Compression Test Advice *Experienced Responders Only Please

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Supra0089

New Member
Jan 13, 2009
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New Hampshire
Hello. I just had a local performance shop run a compression test before I did my upgrades for the year. I am a little worried about the results and am looking for interpretation & input on what's going on.

Relevant Motor Information:
-30k on a remanufactured crate motor from Jasper Performance
-2mm HKS Metal Headgasket installed at 10k by Toyota (Both head and block resurfaced). The tech said that the compression at the time of installation was lower, but still good.
-ARP Headbolts/Studs
-Car drives, responds, boosts strong and is not showing any symptoms of any issues

The Compression Results:
Cylinder 1: 125
2: 110
3: 115
4: 110
5: 125
6: 120

I know that the TSRM says that a 14psi difference is within specs. Here we have a 15psi difference (125/110).

If you need more info about my build, please check my signature link.

The performance shop said that they don't think there is any major issue, but wanted to bring this to my attention before they started my build for the year (JT62, lines, valve cover gasket, electronics, tune, etc.). They mentioned that it's possible with the extra gap from the 2mm Headgasket could cause a lower compression and a minor difference in gap.

In addition to your feedback, I want to know:
1)Is the difference/borderline results due to the 2mm HKS gasket?
2)Should I be worried...ie Am I looking at a rebuild in the near future?
3)Is there any other cause for this difference?

Thanks in advance.

-Jon :1zhelp:
 
Devin LeBlanc

Devin LeBlanc

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Apr 7, 2010
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The reason HKS and other heads gasket manufactures make thicker head gaskets is to try to keep the compression ratio close to what it was from the factory when you surface the head and block removing material. Running a thicker head gasket will bring the compression ratio back to near stock depending on how much was taken off both the block and the head.. However I don't think the head gasket is the problem, do you have any blow by when you remove the oil cap? Any air being pushed out when you put your hand over the oil cap hole with the motor running?

To answer your 2nd and 3rd questions, There is a possibility of a rebuild in the future depending on if there was other block work done other than the block being done, was the cylinder walls touched? New piston rings? There are many things that could cause this, anything from the ring gap being set improper and causing the piston to ware away at the cyl wall, Or could be something as simple as the rings being installed incorrectly, being not offset to each other.

All in all, I wouldn't worry about it, yeah its a little low on compression however if it really ain't broke don't fix it. You said it drives good, runs good and boosts strong, then your probably fine. Great looking car btw :)
 
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Supra0089

New Member
Jan 13, 2009
367
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New Hampshire
TweeT91109;1696353 said:
+1, why didn't Toyota do one?
Click to expand...

Toyota did the original install a few years ago. I believe at that time they did one.

The performance shop did the most recent compression test. They said they will do a leakdown later on in the week. Thanks again.
 
shipkiller

shipkiller

Member
Sep 16, 2010
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Quebec
just saying' the TSRM recommand that you do the compression test with the engine hot, but it is nearly impossible because the time it will take to remove the 3000 pipe and coil will be enough for it to cooldown a bit.
 
Devin LeBlanc

Devin LeBlanc

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Apr 7, 2010
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I can remove the 3000 pipe, throttle linkage, spark plugs and coil packs in less than 10 minutes. If it takes you longer than that something is wrong lol
 
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