Vented oil breather, compression question(s)
08-12-2011, 07:13 PM
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Vented oil breather, compression question(s) car is a 2001 trans am ws6 rear mount turbo, forged pistons, rods...it was built for the mods it has.
I got my car back from the shop and a year and a half later I finally made it to the dyno, no problems at all and ran great. Dyno'd great, numbers seemed low in the low rpms even though my compression is supposedly 10:1 still.
So i took the car to the dragstrip and it ran lean on me and I did let out of it but at 5k rpm...not much you can do anyway (it blipped on the data logger lean from wideband reading) and the car felt funny hence why I let out of it.
So I then pull in the pits and pop the hood to let it cool and re-tune it richer and later to go for another pass. I notice when I pop the hood (it still running) that I'm getting a lot of vapor/steam out of my oil cap breather on the passenger side at IDLE just sitting in the pits.
So I start questioning things, so I borrowed a compression checker and got a leak down tester (be here Monday). I warmed the car up to full operating temperature and drove around and came back home pulled it in the garage and let it cool for ~15 minutes then starting pulling plugs out.
I only pulled 1 plug out and then hooked the compression checker up and rotated the motor over. Gauge read 100psi. Should I have taken all the spark plugs out and then turned it over? or does that matter?
I then repeated (with all other spark plugs in) with the other cylinders on the driver side (going to do passenger side tomorrow) and the reading for all cylinders on the drivers side are ~100.
Also, here is video of idle and vapor/steam coming out of breather. I put my hand over the breather and it is pushing quite a lot of air out.
http://www.youtube.com/watch?v=15YK-_ld4Ts
I'm thinking broken piston ringlands or valve leakage or both.... the car has ls6 heads, no mods to them so 67cc then I have -4cc valve relief pistons and the motor was built to be 10:1 compression. it is a 220 / 226 .605 / .600 115+2 cam
Prior to the dragstrip run and the car period (prior to and after the build) I never once saw or felt vapor being pushed out of the breather like this, nor pressurized like it is. At idle everything should be at vacuum. Now i do realize that under boost I will get some blowby and I will see air come out of the breather...but I strongly believe something is wrong.....
I got my car back from the shop and a year and a half later I finally made it to the dyno, no problems at all and ran great. Dyno'd great, numbers seemed low in the low rpms even though my compression is supposedly 10:1 still.
So i took the car to the dragstrip and it ran lean on me and I did let out of it but at 5k rpm...not much you can do anyway (it blipped on the data logger lean from wideband reading) and the car felt funny hence why I let out of it.
So I then pull in the pits and pop the hood to let it cool and re-tune it richer and later to go for another pass. I notice when I pop the hood (it still running) that I'm getting a lot of vapor/steam out of my oil cap breather on the passenger side at IDLE just sitting in the pits.
So I start questioning things, so I borrowed a compression checker and got a leak down tester (be here Monday). I warmed the car up to full operating temperature and drove around and came back home pulled it in the garage and let it cool for ~15 minutes then starting pulling plugs out.
I only pulled 1 plug out and then hooked the compression checker up and rotated the motor over. Gauge read 100psi. Should I have taken all the spark plugs out and then turned it over? or does that matter?
I then repeated (with all other spark plugs in) with the other cylinders on the driver side (going to do passenger side tomorrow) and the reading for all cylinders on the drivers side are ~100.
Also, here is video of idle and vapor/steam coming out of breather. I put my hand over the breather and it is pushing quite a lot of air out.
http://www.youtube.com/watch?v=15YK-_ld4Ts
I'm thinking broken piston ringlands or valve leakage or both.... the car has ls6 heads, no mods to them so 67cc then I have -4cc valve relief pistons and the motor was built to be 10:1 compression. it is a 220 / 226 .605 / .600 115+2 cam
Prior to the dragstrip run and the car period (prior to and after the build) I never once saw or felt vapor being pushed out of the breather like this, nor pressurized like it is. At idle everything should be at vacuum. Now i do realize that under boost I will get some blowby and I will see air come out of the breather...but I strongly believe something is wrong.....
Last edited by ZL1Killa; 08-12-2011 at 07:19 PM.
