Ok, I have had a thread about this prolly about a year ago and everyone always asks what the compression is. Well i finally got it. I did a compression test and adjusted the gap to the factory .043 on the plugs from the .039 it was originally at.

The compression is as follows from 1-6 cylinders

 

So as you can see I have two cylinders, 1 and 3 that around 125 psi and the rest are over 160psi, which seems strange to me.

I did each individually with a new compression tester and had all tight connections. The only one tat kinda shocked me at first was #6 gave me 90psi on the first turn over and then I didn't believe it so I turned it over a few more times and it shot up to around 180 psi.

Well, after the gap setting and making sure all hoses were connected properly and the compression was what it is, the power is still not what it should be. I mean it is lacking a great deal of power than the original motor.

What am I missing here and is my Compression within spec. I have always thought that around 120psi + was exceptable for a healthy engine. What am I missing here that is holding back my almost new motor. I have 25000 miles on this motor since replacement in May 2010.

 

125 psi is way low. I had a 7:1 motor that produced more compression. Even our 8.8 motor produces 160 psi and the stock motor is around 10.3:1. Do a leakdown test to find out where compression is going. If you hear noise coming out of the intake, it's intake valves. Same goes with exhaust. If you are getting air out of the recirculating tube on the valve cover, that's crankcase and you have bad rings.
Sorry for your troubles, good luck with it.

 

They should all be @ 180psi +/- 10%

When you do the compression test pull the crank fuse and turn it over for 4-5 sec until the needle stops moving. That is your correct pressure.

If you legitimately are at 125 in two of the 6 cyl then you should feel a major loss of power. Also, spart plug gap will not affect compression AT ALL. It only helps with correct burn of fuel.

 

my car is using oil/smoking and still has compression in the 160s...... lol

 

OK, This sounds like it could make sense.
So the story behind the motor is that I bought it supposedly with less than 5000 miles from an Infiniti Technician that got it out of a car some how in Michigan. He said it was extremely low miles. When i shipped it here I figure at the VERY least if it was trash then I could part it out for the money and make more off the parts. Anyways, when it got here it was SO clean and even looking down in the vavles they looked new so I didn't doubt it. It runs perfectly except for the weakness. The car idles perfectly, no oil use or smoke and everything seems perfect otherwise with the exception of a small hickup around 4500 rpm in 3rd gear when I am putting the pedal down.

When I got the engine, it was a complete long block, so I swapped out the Intake Manifold, Exhaust Manifolds and the other appendages such as starter, alt, etc... It was a REAL easy swap, took 3 days.
You can see here https://g35driver.com/forums/g35-cou...ain-broke.html

So I am thinking that it could have an issue with the Intake being mounted wrong or something like that.

If you would look over my swap thread and see anything that would be an issue.

Everything, and I mean EVERYTHING went back on the car just as it came off. Not one bolt left and everything is bolted and tied back the way it should be. I am slightly OCD on it looking OEM. I hate half way done work on my cars, BUT if you can think of a MAYBE situation, I am all ears.

 

Could leaking from this gasket be the issue. I reused the gasket, prolly a dumb move.


You can call it a stupid move, it's ok. I'd rather know than not. LOL!

If there was a leak here could I potentially be loosing my power here. I am thinking this could be it.

 

I knew the gap wouldn't affect compression but I thought maybe a loss of power. But I was wrong..

Guess a Bleed down test is prolly next. I will re-test the low cylinders for correct values.

 

No thoughts on this? Just curious.

 

Your lower plenum gasket is not the issue. Do a leakdown test on the engine. That will tell you where the compression is going.

 

Ok, will do and see. Man I hope it something simple.

 

Any new progress?

 

No, not at the moment. I have been thinking about it really a lot BUT we are moving in a week and I am moving into a 4 car garage where I can really work on the G. Just waiting for the opportunity to have more space. Can't wait to move and then I will dig into the car.

 

In for results

 

Move date to the new shop and house is this coming weekend. So prolly a couple weeks and I'll get to it.