Is 3" exhaust overkill?

**wm_sorg** · 05-09-2003 03:46 PM

Hi All,

Unfurtunltely, I need to run cats. I was considering 3" pipe, cats, etc. from the engine all the way back. Is this overkill for this setup? Since I can not run headers, I was hoping to make up for some of the restriction on the back side.

All thoughts appreciated.

**Domeskilla** · 05-09-2003 04:04 PM

No, its not. but the bigger the pipe, the more low end you'll lose. But the majority of the f and y body ppl are using 3" pipe. So i wouldn't see anything wrong with it.

**cravnpup** · 05-09-2003 04:08 PM

I'd probably say a 2.5" system would be adequate for anything up to about 400hp... Once you get close to 450-500hp you may need some more diameter.. Remember, for N/A engines it's exhaust velocity that makes power.. If you've got a high flow, high velocity system, then going to a larger pipe will only slow down the flow and decrease your scavaging... It's only when you've got a lot of gas flowing (i.e. high HP), that the diameter will become your restriction...

**cravnpup** · 05-09-2003 04:11 PM

Why not have a muffler shop fabricate some flanges on both ends of your cats along with a set of straight pipes of the same length/flange pattern... That way you can stay with 2.5", and swap out the cats when you feel like it for more power....

**Domeskilla** · 05-09-2003 04:18 PM

or buy electric cutouts, install them before the cats and open it up at the track

**farmtruc** · 05-09-2003 04:19 PM

I think 3" will be the way to go, 2.5" will also be good, i guess it depends how soon you think you are going to out grow/mod that 2.5" exhaust.

I know a lot of the truck guys are running dual 3", and they have had good results, i'm def. going with 3" when i get some time, but for now, i think my dual 2.5" is doing ok.

allen

**wm_sorg** · 05-09-2003 04:52 PM

Good points made by all! I would like to keep as much low end as possible since it will spend most of its time being daily driven. I also like the idea of being able to remove the cats.

What do you think of 2.5 from the engine to two cats. 2.5 from cats both joining into a 3" pipe to the muffler back out to two 3" outlets? My existing systems was a ATR pitbull 3" cat back. Will this be a good compromise of both systems.

**cravnpup** · 05-09-2003 05:05 PM

That's probably not a bad idea.. They say that your EGT's are hottest directly after the cats, so by increasing the diameter there you'll allow the hot gas to expand at a higher rate, reducing backpressure...

**wm_sorg** · 05-09-2003 05:25 PM

Thanks. I will keep you guys posted as I get closer to having it built.

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