fantastixvoyage

Looking for a way to determine if an engine (that is complete) is compatible for supercharging. it would seem that using a compression guage to obtain actual compression numbers might be a way to do this. Anyone know if it works and/or the numbers that work with a blower? Say under 150psi is ok, etc.

I am trying to run a small weiand blower from a 525sc and don't really want to tear down the motor to do a compression "ratio" calculation.

fantastixvoyage

would like to work on it this evening...any thoughts....

stevesxm

no. cranking compression means nothing. you need to know the static compression ratio.

fantastixvoyage

That's one vote no and one PM yes....who wants to be the tie-breaker?! I can see it both ways but honestly I'm siding with this being possible. Dynamic numbers would seem to be very real world and would go up as static compression goes up. Not to mention you couldn't really calculate dynamic #s when doing an engine build hence the reason for engine builders using a static number.

Wish I had a 7.5:1 and a 10:1 to compare....

Bajapred

There is some corralation between cylinder compression and comp ratio, however;Compression (PSI) in each cylinder, is not the same as the compression ratio of an engine...compression in a cylinder is basically determined by the ring sealing ability and the valve sealing ability...compression RATIO is determined by the piston geometry and the head dome cc's...among other things like head gasket thickness and rod length & cam timing....

fantastixvoyage

Agreed (except leakdown #s are even better for determining ring/seal leakage) but looking for other options than tearing down the motor. The motor is very fresh (15 hrs/unknown engine builder/parts) so if someone has reference numbers (psi) for comparison that would help. Gonna try to get a bore scope and at least see what model pistons I'm working with but don't have immediate access to one. Hell this sucker could have domed pistons for all I know...

Bajapred

It is different for each engine..take an engine that has 10:1 compression and one that has 7.5:1 and you might see the same cylinder pressure or you might not.....but take an engine that has 7.5 compression ratio with 120PSI cylinder pressure and raise the compression ratio, your cylinder pressure will raise as well, just because of mathmatics.....to know wether or not you have an engine that is a good candidate for a blower application, you must first know what the static compression is..just like Steve said

Bajapred

(Quote from Fantastixvoyage)
"I am trying to run a small weiand blower from a 525sc and don't really want to tear down the motor to do a compression "ratio" calculation.."

Well, I understand your unwillingness to tear down a perfectly good engine, but it might be time well spent if you find out you have some kind of crazy cam in this thing with domed pistons.....

fantastixvoyage

I know, that's why I was trying to narrow it down with mentioning that it was fresh. I'm not disagreeing with anyone just seems to me that these dynamic numbers would tell alot. Wouldn't the numbers change drastically between a 10:1 and 7.5:1 (both fresh)? Say 170 vs 120??

Oh well, its been a long day and maybe i'm not thinking straight. popping a head to start and see what I'm working with (all I know is TRW forged) and if I'm close (flat or reverse dome) I'll run it. Otherwise I'll just cam it down (was a rather large ultradyne) and run N/A till the winter.

fantastixvoyage

Oh ya and this boat really needs a 540 which I hope to build this winter....just like I said last summer!