I had custom pistons ordered for my setup and had 8.75:1 CR pistons made. I see a lot of people on the org. yielding much higher pressure numbers than mine on my motor. On a cold test I get 170 - 175psi across the cylinders. When I test warm, I get 175 - 180psi. The one thing I haven't noticed is the type of compression rings people are using. I was told by Venolia that a chrome moly comp. ring is best for turbocharged motors. I was wondering if anybody has opted to use those chrome moly rings and if they've had the same results(a lower press. number) or are they getting those higher numbers with standard rings???
Time to get it going again.....
that 'chrome moly' ring they were referring to is actually chromed ductile iron with a moly coating. im not sure if its the 'best' but a stainless top ring goes a long way to keep heat handled. unfortunately ive yet to find a company that actually makes a stainless top ring for our size pistons with our ring groove thickness. total seal seals their "ap" or advanced profiling stainless top rings in our size but they only come in 1.0mm or smaller from what ive been told by them.
these "chrome moly" rings are pretty much what most places use anymore anyways... example, order a set of hastings rings for ur quad 4, they are "chrome moly".
IMO the best compression ring is either a napier or a gapless. weather either is best for boost or not i do not know..
also, keep in mind.. ur CRANKING pressure "compression" can change from engine to engine with more than just ring leakage. cam timing, stroke, head deck height (and chamber size) as well as valve size/dish/location, block deck height, piston size and compression height as well as head gasket thickness will also contribute to different numbers.
Edited 1 time(s). Last edited Friday, April 29, 2011 5:31 AM
I would think with compression that low 175 psi is about normal, most people on here havge higher compression than you.
well cory... thats actually decent for a quad... they have less stroke.
read some of the compression threads on Q4F... thats right about where most quad guys are from what ive read.
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