motor project

[loop]

I posted this on S&F but this may be a better place to find this kind of info.
I plan on building an outboard this winter. By building I mean I will use an existing powerhead,probably an OMC v4 and mate it to a fabricated midsection similar to Jon Wrights Tinkertoy. All of this will be on top of a lower unit that I havent picked out yet. I want something smaller with a diameter than the stock v4 has.
I need to find the best gearcase possible that:
1. isnt too expensive,this is a low buck project
2. has parts readily available
3. has a relatively small bullet diameter,smaller than the stock v4
4. has a gear ratio in the 1.87 - 2.0 range give or take a little
5. can handle up to 150 horsepower for short bursts

I really dont care who makes the gearcase as long as it does what I need
the input splines wont matter since I will match them to whatever powerhead I end up with.I know this is quite a wish list but maybe someone out there knows of a good choice.
Durabilty isnt the number one concern as long as its not breaking parts everytime I step on the gas.
My goal for the project is for a 12"-15" shaft ,100-150 horsepower motor thats basically stock and weighs under 200#. It will be on my 13' Allison. My interest is in quick acceleration more than top speed.
If anyone has any tips on what would work I'd really appreciate it

[Aeroliner]

A couple choices might be available. The old Mercury Speedmaster 1 or 2. Parts are a little hard to find but this might work for your application. Another option could be found from the OMC racing applications. We are using a 45 SST lower unit on our 75-H MOD engine.

Alan

[largecar91]

I agree a super speedmaster or a Chrysler speedie but if you have to have a 1.87 - 2.0 gear ratio, that would rule these out.

[loop]

I probably should have pointed out that shiftable would be a plus but not a must.

I was thinking more like a stock type lower just because parts and props might be easier to come by,even if I have to do some adapting. Seems like theres plenty of old SE / EP / SST 60 props around.

Aeroliner- do you think the 45ss ower will handle that much power?

Largecar - My thoughts on the gear ratio was mostly to help with prop selection.
The Chrysler or Merc speedies would be cool. Sad thing is I had a Chrysler racer at one time..

thanks for your ideas and keep em coming!

[Aeroliner]

Look on this page for the 6 cylinder MOD engine. It has the 45 SST lower unit. The folks are also using this on the OMC Super E engines which are making a bit over 100HP. If your not to hard on it I think it should give you good service.



http://www.boatracingfacts.com/forum...t=6393&page=46

Alan

[Rusrog]

Just find a Yamaha V-4 gearcase. I bought a clean one not long ago for $450.00. 2:1 gears, 15spline propshaft and VERY good reliability.

[loop]

Any idea of the Yamaha bullet dia? is it smaller than the OMC?
I may be putting too much emphasis on the dia but since I can put any geacase I want I might as well go for the smallest,most (reasonably)durable,best geared,rebuildable one thats readily available. This will be alot of hp for a 13' Ally so anything done to improve the handling would be time and money well spent.
Was thinking about a Yamaha 3cyl gearcase if I could confirm gear ratios and diameter. Seems like if it would handle 90hp for extended periods,140 wouldnt be too much for one summer at a time.
I like the looks of the Chrysler 60 horse from the '80s. Has a small dia and water p/ups down low on the side of the bullet. Dont know how much hp it could handle or parts availability.
Russ since your in the freshwater part of Texas keep me in mind if you see a crossflow 115-140. Everything down here is corroded together
I appreciate the input everyone has offered.

[Rusrog]

Any idea of the Yamaha bullet dia? is it smaller than the OMC?
I may be putting too much emphasis on the dia but since I can put any geacase I want I might as well go for the smallest,most (reasonably)durable,best geared,rebuildable one thats readily available. This will be alot of hp for a 13' Ally so anything done to improve the handling would be time and money well spent.
Was thinking about a Yamaha 3cyl gearcase if I could confirm gear ratios and diameter. Seems like if it would handle 90hp for extended periods,140 wouldnt be too much for one summer at a time.
I like the looks of the Chrysler 60 horse from the '80s. Has a small dia and water p/ups down low on the side of the bullet. Don't know how much hp it could handle or parts availability.
Russ since your in the freshwater part of Texas keep me in mind if you see a crossflow 115-140. Everything down here is corroded together
I appreciate the input everyone has offered.

The V-4 Yamaha is a 4in case just like an XR6 Mercury but at probably 1/3 the cost. The case off of the 70 Yamaha that I used to have also used a 15spline prop shaft but I think it was a 2.33:1 gear. Not sure how fast that you are wanting to run this thing but that case would spin a 14in prop like a Yamaha or an inline Chopper as well. I just liked the prop selection that is available.

True that there is not a lot of salt water problems up here... I'll keep my eyes open for that sort of stuff. Have you tried E-bay? I have seen a lot of stuff go cheap for the Yamaha engines. Just out of curiosity... Why run the crossflow stuff? If it were me I would either find a later model Looper OMC or a Yamaha.

[loop]

looking for about 80 but quickness is the main goal.Trying to build a jetski killer/mini drag boat
a 2.33 gear would need 7k rpm and a 30pitch =77 @10%.
7k is optimistic at best for a stock 'flow
2.0 + 6500 + 28 = 78 Alot more realistic numbers and easier to find props.
1.87 + 6500 + 26= 77
any idea of the ratios on a 4/6 inline merc?
wondering if a good prop shop could build a "mini ET" out of an inline chopper
Looper would be the motor of choice but I dont think i can get it as light as a 'flow.I have collected lots of looper parts over the years since thats what I have on my xb2002. Plus with a looper I'd be tempted to buy Dave Bush sleeves and pistons I'd need a bigger boat...

[Mark75H]

The 65 and 80 inline 4 Merc ratio is 2.33, the common inline 6 ratio is 2 ... 1971 6's had 1.78, but its really hard to find a good set of 71 gears