I'm going to install the sub 2.5 n/a engine and a s/c in my experimental plane this summer. I'm interested in optimizing the torque in the 3800 - 4400 rpm range. Which exhaust system would be the best performer? Data would be appreciated.

Any equal lenth headers should do. Not the Borla's though, which are the cheapest, but don't breath nearly as well as the other more expensive ones. Go to www.subarureview.com and check out the different kinds that are available. Then go to www.subaruaircraft.com and see what information this guy has to offer.

Thanks Forestar. Actually, I'm buying the engine package from Subaruaircraft.

I'm not convinced Subaruaircraft's exhaust is tuned, though. Tuning requires very exact header (and collector - tailpipe ?) lengths. Tuning is the science of selecting the exact length of exhaust system. The theory states that if you are able to create a vacuum inside the header by the exhaust port at the exact moment the exhaust valve opens, then you will have the exhaust gasses actually be sucked out from the cylinder. This enables better evacuation of the hot exhaust gasses, and therefore better filling with the new, cooler, potent fuel/air mixture. This in turn creates a better combustion, and you end up with more power, better cooling of the cylinders, and longer engine life.

This vacuum is supposedly created by 'tuning' the length of the headers and collector-to-tailpipe distances (and pipe diameters) such that the pulse created as the valve opens and the first blast of exhaust enters the header will travel down the pipe, gets reflected back up the pipe where it hits the open air, and the return pulse's negative pressure pulse has to arrive at the exhaust port again at the exact time the valve opens again to expell the next spent fumes.

To me it's kind of a black magic thing. There's been a couple of papers written on the stuff, but I'd like to know if anybody in the Subaru environment has 'tuned' into this free power gain, and started selling tuned systems for the n/a 2.5 subaru.

Pilot

You can call Burns Stainless and have them help you design a system. Check out their DynoSys service here- http://www.burnsstainless.com

Thanks jerome02rs, I checked their website out. That's a good lead, when I'm ready to install the engine in the plane, I'll call them.