Jeez I really hate blanket statements like this. I can think of one vehicle recently that netted nearly 20 rwhp at the same boost level by going from 3" to 4" at only ~500 rwhp. There is a big difference between adequate and optimized.

 

I gained 2mph when I switched from 3" to 4" with the supercharger

 

 

But lets be honest here..... one 3" exhaust system is not the same as all.. True?? Two people can say they have 3" exhaust and have totally different setups. One may have 4' or straight pipe and a Race bullet dumped... the other may have several bends, a cased muffler, and a tailpipe.... there is power between these 2 setups alone So i could def see gaining going from the 3" "stock" style (bends, cased muffler,tailpipe etc) to a 4" dmax exhaust.... but one "straight" shot 3" setup seems to do pretty well for 600hp which is pretty darn stout for a DD pickem up

 

I have a trick single t76 3" down pipe into a 4" diesel corsa db muffler. F the horse power. I wish I had kept my 2 3" aero chambers. Sounded a lot better as in not as freakin loud. At 75mph on the interstate it drones like hell. I hate it. My lag time went down some but it was not worth it at all. I am thinking about putting a 4" ho flo diesel cat on to calm the noise down. I just don't know if it will fit.

 

Well put. And whats up with the supercharged exhaust comparisons, thought turbo exhaust needs differed.

 

I only have about 3-3 1/2' of 3" down pipe before my cutout.

Who drives there truck around on the street with the boost cranked high enough to need bigger exhaust. When I run 12psi it's way to much to drive around with unless it's in 4wd, let alone 16psi.

The cutout doesn't make much difference under 16psi on my truck. At 12psi with the cutout open it was within a few hp every time, but so was every run at the same boost. At 16 psi it did pick up a few, but less than 20, more like 5-10.

 

For example: A stock cam is adequate for a turbo kit, a turbo cam will help the engine reach it's true potential.

A turbo exhaust is another piece of the puzzle to make a motor reach it's full potential. You can't just keep turning up the boost to cover up other shortcomings. Reduce exhaust back-pressure and your turbo becomes more efficient. To the greater extent, the larger a downpipe, the faster your turbo(s) spools PLUS it helps you stay in the most efficient part of the boost map which in turn raises efficiency and reduces IAT's. Unless your driving around a track car, it's all about spooling as quickly as possible a reaping the benefits of that boost producing low-end torque.

I bet I can make my kit break 600 RWHP with a 2" exhaust, but why would I if I had a choice?

Rick

 

i guess its just what you want to do with your truck. if you want a optimized, loud droaning turbo/supercharged truck that makes 500rwhp and weighs 2 1/2 tons thats cool.

personally i want a stock sounding truck with a turbo that will tow like a diesel. i mean honesly these trucks with a 3inch or 5 inch exhaust are not going to be fast. yes maybe run a low 7 in the 1/8, but thats not fast. and the money spent could be used in a lighter vehicle and go much faster.