Lance_S Posted June 27, 2012 Report Share Posted June 27, 2012 Hey guys, Lizzord30 and I were working on the quest tonight and did a run. With the engine was still nice and hot we ran a compression test. 123 to 126 straight across the board. I am running a clearwater head, ported with 1mm oversized SS valves, Ajusa HG with ARP studs, stock cam and rocker setup. Motor was rebuilt 20K miles ago. Car runs great, no complaints. But I was wondering if the compression numbers seemed a tad low. I have seen people stating they are seeing 145. I realize a difference of 10 percent or more between cylinders is a concern and mine are with a few percent, just wondering if the numbers seem low to you. What do you think? Link to comment Share on other sites More sharing options...
Technology Posted June 27, 2012 Report Share Posted June 27, 2012 Nah, that's fine. It's a 7:1 engine. It won't be too high. Feels slow? Turn up the boost. 25 psi seems to work for my car. It corrected the section of head gasket missing between cylinders 3 and 4. Fast as crap and only 45psi compression on those two. lol Link to comment Share on other sites More sharing options...
Chad Posted June 27, 2012 Report Share Posted June 27, 2012 was the throttle held wide open with all the spark plugs out while you did this test? Those factors skew the results. Link to comment Share on other sites More sharing options...
Lance_S Posted June 27, 2012 Author Report Share Posted June 27, 2012 Actually no. The plugs were out but the throttle plate wasn't open at all. Forgot about that one, now that I think about it, it would restrict the motors ability to pull air in. Thanks Chad, that was a no-brainer that I clearly missed. I will redo the numbers. tech, It doesn't feel slow per say...lol...but it's never fast enough, is it? Link to comment Share on other sites More sharing options...
Chad Posted June 27, 2012 Report Share Posted June 27, 2012 depending on a few factors, it will be 5-6 PSI, maybe even as much as ten. That would put it in the range of a very healthy stock bottom end. Much higher and I'd suspect the gage. 145 is for a fresh build on a higher CR motor. Link to comment Share on other sites More sharing options...
Lizzord30 Posted June 27, 2012 Report Share Posted June 27, 2012 Opps totoaly forgot about opening the TB lol altho I think wont be much diff at all was noticing that it was taking more cranking over then seams it should guess that was probly why. but it did have good pressure at first turn over about 85-95psi ish. Link to comment Share on other sites More sharing options...
Chad Posted June 27, 2012 Report Share Posted June 27, 2012 the length and diameter of the gauge hose dictates how long it takes to get a "full" reading. That air in the gauge hose is like a spring, takes a few compression cycles to compress it before the gauge needle will = actual cylinder pressure. Link to comment Share on other sites More sharing options...
Lizzord30 Posted June 27, 2012 Report Share Posted June 27, 2012 the length and diameter of the gauge hose dictates how long it takes to get a "full" reading. That air in the gauge hose is like a spring, takes a few compression cycles to compress it before the gauge needle will = actual cylinder pressure.Yes but it does seam to take one or 2 less fires to get it full with the throttle down. but from my experiences should be about the same. I have had other engines get 55 to 60 on the first fire with the same gauge so i think his engine overall is in good condition based on that plus the even readings. Link to comment Share on other sites More sharing options...
DurbenQuest Posted July 19, 2012 Report Share Posted July 19, 2012 Nah, that's fine. It's a 7:1 engine. It won't be too high. Feels slow? Turn up the boost. 25 psi seems to work for my car. It corrected the section of head gasket missing between cylinders 3 and 4. Fast as crap and only 45psi compression on those two. lol GEEKED! Link to comment Share on other sites More sharing options...
Recommended Posts