1979 20' ma 140 suzuki

[flyingfrizzle]

Originally Posted by Bushwacker

210 psig is almost certainly a bogus number because that works out to be a compression ratio of 15.3:1, which is way too high, even if you're running 103 octane Av gas with aluminum heads!! I'd see if you can find what the specs are from a Zuke service manual. 85 psig does sound a bit low for the 150, so it may have some stuck rings and need a good decarb. And compression ratio primarily affects BSFC, but has sort of a 2nd order effect on power. And if you have to back off on spark advance to avoid detonation with the high compression ratio, you will lose more power from that than you will gain from high compression. I own an old muscle car and the race block I bought for it turned out to have about 12:1 compression ratio which is way too high for premium pump gas, so I tore it down and installed 9.5:1 pistons in it!

I agree, I have a Camaro with a small block Chevy in it with 14.8 to 1 compression and I have to run at least 112 octane. I usually run 113 oxygenated race fuel which is as good as 114. A stock mercury 200 has 125-130 lbs but we shave the heads down to 34 cc's to run 145-150 lbs but even then that is the absolute limit for 93 octane. Most go easy on the timing to run this much compression. The drag racers with 2.5 drag outboards are only 160ish from the factory and some of them guys cut them down to get over 200 lbs but they are running 112 octane at least!

*EDIT: I was wrong in my post earlier, I did some checking around and found this: "2005 Suzuki 140 hp - Specks: 185 psi to 242 psi with a 14 psi delta maximum between all cylinders" So I guess they are doing it some how with low octane fuel???