i have a 2.5" exhaust system from turbo back, with a "see-through" high-flow ebay cat converter, so it is truely a 2.5" exhaust system.

now, right now i have a major exaust leak between the dp and the cat converter. there is an appx. 3" length of pipe i had to cut out of the DP (long story, dont ask), and this gap resides right after the flex section.

ok, so basically i am running open dp, but here is where my pondering began. since i am running a complete 2.5" exhaust system exhaust velocity remains high, and EV is what matters most, as i recall. so would open dp effect performance seeing how cat back or no cat back, piping remains constant. so no bottlenecking would be present. i would actually think that open dp would help performance due to that EV is at its maximum, whereas with a cat-back the exhaust gases would have time to cool, thus hindering EV.

let me know what you think the results would be.

-dave

Originally posted by davo345
i have a 2.5" exhaust system from turbo back, with a "see-through" high-flow ebay cat converter, so it is truely a 2.5" exhaust system. now, right now i have a major exaust leak between the dp and the cat converter. there is an appx. 3" length of pipe i had to cut out of the DP (long story, dont ask), and this gap resides right after the flex section. ok, so basically i am running open dp, but here is where my pondering began. since i am running a complete 2.5" exhaust system exhaust velocity remains high, and EV is what matters most, as i recall. so would open dp effect performance seeing how cat back or no cat back, piping remains constant. so no bottlenecking would be present. i would actually think that open dp would help performance due to that EV is at its maximum, whereas with a cat-back the exhaust gases would have time to cool, thus hindering EV. let me know what you think the results would be. -dave

See through high flow cat = resonator as far as I'm concerned.

Drag cars run open downpipe so there is no backpressure on the turbo, yes it;'s more efficient for the turbo on open downpipe. The issue is sound, I'm sure your car is pretty loud. Also heat, you have very hot exhaust dumping under your car as well as teh possibility of some unburned fuel aftterburning under your car. If you want to run open downpipe I suggest rouiting the downpipe out from under the middle of your car.



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see its not a permanent situation. as soon as i get access to a welder i will fix that missing link in the exhaust system.

i guess the real question i asked was during that time frame while i am essentially running open DP, will it effect the performance of my vehicle in a negative, neutral, or positive way?

I think running an open downpipe will allow the turbo to spool up a lot quicker, which can be good, but you will notice a loss in torque from the lack of back pressure. Also, as stated in the last post, the hot exhaust gases exitting just below the engine area is not good. I don't have an open downpipe, but I have a setup that is similar to that.

I have an exhaust cut-out just before the cat-converter location. When it's opened, it's pretty loud and has the same affect as an open downpipe. I've noticed there's boost spike from the open exhaust. The boost level will also be higher. For instance, if I set my boost at 15 psi, and with the open exhaust, boost level will rise to 17-18 psi at WOT. Just something to consider.

Originally posted by fly1
I've noticed there's boost spike from the open exhaust. The boost level will also be higher. For instance, if I set my boost at 15 psi, and with the open exhaust, boost level will rise to 17-18 psi at WOT. Just something to consider.

that could really hurt me ;/ hrmm.