Finally going to order my turbo kit. I currently have a 2.5" cat back exhaust going into an ANSA silverline dual outlet exhaust. This exhaust came on the car when I purchased it a few years ago, but I really enjoy the sound. I'd like to keep it and save some cost on the turbo kit, however I realize that a 3" exhaust would be better. My question though, is how much better? Does anyone have any concrete stats comparing the 2 sizes?

 

On a 200hp setup its mostly transient response which no one will have data for, no.

Dann

 

Tests have been done. You want the 3". Tests are 10+ years old so you will have to do a ton of searching to find the data if you don't believe us.

 

Sound will change, so don't keep an exhaust based upon sound. Adding a turbo is like adding a HUGE muffler all by itself.

 

You can keep the small exhaust for now if youre trying to save money. If its just a street car it will still be a load of fun even if it isnt optimized to the max.

Maybe in a couple years youll throw a full 3" at it with the MTnet approved muffler and see what you were missing.

 

how loud is it now?

 

If Flyin' Miatas numbers are to be trusted, on a 266rwhp 1.8 they got 16hp and boost 200rpm earlier with a 3" exhaust vs a 2.5".

 

Thanks for the info! I feel that's pretty significant. Really appreciate it!

Haha, I always trust all of you miata guru's, that's why I asked here.

It's definitely louder than stock by a few decibels, but has a really nice deep tone at a low pitch. I would like to say it's not obnoxiously loud, but I've had some neighbors complain about the rumble from my morning warm-up enrichment cycles lol.

 

Bottom line:
if already have, keep 2.5 until you get to it's limit.
if buying/building/upgrading, 3" no question

 

FMs big bore exhausts are not straight through.

Those tests are not testing what you and I think of as a 'turbo exhaust'.

Dann

 

https://www.miataturbo.net/engine-pe...63/#post961510

 

Lots of good info proves 3”>2.5”. Where things got fuzzy for me was length and muffler volume. With the smaller 2.5” size I was able to get 2 smallish mufflers in-line and terminate just before the diff. With the 3”size I would not have enough muffler volume in the same location. I would have to use a large oval in the back and terminate near the bumper.

With my 300 WHP 9 psi Rotrex It was hard to imagine the larger size helping out. If anything it may have hurt midrange torque where I needed it the most. Someday I’ll pull the system and dyno it wide open just to see how much it’s holding back HP.

Just another perspective to consider for SC cars.

 

what makes you say this?

 

 

Yeah I've heard that many times before. But have yet to see a dyno plot to confirm it, which is why I question it.

 

 

300hp at 9psi?? That's gotta be a record and one hell of a supercharger, no turbo can do 300hp at 9psi. Very curious how you accomplished this.

 

 

No worries. It's more just out of curiosity

incorrect.
there are several that can, but no real reason to do that

 

Completely false.