Optimum Back-Pressure for Exhaust Systems?

[edevlin]

I have been playing with exhaust systems lately on my 2.7L 2000 Boxster. I have tried different combinations of Fabspeed Cat-Bypass Pipes, TTP headers, 100-Cell cats and both stock and Gemballa mufflers.

The car seems to like the stock header/Fabspeed Cat-Bypass/stock muffler combination pretty well (198 whp). But it runs and sounds best with TTP headers/100-cell cats/stock muffler (202 whp).

But what suprised me was that it did not like the TTP headers/100-cell cats/Gemballa muffler combination. I did not even run a dyno on the rig because it was not running well at all (also, that combination was too loud for my tastes).

The Gemballa muffler seemed like it had pretty free flow compared to the stock muffler, so it got me thinking about what the optimum back-pressure in the exhaust system is for the 2.7L engine.

Anyone have any ideas about what is the optimum back-pressure or exhaust is for this engine,

Cheers,

Ed

2000 2.7L Boxster, 50K

[MNBoxster]

Originally Posted by edevlin

I have been playing with exhaust systems lately on my 2.7L 2000 Boxster. I have tried different combinations of Fabspeed Cat-Bypass Pipes, TTP headers, 100-Cell cats and both stock and Gemballa mufflers.

The car seems to like the stock header/Fabspeed Cat-Bypass/stock muffler combination pretty well (198 whp). But it runs and sounds best with TTP headers/100-cell cats/stock muffler (202 whp).

But what suprised me was that it did not like the TTP headers/100-cell cats/Gemballa muffler combination. I did not even run a dyno on the rig because it was not running well at all (also, that combination was too loud for my tastes).

The Gemballa muffler seemed like it had pretty free flow compared to the stock muffler, so it got me thinking about what the optimum back-pressure in the exhaust system is for the 2.7L engine.

Anyone have any ideas about what is the optimum back-pressure or exhaust is for this engine,

Cheers,

Ed

2000 2.7L Boxster, 50K

Hi,

I'm not sure anyone has any actual measurements to go by. But, some backpressure helps the engine create low end torque. Increased size exhaust piping lowers backpressure and lets the engine "breathe" easier, creating more power.

But, if you make the exhaust piping too big, you lower the backpressure too much (engine "breathes" too easily). This will cause a loss of low-rpm torque. It's all a trade-off at a certain point.

The best thing to do is to try that combination which both you, and the engine (as evidenced by Dyno data, but look at the curve not just the RWHP numbers, it's got to be usable power), like best. Hope this helps...

Happy Motoring!... Jim'99

[edevlin]

Thanks for the input Jim, I was hoping you might have some ideas. I have tried to enclose a dyno readout, see what you think. I was hoping for a little more power with the mods in the system, but I dont think I need any more. The car sounds very good and seems to be running great.

The current custom tune of the ECU chip I am using makes the car very responsive, great low-end torque, perhaps at the expense of the maximum high-rpm hp. That combination makes it very fun to drive now.

I may have them massage the chip paramaters somewhat as the dyno readout shows the engine is running a little rich over 5k, but I will take a flat torque curve over a few extra hp at max rpm anyday,

Cheers,

Ed

2000 2.7L Boxster, 17"
Arctic Silver/Black 50K
TTP intake/headers/cats
AutoThority Chip