aribop

I am guessing that the design of the exhaust is on purpose, i.e. crossing it before the cats. What would happen if you ran each side of the exhaust independently of the other without crossing?

Also, how much does back-pressure play into the equation for proper engine performance? If you run straight pipes out, would it help or hinder performance?

Please discuss...

ca993twin

I'll throw in my wild-*** guesses... the pipes cross-over because of space limitations for those pre-heater gizmos and the cats themselves. As far as straight pipes go (no mufflers, no cats), there is probably a small bit of horsepower to be had, but a re-tune of the ECU might be required to take full advantage. Then there's the problem of the O2 sensors and passing smog (I don't know if that's a concern where you live).

The sad fact is the Porsche did a remarkably good job of extracting great performance out of these little buggers... its actually quite hard to find any easy horsepower gains without sacrificing reliability.

The car in your avatar looks pretty nasty!

vincer77

I agree with ca993twin. The exhaust design on the street cars is for convenience, not performance. The Cup cars and most of the race cars use independent 3-1 systems. There could be some advantage to running an X-pipe, however the limited space makes packaging one difficult. The extreme angles needed to make it fit may offset any gains there might be from the X-pipe. I have not seen any data to convince me otherwise - though many claim there are benefits.

steve porter

I was running non crossover Cat bypass pipes ,the car lost some low down torque but did seem to gain some top end power (seat of pants dyno only) the inability to run at 100 kph in top gear made me take them off

jscott82

One man's experience here:

Stock Cat, no mufflers, stock chip = 219hp (mustang dyno)
200cell cat, no mufflers, stock chip = 229hp (mustang dyno)
200cell cat, no mufflers, stock chip = 259hp (dynojet)
200cell cat, no mufflers, perf chip = 269hp (dynojet)
No cat, no muffler, perf chip = 289hp (dynojet)

edit: in each case gains were across the RPM range

vincer77

Thanks for the data! Just a few of questions:

What was the configuration of the 200 cell cat you ran?

No cats and no mufflers is running straight pipes off each bank w/o cross-over, correct?

Stock headers in all cases??

The perf chip with and w/o cats was retuned I assume?

chaoscreature

I think the cheapest way to gain horsepower is to put your car on the dynojet versus the Mustang

Seriously though backpressure is a topic that has been debated and discussed a gazillion times on every performance forum out there. The key really comes down to getting a combination of HIGH EXHAUST VELOCITY with LOW PRESSURE. This is especially important in the primary and secondary pipes (everything before the cat/muffler or the atmosphere).
So what this means is that if you put dual 5" pipes on your Porsche right after the headers you will have succeeded in getting very low backpressure but at the expense of gas velocities.
I am still not sure about the difference on the X-pipes. If it was designed properly an X-pipe should probably net some power at certain rpm's, but I think it's been proven on the even fire Porsche engines that keeping seperate dual exhaust is the way to make the most peak Hp.

vincer77

Agreed.

jscott82

200 cell DACH cat with x-over
yes, stock headers in all cases
nope, same perf chip, no changes... The ecu was able to compensate and keep a/f ratio in check...

jscott82

Actually, cheapest was to take off the cat... I would have made money if Fed-Ex hadn't dropped it in shipping.....

edit:
Now that I think about it... You are right... the hearing aids will be expensive (defered cost).......