: Normal Compression on a correctly timed 1996 N*



IXSLR8
03-05-10, 11:26 PM
Does anyone have an idea on what normal compression is for a correctly timed 96-99 Northstar engine when tested with a compression gauge?

General Engine Specs: Heads were done at a shop. The shop said they were beautiful before they did any fine tuning on them. I strapped them down with studs, inserts and Cometic gaskets. Engine has approximately 50K on it.

Context: I'm currently working on a N* in another vehicle and am trying to determine if my compression indicates that I'm out of time by a tooth on my intermediate shaft to crank chain. I keep getting a PO300 code stating random misfiring and I've replaced all engine sensors, wires, coil packs, plugs, etc...:

Compression test (Cranked Over for 5 seconds):

1-145 lbs.
2-150 lbs.
3-150 lbs.
4-150 lbs.
5-150 lbs.
6-150 lbs.
7-150 lbs.
8-170 lbs.


Second Test (while running):

1--75 lbs.
2--80 lbs.
3--83 lbs.
4--80 lbs.
5--80 lbs.
6--83 lbs.
7--85 lbs.
8--83 lbs.

Any thoughts are appreciated. Thank you, Dave.

Submariner409
03-07-10, 10:51 AM
The 150 psi group is perfect. The 170 is high (carbon ???)

I have never done a running compression test and see no need for one.

The guideline is that all cylinders should be within 10% of the mean - you're still in the ballpark.

Are the coils/plugs connected exactly as shown in the diagrams ? That's critical to prevent a nagging miss.

Click on the diagrams to enlarge.

IXSLR8
03-08-10, 05:24 AM
Thanks Sub. for your help.

I thought the compression looked pretty normal except for the high number 8 cylinder. I was thinking carbon too.

I'm very sure that I timed the motor, as per the posted diagrams, when I did the block inserts and such. I was hoping to see if my compression readings, as compared to someone elses correctly timed northstar, would tell me anything about my timing. This is the first time I have done a running compression test. Someone mentioned to do that kind of reading as well.

I was thinking that I may be off a single tooth on my counter balance shaft to crank sprocket but have the cam chains correct. I have a mild misfire and get the P0300 code as mentioned. I've replaced just about everything I can think of and am now second guessing the timing work I did.

Once again, thank you sir.

Submariner409
03-08-10, 09:51 AM
Hmmmmm.........Call Jake up in Canada at Northstar Performance - www.northstarperformance.com

or go back and find some posts by MikeLawson - he does some Northstar work out near Lexington, KY.

Ranger
03-08-10, 06:23 PM
If I recall correctly it is pretty easy to get the Northstar timing off by a tooth. I remember our old Guru mentioning something about rotating the crank 7 times to get it back in sync or something like that.