5 inch Exhaust pipe

[ted2020]

A friend of mine has a Dodge with a Cummings Diesel (5.9 maybe) and he recently installed a 5" exhaust. He claims it increased his mileage by 20%. He admits some disadvantages (very loud, it is basically shooting straight out the back of his truck) but he has found a work around for the noise.

My question is this: I currently have a 3" exhaust, is it worth (by worth, I mean increased mileage of say 15%) going to a 4 or 5"? What are the advantages and what are the disadvantages? Is 5" better than 4"? This would be used on a 1995 6.5TD.

[6.5TDTahoe]

I don't think you will see any measurable power difference between a 3in. down pipe with a three in. exhaust system or a 4in back from down pipe. 4 in will just make more noise.,and that is guarnteed!!

[6.5 Detroit Diesel]

a four inch will open up the exhaust nicely. lower egt's because your engine isn't working hard to get rid of that hot exhaust. i noticed a difference in noise, mileage, and power.

going from a 3'" to 4" is kinda pointless unless you do a aftermarket downpipe.
i would do the downpipe, and then run a 4" exhaust in the position of the stock exhaust. getting it bent over the rear axle can add some price to your system, but the noise isn't that bad then and your rear tire isn't always covered in soot.

when i got my first truck, i was working at a heavy truck shop. rigged up my own exhaust that ended up with a 6" tip poking out the side behind the passenger door. rattle your ears and make a lot of noise, but did give back small power increases and a mileage increase.

having done a bunch of 6.5's ranging from my stacked truck to rear exhaust, to side exhaust, the best way is to put it out by the bumper. it won't buzz your ears, but with a good flow through muffler, it will sound good.

a 5" exhaust on a 6.5 won't do anymore then a 3.5" or 4" exhaust. it will give a little more sound.

[6.5 Detroit Diesel]

sorry, i was going to say as well that you will not see a 15% increase in mileage with only an upgraded exhaust. you would have to do some crazy work to get a 15% increase. even with a cummins, i am rather skeptical that a simple exhaust upgrade would get him that much of an increase. ;)

[ted2020]

The guy giving me the information is cheap dude and does nothing without a payoff, plus a pretty honest guy, so I am tempted to believe he is getting mileage. It might be because he is driving better who knows.

I would love to get some better distance out of tank of diesel on the truck, so finding aftermarket stuff that is not too expensive is always interesting.

Thanks

[JohnC]

If going to a 5" exhaust would give you 20% better mileage, I think the factory would do it if only for bragging rights...

[Robyn]

Beyond a 3-1/2 to 4" system on a 6.5 is overkill and just not gonna do anything but make noise.

Now if ya wanna talk on the Cool scale, then thats a different matter :D

Saw a 97 GMC DaHooooley crew in town with some very pretty and very HUGE chrome Stacks the other day.

Had to take a peek.

Fellow had a square tube "Log" in the bed of the truck with an 8" chrome stack on each side that went up about a foot over the top of the cab.

Had the way cool "cowboy cut" angled top on them too.

Not sure what the guy had in the log to dampen the noise but, the truck was supprisingly quiet with only a low rumble as he got into it.

Lots of turbo whistle though, yeah buddy.

This was definately a real "10" on the cool scale.

Now who knows if it made any difference in power or MPG but we all know the value of "cool" :D

Missy

[6.5 Detroit Diesel]

cool value is why i stacked the 93'.

it doesnt return any more mileage or power gains than a four inch exhaust in the stock location. but, with a ton of lights, bed rack, big tires, it sure looked good with the stacks factored in.

when it is reincarnated, it will have a full front bush bar which is on order. won't add anything to mileage, but will protect the front and yea, once again, the cool factor is huge. :D

[jhornsby3]

When I went from stock to the stacks i did see the improvment in the EGT area. As far as milage, I think it was a huge whopping 0.8mpg after the foot relaxed.

John

[AllThumbs]

I finished the 4" system today. I'm not sure how you would put a 5" in, certainly not in the factory location. Maybe stacks out the top. But then again, I hate anything that takes up bed space. My truck works and I need all the space I can get. We will see if the 4" gives me any advantage in mileage. This is a hard time to determine that as the cold weather always knocks the mpg in the head and I don't do long trips or trailer hauling in the winter.

[6.5 Detroit Diesel]

yea, the foot factor takes a while before you will see any returns on mileage.

as for the exhaust i had, it was four inch until it did a 90 in front of the tires, and then i used adapters to make it a six inch.

as for stacks, i didn't really lose to much bedspace. the stacks are in line with the wheel wells, so they don't interfer with eight foot long cargo. the crossover is a foot up, so you can still slide sheets of plywood in. i also built and installed my own dry box that mirrored the stacks design.