long vs. short tube headers on E30 M20b25

[g22]

I've done some intake work on my m20 and now think it's time to free up the exhaust with some headers. Can anyone explain what is the difference between long and short tube headers? Thanks

[e30 gangsta]

Anyone wanna chime in? I say go long tube. All real headers that actually do something are always long tube.

[g22]

Thanks for the reply, that's also what I've heard too but I want to understand why that is. The shortys would seem to be at least better than the stock manifold...

[NC325iC]

something about exhaust gas velocity

[trent]

the shorts are just race, the longs are fuh race

[g22]

Trent, I'm not sure what you mean... ?

[MrK]

Shorty headers just increase the size of your exhaust at the ports, and make the flow from 6-3-1 smoother than it is with the stock manifold. Long tube headers 'tune' your exhaust pulses so that there is a certain (high) rpm at which the pulses are timed to pull each other along, increasing velocity, upping hp. Of course, headers in general are more beneficial if the rest of your air-system (intake, cam) is already taken care of.

Someone correct me if I'm wrong.

Edit: Oh, and I believe Trent means "neither are worthwhile mods". Depending on how much money you have to throw around, he could very well be right.

[g22]

Thanks Mr.K. I've got a big bore throttle body, M50 injectors and I'm looking for the 027 M30 airflow. I was thinking I would benefit from some exhaust work. I'm trying to weigh the cost benefit of shortys vs. long and any performance gains. My thought was that at a minimum the shortys had to be better than the stock mani and not too expensive.

[CarsSuck]

Unless you're really on a budget, I would skip the M30 AFM and just pony up for an MAF conversion. Split Second makes a kit as does Miller Motorsport, your you can do your own with a piggy back setup.

[sticksdaman]

how much for that Maf kit you speak of?

[JRKOUPE]

how much for that Maf kit you speak of?

miller performance..;;;;;;;;;;;;;;;;;.....like 599. Look 4 group buys.

[NC325iC]

the split second is upwards of 700

[StereoInstaller1]

A quick explanation of headers: Properly designed headers use exhaust pulses to create a vacuum behind each pulse. The "tuning" of these means that each wave is properly spaced to create maximum suction at the RPM you are running.

Longer tubes are tuned for lower RPM (lower resonant frequency) thus are more appropriate for street.

Basically, the "long tube" types are still not long enough for 2500~3500 RPM that are typical cruising speeds, so will make more of a difference above 4500 RPM.

Placement of the "X" or "Y" makes a huge difference too.

The shorties are so short that there will likely be a big loss of low end torque, but much better power above 7500 RPM...not too helpful on the street.

Luke

[e30_325es]

I've got a 2.7l beast of an eta engine, 283 cam, 325i intake stuff, m30 afm, markd chip, etc. I just installed Bavauto Longtube headers (y-piped to single 2.5in all the way back) and noticed quite a difference. It used to start really pulling at ~3500rpm all the way up, but now it starts around 2500rpm, and even harder at 3500rpm, all the way to 6500rpm (where the small valves limit air flow). I noticed a definate difference. I'd get these headers again in an instant, and they were definately worth the $600 price tag.