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5.3 Gen IV Compression Test Results - Do these look alright?

 
Old 01-11-2019, 01:56 PM
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Default 5.3 Gen IV Compression Test Results - Do these look alright?



Gen IV 5.3
3.80 Bore Size.

Compression ratio is 9.95
Mahle Forged Pistons
TSP 243 2.5 CNC Ported Heads
TSP 212/218, .600"/.600", 112 LSA

I just finished rebuilding my engine not to long ago, Iíve learned everything from Books, Youtube, and The Forums. The engine runs great it fired up on the first crank about a week ago but it was leaking coolant from the head bolts. So I changed the head gaskets and added sealant to the head bolts, after reading some solutions on here about it. Hopefully that will fix the problem. But before I add coolant again I want to make sure my compression results look alright.

My compression ranges from 160 to 195 PSI which is about a 20% difference from the highest to the lowest number.

Also the rings were gapped a little wider because I plan on putting a turbo in the engine after I get everything sorted out N/A.


I was hoping to reach out for some advice if these compression test results look okay? Thank you!



The test was done with the engine cold and all the spark plugs removed.
(I read about propping the throttle open but when I did the engine wouldn't even crank over)

The outside temp when taking the readings was 30 Degrees Fahrenheit

COMP (160 PSI) Cylinder #1. - PTW(.00385) Top(.023) Second(.020)

COMP(190 PSI) Cylinder #2 - PTW(.00382) Top(.024) Second(.020)

COMP(160 PSI) Cylinder #3 - PTW(.00370) Top(.024) Second(.020)

COMP(190 PSI)Cylinder #4. - PTW(.00380) Top(.023) Second(.020)

COMP(190 PSI)Cylinder #5. - PTW(.00410) Top(.023) Second(.020)

COMP(195 PSI)Cylinder #6. - PTW(.00400) Top(.024) Second(.020)

COMP(165 PSI)Cylinder #7 - PTW (.00395) Top(.023) Second(.020)

COMP(180 PSI)Cylinder #8 - PTW(.00410) Top(.024) Second(.021)

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Old 01-11-2019, 02:26 PM
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Are you doing this test on a brand new build before seating the rings? If so, that plus a cold engine will give skewed results. I suspect this might be why youíre having such a high deviation between cylinders.
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Old 01-11-2019, 02:44 PM
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Originally Posted by s30.hybrid View Post
Are you doing this test on a brand new build before seating the rings? If so, that plus a cold engine will give skewed results. I suspect this might be why youíre having such a high deviation between cylinders.
The trucks been ran for maybe 45 minutes total. I can't really drive it without getting a tune.
That does make sense about seating the rings. I didn't even think about that. Thank you!

How long of a wait to properly seat the rings do you think?
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Old 01-11-2019, 09:17 PM
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Originally Posted by lacfiremx02 View Post
The trucks been ran for maybe 45 minutes total. I can't really drive it without getting a tune.
That does make sense about seating the rings. I didn't even think about that. Thank you!

How long of a wait to properly seat the rings do you think?
Lacfire,

This is a question that you will get various answers to. So, take any answer anyone gives you with a huge grain of salt. But one thing is CERTAIN, and please do not ignore it:

Get a proper tune before you even attempt to seat those rings. You may already know this, if so - great. If not, take heed. If you're running too rich, you'll glaze the cylinder walls, and you won't seat anyway. If you're running too lean, you'll cause damage, and your rings will never seal as they should anyway.

*DO NOT* attempt to seat those rings on your own without a tune, period. Get that thing towed/driven to the dyno, right off the bat. You have a very limited window of getting the rings to seat correctly.

With a proper tune aka proper a/fr, proper timing, you can seat those rings as quickly as a few WOT runs... this is typically done on the dyno anyway.

Edit:

Regarding your compression test results, if the engine is brand new and not properly seated/broken in, those results are null and void. Do not be alarmed with the differences right now. Put a few thousand miles on it after a good tune, then do a compression test. This will paint a MUCH more accurate picture. Of course, if you are seeing symptoms of what you may feel is potential damage or your engine is not running as it should, a compression test after even 500miles will serve you much better than doing one now.

Last edited by AndyTA; 01-11-2019 at 09:25 PM.
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Old 01-11-2019, 10:03 PM
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^^
Beat me to it. Agree with all of the above.
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