3” vs 2.5 “ tailpipes question

[XLexusTech]

500 hp naturally aspirated ls3 I am going with 3” to the muffler starting to wonder if I am going to be able to get the 3” over the rear suspension...so I am considering 2.5”

what would the performance impact be?

[WSSix]

Minimal to none that you'll feel. You might be able to show it on a dyno, but the driving will be the same. If packaging looks like it'll be difficult, I'd stay with 2.5" the whole way.

My exhaust is only 2.5" the whole way as I wanted to retain as much low and midrange power as I could. It's just a street car. I'm 500hp NA as well.

[Flash68]

I seem to recall testing showing the step down from 3 to 2.5 AFTER the muffler showed little to no change in power numbers. But the 2.5 before the muffler coming out of collectors did show a material change.

As said, If you are at 500ish hp I would not be concerned about stepping down to 2.5 to get over the rear.

Or, just dump the suckers at the axles. :D

[CamaroAJ]

There is an in depth amount of information on this if you google about exhaust flow. Stuff along the lines of stepping down the size of the pipe because the gasses cool and lose velocity if you keep 3" all the way back and stepping down helps keep the velocity for scavenging. I'd post some links, but that computer is toast and I lost all of it.

[Vegas69]

You'll never know.

[SSLance]

My 3" header collectors adapt down to 2.5" and run all the way back through tailpipes out the back with 467 HP, 525 ft lbs at the crank. Packaging on street cars is tough and I'd rather have a tame exhaust that fits than forcing a 3" setup in where not really needed.

[NOPANTS68]

You spend 99% of your driving time under 4500 rpm so the flow isn't an issue. Plus, you're not dragging extra weight around from the larger pipe. 2.5 mandrel is good for an NA LSX all day long. I had 2.5 to the bumper on my LS1 Nova and still trapped 118 mph with just a cam.

[Ripped]

I think some of it depends on engine cubic inches. I switched recently from 2.5" to 3". The diameter change in the pipes is massive. Fitment is tough. I cannot tell you what a combo system will look like 3 and 2.5.

There's an engine masters episode on 3" exhaust here; https://youtu.be/_PVXvHkr-Vs

When I made the change, the exhaust note went from loud to deafeningly loud with the 3". I freed up a lot of power, and went from scary fast to dangerously fast and you better respect the power or else fast.

What cubic inch is your 500 coming from?