Rebuilt Motor Question

[HyperDonzi]

On a 406SBC, "had" a 40% blow by last season, could spin a 23" Laser through a 1.5 Alpha SS to 5400 (peak performance 54-5600) which was 73 on the spedometer. The motor was rebuilt, and the spedomoter still says 73, same prop, 5400max rpm. Does something sound a bit off? a 40% blow by sounds like a LOT of missing power.

[Rootsy]

are you talking about a static leakdown test?

did he have the valves and seats done?

new pistons and rings?

what kind of rings and what are the gaps?

has this motor been run enough to seat the rings properly?

on a new engine (non anal racing motor), broken in... with gapped rings you should see 10 - 15% leakdown... with gapless rings, significantly less... but they do tend to result in less hp for various reasons

but a high rpm leakdown is a different matter altogether...

[Zinger]

Hyp. did you mean the compression was off by 40 % per cylinder , i think mercruiser allows 25% difference between cylinders on there engines.Jeff