7.3L IDI diesel not very loud without exhaust.

[cleandan]

I have a 1990 F250 with a 7.3L IDI diesel as my daily driver. Recently the factory exhaust has come apart and I am in the process of fabricating a new exhaust...The Y-pipe is done, but it was a pain in the buttinski.

Anyway, as any good car guy does when he has the exhaust off the vehicle...he runs the motor to hear what it sounds like.

I have run the engine in two configurations now. Straight mainfolds only, and the Y-pipe with a short extension only.

I am completely surprised how relatively quiet the exhaust is.

With either, just manifolds, or just the Y-pipe, the exhaust sound is still not louder than the diesel itself at idle.

On a short drive I accelerated as normal and it is a bit loud after about 1/2 throttle, but only when accelerating. As soon as you get to a steady cruise speed it is not loud at all.

The straight manifolds are a bit more quiet than the Y-pipe but again, nothing even remotely close to my 428 or 289 with open headers. Not even 10% as loud as the gas engines.

I would have figured with the 22.5:1 compression ratio it would bark pretty well...But nope.

Learned something new today while building an exhaust.

[Drew Pojedinec]

I ran one for years with nothing but a turbo for a muffler.
Was a nice 89 F250

[BigBlueIron]

Had an 89 with 2.5" dual exhaust with some glass packs. Moderately quiet until about 2000 RPM then it got loud and sounded awesome!

[FrozenMerc]

It's not that the exhaust is any quieter than any similar displacement gas motor with straight pipes.  It's that the injection pumps on IDI's are so damn loud that the pump masks the exhaust note....

It is always fun to see the reaction of someone driving past me with their windows down when I am out and about in my 6.9 powered '85 F-350.  That IP at full song will just about make them jump out of their seat.

On a more serious note, the rest of what you are noticing may be related to the cam spec.  Someone correct me if I am wrong, but the cams in these engines have a narrow lobe separation angle (103 deg) and very little overlap, which would help to keep the noise level down.

[RustyCrankshaft]

It's not that the exhaust is any quieter than any similar displacement gas motor with straight pipes.  It's that the injection pumps on IDI's are so damn loud that the pump masks the exhaust note....

It is always fun to see the reaction of someone driving past me with their windows down when I am out and about in my 6.9 powered '85 F-350.  That IP at full song will just about make them jump out of their seat.

On a more serious note, the rest of what you are noticing may be related to the cam spec.  Someone correct me if I am wrong, but the cams in these engines have a narrow lobe separation angle (103 deg) and very little overlap, which would help to keep the noise level down.

The IDI cams actually have negative overlap. Both valves are closed for about 15* (depending on which version you have, I'm aware of and have measured 3 different IDI grinds and 2 different 7.3/T444E grinds). I have a cam grind I use on the turbo engines (both IDI and PowerStroke) but I found, counter-intuitively, it had too much overlap for the NA IDI's and it didn't make up the low RPM loss until well over 3k rpm. If you were going to run it to 4k-4200 the turbo cam did pull harder on top even on the NA's.

20200315_120054 by Patrick Oilnut, on Flickr
A friend's 86 I'm working on for him. He bought it new, all the options and EVERYTHING works in it. Even the clock. Ok, the rear brakes and the AC don't work and the pump has 240k on it and is worn out, but in a few weeks everything will work in it.

[allrightmike]

Does the fact that a diesel has no throttle and the engine has all of the air it wants at any time contribute to the lesser exhaust signature?

[BattlestarGalactic]

Loved my 2000 PSD, as once I straight piped it, it sounds like a mini V8 Mack motor.   Though it was only 444 ci compared to the Mack 998 ci.  It has the same V8 bark pulling a load.   Pulling my race trailer with the rear slider open was awesome.

The 2000 was the last without a CAT, as they upped the HP the next year(from 235 to 275) and added the CAT.

[GJCAT427]

Larry, Not to argue, My 95 PSD F350 had a converter from the factory. It was removed several yrs ago and the snake head and a straight piece were put replaced. It made it breathe a lot better and the turbo whistles. It did improve fuel miles. Now I`ve got to replace the whole exhaust due to age. The trucks were avable with or with out the converter depending on weather it was built in the states or Canada. Garry

[64PI]

I had a '02 7.3 in a crew cab short box.. I loved that truck. Ran it for years with a straight exhaust coming out behind the passenger rear wheel. Then the last few years it was dumping behind the passenger seat(thanks to the NYS road salt in the winter). Passengers complained about the diesel smell but it didn't bother me. That truck nickle and dime'd me to death in the last year. The electrical system wall full of gremlins. The truck would randomly die. I shut the door once and truck shut off.. Fired it back up opened the hood looking for who knows what.. Shut the hood and it shut off. Had the engine wiring harness replaced. Driving it home hit a bump in the road and the check engine light came on... Pulled in the driveway and it shut off and never started again... I hated to see it go but I couldn't afford to keep chasing the gremlins on it. I'd love to have another one just like it but the prices are higher now than when I bought mine 12 years ago. Maybe someday....

