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Generation III Internal Engine
1997-2006 LS1 | LS6
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Old 09-03-2010, 08:42 PM   #1
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Post is 240 cylinder compression normal?

Hi i did a valve job and install new valves to my heads because i had poor compression 155 average and now that i re-install my heads i have 240 on every cylinder is that normal? My Compression Ratio is 11:1 Post your cylinder compression and your compression ratio!!
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Old 09-03-2010, 10:53 PM   #2
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Well to have the same on every cylinder isn't normal so it makes me ??? your #'s. That is high also... Your cam will also affect #'s... A bigger cam will bleed off cylinder pressure so.....
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Old 09-03-2010, 11:16 PM   #3
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Good thread. I just bought a compression tester, time to change plugs anyway. I'm almost at 175k miles. I'll post what I get.
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Old 09-03-2010, 11:24 PM   #4
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How much smaller are the combustion chambers and did you verify?

If that figure is accurate your going to have a heck of a time keeping it from knocking. On 93 octane you have a slim shot with a perfect tune but honestly even that is stretching it and detonation is likely.

Check it with another guage to verify.....ideally you want to be in the low 200's for a good running pump gas combo. The 417 and the 407 I built a few months ago both cranked about 205 PSI.

Big cammed cars can show less as Guy pointed out because they bleed off more cylinder pressure on the overlap cycle but even a big cammed car should be in the 185 - 195 range or you left some "money" under the table.

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Old 09-03-2010, 11:32 PM   #5
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it was in the 235-240 to be exact I did the compression test with 2 different gauges and i got the same results!! But now that i think about it i did clean my cylinder walls with a rag and some oil before instilling the heads so i think that's why i got high readings!! I will run my car and check my compression again and will post the results!! so if you guys do a wet test also post the results!! It never hurts to do a wet and dry compression test!! it will tell you how your rings and valves are doing!!
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Old 09-05-2010, 08:06 PM   #6
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Did my 1st compression test on the LS1. I've done the plugs enough times to be good at it but getting the compression tester threaded was annoying.

Anyway I masured a max of 215psi, had a min of 195psi. Average for all 8 was about 207psi.

My static compression is about 10.8, stock 346 LS1 long block, 243s with 62cc chamber and stock graphite head gaskets ~0.057. I do have high miles on my long block but the 243s were all new with a good valve job and went in about 65k miles ago.

My cam is just a TR224 114lsa. Small cam with negative overlap.

To the OP, I put some numbers in the SCR calculator for your setup. For a 383 stroker I used a bore of 3.9 and stroke of 4, 61cc chamber and gasket thickness of 0.057. That came out to a SCR of 12:1. But I don't know your setup so I might not have all the right numbers. It would explain your high compression numbers though.
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Old 09-06-2010, 09:36 AM   #7
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Does are very good compression numbers for a high mileage engine you still have a lot of life left on your engine!! I did re-check my compression after running my engine because i figured my cylinders were wet and a got a average of 185-190!! I think my numbers are expected because of a larger cam!!
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Old 09-06-2010, 11:10 PM   #8
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Those numbers are probably what you want with a healthy cam like yours. Looks like you have all the other supporting mods too, very nice setup. Must be fast.

My car is just a daily driver, mostly highway miles. Hope it holds together for a while longer. (knock on wood!)
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SSRA, Dynatech LTs & Y w/cats, Magnaflow cat back, 17x9 ZR1s, LS7 clutch, Slowhawk tuned.
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Old 09-07-2010, 08:09 PM   #9
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Quote:
Originally Posted by massls1guy View Post
Those numbers are probably what you want with a healthy cam like yours. Looks like you have all the other supporting mods too, very nice setup. Must be fast.

My car is just a daily driver, mostly highway miles. Hope it holds together for a while longer. (knock on wood!)
Is very fun to drive and is the fastest car i owned!! i will soon post a video when the z28 was dyno and will show the dyno graph so everyone can see my numbers!!
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Old 09-08-2010, 11:26 AM   #10
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last time I did mine they were 190-210

stock block, 99 heads surfaced, comp 230/224 reverse, fel pro .051 replacement gaskets
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Old 09-21-2010, 06:31 PM   #11
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I have ran uptop 225-230 psi no problems, I have always gained in doing so, but tune has to be right, less timing is more efficient, every motor is different we run turbo engines at 180 psi with 23 psi on pump gas, because the chamber has had a lot of work and quench is tight still running 11 deg timing, So one motors 240 psi is not another, depends on the quench, chamber, rod length etc. In general most NA motors I shoot for 225, I find on 200 they feel a little soft and take a **** load of timing with 225 it gets them moving free 20hp. But again you have to see how the motor reacts to its current cranking compression, If it is taking less then 20 deg timing at pk tq I would run a wider lobe sep or more work on the chambers. Stock head LS1s tend to like less cc then the L92s for instance. I was running 32 deg lead on 205 psi and 26 on 230psi. Changing exhausts and intakes tends to alter what timing it likes aswell. The more compression you run though the more timing sensitive they are.
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Old 09-21-2010, 06:31 PM
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