One of my son's friends has a really clean 80s model diesel 4x4. He got it from his grandpa who bought the truck new. Anyway, he asked me to post a question on this forum. He says that right now he's only getting around 13-15 MPG. The truck is stock with the 3 speed C6. If he replaces the stock exhaust with a straight pipe, would that increase his fuel mileage? Apparently, one of his friends told him doing this would increase his MPGs to around 19 or so, but he's worried about doing something to this truck that could end up ruining it. I can't say that I blame him either. You should see this thing. The original red paint is still shiny, it doesn't have a scratch on it, it has diamond plate running boards on it, and one of those farmer type spring loaded bumpers. If I can I will take some pictures of it for you fellas to drool over.

 

Nope won't happen, might feel more power/ mean sound....but that will be about it. Gears, tranny, turbo and managing throttle is about all that will help (noticeably)

 

what gears does his truck have ? if 4.10 and a C6 then the mileage is about right ! nothing wrong with a straight piped exhaust ! if the exhaust is in bad shape then i would do the straight pipe !

 

A straight pipe will slightly increase power/economy, but not enough to bother noticing.

However, straight pipe also reduces by a good number, EGT levels (Exhaust Gas Temps) witch is a good thing.



Now, let me warn you, a non turbo straight pipe diesel will be ungodly loud if he lays his foot on it. So just tell 'em to take it easy around the boys in blue

 

13-15 mpg with yesteryear's trans which is a basic 1-2-direct drive (3rd) and a non locking converter,is pretty dang good.
he's doing as good as i am (minus empty on the interstate ) with the much more advanced E40D trans.
tell him he should be all smiles with economy like that, given what the trans is.

as far as ruining the truck by ditching the muffler.tell him not to worry about that.unlike gasoline engines,a diesel requires NO back pressure.
the only thing he'll be ruining is his hearing.



for more helpful tips of increasing FE.be sure to check out this thread!!! it's a MUST read!

https://www.ford-trucks.com/forums/7...ht=hypermilers

at the very least.pass this tip onto your friend:
https://www.ford-trucks.com/forums/7...l#post10637561
(because it really helps and its CHEAP!!!)
of course,following davids c6 to E40D trans swap (which cost pretty big $.so must be sure the truck is worth it) will yield the largest gains.

 

Just ripped my muffler off the other day, haven't gotten the exhaust to exit out the side yet (Got the parts, just haven't installed them) I hadn't thought to check the EGT levels. But she has a great startup sound, and great for shutting up annoying passengers.
In my area 90 db is the legal limit for Diesel engines in the city. Outside it's kinda no rules. Any chance this ole pig'll go over that? Haven't had a chance to get out and test her with a decible meter. I have a feeling she's gonna get annoying towing up steep grades.

 

My 87 is straight piped with no turbo...super loud and annoying. I wear earplugs when I drive it....yes seriously.

Thad

 

i straight piped my early 94 years ago and used to love the sound, but have now grown irritated w/all the noise,especially bouncing off of the trailer. i now long for the whistle of a turbo........coming soon

 

For a kid or new driver trying to impress friends it is great. If you want to ride down the highway and try to talk to him it will not happen with a straight pipe. Honestly get a turbo, then get the good down pipe and then run the straight pipe. the turbo acts like a muffler. I have a turbo straight pipe and it is fine, still sounds great and you can still have a conversation in the cab without yelling at each other

 

I straight piped mine a month or two ago and I don't think it is that loud. It actually sounds pretty good. The only downside I see is that he will need to install a muffler on it to pass inspection in some states. I will have to do that for mine once I find a driver's side headlight/parking light assembly. Mine is busted. I need a muffler and the light to pass.

That's not horrible MPGs depending on the driving conditions and how he drives. I get about 15MPG mixed city and highway driving but I drive like a granny.

 

Str8t pipe is the way to go on an old non turbo idi!!! Its not 2 bad

 

Here's a quick clip of mine. I've started watching EGT reading when pushing her up a hill, I've started to notice about when I normally have to start backing off a bit up steep hills (EGT is usually 1000-1200), it's like 800-900. Kept the hammer down all the way up the hill, and left the lifted tacoma I was passing in my dust.

She's currently not all the way out from under the bed, I figured it was good enough for now, instead of just exiting right in front of where the muffler used to be. Do exhaust tips do anything for these ole IDI's? I know my buddies PSD sounded better with one after his exhaust system got re-designed. Not sure if I care enough to buy one to find out it does nothing.

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Guys, thanks for all the replies. I haven't been around to check this thread since I started it. I haven't seen my son's friend either, but my son told me he went ahead and went with the straight pipes but doesn't like the noise. LOL! Guess you can't have it all.

 

Haha yeah, i've noticed it can be loud. But it has a much more satisfying throttle responce I find, a lot of it has to do with the sound I know. But with the recent work I've done I find myself going faster than the speed limit long before I used too.

 

witha turbo a straight pipe isn't too loud with a late 90's crew cab you can bearly hear it with the windows up. As for it afecting mpgs it can drasticly raise them in some situations but if you are getting 13-15 it won't. if your stock mufler is pluged like mine was it will.