Hello everyone. I am currently looking at the purchase of a new exhaust system. I have it narrowed down between the Ravin or Vortex. The concern I have is, if I increase the airflow substantialy by increasing pipe diameter and putting on a high flow muffler will my gas milage go down. The reason I ask is because when I owned my Dodge Dakota, I cut the muffler right off and straight piped it. It sounded pretty cool, but because the O2 censor was directly infront of where the muffler used to be and there was no backpressure thus the computer thought the engine was cold and therfore the engine ran rich, even thought I had been on the highway for an hour or two. Has anyone had this happen? I know when I talk muffler guys they all claim gas milage should increase slightly, but I don't want to find out the opposite after I have spent the money on the muffler etc...

I also have another question. Should I go 3" or 2.5" on the tailpipes on a single in dual out set up? Help guys I am getting close to decision time
Cheers
O

 

Increasing exhaust flow is not going to decrease MPG, if you do it right. If you replace the stock muffler with a good aftermarket muffler, you will increase the flow. I used a Flowmaster 50 series and got about a 1 MPG improvement (and a noticable gain in HP, but I have no way of measuring it). I left it as a single 2.5" system.

If you replace the stock muffler and go to dual 3" pipes, you will hurt low-RPM performance. But not because the system is too free-flowing. A bigger pipe reduces the speed of the exhaust gases. Keeping the speed up helps suck out the exhaust gases.

The whole exhaust system is a compromise. A large diameter system will give you great WOT performance, but won't be good for low-RPM use. A small diameter is great for low end torque and MPG, but at high RPM it will be too restrictive and the engine will waste power having to force the exhaust through the tiny pipes.

I think the proper size pipe is 2.5" for the 4.2L and 4.6L, and 3" for the 5.4L. That's for a single exhaust, I forget the numbers for dual.

 

if i were you, id go with nothing bigger than 2.5" piping for a single in/dual out exhaust. 3" would be good if you had more egnine mods, but with your engine you might lose some back pressure. just my opinion, good luck!

 

Thanks for the imput guys. It actually makes sence. Are there any other oppions out there??

 

will there be any loss in low-end with the SI/DO 2.5" set-up? and what does WOT performance stand for? Does flowmaster make a single exhaust tube coming out the side(s) like the L's?

 

W ide O pen T hrottle

 

opipe,
if you're planning on running duals i would not run anything other than 2 1/4" pipes. at least on my 4.6 the pipe size made a huge difference. i first went with 2 1/2's and lost some low end. i went back with 2 1/4's and got it back. good luck, rich.

 

I recently had a SI/DO setup installed on my '97 4.2L F-150. The service manager advised 2 1/4" pipes and 4" tips. I gained a lot of low-end and didn't loose anything at WOT. The 4" tips make it sound very nice . My V6 doesn't sounds raspy at all. Sounds just as deep as my neighbors 5.0 F-150 with a stock exhaust.

I can't verify that the gas milage has increased yet but my engine seems to breath easier and transfer power to the rear wheels with less effort. The idea is that by opening up the exhaust you will make it easier for the engine to push out the burned up fuel thereby making it work less and increasing your MPG.

Looks very classy too.

 

hey aj..

 

hey aj..
can you post some pictures of ur 4 inch tips...i just put 3.5 and i was interested in the 4 ...thanks

 

I'll try to get around to it. Trouble is that I don't have a scanner or a digital camera so I need to wait until I've used all the film in my camera and then have my girlfriend scan 'em.

Soon