E21 track car with M52B28 low on power - dyno sheets

**Briner** · 04-14-2019, 01:30 PM

Posted this in the engine conversions sections, but no feedback. Hopefully I can get some comments here

I have an E21 track car, that had an M20B25 engine, but I recently swapped it for an M52B28. The new engine was bought from a friend who had it on his track ready E21 and has the following list of mods; Its a manual transmission, with M50 intake manifold, pink injectors, M54B30 cam with lifters and valves, Schmiedmann type 2 exhaust manifold, 6in2in1 with a Y pipe into a single 60mm exhaust straight pipe with single muffler, lightened flywheel with a Sachs racing clutch kit, a custom remapped ECU with the limiter set to 7200 rpm.
The car has also a 3.45 E21 LSD diff.

It was never dynoed before, but we were all expecting something around 240hp

However I've had it on the dyno and could not get more than 197hp at the flywheel and around 245NM of torque.
I have two other friends with E30 with the same engine, both with an M50 intake and a custom remap and everything else stock (different diffs of course since it is an E30), and one of them is making 215hp, while the other exactly the same as me using my ECU.

After the first dyno I've had the injectors cleaned and tested (they were not all spraying the same, now they are perfect), put new spark plugs, did a compression test (all cylinders running the same at 9.5), installed a new BMW air filter with a heat shield, installed an adjustable fuel pressure regulator but set to the standard 3.5bar, so I can monitor fuel pressure. The car has a Bosch 044 fuel pump.

I did a new test today, exactly the same results as before, no change. Swapped different remapped ECUs, with insignificant changes.
The car revs free, but lacks torque low down, pulls very hard after 4000 until 6- 6500 rpm.

I would appreciate any comments that can help me find out why it is so low on power, I am basically making stock hp, and lower than stock torque, the only thing that is changed is the character of the engine.

Thanks.

**Somjuan** · 04-14-2019, 03:05 PM

That’s odd. My exes old m42 did a strange thing where it wouldn’t throw codes but a knock sensor was faulty, causing it to retard the timing. Maybe something similar is happening for you? What’s stock compresson supposed to be in the m52? A leakdown/compression test might be in order