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05-20-2023, 12:19 PM | #1 |
Scooby Newbie
Member#: 458603
Join Date: Nov 2016
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Rcm high compression pistons compression test help
Ok so I have a 2011 sti with stock heads, but with the rcm high compression pistons ans the rcm head gaskets. I wanted to perform a compression test, do.i do it when it's cold or hot? When doin the compression test, should press my throttle all the way when doing the test? How.many cranks should.i give it per cylinder?
I know there is ALOT OF forums about doin compression tests, but I see nothing on here with the pistons or head gaskets I have in. Also what isa good compression test result with my build? Compression ratio.currently should be around 9.2:1
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05-20-2023, 12:26 PM | #2 |
Scooby Specialist
Member#: 510366
Join Date: Jan 2020
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Have you considerd calling or emailing rcm? They seem fairly responsive.
*or the rcm distributor you got them from. |
05-20-2023, 12:47 PM | #3 |
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Member#: 458603
Join Date: Nov 2016
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Last edited by euroP; 05-20-2023 at 01:09 PM. |
05-26-2023, 04:02 AM | #4 | |
Scooby Specialist
Member#: 419354
Join Date: Apr 2015
Chapter/Region:
MAIC
Location: Newark, Delaware
Vehicle:2007 STI Crystal gray metallic |
Quote:
Per the Subaru factory service manual, the cranking compression for a 10:1 engine is 145-185 psi @ 350 rpm, whereas the range for an 8.5:1 engine is 142-171 psi @ 350 rpm. So, a 9.2:1 is basically the same range. Do it when the engine is hot if possible. No need to press the pedal. Warm up engine, & turn off. Disconnect fuel pump harness in passenger side foot well. Remove fuel cap & bleed off fuel pressure (optional). Remove all 4 plugs. Thread compression guage into any cylinder. I start with the closest to the windshield & prop the gauge up so I can see it. Crank engine ~4-5 revs continuously. Go check guage & record peak pressure. Reset guage & repeat for remaining cylinders. |
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05-30-2023, 01:01 AM | #5 |
Scooby Newbie
Member#: 458603
Join Date: Nov 2016
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Ok. So far compression test results. Done on a cold engine
Cyl1-145 Cyl2-145 Cyl3-145 Cyl4-125. Wat u all think? I'll try do leak down tomorrow |
05-30-2023, 02:19 AM | #6 |
Scooby Newbie
Member#: 268286
Join Date: Dec 2010
Chapter/Region:
W. Canada
Location: Alberta
Vehicle:2011 STi Dark Grey |
If you put a teaspoon of oil in cyl 4 and test again, does the compression come up?
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05-30-2023, 10:17 AM | #7 |
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Member#: 458603
Join Date: Nov 2016
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05-31-2023, 09:25 AM | #8 |
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Member#: 458603
Join Date: Nov 2016
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05-31-2023, 03:47 PM | #9 |
Scooby Specialist
Member#: 515308
Join Date: Jun 2020
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Next leak put some air in there and see where it is going
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06-02-2023, 01:41 PM | #10 |
Scooby Newbie
Member#: 458603
Join Date: Nov 2016
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So jus did a complete leak down. Cyl 4 seems to be jus a rings issue, so ill leave it as it is. It's only a 10% leak. Cyl 1-3 has 6% leak. So I guess that's y difference I'm compression test. Does that make sense??
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06-03-2023, 11:03 AM | #11 |
Scooby Specialist
Member#: 515308
Join Date: Jun 2020
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It will run like that and use oil, like a ring land issue would. But I will say it’s easy enough to fix, 300$ gasket set and set of rings, and I have killed one I let burn oil cause I eventually ran it low.
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06-05-2023, 11:50 AM | #12 |
Scooby Newbie
Member#: 458603
Join Date: Nov 2016
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thanks i think im just gona leave it like this for now as the car still makes power...and deal with it when the cash is a little better than now..jus hope she doesnt fail until then lol
thanks for all the help and assistance everyone who posted!! much appreciated. |
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