Defined Autoworks Header Install!

NoDOHC · 06-25-2011, 10:12 PM

The front and rear headers are the same length, I wrapped them with super high-temp header wrap and I can assure you that they are the same.

I have some more info that I haven't fully digested yet, so before I post anything, I am curious if anyone has tested the exhaust backpressure on an open set of Racing Beat headers at 9,500 RPM. I hope someone has, because I can't find a good way to test mine without drilling holes in them, which I hesitate to do because I want to sell them.

I cobbed a $30.00 tractor muffler up to the headers in true ghetto ricer fashion (hanging down under the car) so that I could take it for a spin (I am still waiting for the mufflers that I ordered). My initial impression on my butt dyno was that I picked up an immense amount of low-end torque (below 2,000 rpm) over the racing beat headers. 2,000 to 5,000 felt about the same (although the tractor muffler is probably creating significant backpressure by then). I couldn't bear to rev the engine past about 5,000 rpm on the street (rotary engines laugh at the puny sound attenuation of tractor mufflers), so I don't know about the high end.

I am running 0.3 AFR leaner at idle and about 1.2 AFR leaner at 1,500 RPM WOT.
About 0.8 AFR lean at WOT at 2,000 RPM, 0.3 AFR lean at 3,000 RPM, about the same above that.

I suspect that I have my tractor muffler to thank for flow restriction at the higher speeds (choking the headers). I can hardly wait until my new mufflers come in.

j9fd3s · 06-26-2011, 12:31 PM

i haven't checked backpressure on the P port yet, but it is on the agenda shortly. i did check it on my stock FC though, and it made tuning so simple its funny, i don't know why we don't use it more.

Libor · 06-26-2011, 12:49 PM

Quote:

Originally Posted by j9fd3s

i haven't checked backpressure on the P port yet, but it is on the agenda shortly. i did check it on my stock FC though, and it made tuning so simple its funny, i don't know why we don't use it more.

Could you contribute more? This is something very interesting, unfortunately not much examined on public rotary forums

j9fd3s · 06-27-2011, 11:49 AM

sure, um the gsl-se and the 86-88 NA cars make doing this very easy, so its a good place to start. my car happens to be 100% stock, mileage is 76K now, 74k at the time.

so the 6 port cars use exhaust backpressure to move the 5th and 6th ports, so all i did was tee a boost gauge in the 6 port hose, and then go for a drive.

the results were interesting, the gauge and the butt dyno agreed 100%, or more accurately the boost gauge and the tq curve agreed.

the stock exhaust did ok, up to about 4500, then backpresssure starts to climb. so its under 1psi, until 4500 then it comes up pretty quick and peaked around 4.5psi.

i pulled the cats off, and behold the center cat was all melty, so i hollowed it out, and was rewarded with 3.5psi of backpressure. seat of the pants improvement was bigger than the SAFC.

the next step would be to put the gauge actually in the exhaust manifold, i'm not sure but i suspect i'm measuring the rear half of the exhaust. as the pickup is in the main cat.

the concept works though, and its easy to do. higher exhaust pressure = lower power.

06-25-2011, 10:12 PM	#1
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 18	The front and rear headers are the same length, I wrapped them with super high-temp header wrap and I can assure you that they are the same. I have some more info that I haven't fully digested yet, so before I post anything, I am curious if anyone has tested the exhaust backpressure on an open set of Racing Beat headers at 9,500 RPM. I hope someone has, because I can't find a good way to test mine without drilling holes in them, which I hesitate to do because I want to sell them. I cobbed a $30.00 tractor muffler up to the headers in true ghetto ricer fashion (hanging down under the car) so that I could take it for a spin (I am still waiting for the mufflers that I ordered). My initial impression on my butt dyno was that I picked up an immense amount of low-end torque (below 2,000 rpm) over the racing beat headers. 2,000 to 5,000 felt about the same (although the tractor muffler is probably creating significant backpressure by then). I couldn't bear to rev the engine past about 5,000 rpm on the street (rotary engines laugh at the puny sound attenuation of tractor mufflers), so I don't know about the high end. I am running 0.3 AFR leaner at idle and about 1.2 AFR leaner at 1,500 RPM WOT. About 0.8 AFR lean at WOT at 2,000 RPM, 0.3 AFR lean at 3,000 RPM, about the same above that. I suspect that I have my tractor muffler to thank for flow restriction at the higher speeds (choking the headers). I can hardly wait until my new mufflers come in. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic) Last edited by NoDOHC; 06-25-2011 at 10:30 PM.

Thread Tools
Show Printable Version Email this Page
Display Modes
Switch to Linear Mode Hybrid Mode Switch to Threaded Mode

06-26-2011, 12:31 PM	#2
j9fd3s Rotary Fanatic Join Date: Mar 2008 Posts: 123 Rep Power: 18	i haven't checked backpressure on the P port yet, but it is on the agenda shortly. i did check it on my stock FC though, and it made tuning so simple its funny, i don't know why we don't use it more.

06-27-2011, 11:49 AM	#4
j9fd3s Rotary Fanatic Join Date: Mar 2008 Posts: 123 Rep Power: 18	sure, um the gsl-se and the 86-88 NA cars make doing this very easy, so its a good place to start. my car happens to be 100% stock, mileage is 76K now, 74k at the time. so the 6 port cars use exhaust backpressure to move the 5th and 6th ports, so all i did was tee a boost gauge in the 6 port hose, and then go for a drive. the results were interesting, the gauge and the butt dyno agreed 100%, or more accurately the boost gauge and the tq curve agreed. the stock exhaust did ok, up to about 4500, then backpresssure starts to climb. so its under 1psi, until 4500 then it comes up pretty quick and peaked around 4.5psi. i pulled the cats off, and behold the center cat was all melty, so i hollowed it out, and was rewarded with 3.5psi of backpressure. seat of the pants improvement was bigger than the SAFC. the next step would be to put the gauge actually in the exhaust manifold, i'm not sure but i suspect i'm measuring the rear half of the exhaust. as the pickup is in the main cat. the concept works though, and its easy to do. higher exhaust pressure = lower power.