No bent valve...help diagnose why I'm slow.

[permit]

Ok, so at the end of August, when the engine had just been put in, we did a leak down test and compression test. The leak down resulted in air coming out the exhaust pipe when testing the first cylinder, and the compression test showed that the first cylinder was ~20psi less than all the others. Bryson and his dad (professional BMW technician for longer than I've been alive) conclude that there is a bent valve.

So, I go along with this, I accept that my car is moderately fast, and that it paces e30m50s. Along comes a holiday where I have the time to get the valve fixed, so it goes to the repair shop, and they start by doing a compression test. The test shows 175psi across the board, they even do the test again when I'm there to prove it. So they determine there is no bent valve, and it isn't worth pulling the head to look at since a bent valve would allow a lot less compression 175psi.

Now my question is: why is my e30 still pacing m50s? 175psi is a damn good compression number, the bottom end is for sure a 2.8, and my software is not fucked up. I'll be looking to get it dynoed when I get back to AZ, and also racing eightyfoure again. Any insight as to my problem would be great.

[BimmerToad]

Get a dyno chart with some AF figures and absolute manifold pressures and go from there.

[NickP]

maybe your exhaust valve wasn't properly seating and now it is

[permit]

maybe your exhaust valve wasn't properly seating and now it is

Possible, probable..but I think I would have noticed the 30-40 horsepower incurease.

Todd, dyno will probably tell me everything I need to know, you're right.

[BimmerToad]

Remember that you can't really feel horsepower. You can feel torque, which is probably only a little bit more than your 2.5L M50. The 2.8L is torquey out of the box, but when you put in the S52 cams and M50 manifold on, it probably takes away from the overall torque output, but pushes the torque curve to higher rpm, hence higher hp.

Does the M52 at least feel like it pulls longer? (i.e. more torque output over a broader rpm curve)

Regardless, dyno that bitch and go from there.

[Jand3rson]

I'm anxious to see the outcome of this, keep us posted Jeremy.

[DaN]

Is it possible to get some diagnostic information out of the DME? Anyway to know if there are codes in the system?
The m52 was made after 96 right? Is it still obd 2, or has it been converted to 1?

[permit]

Is it possible to get some diagnostic information out of the DME? Anyway to know if there are codes in the system?
The m52 was made after 96 right? Is it still obd 2, or has it been converted to 1?

OBD1, correct.

Todd, true about the horsepower and the curve, maybe I do have that 40 horses back, but I just can't feel most of it. Who knows, this thread can die for a while until I get the car dynoed I guess.

[Brew]

maybe your exhaust valve wasn't properly seating and now it is

I'd say thats a good possibility. We had the same thing happen in class last week. Did a compression test on a guy's 4-cyl Mazda truck. It showed 200-210psi across the board except for cylinder 3, which was at 150psi. We then did a leak down test and determined that it was leaking compression through the exhaust valve.
We tested it again the next day, after the guy did a longish highway trip and the compression was 200+ on all cylinders. We concluded that a piece of carbon probably got stuck in the valve and didn't allow it to seat all the way.

I'd say that there is a good chance that you have/had the same sort of deal.

Does the engine run well other than the lack of power? Idle smoothly? Any misfires? Bad coils are very common with these motors.

[permit]

Idle is flawless, revs all the way to 7k beautifully, doesn't backfire...even feels like it isn't missing power, I only know its missing power because I couldn't outrun eightyfoure. If anyone else were to drive this car, they would have no clue its missing power.

I'm really thinking its running how it should, and I just can't tell.

[Jordan]

I only know its missing power because I couldn't outrun eightyfoure.

Well, if that is your reasoning there is more here in play then just your larger bottom end.

What tranny are you and he running.
What diff are you and he running?

[DEV0 E30]

I'm pretty sure he has the same setup as me. Getrag 260 and 3.73 LSD.

[rwh11385]

whoa, i can test the condition of my engine by drag-racing??!??! i never knew!!

[permit]

I'm pretty sure he has the same setup as me. Getrag 260 and 3.73 LSD.

[Jordan]

Have the 2 of you weighed your cars? Thats also critical to compare in the method you are.