Lynn,

I have a question regarding exhaust/inlet lengths that I've wanted to ask for quite a while. 

Q:  Do the optimum lengths of 12/24/36/102 hold true only for the 2-rotor engines or does it work for the 3-rotor engines too?

Mark S. 

The object of the headers, is that the supersonic pulses need to be neatly laid into the collector one after the other in exactly the same spacing. This makes for a good sounding engine, even after muffling. It also makes for great scavenging, and if the muffler is not too restrictive, can maintain a low pressure in the exhaust system. That becomes free HP. For example: I use GE silicone tub and tile caulk on the exhaust header flange. No gasket. It need not be high temp anything because it just is never very hot being clamped to the rotor housing. There is no pressure at all to deal with in this junction, as the supersonic flow is well below sea level pressure (One Barr). If it did ever leak it would draw in local air into the header pipe, and make cracking sounds on closed throttle. If it leaks at all, it will leak at idle because velocity is nearing zero.  

The lengths are from collections of street headers designed to help street engine build up the rotaries dismal low speed torque. The longer the header pipes the more solid the slugs from each firing event, and the better the scavenging and low end torque. 

Once you have a 11" of header, you have two full pulses from each housing and if you collect them with the exact same length of pipe you have done as much as you need for anything over 3,000 RPM. As the revs go higher, the headers (In effect) become longer because more full pulses will fit in each pipe. And here is the important part.

The pipes need to be exactly the same length to the collector. The collector needs to be uniform and silk smooth inside. At 6,000 RPM you are blending 12,000 pulses together, or 18,000 pulses from a three rotor, just like cards being shuffled. If you get any two pulses impinging on each other there will be far less than the very best performance available. Plus the engine will be annoying. Too loud but sounds great entering the pattern is way better than nobody talks to you, and Jimmy's dog won't come out from under the truck.

I had a length of corrigated plastic hose looking stuff, used to cover bundles of wire in trucks. It just fit inside of 1 7/8" ID tubing. I had bends made up and with my abrasive saw I would fit together the headers, tacking on pieces and fitting them into the spaces as I went along. I smoothed the joints inside just as though each piece would be a finished piece. Once at the collector. (both pipes parallel for 3 inches) I would shove the plastic hose up each pipe to the flat plate gasket over each exhaust port. Add masking tape to the hose at the end of the front header, then pull it out and shove in the rear header, to see where the tape ended up. It is easy to lengthen and shorten the straight runs out of the flange to correct small differences in length. 

I am not trying to tune the engine with header length. Just trying to get the exhaust out without screwing away any HP that a poorly designed system will do. The 4 cylinder engines seem to favor a 32-34 inch header to fluff up the torque that a big cam will take away. So if you need help in a 4 cylinder from 3,000 to 4,500 there is your header length. I used 24" because the engine builder uses that on the dyno. It is typical to have two nodes where any paticular header length will add a bit of power. The lower of the two is seldom high enough to use for anything but a street engine.

Just as in piston engines, long, shallow angle collectors produce better torque over a wide RPM range. Short, steeply angled collectors produce better torque over a short range of RPM.  

The two rotor is two one rotor engines on the same crankshaft. The three rotor is three one rotor engines on the same crank shaft. The best outcome is to have both, or all three perform at about the same rate as the others. You will notice that there seem to be complaints as to EGT, water temps, compression, vibration fuel flow, exhaust color, and so on with every recoverable piece of data. The front housing gets the coldest coolant on one side and the hottest coolant on the other side.  The three rotor (I suspect) may have even greater differences). So in those areas where you can get the same outcome, you should try to get the same outcome. As in the intake and header lengths. There you go..........

15 free HP.

Lynn E. Hanover