M52 Low on power

[Dissembler]

My M52 swap has been running great for about 4 months now. The engine idles smooth when hot (although the idle is a little lumpy when its bone cold), pulls strong, revs to 7200 no problem. Sometimes I can feel it stumble at idle, but it is very subtle and intermittent. This car pretty much only drives to and from the track, and I have never once had an issue with it until I dynoed it.



The amount of torque it makes and the dip at 4500 rpm do not seem right at all.

-M52B28, rebuilt top to bottom. New seals, bearings, rings, rebuilt vanos (dr. vanos) etc, OEM head gasket. The only things that weren't replaced where the ignition coils and injectors. Has 1500km on it, broken in at the race track (followed motoman break in method)
-S52 cams, installed with BMW tools and a dial indicator to verify true TDC
-M50 intake
-eBay long tube headers, 3" exhaust, borla mufflers
-TRM tune for all the above with rear o2 delete
-Compression test showed 150psi after 4 puffs, Leakdown showed 3% at 100psi.

A friend of mine with the exact same build (but using an AA tune) made 220 and 200 at the wheels, smooth curve so I was expecting something close. His motor also showed 210 on a compression test.

Any ideas if there may be something wrong with my motor, or is this normal for m52s? Sorry, do not have AFRs as this was done on a mobile dyno at Bimmercruise.

Thanks!

[e46s54dr]

Ive seen plenty of dyno charts on the m5x/s5x and its safe to say that the spontaneous dip at around 4500 rpm definitely seems weird. The first thing that you can probably do us barrow your buddys dme with the aa tune to see if any changes in the power curve are apparent. Im not saying the trm tune is the culprit but it doesnt hurt to eliminate it from the equation. Also, bmw's vanos usually engages at around 4k so I wonder if the problem has anything to do with the functionality of your vanos system or possibly even timing? Anyhow, Im just thinking out loud and not too sure on the validity of assumptions. Good luck either way and please let us know if you do solve the problem.

[lbreevesii]

hes right about vanos. It could be the tune that is causing it though. Might be a good call to test the noid or put an air fitting on the vanos for travel testing if the dme swap doesn't change it.

[Dissembler]

I'll give that a try, probably won't be able to dme swap for a while but I will update the thread when I eventually do.

[325issguy]

My compression numbers are all around 210 as well i believe. 150 sounds low.

[bloodshot-e30]

my tq stayed constent till like 6100 but im making low tq and hp and my compression numbers are reading 220 give or take on all 6

[nrubenstein]

Swap dmes with your friend and redyno. Looks like an early vanos switchover, but it could also be timing or other interesting things.

[bloodshot-e30]

im gonna post my dyno graph that is the smoothest and hase the most power out of the 6 i did but the least tq lol

[Wanganstyle]

for reference a stock S52 is about 210psi compression x the board, any one do a compression test on stock m52 and or s52 cammed m52?

[328ijunkie]

Vanos Issues/Cam timing is my bet.