Thread: Catback 2.5" or 3"?

Hello. Not really new to the gtp world but new to taking my car this far in mods. Have searched a bunch and have only come up with 3" catbacks being needed when going turbo. My previous GTP had intake/headers/intercooler and just ran the stock catback.

My new 4 door has intake, SD headers w/magnaflow cat, S2 intercooler, gen v swap, N*/LQ4, s1x cam, 42# injectors, built trans with 3.29 chainset. Will be starting out running a 3.2 pulley and going as low as I can with no KR and 18 degrees of timing on 93 octane.

Now that all the info is out, the question is would I benefit from switching out the stock catback and should I go with 2.5" or 3"?

Keep in mind this is my DD so if I would not see more than 10whp from spending $500+ on it I would rather just not do it. I already have 2 other v8 muscle cars.

Thanks for reading.

Catless headers...glasspack for a resonator...and whatever mufflers you want to run...

Honestly with an IC/S1X/GenV...you're probably at the power level to benefit from actually running a larger diameter catback...if you've got a local mom and pop shop..have them just make you one from scratch. Dynomax super turbo's are a very quiet muffler...especially for the price. Something to consider there.

Originally Posted by blueguy

Catless headers...glasspack for a resonator...and whatever mufflers you want to run...

Honestly with an IC/S1X/GenV...you're probably at the power level to benefit from actually running a larger diameter catback...if you've got a local mom and pop shop..have them just make you one from scratch. Dynomax super turbo's are a very quiet muffler...especially for the price. Something to consider there.

I know all about those mufflers. Got them on my 9 second camaro with an x pipe and love them. Very quiet street driving. Can have a conversation in the car without yelling. Catch many people off guard when i open the cutouts too haha.

Keeping the magnaflow cat though. Want to stay emissions legal at least with the visual check. Not to mention it is high flow 3" bullet with metallic core that I am sure flows fine.

is that you Bret?

Originally Posted by gtpsleeper

is that you Bret?

No my name is Justin. Only other grand prix guy I know of in this area is Rick Tyree.

Originally Posted by That SlowPontiac

so its been a couple years. how were the speed daddy headers. and did you switch to different ones. i ask because im looking for headers

Thanks for bringing this back from the dead...

There are plenty of reviews...those headers are just fine; like everyone says. Only thing you need to fix is the crappy single wall flex and remove the low hanging neck in the downpipe.