Perfect leakdown numbers but 30 lbs difference in compression from bank to bank ?

[fastfredracing]

I checked this car out a few years ago, and got the same results . The customer believed that I may have run the test wrong, but I have done it the same way my whole life .
Engine hot, fuel pump/ignition disconnected, throttle blades blocked wide open, and a battery charger connected so it spins same speed . . I checked the cylinders in the order of the firing order .
This is on a 2.0 e motor . I got less than 4 % leakdown numbers on all cylinders . Only one was 4, the rest were 3 or less.
The left bank ( 1, 2, 3) show compression numbers between 157-160. The right bank show numbers in the 128-130 range . Car runs flawlessly, no smoke, or strange noises, no blow by in the tank, and it will sit and idle at 500 rpm all day, smooth as can be , if you want it to .
I am guessing that cam timing is skewed between banks, or that maybe it suffered a timing chain failure at one point in its life, and maybe had heads/barrels, cams got replaced with mis matched parts ??
Any other ideas ?

[yelcab1]

Cam timing is my guess.

[john walker's workshop]

You're probably right. Hang that dial gauge on it. Had a 964 recently that was 1 whole mm different.

[3stewartS]

No timing chains in that 4 cylinder. Would be hard to change timing bank to bank. When the dots line its is in time.
Thinking outside the box here but maybe an exhaust or intake restriction.
Perhaps the valve lift is shorter on that side? Bent push rods? Flat lobes?
Interesting question!

[dafischer]

We're talking 911. No push rods in that 6 cylinder.

[gomezoneill]

Originally Posted by 3stewartS

No timing chains in that 4 cylinder. Would be hard to change timing bank to bank. When the dots line its is in time.
Thinking outside the box here but maybe an exhaust or intake restriction.
Perhaps the valve lift is shorter on that side? Bent push rods? Flat lobes?
Interesting question!

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[yelcab1]

Originally Posted by 3stewartS

No timing chains in that 4 cylinder. Would be hard to change timing bank to bank. When the dots line its is in time.
Thinking outside the box here but maybe an exhaust or intake restriction.
Perhaps the valve lift is shorter on that side? Bent push rods? Flat lobes?
Interesting question!

Wrong forum, perhaps?

[yelcab1]

Originally Posted by fastfredracing

I checked this car out a few years ago, and got the same results . The customer believed that I may have run the test wrong, but I have done it the same way my whole life .
Engine hot, fuel pump/ignition disconnected, throttle blades blocked wide open, and a battery charger connected so it spins same speed . . I checked the cylinders in the order of the firing order .
This is on a 2.0 e motor . I got less than 4 % leakdown numbers on all cylinders . Only one was 4, the rest were 3 or less.
The left bank ( 1, 2, 3) show compression numbers between 157-160. The right bank show numbers in the 128-130 range . Car runs flawlessly, no smoke, or strange noises, no blow by in the tank, and it will sit and idle at 500 rpm all day, smooth as can be , if you want it to .
I am guessing that cam timing is skewed between banks, or that maybe it suffered a timing chain failure at one point in its life, and maybe had heads/barrels, cams got replaced with mis matched parts ??
Any other ideas ?

I see this a lot with Ferrari V8 where cam timing is very sensitive...
3 dergrees at the crank will cause compression to drop on one bank vs the other. You look at the results and all cylinders on the same side is uniformly lower and you just have to conclude that cam timing is out on one side.

[gomezoneill]

Originally Posted by yelcab1

Wrong forum, perhaps?

Or wrong planet!

[3stewartS]

Originally Posted by dafischer

We're talking 911. No push rods in that 6 cylinder.

I misunderstood. When the OP mentioned 2.0 E motor I thought 912E (type 4 VW)

[ClickClickBoom]

Static differential is a great tool for diagnosis.
http://www.aviationpros.com/article/10388599/cylinder-differential-compression-testing-subject-to-interpretation

[T77911S]

right side cam may be retarded(in relation to left).. gives it less time to build compression. that's a lot though, I would be curious how much cam timing that would have to be if that was it.