Compression test results, need some input

**VegasSpeed** · 03-12-2008, 21:34

I had a compression test done on it today on that yellow 97 NSX-T. It came out pretty well I think. All Cylinders were 190 except one being 160. I believe it was the first cylinder. Factor X did my test and Mikey didn't seem concerned and thought it was just carbon build up from not driving it hard. So it was consistant with 190 across 5 of them and either the first or last cylinder had a 160. Two members here gave me mixed opinions. Let me hear what you think? Will the engine deal with a CTSC in the future? This is the car with 119k miles on it.

**RON98** · 03-12-2008, 23:12

I was always taught that its not the compression numbers but rather what it looks like across the board. If they are about for 10-15% off your usually ok.

190 across the board + 160 would be a little cause for concern since its about 15% lower than the others and pushing the limit. I would get a leak down test to see exactly where the leak is from.

valves, (intake/ex) or rings.

If its the carbon theory, I would run a little bit of seafoam or water through the car and then go for a real hard drive and see if it flushes out the carbon.

happy motoring

Rob

**NSXFRIEND** · 03-13-2008, 04:52

I would say 190 above is good with open throttle compression test and a functional gauge to measure the numbers. 160 is not acceptable for that much miles could indicate future rebuild. I am assuming the test was conducted at sea level and not higher elevation?

**VegasSpeed** · 03-13-2008, 09:14

It was done at 2150 elevation in Vegas.

**davidf** · 03-13-2008, 09:38

Originally Posted by RON98

I was always taught that its not the compression numbers but rather what it looks like across the board. If they are about for 10-15% off your usually ok.

190 across the board + 160 would be a little cause for concern since its about 15% lower than the others and pushing the limit. I would get a leak down test to see exactly where the leak is from.

valves, (intake/ex) or rings.

If its the carbon theory, I would run a little bit of seafoam or water through the car and then go for a real hard drive and see if it flushes out the carbon.

happy motoring

Rob

Agree, 30 lbs difference is a red flag IMHO. Do what Rob said then test again.

**swerve** · 03-13-2008, 10:56

it is not unusual to see a lower compression on the first cylinder in the firing order as it is the one getting the most abuse. i do agree that it should be a bit closer to the range of others but i suspect it is a valve adjustment issue.

**s14_tat** · 03-13-2008, 11:38

also if it is a carbon build up issue than cylinder #1 would most likely be reading higher than 190 psi because 190 psi appears to be the norm, and carbon build up generally raises compression.

**jond** · 03-13-2008, 11:54

Originally Posted by RON98

I would get a leak down test to see exactly where the leak is from.

valves, (intake/ex) or rings.

Same here. I would find out if it's the rings or the valve seats. I would assume valve seats aren't TOO expensive to replace if that's the problem?

I wouldn't consider supercharging it though until its fixed. If a ring is broke you're going to cause problems, IMO.

**swerve** · 03-13-2008, 13:19

carbon buildup in the ring groove will prevent the compression gases from pushing the ring against the cylinder wall yielding lower compression and the same can be produced by out-of-adjustment valves. i seriously doubt there is any damage to the seats etc. it is almost for sure one of those two causes. there are products designed to de-carbonate the combustion chamber and the ring-grooves as the engine is running- the best one i ever used is sold under "yamaha" brand in the motorcycle stores. before you do anything else, get a can of the stuff, spray it into the intake while revving the engine slightly, them test the compression. if that does not change anything then check the valve adjustment. only if those two do not produce results you can start ASSuming ring and valve problems.

**RON98** · 03-13-2008, 14:14

Originally Posted by swerve

it is not unusual to see a lower compression on the first cylinder in the firing order as it is the one getting the most abuse. i do agree that it should be a bit closer to the range of others but i suspect it is a valve adjustment issue.

carbon on the valve seats will cause problems and can lead to lower compression due to inproper valve seating, also carbon builds up on the pistons which increases compression and traps fuel which causes more carbon and hot spots leading to detonation which leads to more engine problems.

you have to try very hard to drive that nsx like a dead man to build up that much carbon.

Do the easiest things first.

Right now, your fastest option is take the car out, do an "italian" tune up (drive it hard). Take a 5 mile run. Redline it a handfull of times then run a compression test after that. If you still 30 psi lower, i would run a leak down test to see where your losing all the psi.

Im sure Mike at Factorx can run the tests.

Usually on hondas, they are pretty consistant across the board. 0-5% difference is the norm i have seen.

warm regards

Rob

**MartinSD** · 03-13-2008, 16:21

Greetings

Take it for a 5 mile drive and don't get above 2nd gear. You will blow the carbon out and not get a ticket.

Cheers,
Martin

**RON98** · 03-13-2008, 18:54

Originally Posted by MartinSD

Greetings

Take it for a 5 mile drive and don't get above 2nd gear. You will blow the carbon out and not get a ticket.

Cheers,
Martin

should be illegal to have such a fast car and go so slow

**swerve** · 03-14-2008, 07:33

[QUOTE=RON98;966288]carbon on the valve seats will cause problems and can lead to lower compression due to inproper valve seating, also carbon builds up on the pistons which increases compression and traps fuel which causes more carbon and hot spots leading to detonation which leads to more engine problems.

you have to try very hard to drive that nsx like a dead man to build up that much carbon.

Do the easiest things first.

sure, but it only takes few specks of carbon in the ring-groove to make the ring stick- notice i said nothing about carbon buildup on the piston dome or valve seats! with 30points lower compression on one cylinder only there has to be an obvious cause- a stuck ring or a tight valve, both an easy fix. yes, an 'italian tuneup' does work a lot of times but why not spend 5 bucks on the decarbonizer before you run the snot out of it? you just increased your chances of success!

**sahtt** · 03-14-2008, 09:15

190 ccross the board and a single cylinder in itself at 160 isn't a big problem today. For instance, it would most likely still dyno about where it should.

The problem is if that figure drops much lower, you are in for a rebuild. Since you are probably planning on driving the car for at least a couple years, it's a fairly serious concern IMO. With forced induction in mind, I'd have to pass unless you fix the issue and get that figure up to 170~175 at least.

This is only an issue because rebuilds are expensive both in parts and labor.