Strongest 2cyl single carb.

[AirRacer]

Im building a 46% P51 r/c airplane. The 2 cyl 25/30 omc powerhead fits under the cowling nicely. I also have a 25 merc powerhead that fits also. My thoughts are i can get even more power from the omc being able to cut the head a little. Or does the little merc have more available potential just by its porting alone V/S the omc being an old crossflow design. But airplanes need torque to turn propellors and I feel the omc is more torquey just by seat of the pants driving them on boats. So what are you guys thoughts? Thx, Jeff

[DeanFHobart]

Find someone who can put the powerheads on a dyno and get real results. That would be my recommendation.

[25XS]

Look at air cooled/water cooled snowmobile engines...? Loop scavenged (looper) with WAY more power per cc. The snowmobile engines usually have waterpumps.

Also, the personal watercraft engines if you can run watercooled. TONS of over the counter aftermarket performance parts & engineering for them as well.

A Rotax 650 or 750 would pretty much give you the commercial engine linked below, but without the gear reduction unit.
https://www.flyrotax.com/produkte/detail/rotax-582-ul.html

[AirRacer]

The Problem with snowmobile jetski or rotax aircraft engine are they are too big. Those engine designers have way more freedom in design due to sleds and skis having big engine compartments. Outboards have everything where i need it. Exhaust pointing to the rear and nice big crankshafts. Im testing a mikuni sbn carb on the omc right now but looking like i will have to build a intake and move carb. Not a big deal. There are 250cc inline r/c engines that would work but cooling it in a tight cowl will be tough. The p 51 only has a small chin scoop to get air. I just want to do something different. Ive built an zodiac aircraft with a subaru so i learned alot about liquid cooling and building ventral radiatior ducts.
Tohatsu 25 would be the other to look at but I dont see many of them come through my shop. But if i remember they dont have a big fat crankshaft like the omc.

[maartenk79]

Did'nt nissan / tohatsu do a 70hp twin once upon a time?

[AirRacer]

Too big. I have several 45ci omcs and ofcourse that was the first motor i tried. I dont need 40+ horsepower either. The 30 h.p. omc is the best candidate, I dont know why im letting crossflow design bother me so much.