Plugs + Compression test

[MikeV]

Since I didn't own this vehicle from Day 1, I wanted to give the Mighty Jeep a compression test to see how tired it was. I readied 16 NGK copper plugs in the stock heat range to replace whatever was coming out, and went at it. I was a bit surprised to find NGK Platinum plugs in it. Apparently the previous owner knew a little something about it and upgraded the stockers. I took one plug out of each cylinder and performed my test,and here are the results per cylinder in psi:

1 - 200 2 - 190
3 - 195 4 - 195
5 - 191 6 - 194
7 - 200 8 - 189

I could never find what kind of compression it is supposed to have, but I do know that each cylinder should be within 10% of each other. Mine look good after 69.5K miles with the highest and lowest numbers being 5.5% apart. I replaced the Platinum plugs, which were gapped at .045", with the new Copper plugs gapped at .050". I know Platinum plugs are supposed to be "better", but that's only because they last longer. The SRT seems to like the slightly wider gap and it felt good on the test drive. If anyone knows what the 6.1's stock compression psi should be, let me know. I'm curious to see how mine stacks up.

Next up is replacing the stock Goodyear runflats in front with the same Nitto NT420s that I have in the rear. The new tires are in the garage now and will hopefully go on over my lunch break early this week.

[Centurion]

That sounds about right for PSI... Don't know what the actual #s are supposed to be...

[SMosher]

The gaps call for .045 in some applications.
Like for the blower application I have to run 2 steps colder and I use the iridiums from NGK. Not cheap! Also gapped at .050.

I can ask for the stocker compression numbers if you'd like Mike.

[MikeV]

I'm surprised you're running that wide of a gap with a S/C. Maybe I'm thinking of nitrous when it comes to a lower gap. It says .050" on the sticker under my hood. It feels better at .050", so I'm happy.

If you can find out what the compression is on a 6.1L, I'd be oh so happy.

[SMosher]

Originally Posted by MikeV

I'm surprised you're running that wide of a gap with a S/C. Maybe I'm thinking of nitrous when it comes to a lower gap. It says .050" on the sticker under my hood. It feels better at .050", so I'm happy.

If you can find out what the compression is on a 6.1L, I'd be oh so happy.

Give me a call. I'll pm you my number.

[SMosher]

My apoligies. Mine are gapped at .035. I have NO IDEA what I was thinking.

Originally Posted by SMosher

My apoligies. Mine are gapped at .035. I have NO IDEA what I was thinking.

[EPIC SRT]

I checked my 2006 service manual today and as far as I can tell, it doesn't even provide what compression should be.

For 6 cylinders and the 5.7 it says that the compression should be at least 100psi but not vary more than 25% between all cylinders and to basically cycle the engine to a few readings on each cylinder to check for differences within one cylinder.

On the 6.1, it discusses a special tool use shop air to pressurize each cylinder to test for pressure loss.

Interesting stuff! Not sure why the instructions are different for the 6.1.

Hmmmm.....

[MikeV]

100psi seems awful low. I wonder if that's the service limit or something. Strange that the info isn't more readily available. Guess I'll have to wait for the next chat session with the engineers that some of the forums have.

[EPIC SRT]

Give Bob at SVS a call: (916)*489-3072

Tell him your from the forums and just ask him if he knows. He has done a lot of work on LX's and 6.1's .