carbs and ran them on his SST60 powerhead. They did not work.
When we see these carbs listed on EBAY they normally say they are for both 60 and 70 hp motors. I have never seen the 70 hp larger bore carbs.
Craig Fraser has a complete 70 hp oval port powerhead?? Dave Elsey has seen the carbs on it and they are larger.
I have a fresh 30 over oval port with carbs. They are the small bore carbs. We need to get the part numbers off Craig's carbs and we need to test those carbs on an oval port.
It could be that the larger carbs were on some but not all 70 hp oval port models. OR we just have not seen a real 70 hp oval port. "
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that explains why it was not fitted with the larger carbs, and that means it was the 60hp version, it also explains why the larger sst60 carbs gave it an extra 8-9hp...
if this had been fitted with the bigger carbs he certainly would of known about them when they got changed over...

Houndog has been a around a few motors so knows his stuff, and for someone like him and a few of his friends to have not seen the bigger carbs on a real 70, just
goes to show that all its not always what it seems. always something to surprise us all.
he is 100% right about carbs being falsely advertised as for 60/70hp motors when they are just the small ones.

[ferdthe4]

Sorry phill I didn't find hounddog's post from 2016 about it I was merely going off what he posted in this thread. I agree that many carbs on ebay are falsely advertised and don't have the throat measurements to verify what they truly are. I will measure a carb off each of my engines one being the one on my boat a 1994 70hp. Being a 1994 it should be a oval port, and according to the model number it's factory 70hp. Can't remember it off the top of my head and I'm not at home to see it, when I get a chance I will see what carbs it has. I will also do the same on the 1987 70hp I have sitting on a stand in the garage to see what carbs it has. I'm hoping that between the two of them one of them has the proper larger carbs 1.5" throat front and back not going to call them 70hp ones anymore since apparently engines sold as 70hp may have come with either or. If I don't have the larger carbs guess I will be searching for them, which from the sounds of it is a pain since most sellers on ebay usually don't have measurements of the inlet and outlet throat to know what your getting or not. I was never trying dispute weather or not hounddog knew his stuff or not, I've appreciated all the info from him and others on here. I'm not new to engine performance, but I am some what new to trying mod outboards, and info on what parts are right is hard to find since aftermarket is nearly non existent in terms of performance parts for these outboards. Not like cars that I'm use to their are more holley carbs, edelbrock carbs, demon etc and various intakes from the aftermarket than you can shake a stick at to choose from. Versus outboards you gotta first figure out what factory stuff was the best then hunt it down and hope you have the right parts in mind and that the ones your buying are listed correctly. I know many of you piles of old engines and parts to mix and match from to figure out what works not the case for me and many others I would imagine, and unfortunately most the parts cost enough to keep me from just buying a ton and just experimenting. Sorry I don't have the money to have a small warehouse of omc triple parts, and to blow up a bunch of engines. Hence why I'm on here trying to get as much info as I can, and it is all very much appreciated. If I could squeeze 80-85 hp reliably out of one of my engines I would be tickled. I'm just a gear head that has a hard time leaving his toys alone.

[filthy phill]

some of the guys on this forum have some extremely powerful motors, and when you watch their videos its unreal what they go like.
I could not believe just how fast they are going, 70mph seems the norm on the racing v hulls !!!
Power wise these fella's have got it nailed big time, they dont just go fast flat out, they come out the corners like bullets.
Untill recently I thought it was all down to gear ratio and smaller gear cases with short mid sections but could not find a reason for this apart from
longshaft being heavier and bigger gearcase is more drag, as the long shaft with its 2.42 can swing a bigger prop.

But the guy named hupiveneilija has got his longshaft going extremely quick and its on a 17ft v hull. over 64mph with 2 people in the boat !!
Now that is fast, what will it do with just 1 person ? and what would that do on a lightweight boat like those running in Canada with the t0noat classes ?.
no idea of how many horse power but it must be very high to get these speeds.

