s52 OBD2 headers vs TMS/JetHot/Evo shorties

[MC Hammered]

I'm doing a bunch of digging and have found information that says installing the equal length shorties provide no gains and possibly worse performance, but most of this was with OBD1 setups 6-7 years ago.

I couldn't find much information if this is still true with the OBD2 setup, if the losses have been tuned out, etc.

Is anyone here running an OBD2 setup with shorties? Or point me to information that shorts shorties are better/worse than running the stock OBD2 setup?

TIA for any information.

[Bimmerman325i]

Search the bimmerforums E36 M3 dyno thread for posts by me and fsmtnbiker.

Both of us have done the TMS shorty vs OBD2 comparison, and fsmtnbiker also compared to AA and Raceland headers. Also, different cams, throttle body, intake setups...we're both data junkies and tested the vast majority of the legitimate bolt ons for these cars.

Cliff notes: all are better than OBD2, which are comparable to OBD1 (headers, not mids), but the TMS provide a wider torque band but not as much top end power. AA and raceland provide good top end power but have a lot of torque loss (~25tq) between 3-4000rpm, when paired with M50 manifold and standard 3" race exhaust. TMS does not have the torque loss, and loses ~5-10whp up top. If you're only using 4-7000rpm, AA or Raceland/Supersprint euro. If you're not on a track all the time, TMS absolutely. Keep in mind that if you're just changing the header with zero other changes, you're not going to see any tangible results. A tune is needed to extract power, and an uncorked exhaust/intake will compound the gains.

Anyway, search that thread. Lots of good info. Also to note-- he and I used the same dyno. OBD1 or 2 is irrelevant if the midpipe is the same, and our results show that. An S50 won't see quite as much gain as an S52, but the trend is quite obvious.

[MC Hammered]

Thanks for the information and the cliff notes!

[digger]

One glance at the AA headers shows why they might provide a torque loss below 4000 rpm it isn't anything to with primary pipe diameter, primary length or anything to do with equal length it’s the collector length is too short for good bottom end. You get huge reversion as instead of a suction wave there is positive exhaust pressure during overlap at low rpm hence you can cop a massive hit to torque. A longer collector length provides a nice suction wave 2000-4000rpm and basically reduces reversion or even eliminates it. Run some 1D sims in ENGMOD4T and it becomes apparent why the dyno results are what they are...

It doesn’t matter on track if you use a short collector as long as it’s not too too short in fact it’s often better with this style exhaust as it can work better at higher rpm but on street it isn’t much fun. It’s an easy fix just add more pipe between the flanges.... All the BMW inline 6 seem to respond the same to it M20, S50, S54 etc. It’s no coincidence that the S54B32 and S50B32 both have the merge where they are and the torque curve from the factory is awesome from both of them.