Exhaust Upgrade Question

[JustinSane8000]

Hey all, as always, ive done a good share of searching before making a new thread, but heres my question.

i know in N/T cars, exhaust upgrades can just be thrown in and your good to go. But as i understand it, turbo cars require precise sizes in in pipe width in order for the turbo to work properly.

(Q: ) I just bought a new high flow cat converter, is it safe to just install that with the stock downpipe and catback system? How much does an upgraded exhaust system (downpipe back) effect the cars performance? mods are in my profile, but im running a 14b

 

[andymoraitis]

The actual requirements are much less precise than you would think. Since backpressure robs power in a turbo exhaust setup, we have a tendency to run larger diamaters than our N/T bretheren.

While you can add the high flow cat and see some improvement, the best systems are turbo back (including the use of a high flow cat or test pipe). Most downpipes are 2.5" or 3" diameter and you'd do well with a full 3" catback. Don't get too crazy regarding brand names and waste your money on something because it has an HKS or Apexi label on it. Any competent exhaust shop can build you a complete catback for a reasonable cost. All you need to ensure is that they have a mandrel bender so that the inside and outside radius of the bends is equal and will flow more than a press bent pipe.

But getting back to it, a 2.5" or 3" downpipe with a high flow cat and 3" catback will do just fine. There's no reason to go larger so don't even consider 3.5" or 4" as the pipe diameter will negatively affect exhaust exit velocity (scavenging). Changing from the stock system to a full turbo back exhaust with less restriction than the stock piece will help the motor breathe more efficiently throughout the RPM range. It's a very worthwhile mod and you'll feel a seat of the pants difference, especially on a 14B. Couple that with a less restrictive intake setup and you'll be well on your way to making more power reliably.

Here's a sampling of some exhaust systems listed in our tech guides just for reference:

http://www.dsmtuners.com/parts/default.php?cPath=3_55

Let me know if that makes sense.

Andy

 

[JustinSane8000]

thanks for the help, im definitly aware that pipes are pipes and am not about to drop $400 on a full system when i can get it for maybe in the $200 range. I ordered the cat because it was only like $25, so i figure, maybe $40 for the catback setup, and an unknown cost for the downpipe. Ebay is good for a few things... but not all

 

[toojung2die]

(Q: ) I just bought a new high flow cat converter, is it safe to just install that with the stock downpipe and catback system?

Since Andy addressed the performance question, yes it is safe to add just the 3" high flow cat convertor at this point as long as you get a good seal between the 2" stock down pipe and the 3" cat convertor. You won't want to stop there though. The exhaust only flows as well as the smallest restriction will allow. The stock down pipe is only 2" so your exhaust will only flow as much gas as can get through that section.

 

[JustinSane8000]

the cat i bought as a 2.5'' inlet, so looks like ill be buying a 2.5'' system, or can i still go with a 3'' catback and downpipe?

 

[andymoraitis]

If your cat is flanged for 2.5" on the inlet, pick up a 2.5" downpipe. If the rear connection is more of a slip-fit style, no flange, then an exhaust shop can flare this and make a good connection with a 3" pipe. It's not ideal, but it's much better than what you have.

High flow cats aren't expensive. You could always pick up a true 3" inlet and outlet design and sell your 2.5" or see if you can return it.