should my compression by higher?

[AWDtalontsi96]

So I got roughly 1000 miles on my fresh build. and did a compression test. 1. I wanted to make sure the rings were seating in right. 2nd I keep seeing a small amount of smoke that looks and smells like burnt oil coming throw my oil catch can breather. 3rd I get a slight misfire here and there if I don't let the motor warm up for about 2 or 3 minutes before I first drive it in the morning. I got 160 +/- 2 psi per cylinder. Did the compression test on warm motor . Wasn't fully up to temp , but it ran and I let is sit for about 2 hours before checking it. The car runs mint tho once she is warmed up and couldn't be happier and once warmed up the smoke stops coming out of the breather. here are my engine specs

6 bolt block Balance shafts removed arp head studs arp main studs mitsu mls head gasket acl race bearings bored .20 over Wisco 9.0 to 1 pistons Manely H beams Balanced, polished and lightened stock crank Head ported and polished 1mm os ss valves gsc behivee springs gsc chromoly spring seats gsc titanium retainers ferra locks ferra guides ferra seals gsc 280/280 11.7/117mm lift cams 1g intake 1g throttle body bored to 65mm from steve at tb.com. milspec shaft seals

 

[dsmcurse]

Those numbers sound correct. I wouldnt worry about it. Brand new perfect condition 2G engine only makes like 150psi on compression test's (hence low compression motor intended for boost) Since you say you have 9.0-1 pistons (slightly higher compression than stock 8.5-1) then ya, expect the compression test results to be a bit higher than factory specs. Sounds like compression test results came back good.

Just a side note, when doin compression I always disconect the MPI relay so all of my fuel injectors shut off and cant spray any fuel, this is intended so that fuel spray doesnt wash away the oil/surface of the cylinder walls. Also, I dont crank consistant like 3 seconds or whatever on each round of testing, I crank on the starter until the needle of the compression tester gauge quits goin up.

 

[miguelmcv]

Talking about the smoke coming out of the breather,
You might have a simple bad PCV,.

Check if its working correctly, add some pressure to the PCV and see if it holds, they all hold light pressure but not all of them hold to much.

Test it, to Rule that out so you can go to the next step.

 

[AWDtalontsi96]

Those numbers sound correct. I wouldnt worry about it. Brand new perfect condition 2G engine only makes like 150psi on compression test's (hence low compression motor intended for boost) Since you say you have 9.0-1 pistons (slightly higher compression than stock 8.5-1) then ya, expect the compression test results to be a bit higher than factory specs. Sounds like compression test results came back good.

Just a side note, when doin compression I always disconect the MPI relay so all of my fuel injectors shut off and cant spray any fuel, this is intended so that fuel spray doesnt wash away the oil/surface of the cylinder walls. Also, I dont crank consistant like 3 seconds or whatever on each round of testing, I crank on the starter until the needle of the compression tester gauge quits goin up.

Yeah I just pull the plug on the coil back and pull the plugs off the injectors.

Talking about the smoke coming out of the breather,
You might have a simple bad PCV,.

Check if its working correctly, add some pressure to the PCV and see if it holds, they all hold light pressure but not all of them hold to much.

Test it, to Rule that out so you can go to the next step.

I don't have a pcv. I just have 2 -6 an fittings going from the valve cover into a JM fab catch can/breather

 

[My1GLaser]

Sounds pretty close, but a little low. Was the throttle fully open when you did the test? The numbers would probably go up on a fully warm engine also.

FWIW- stock 1g 7.8:1 motors are 158psi. I believe I read that 2g 8.5 CR motors were around 175psi. Mine was 9.15:1 when I built it and compression was 185-190psi. (I cc'ed the head and actually calculated my CR by measuring everything) I only have HKS 272s and you have high lift, longer duration cams, so yours should be lower than mine.

Personally, I would have expected 175-180psi if I had done the test, but like I said you aren't far off.

 

[AWDtalontsi96]

Sounds pretty close, but a little low. Was the throttle fully open when you did the test? The numbers would probably go up on a fully warm engine also.

FWIW- stock 1g 7.8:1 motors are 158psi. I believe I read that 2g 8.5 CR motors were around 175psi. Mine was 9.15:1 when I built it and compression was 185-190psi. (I cc'ed the head and actually calculated my CR by measuring everything) I only have HKS 272s and you have high lift, longer duration cams, so yours should be lower than mine.

Personally, I would have expected 175-180psi if I had done the test, but like I said you aren't far off.

Yeah I am going to do the test again with the motor fully warmed up. Like I said the motor was just slighty warm. My big question is people who run no pcv and just hoses right to there breather catch can is it normal to see a little smoke until everything warms up. I assume with a pcv system you never see it cause the intake mani is just sucking in the that smoke. Also yes TB was wide open

 

[boost97gst]

Hot motor should see ~185 per cylinder with 9:1

 

[AWDtalontsi96]

Hot motor should see ~185 per cylinder with 9:1

Okay , fingers crossed when I do a hot compression test

 

[jayson427]

You need to put a check valve in between the head and catch can. You won't get the right vacuum with it straight open. Some people run more then one check valve too. Best thing to do is look up a proper 4g63 vented pcv system with catch can. There's a good thread on it with diagrams.