Compression Test SR

[defiantmofo]

My car has been running like ass since it was rebuilt. I did a compression test by doing the following.

Pulled all spark plugs/coils/injectors and fuel pump relay.

Motor was warm.

Cyl. #1: 100
Cyl. #2: 115
Cyl. #3: 110
Cyl. #4: 115

I cranked the car about 4 times with the throttle open and got these results. Dropped oil in each cylinder and pressure did not go up. That means the rings should be fine, correct?

Motor has Carrillo Rods, JE pistons, BC cams, rocker arms, valves, cosworth 1.1mm HG, the whole 9 yards.

So the motor has to be pulled and rebuilt, correct? I didn't do the compression test incorrectly did i?

Thanks for your input.

[Sileighty_85]

I fresh rebuilt SR compression should be around 150-157

keep cranking until the needle stops rising

how long have you been driving the car?
Check mechanical timing

[fliprayzin240sx]

Did you break it in properly? If the cap trick didnt change the compression, then it could be the HG or maybe even the valves not sealing properly?

[steve shadows]

MAKE SURE

you are holding the throttle plate full open when performing this test otherwise all readings will be about 30 psi lower than they should be


...

If you did that right then I would check your CAMSHAFT timing and valves

[SoguRacing]

compression is low compared to a stock setup. crank 4-6 times with throttle wide open. if you dropped a teaspoon of oil into the combustion chamber and the compression didn't go up then your rings are probably not sized properly. also, since you upgraded to BC cams your valve overlap will be more prevalent at a lower rpm and cranking rpm is roughly half of idle rpm your overall compression will be lower. Number are close to eachother so that's a good sign. Check your vacuum with the car on. aroud 14 inches of Hg should be correct with BC cams and a 1.1mm head gasket. IF that's good then I'd say you're good to go. you could always do a leakdown test if you're that bothered by the low compression numbers. check the fsm for the leakdown numbers.

another thing...what compression size rods/pistons did you use?

[jamg]

wow, low compression..

[TheWolf]

My car has been running like ass since it was rebuilt. I did a compression test by doing the following.

Pulled all spark plugs/coils/injectors and fuel pump relay.

Motor was warm.

Cyl. #1: 100
Cyl. #2: 115
Cyl. #3: 110
Cyl. #4: 115

I cranked the car about 4 times with the throttle open and got these results. Dropped oil in each cylinder and pressure did not go up. That means the rings should be fine, correct?

Motor has Carrillo Rods, JE pistons, BC cams, rocker arms, valves, cosworth 1.1mm HG, the whole 9 yards.

So the motor has to be pulled and rebuilt, correct? I didn't do the compression test incorrectly did i?

Thanks for your input.

Compression numbers are to be used for intercylinder comparison only. Not to compare different motors.

That's not low compression if your running some high lift long duration cam like 272's or something. Or if you went with a different compression on the pistons. What material was used in the JE pistons? 2618 or 4032? If you got 2618 and had your machinist follow the specs on the piston then they're going to fit loose and the test should be done with the motor warmed up. 3rd. Get a cylinder leak down tester. Pressurize the cylinder and then use a mechanics stethoscope to listen and you'll hear where the air is leaking out. That way you can determine if your slightly lower compression on #1 is because of a leaking exhaust or intake valve seat or compression blowby. If all this checks out. Then you know the reason it runs shitty is because you've got a bodged up tune which is more likely the reason.

[defiantmofo]

The car does have 272 cams. The pistons are the 2618s and the test was done while the motor was warm. Thanks for everyone's imput.

[defiantmofo]

Did a leakdown test properly. All cylinders were between 2-3% so i think that's good. Gonna keep going through the car and trouble shooting, but for now i think the motor is ok. Anyone have any other suggestions?