I have had 5 different exhaust configs on the truck and this on seems to be the best. Good low end torque very responsive on the highway speeds but the best part it is the only exhaust the has lowered my egt by 225 deg while towing. No mileage change. What smog canister , never saw and you can't prove it

 

No need for any technical posts - it is a simple math problem. How much the pipe can flow is primarily dependant on the cross-sectional area of the pipe - (pi) times (radius of the pipe) times (radius of the pipe), or pi (r) squared. (pi is appproximately equal to 3.1416, r = the radius, or one-half the diameter of the pipe)

A single 4-inch pipe is (3.1416) x (2 in.) x (2 in.) = 12.6 square inches
2 2.5-inch pipes is (3.1416) x (1.25 in.) x (1.25 in.) x 2[ pipes} = 9.82 square inches.

In other words, all else being equal, a single 4-inch pipe has 28% more cross-sectional area than two 2.5-inch pipes. In order to exceed the cross-sectional area of one 4-inch pipe, you would need duals of almost 3-inch diameter - and that still doesn't mean that size duals would flow as well as a single 4-incher.

In short, if you are going to use two 4-inch tailpipes, no problem. If you use two 2.5 inch tailpipes, you will see an increase in backpressure, and probably an increase in EGT and decrease in performance. Probably.

 

Although I do admire your math equations, and you are correct that a 4 inch would flow more, But i would be carefull in saying a "decrease" in performance for a dual 2.5...... because they flow a little less, you can keep some of the low end that you would normally loose w/ a stock rig and 4" exhuast... the 4" is great if your running up higher in the rev band.... but a 2.5*2 will keep at least some of the low end for ya.... i'm very happy w/ my dual 2.5 er's... my .02

-Robb

 

You are correct, robb. Please note the "probably". That was put there because of the extreme variables in setup and performance between different trucks.

Just wanted to give a reasonable reason for the difference in flow between the two exhaust types.

 

i thought that backpressure didn't matter with diesels ??? Also is it possible to by this 1 4" to 2 4" Y pipe online or do I have to have it custom made??

 

would a 4" midpipe then splits out to dual 4" be better then a 5" midpipe and that splitting out to 4"s?

 

arnintyes, thanks for figuring that out!

 

It doesent matter if it is a 4" or 5" midpipe, I did 5" because it gives it a lower tone to the exhaust sound, you can find premade splitters at any place that carries diesel truck exhaust components.

 

yeah thats exactly what I want to do...haha i have 3 questions for u: stainless or aluminized? where did you get it done? and where do your tips come out?

 

I have three answers possibly - 14 gage aluminized ( it will all depends on your environment what tape of tubing) , did it myself (I own a shop), behind the wheels at a 45 deg angle any questions?

 

I was just thinking, when I do my duals, they will go over the rear axle, but dump at an angle facing down on each side behind the rear tires. I don't know if I would go as big as 4" a side or not. Sounds like the performance of the 2.5" or 3" duals might be best for a slightly modded truck. I don't want to be breathing all those diesel fumes while I'm hooking or unhooking my trailers!

 

Stay with the 3-inchers... 2.5s will reduce flow.

 

do you sell any of your stuff like on ebay or something??

 

I got stock DP, into 3" back to a Y-pipe and 2.5er's to 4" tips, works great and saved me some low end, having a slight backpressure. for my slightely modded truck this is enough... and it sounds different that 3, this has more turbo sound compared to 3, i don't have any idea why, but a buddy of mine did his w/ 3 inch and it sounds different than mine, deeper tone, which is nice, but the turbo whisle which i love is almost drounded out.... just my .02.... I'm not going to go crazy w/ my rig, a few mods here and there, and that seems to be sufficent... good luck!!

-Robb

 

The larger pipe will create a resonance inside and inturn will give it a deeper tone. You shound hear one of these trucks with a 6" tailpipe on it. If you don't want to go to 4" or 5" pipe a 3 1/2 dp with a 3 1/2 midpipe split into two 3" tail pipes works great on these trucks that are slightly modded, we have done a few of these and the guys like them.

edub32- we are a drive in shop only