what would be better for better performance and mpg aftermarket 4in exhaust with out muffler or just delete the muffler on my stock exhaust?

 

Full 4" Exhaust... larger down pipe is the key.

 

what would the benefit be? just little better flowing?

 

Better flowing yes, but primarily lower EGTs. No backpressure is needed because of the turbo....so the easier the exhaust can get out..the better it will spool!

 

sorry for all the questions what would the difference in egts be?

 

Little to anything... The factory exhaust is pretty well matched to the factory tuning...

 

I have a magic number that I've learned. If your boost goes over 22 PSI, I'd recommend a bigger exhaust. Anything lower than that just serves to alter the "note" of the truck.

 

I don't think there is any significant gains from stock w/no muffler to 4" system. MAYBE a few degrees lower EGT, but with good tuning EGT is not an issue anyway.

I've been running stock system w/muffler delete in the dually for 250k miles and have had Stage 1.5/Stage 1 injectors for 70k/50k miles with a GTP 38R for the last 50k. Truck's been making ~30psi of boost for 120k miles and made 370HP on the dyno a couple months ago.

I did have an issue with EGT's - but I got better tuning and now I don't have to drive-by-pyro when towing heavy up long grades anymore!!

The Excursion was all stock WITH stock muffler and EGT's were not an issue towing at 22k lbs GCVW - with good tunes. There was no SOTP/MPG gains from 4" system.

I used a piece of stock 3.5" tubing from someone who 'upgraded' their exhaust to replace the muffler on F350...

 

Without going into the mess that is my injector configuration (recent discovery), my stock turbo can pop 30 PSI. My reasons for the 4":

1. Engineering - math with the charts from engine manufacturers shows the 4" has benefits.
2. Data after the change - My AE shows some benefits in performance.
3. My boost gauge - My boost popped to 20 PSI, then slowly crept up to 28 PSI with stock exhaust and my most powerful tune. Immediately after the 4" install, my boost popped to 22, 25, or 28 (depending on which tune I'm running) then my 60e and 80e tunes would climb that last 3 PSI. I didn't see the overboost SES light until I had the 4" exhaust.

This forces me to surmise stock exhaust is good to 20 PSI, then just OK above that. The math backs this up as well. Ultimate boost gets a small bump, but spool up gets a huge slap on the back with the 4".

$0.02

 

Did you compare stock system with no muffler to 4" system?

The only significant change I saw with stock w/muffler to 4" was faster EGT cool down when I parked it.

The SES lite can be fixed with good tuning. I don't even have a 'boost fooler' on the X and never saw an overboost at up to 35psi w/current tunes.

 

My truck felt like it spooled quicker. Is that not really true?

 

I had a muffler delete for about 10 miles and I hated it, so I never really compared that particular configuration in-depth. That being said, I saw no difference in boost performance in those few miles... but I was very distracted by the racket at the time.

That was my experience.

 

I went with the oem straight pipe, and I love it. The sound is almost the same as my dads with a 4in exhaust. It is not overly loud, you hear the turbo, and it is alot cheaper.