I know this question is asked a lot, but I was told in some earlier posts I make that I have some decent upgrades/mods done. (check sig) I bought the truck with these mods. Given the larger turbo, injectors, inter-cooler, and enough oil pressure and fuel to supply them do you guys think a 4" exhaust would hinder my power or raise my egts?
to be clear on what I'm looking for... The quietest exhaust I can use while still getting full power. I intend to get a full exhaust that empties behind the rear wheel to keep it as far away from the cab as possible, and I'm going to run a muffler for the same reason. I've read time and again that no need for 5" (except for personal sound choice) on a stock system. I've read 5" for moderate to heavy mods. I don't know if my truck is considered "Moderately modded" or not. If I'm leaving power and egts on the table I'll go 5. if not 4. Would like to hear as many opinions as I can please.
(side note) What is the difference between a D66 and stock turbo?

Right now the truck has a Diamond Eye 3" DP into a POS 3.5 or 4" flexible "pipe" dumping before the rear tire. Pretty loud... I assume a 5" with a muffler all the way back would still be a big improvement on noise?...

 

Ive ran both on my red one and actually have 2 trucks, one has each size. I like the 5, it is a deeper and little quieter. Either will be big enough and support your power.

 

Okay. So you're saying the four doesn't restrict anything but actually ends up being a little ladder or higher pitched. Something to consider. I'm a little worried about a 2000 RPM Highway drown that I might get out of the 5-inch. You don't notice that at all? I've heard others comment about that.

 

I have a 4", works fine. Probably cheaper too. Mine is a Diamond Eye SS, bought from Thoroughbred last November. Received free freight and a free tip!

Few pics of it in my build thread too.

 

I don't notice that drone at all, but I only use my truck to tow and I'm boosting fairly good at that rpm which would make a difference

 

ive got a straight piped 5inch diamond eye on mine, run all the way out behind the tire. honestly I couldn't hear much difference while driving between 3.5inch and 5 inch straight piped unless I get on it. and with the windows up I can have a conversation without raising my voice. the benefits are lower egts, and beefier tone. plus you gotta love going through tunnels and overpasses with the windows down. that said im positive its a lot louder for the people/houses im driving past and keep it tame in town. I haven't had a four inch but id say there isn't much difference in egts though, and they are $50-100 cheaper.

 

Mine was tunneled out just for a 3" DP. I'm wondering if there would be any gain in a 5" from a 3" DP?

 

not quite sure how much clearanceing/inches of body lift youd have to do to get one in there lol I read a good while back a 4 inch is good until you get up to like 600 hp or so. don't really have any solid comparative numbers for my new setup but stock inj no tune no intercooler 6637 3in dp 5in out, pedal to the floor going uphill I could only reach 1000* im sure itd be a different story if I was towing though. I can still reach 1000* but it goes down a lot quicker when I let off and haven't done any wot on the same hills to compare.