j9fd3s

ok so i'm building a 1st gen with a PP 12a engine. it should spend about 80% of its time on the track or in the mountains. the other 20% is on the street.



i'm looking for an exhaust setup that is silenceable (all the race tracks have sound limits) and since i'd like streetable i'm looking for a broad power band over max peak hp



i cant decide between a long primary, which in theory leaves more room for mufflers, and should have my broad power band



or a short, which means maybe more power, but mufflers would have to go inline...



i dunno, why one over the other?

Maxt

Here's a visual tip for you....

setzep

Oh that looks just horrible

Lynn E. Hanover

I can give you some factors, and you will have to choose among them. I don't think you can have it all in one package. The Pport has a much better connection between the intake and exhaust during overlap than does the side port. So, muffling has a more powerfull effect on killing HP.



The most important feature of headers is that the two primary tubes be exactly the same length.



The next most important feature is that the primaries be the right length for what the engine needs to spread its power band up or down. Where do you want the headers to help the engine the most, RPM wise)



The next most importand is tube diameter. Bigger makes more all other features less sharp. Smaller diameter perks things up and makes a real good feel to the engine. This is less scientific but the grin will be wider.



How big? The same ID as the port or just slightly larger. Like 2" ID max.



There is the short system as seen on one national champion. About 11" to a very short collector and a 3" 90 and pipe to a long custom steelpack cut into the passenger door bottom and the pipe turned down right in front of the rear wheel. Those 11" were straight out of the port with a gentle radius to get into the collector.

Much better looking than it sounds, and built to help spread the torque of a Pport being shifted above 10,000 RPM. A more common system is the primaries being in the 24" to 26" to the collector. Good all arounf power up to 9,600 RPM. The last is the early IMSA RS system of about 102" and that puts the muffler under the rear bumper of an RX-2. But the total length is not that critical so you could do that and swap between race mufflers and street mufflers without getting under the car. In that system both primaries meet the collector just behind the rear wheel. This is described in the Racing Beat manual. If you can weld and like to fabricate stuff, they have a kit that works rather well for the street, and holds up about 2 seasons in a race car.



If the design permits it, the longer the run straight out the port centerline before the first bend. The largest radius bends you can fit into the design.



Most people leave in the liner and do some porting on the engine side of it. Other wise (If you take it out) there is a big discontinuity that makes exhaust flow unhappy. The higher the velocity of the gas, the more energy will be lost to any imperfection. So, that step must be replaced with a machined ring of aluminum to return the floor of the port to dead smooth.



Then there is the angle of the primaries entering into the collector. The longer the collector the broader the power band. Tubes at a steep angle makes it more peaky, and closer to parallel makes it less peaky.



You need the collector to blend the pulses from each primary. They are moving above super sonic and the closer you can get to a perfect blend the more power it will make.



From the end of the (6" to 8") collector (about 2 1/4" to 2 1/2" inch diameter) a long megaphone (maybe 18" to 24") up to your exhaust pipe size.



Burns stainless has some great tube bends in stainless if you like to build stuff. Use .062" minimum wall.



Exhaust pipe as close to 3" as you can fit in the car. I use 4" and 4" diameter Borla muffler to get about 100Db. at 50 feet. This is with the exhaust dumped out the passenger door rear corner and pointed at the ground. This is not a streetable system. The passenger door is on the inside of the race track and the sound equipment is on the outside of the track to protect the neighbors.





Go to Paul Yaws web site and look at his street headers. Better yet buy a set from him. All stainless and dyno tuned over years of engine building. WWW.Yawpower.com



Lynn E. Hanover

j9fd3s

that was very helpful guys!



i guess we'll see how fabricatory i wanna get

Maxt

On my street driven p-port, noise did get worse with the shorter primaries, but long primaries totally killed the power everywhere..I am running a border 4" single system on the car with a 3" resonator off the collector, the resonator I felt put a very small dent in power, I have a removable silencer in the rear 4" fart cannon, its 2", it makes it tolerable but does significantly hurt the top end power. When I am highway running, I knock the silencer out, and run with 4" open, but for in town I reinstall..

The header is equal length, it makes the fabrication that much more difficult, but probably worth the effort in the end.

j9fd3s

i'm debating running it sorta like an X pipe too.



couple things in my favor, my engine is prolly the spare motor from that rx2 in the picture, so the exhaust stud pattern is normal.



other thing, is that the cars a 1st gen, so the exhaust has to fit under the axle, 3" is tight, 2x2.5 is ok

heretic

I wonder how beneficial it would be to cut a section of floor out behind the passenger seat and raise it up, to allow for more exhaust clearance to go over the axle. Once you're over the axle, it's a straight shot back anyway.



Or, to get really crazy, eliminate the passenger seat and run the exhaust through the passenger area, suitably enclosed of course.



I recognize that it's somewhat common practice, but routing the exhaust under the axle just seems like a bad idea somehow.

PDF

How short were the primaries if you don't mind me asking?



I've had good results with long primaries (90in or so) but I'd like to dyno a short system.

j9fd3s

*seems* like the biggest hassle is full droop ie jacking the car up, but it might be worth a look to go over...