[RustyCrankshaft]

I had a '02 7.3 in a crew cab short box.. I loved that truck. Ran it for years with a straight exhaust coming out behind the passenger rear wheel. Then the last few years it was dumping behind the passenger seat(thanks to the NYS road salt in the winter). Passengers complained about the diesel smell but it didn't bother me. That truck nickle and dime'd me to death in the last year. The electrical system wall full of gremlins. The truck would randomly die. I shut the door once and truck shut off.. Fired it back up opened the hood looking for who knows what.. Shut the hood and it shut off. Had the engine wiring harness replaced. Driving it home hit a bump in the road and the check engine light came on... Pulled in the driveway and it shut off and never started again... I hated to see it go but I couldn't afford to keep chasing the gremlins on it. I'd love to have another one just like it but the prices are higher now than when I bought mine 12 years ago. Maybe someday....

Very common symptom of the IDM going bad (not uncommon to see bad solder joints on the SMD's on the later boards) and also the IDM to engine harness having loose pins or broken wires. Also on the 02's it was the first year that they actually used real multiplexing in the SuperDuty's and they can have some odd stuff go on with gauge cluster as well. But slamming the hood or drivers door and having the truck shut off is most commonly an IDM problem.

[RustyCrankshaft]

Loved my 2000 PSD, as once I straight piped it, it sounds like a mini V8 Mack motor.   Though it was only 444 ci compared to the Mack 998 ci.  It has the same V8 bark pulling a load.   Pulling my race trailer with the rear slider open was awesome.

The 2000 was the last without a CAT, as they upped the HP the next year(from 235 to 275) and added the CAT.

998 so probably a single turbo E9?



I had one in my Superliner. When I rebuilt it I built it to the same spec as the Military test engines (Mack ended up not winning the big and Cummins got the contract from what I've been told, but who knows), didn't get good mileage but it pulled real nice. Never did get good dyno numbers on it, at about 800 we started spinning the tires on the rollers and I chained it down with some extras to tighten it up some and then started ripping caps off the tires. Since I was "borrowing" the local Cat truck dealers dyno on a Sunday evening I decided to call it quits before I broke something.

It wasn't the HP that dictated if a 7.3 got a Cat or not. It was a combination of GVW, HP, transmissions and which state/country it was sold in. Our fleet of OBS F450's with 5 speeds had Cats. THe OBS F450 fleet with E4OD's had no Cats. My 2001 F350 with a 4R100 had no Cat but my 01 with a 6 speed does.

Most SuperDuty automatics were actually rated at 250hp and the sticks were 275, with some exceptions (such as 99 to 99.5's that were 235hp and used a similar injector to the OBS trucks but in a split shot configuration).

[BigBlueIron]

My 2003 f250, ext cab, short box, automatic did not have a cat. Seemed to me the manual trucks usually had one tho. This has been a hell of a good truck, I beat the piss out of it through my 20's still runs good.

[BattlestarGalactic]

My information might be fuzzy, I suppose most did have a CAT early on, but I know my 2000 CC DRW/6spd didn't(I ordered it new in very early 2000, delivered it like April?). It was only a couple months old when I cut the muffler out of it and made my own filler pipe to take the place of the muffler.  If I recall the pipe was 3 1/2"?  I bought a U bend, split it and welded it into a Z shape and it worked perfect.
I know after that they upped the HP and talked of CATS on everything.  Guess that might be a bit of a stretch.

I bought a new '99 F450 PSD/6spd for our work.  No cat on it.  300K on it and stilll running well.  It's had valve cover gaskets replaced(wiring harness) and a few things, but overall still sound.


My friend in the truck club has this Superliner:
https://www.youtube.com/watch?v=9CNkXVykjI0


Few years ago I got to move it from inside the IX center after a show.  He always told me to come take it for a drive, but just never got around to it.  His is pretty stock as far as I know.  He also bought a CH E900 a few years later.  Painted it the same Mack green color.  That's his B model I parked next to.
https://www.youtube.com/watch?v=bXpnAgpauAQ

[RustyCrankshaft]

In typical Ford fashion, trying to decode which trucks got CATs and which did not is a little research, a little regional and a little, well no one really knows why that one happened. But there are some guidelines that mostly hold true. That F450 you had at work was probably a 50 state truck, which because of GVW was exempt at the time I believe even if it was a 275 manual trans truck.

Those are some nice looking Mack's! Always loved B models, I've owned a few over the years but don't currently have one. Honestly I'm not a huge Mack fan anyway but I liked that SuperLiner I had. E9 and a triple shaft, cammel back with Mack toploaders. Pretty bullet proof drivetrain and pulled nice.

Swore I'd never own another Freightliner and ended up buying an FLC (I tell myself it's ok because it was before Daimler bought them). I've retired the Peterbilt and will start restoring it next winter. The FLC has taken over pretty much everything including hauling stuff the pickup used to. Because why not......

Funny thing about it is, it gets almost as good of mileage as any diesel pickup I've owned has pulling! FLC gets about 7.8 hauling the baby trailer, my buddies brand new 2020 Duramax got 8.1 pulling the same trailer.

FLC trailer by Patrick Oilnut, on Flickr
I couldn't find one with it hauling the race car, but there it is with the Sandcar loaded in it.

Still love my 7.3 PS, but I've started using big trucks for almost everything. Just more comfortable. The 7.3 PS was probably the best diesel they've put in a pickup overall. No after treatment to worry about, very few design failures. With good maintenance they go a long time. My service truck has over 500k on it and I've done 1 set of injects, 2 turbos and 3 clutches and a LOT of oil changes.

[427Fastback]

I had a 92 7.3 IDI...I put a banks y-pipe on it,switched to 3 1/2 pipe and a large flowmaster muffler..Truck was far from quiet and sounded great.Lost the truck in a head on collision 7 years ago..It was a good truck...Owned it for 13 years.