Compression test - what range values?
 

Hi guys,

2014 Nismo 370z here with 34k miles. I’ve been contemplating selling it for a while and think I’ll just hold on to it for now. Still having a lot of fun with it. I figured if I’m keeping it then I want to do a compression and leak down test. I don’t have a service manual so I’m not sure what psi range the compression should be aside from the universal rule that all cylinders should be within 10% of each other. What is the range I should be shooting for?

For leak down I’m hoping for 7% or less. It’ll be real interesting to see what numbers I get!

Thanks in advance

Bump

Give it a little more time and someone will probably provide a number for you.

Assuming the car has been taken care of, you should have more than one good cylinder (probably six of them) for comparison. 34K miles ain't nothin' nowadays.

The FSM has gotten hard to find but it would be well worth the time and effort to search for a copy.

Compression values themselves are not as important as the % ranging between cylinders. i say this because you can get different reading with different gauges on the same cylinder. From my understanding these motors should be anywhere from 180-220psi on a wet or hot test depending on gauge and motors condition and a good rule of thumb is 10% between highest and lowest cylinder.

I just did a cold test on my motor and ranged from 160-170 psi with a range of 6% between my highest and lowest cylinder. Unfortunately i have not done a wet or holt test, but those number should only go up.

Husam2012 can chime in, i think he was reading 220psi on his new (Stock) motor.

Alright! I was able to track down the FSM online, although it seems like it’s for a non-Nismo. Not sure there should be a difference between regular trims And a Nismo in this respect - correct me if I’m wrong.

See attached. It looks like the range should be 242 - 341, if I’m reading this correctly

Yeap, that is correct. Minimum should be 178.

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.



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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.

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.

Just a head up for anyone worried about their compression tests.

I tested a ton of Zs recently as I work/tune them everyday and most healthy ones are around 180-190 psi.

Keep in mind that most gauges vary a lot, even the same branded ones. I was able to get 220 psi on a older HF compression tester vs about 180 with a newly purchased one. Snap on tester were usually higher reading than the HF testers.

I just did mine with a new snap on compression gauge kit.

This was 10 rev per test, on a stone cold motor, with 50k miles.

Compression test 11/4/2020
10 cycles per
#1 230 psi good plug
#3 220 psi bad plug
#5 228 psi really bad plug
#2 250 psi good plug
#4 250 psi bad plug
#6 0 psi real bad plug

Burned valve in #6 hole.