It seems that porting is the way to go and getting rid of the rpm limiter. also the head skim to sst60 spec and what the others have already said can realy
wake up the motors.

people on here will tell you what you need to know if you want to get lots of power, they know their stuff when it comes to modifying outboards.
lots of true racers and engine builders to put you on the right track.

[ferdthe4]

I've read through hupiveneilija mod 70 thread it was very helpful I probably won't go as extreme on porting as going much past 6200 rpm with a jet just doesn't do it much better from what I've heard. I picked up those etec reed cages gonna keep my eyes peeled for another set. Will start there and make sure I have the bigger carbs and shaving the head some and see where that gets me. The oval port on the boat currently is in pretty good shape so I'd rather not tear it down. I may at some point tear down the 87 and do more extensive work on it but that is probably a ways off with life taking place.

[Mike Wienandt]

The best block for mod engines is the early 56 ci permanent mold block, not the foam block. Bridge port, not oval port . I think about 87-88 I have built with all of them . The transfer ports are shaped better and the bridge port allows you to make wider exhaust port. The port timing of All ports is critical, you must measure, there are many different versions. I have not studied the carbs details closely to see why the three jet carb does not work. But watching the fuel flow and BSFC on the dyno I can quickly see it's wrong for this engine.

[LittleCharger]

The best block for mod engines is the early 56 ci permanent mold block, not the foam block. Bridge port, not oval port . I think about 87-88 I have built with all of them . The transfer ports are shaped better and the bridge port allows you to make wider exhaust port. The port timing of All ports is critical, you must measure, there are many different versions. I have not studied the carbs details closely to see why the three jet carb does not work. But watching the fuel flow and BSFC on the dyno I can quickly see it's wrong for this engine.

Thanks Mike that was what I had thought but always nice to hear straight from a top builder of the 3 cylinders...cheers,

[ferdthe4]

Glad I have a 1987 as well. From my reading on the mod 70 build which heads are better to shave. If my memory serves me correct in the mod 70 build the oval port ones didn't require as much decking to get the bowl depth and volume to around sst60 spec. Or maybe I have it backwards and it was the bridgeport ones that were better.

[Mike Wienandt]

When milling the head, if you make it very tight spec the head will flex and not hold head gasket seal. That is one reason why I weld the thermostat hole. To give the head strength there. Would not recommend tighter that SST 60 spec unless you raised the ex port to high. You do not want more than 8.3:1 ECR It will cause engine to slow down as it heat soaks. And certainly good Fuel is required.

[ferdthe4]

When milling the head, if you make it very tight spec the head will flex and not hold head gasket seal. That is one reason why I weld the thermostat hole. To give the head strength there. Would not recommend tighter that SST 60 spec unless you raised the ex port to high. You do not want more than 8.3:1 ECR It will cause engine to slow down as it heat soaks. And certainly good Fuel is required.

I wasn't going to go extreme on the head decking want to be able to run premium pump gas don't wanna have to buy race fuel for my fishing/hunting boat. So I don't even know if I would go as far as sst60 spec

[Hounddog]

Having Mike Wienandt add posts to this thread has confirmed most of the findings posted on other threads about the 3 cylinder 56 cubic inch OMC. The SST 60 is a spec motor and you must use original OMC parts. You cannot alter or modify parts past the given spec measurement. It is more time consuming and usually more costly to build a 100 plus hp SST 60. You MUST find near perfect parts. The motor that Mike builds will only be as good as the parts he has to work with. That being said. Some motors perform better than others. Plus the motor is only one part of a successful winning boat. Many will say the late 80's SST60 motors produced the same power as Mike's motors. A few may have. But there was a wide difference in SST 60 motors. Mike was able to equalize the motors and even out the playing field.
I do think we will see improvement in the oval port motors. The builders have played with the bridge ports since the 1980's and I do not think they have spent a lot of time...YET! playing with the oval port. For the low budget lake runner we have seen first hand in Canada that it is very easy to get good performance out of a stock oval port by just changing the carbs. We have a few T850 boats running over 76 mph, we only had one confirmed that ran over 80 mph and that was an oval port.