Exhaust 4" or 5"

Whit

Registered User
Joined
Dec 20, 2003
Posts
3,808
Reaction score
0
Location
lost in Why-homing
Some good info here fellas

A clip from the latest Diesel Power magazine

Pipe Dreams

Diesel enthusiasts already know the great power potential and more efficient fuel consumption offered by a diesel truck.All that power and economy doesnt come without picking the right parts though. An after market high flow exhaust system has to do more than simply make your truck sound better. Point in case with a 4" vs. 5 or 6 inch system, how big do you need to go? To answer that first we need to go over a few basics.
On most contemporary turbodiesel engines, the exhaust comes right off the exit of the turbo and after market exhaust manufacturers offer more than one tubing size to vent the exhaust more quickly.
One advantage of moving exhaust gasses quickly and efficiently is to reduce buildup of heat. Turbo diesel engines generate alot of heat, especially when the engine is under a heavy load. A high flow exhaust actually allows your diesel engine to run cooler and adds the potential for more boost when towing.
Large diameter tubing also reduces backpressure, making it easier for the pistons to shove that exhaust out of the cylenders and resulting inmore horsepower. Less backpressure allows the turbin to spin more efficiently, therefore it will build boost quicker and run cooler.
Interestingly enough however there is a point where bigger isnt necessarly better. While engine testing indicates that going from 3-1/2" to 4" can reduce backpressure by as much as 98%, ther can be less than 2% reduction above 4" exhaust. SO while a 5 or 6" exhaust looks cool it wont give you much more than just a coolness factor.

Cheers, Kevin
 
Last edited:

sle2115

NRA LIFE MEMBER
Joined
Dec 3, 2005
Posts
7,147
Reaction score
2
Location
Southeast Ohio
I know first hand on my 6.9 NA that going from the puny 2 inch true duals to a 3 inch mandrel bent system (y pipe, muffler then 3 inch 90 into a crossbox with stacks) that my EGT's dropped at least 200 degrees when pulling a load. I have a dual sweep EGT gauge and can watch both "sides" I was amazed at how much more power my truck has and how much cooler it runs.
 

Headhunter_5.9

there it is Johnny!
Joined
Oct 20, 2005
Posts
133
Reaction score
0
Location
ILLINOIs
not real sure how I missed this thread before but I did! it's over a week old!

at any rate, I know that when ever my cat and muffler "fell off" there was a drastic change in performance, seat of the pants Dyno if you will. and I'm positive that was due to the decrease of back pressure.

and I'll have to get back to ya'll on the update after I go to the 4' into the 5" stacks! the decrease in temp should be noticable.

when I put the straight pipe in I didn't have the Pyro in to note the difference there but now that I've got it I'll have to do some comparing!
 

Swany

Consiglieri
Joined
Feb 18, 2004
Posts
3,852
Reaction score
0
Location
California
tell that to a woman :rotflmao sorry honey, 4" is the best performance, everything else is just cool
 

snoracer614

smokinEclipsedually
Joined
Jan 25, 2006
Posts
4
Reaction score
0
Location
le center, MN
Thats some good info... thanx!

2000 psd eclipse ed. used to pull sled racing trailer
2002 psd short box crew cab (Just starting)
 

Tinman875

Full Access Member
Joined
Sep 27, 2004
Posts
69
Reaction score
0
Location
Caldwell, id
well i was just wonderin, cause with twins your actually moving up to over twice the air around. I think 5-6 in exhaust would be the choice in that situation, but I agree 4in is all you need for all other upgrades.
 

JohnBoyToo

Registered User
Joined
Apr 10, 2004
Posts
457
Reaction score
0
Location
DFW, Tx
good info...
and at the most granular level,
it also has something to do with the exhaust "impulses"
meaning ...
with the exactly correct exhaust,
the impulse frequency WITHIN the exhaust exactly matches the firing impulses and, therefore, exhaust frequency so that everything is pushing OUT at the same time
(or at least not trying to breathe IN while breathing out..... :))

So the "scavenging" effect of the exhaust pipe actually helps to "pull" the exhaust out the cylinders...
 

Mike

Stroker
Supporting Member
Joined
Mar 24, 2004
Posts
12,389
Reaction score
15
Location
Cora
Lets explore this question;

You have a 5" open exhaust that turns up into the bed and dumps into two 5" stacks.... now what we got?
 

Ramprat

Inside your OODA
Joined
Dec 21, 2003
Posts
8,518
Reaction score
31
95_stroker said:
Lets explore this question;

You have a 5" open exhaust that turns up into the bed and dumps into two 5" stacks.... now what we got?


Lots of black smoke :rotflmao :rotflmao :rotflmao :rotflmao :rotflmao
 
Top