Compression test - what range values?

RanRich · 05-21-2020, 10:11 AM

Bumping this thread to inquire about compression on higher mileage engines.

I have a 2009 with 112K miles on it, that's been tuned for about 50K. Just got a compression test and all cylinders were at 150, give or take a couple psi. I don't know if this was done hot or cold, and was just done at my local shop vs. a dealership. A bit worried about those numbers given what I've just read even though they're consistent and the car seemingly runs and drives just fine.

The shop (which has a lot of experience building their own and working on tuned cars) didn't sound at all concerned over the phone either. Is this engine on its way out or am I worrying about nothing?

ZoomZ · 05-21-2020, 11:32 AM

Quote:

Originally Posted by RanRich

Bumping this thread to inquire about compression on higher mileage engines.

I have a 2009 with 112K miles on it, that's been tuned for about 50K. Just got a compression test and all cylinders were at 150, give or take a couple psi. I don't know if this was done hot or cold, and was just done at my local shop vs. a dealership. A bit worried about those numbers given what I've just read even though they're consistent and the car seemingly runs and drives just fine.

The shop (which has a lot of experience building their own and working on tuned cars) didn't sound at all concerned over the phone either. Is this engine on its way out or am I worrying about nothing?

Try different gauge, and hot. Also note the FSM calls for 200 RPM for those numbers. Make sure you are on a power supply not just battery. I'm guessing 150 was taken cold. FSM calls for warmed "thoroughly" engine, Fuel depressurized/fuse out, all plugs out, ACCELERATOR PEDAL FULLY DEPRESSED, and fully charged battery (I'd use a power supply).

If you get low readings still, pour some engine oil into cylinder from plug hole. take readings again, If pressure increases, you have worn rings.

zz

Rusty · 05-21-2020, 04:00 PM

Quote:

Originally Posted by ZoomZ

Try different gauge, and hot. Also note the FSM calls for 200 RPM for those numbers. Make sure you are on a power supply not just battery. I'm guessing 150 was taken cold. FSM calls for warmed "thoroughly" engine, Fuel depressurized/fuse out, all plugs out, ACCELERATOR PEDAL FULLY DEPRESSED, and fully charged battery (I'd use a power supply).

If you get low readings still, pour some engine oil into cylinder from plug hole. take readings again, If pressure increases, you have worn rings.

zz

Make sure that you pour an equal amount of oil in each cylinder. If not, you can get one or two cylinders reading a lot higher.

ZoomZ · 05-21-2020, 06:35 PM

Quote:

Originally Posted by Rusty

Make sure that you pour an equal amount of oil in each cylinder. If not, you can get one or two cylinders reading a lot higher.

Absolutely. Those 50ml syringes with extended nipples would work great. That way you get exact quantity and you can swirl the nozzle (as best as possible) to get even coating on cyl wall.

Rusty · 05-21-2020, 07:52 PM

Quote:

Originally Posted by ZoomZ

Absolutely. Those 50ml syringes with extended nipples would work great. That way you get exact quantity and you can swirl the nozzle (as best as possible) to get even coating on cyl wall.

That's what I use. After you are done with the syringe. You have to pull it apart and wipe the oil off the rubber to keep it from swelling up. The rubber hates oil.

05-21-2020, 10:11 AM	#1 (permalink)
RanRich Enthusiast Member Join Date: Mar 2015 Location: St. Louis Posts: 425 Drives: 09 PG Sport M6 Rep Power: 3374	Bumping this thread to inquire about compression on higher mileage engines. I have a 2009 with 112K miles on it, that's been tuned for about 50K. Just got a compression test and all cylinders were at 150, give or take a couple psi. I don't know if this was done hot or cold, and was just done at my local shop vs. a dealership. A bit worried about those numbers given what I've just read even though they're consistent and the car seemingly runs and drives just fine. The shop (which has a lot of experience building their own and working on tuned cars) didn't sound at all concerned over the phone either. Is this engine on its way out or am I worrying about nothing? __________________ AAM \| Dynosty \| Ecutek \| Eibach \| Hawk \| H&R \| Nismo \| Stillen \| Stoptech \| Z1 Last edited by RanRich; 05-21-2020 at 10:40 AM. Reason: clarified running condition

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