Hey Guys,

New member here and wanted to touch base on exhaust size for our 3.5L motors. From my knowledge Twin 2.5” pipes are used on V8 motors pushing decent power. Twin 2.5” pipes are equivalent to a single 3.5” pipe in volume. In comparison we have cars over here in Australia pushing 700HP with a single 3.5” exhaust. Is there any evidence that 2.5” pipes are an actual benefit our cars? I would of thought twin 2 1/4 pipes would be more suitable pipe size.

cheers

 

After speaking with a performance exhaust shop (specializing in V8s) here, I went with 2.25 piping and an X-pipe. They said 2.5 inch piping would be too big for the size of the engine.

 

The difference between 2.5-inch and 3.5-inch exhaust pipes for cars is as follows:

• 2.5-inch pipes are better for vehicles with smaller engines or those that operate at lower RPMs. They allow the engine to maintain more backpressure, resulting in better low-end torque.
• 3.5-inch pipes can increase horsepower and torque throughout the entire powerband, especially on V-8 engines.
• If you care more about a nice tone than power, 2.5-inch pipes are perfect. If you want performance, a 3-inch GHL system paired with a 3-inch DP without a cat is recommended.

 

Evidence is right here.

A few years back.I went from a custom 2.25" dual exhaust to a similarity setup 2.5" exhaust. The improvement based on MAF values was somewhere around a 3% gain after 4000rpm. Which might be upwards of 10hp more over my previous custom 2.25" exhaust.

Go with a 2.5" setup if you are spending money and are concerned about power

 

Hey mate. I seen a video of a 370Z same combination went from a 2.25” to 2.5” exhaust he gained 1HP going to the 2.5” exhaust but lost 13NM of torque..

I thought being a bigger motor at 3.7L surely a 2.5” setup on our cars would be overkill and loose torque. Thankyou for chipping in with real life Data. I’m getting a full catback exhaust done next month. I’m assuming there is a loss of torque down low compared to a 2.25” setup? How noticeable is the gain of power going from 2.25” to 2.5”?

 

I couldn't say how much of a loss there is down low. If there is, I imagine it's below 3000rpm and notit much. I bet the difference down low is not noticable with the steep gearing. Up top 10hp is probably not something you can feel, but it's not a negligible amount at the power these cars make.

I think the most notable difference for me is the 2.5" exhaust shifted to a slightly deeper tone which in my opinion sounded better. My exhaust setup includes headers with a 2.5" dual exhaust with a double x configuration. If I had to do it again I'd go with an h pipe instead to try to bring the note a little lower. I'm not really a fan of how catless NA V6 engines sound so I would also recommend at least high flow cats if you do headers. I haven't compiled and compared logs in a nice chart, but I was not able to notice any difference in peak MAF values between being catless and having high flow cats.

 

Was thinking of running high flow cats for the reason of sound control aswell.

 

No worries mate. Wasn’t sure if it was yourself but seen a post when someone swapped to 2.5” pipes and was struggling with slower 0-100 times? Just wanna make sure I make the right decision 😅