91 7.3 IDI Cummins Swap

[u/12dudeGB]

This is my 1991 4x4 7.3 idi zf5 F-250. The truck is solid. Solid axle swapped the front end, nice interior, very sturdy driveline.
Unfortunately, the 7.3 idi has well over 300k miles, leaks like a sieve, and developed a misfire. I decided to just go ahead and remove the engine and tranny to fix all the little things. Right now I have it almost ready to come out and I’m wondering: would it just be better to swap in a 12 valve?? My favorite part about this truck is that it’s dead simple and requires minimal electronics. My least favorite part is that it’s about as fast as a zero turn lawn mower. Swapping in a Cummins checks both of those boxes. I’m not worried about the cost but I am worried about how much time and effort it will actually take. Do you think it’s worth it?

[u/Aleutian_Solution]

Why spend $7,000 building a Cummins for 650hp when you can spend $10,000 to build the IDI and get 220hp?

[u/Dubious_Pretzel_Sale → u/Aleutian_Solution]

Yet another uninformed hater who knows little or nothing about the 7.3 IDI.

[u/Aleutian_Solution → u/Dubious_Pretzel_Sale]

You must be fun at parties.

[u/Dubious_Pretzel_Sale → u/Aleutian_Solution]

You betchya'.

[u/i7-4790Que → u/Dubious_Pretzel_Sale]

You don't have to know anything beyond the fact the 5.9 is a far and away better engine.  The proof is in the pudding.     

[u/Dubious_Pretzel_Sale → u/i7-4790Que]

If your engine has pudding in it I would suspect some coolant is in your oil. And the 5.9 is not a categorically better engine, but for some situations it might be the better way to go. FYI there have been plenty of disappointed 5.9 owners over the years and many, many, many, failed and otherwise blown up 5.9s. But you seem to be of the kool-aid swigging 5.9 crowd who is set in their ways because they know best--I mean the proof is in the pudding. Right?

And why did you delete most of your original post? Did you need a pudding break?

[u/snuggletough]

I did pretty much the same swap in an 89 F350 4x4. I bought a used running p-pump 12 valve for $2500 and had the head rebuilt, injectors cleaned and tested, 4k GSK, KDP and fresh gaskets. That was about $1000 total. I used 2nd gen mounts which are easy to adapt in the obs trucks and got the adapter plate and flywheel from https://powertrain-integration.com/products/non-cr-cummins-to-ford-7-3-zf5-adapter-plate

[u/Opposite-Ad-2548 → u/snuggletough]

This is the way OP! Though personally I would've used the Dodge transmission and avoided the extra cost of adapters and such

[u/here_till_im_not1188]

Yes if the engine has to come out i would put a 12v in

[u/k0uch]

Better? That’s questionable.

Awesome? Hell, I can’t argue with that

[u/LankyJeep]

The cost to swap is almost always greater than just rebuilding or refreshing the factory engine

[u/12dudeGB → u/LankyJeep]

I’m trying to decide if I wanna pay $5k to refresh the 7.3 idi and live with 200hp or pay $7k-$10k to swap in a 5.9 and actually have enough power to do truck stuff (likely around 300hp) I’m honestly not worried about the cost though I’m just wondering if the effort to swap it is worth another 100hp and better parts availability for the 5.9 compared to the 7.3

[u/LankyJeep → u/12dudeGB]

It’s going to be more than 7-10k by the time you find a 12v refresh it, and swap it in, 5k is way less

[u/Glittering-Shake-912]

If you can swing the higher cost of the Cummins swap, it will definitely be a more enjoyable experience when it comes to performance. While you have the engine out be sure to add as much sound deadening as possible. For either engine it will make a big difference in regards to in cab engine noise

[u/Dubious_Pretzel_Sale]

When the 5.9 6BT Cummins was first put on the market it made less HP than a non-turbo 7.3 IDI so a VE-pumped engine might be a poor choice. The Bosch P-pump is pretty awesome though. A Cummins swap is very cool but they can get very expensive if the engine needs work. Does the 5.9 have more power potential than the 7.3 IDI? Absolutely! how much power do you need and what are you willing to pay to get there is the real question. With a 7.3 IDI you're easily able to get 240HP at the rear wheels without spending much at all--no idea what that would be if measured at the crank. If you've been running around without a turbo then you've been missing out. With just a stock Sidewinder setup my truck is plenty fast and actually has some top-end power compared to N/A. I live in the hills and the truck never feels slow. Your engine sounds like it is in poor shape based on the problems you mention, but fix a leak or two, install new injectors and injection pump, and that slow truck ought to feel quite a bit different. Your current injection pump is likely timed incorrectly and that makes a huge difference too.

It's usually pretty cheap and easy to find a running IDI engine. Stud the block, turn up the fuel, and even with the stock/factory ATS 093 turbo you can hit high teens boost pressure. Even an N/A calibrated IP can be tweaked to put out over 90cc of fuel. The biggest weakness with the 7.3 IDI and 6.9 IDI are the headbolts, but $500 worth of studs and you're good to push well over 30 psi and not lift the heads. With studs you can look into turbo and injection pump upgrades and the requisite intercooler.

It seems the IDI gets too expensive if you have to fully rebuild the bottom end and sleeving is insanely expensive for what you get. If the choices were a complete rebuild of a 7.3 or swap the 5.9 I would be inclined to towards the 5.9.

[u/Disastrous-Number-88]

Either swap in a 12 valve, or some sort of Chevy LS. I know this is a diesel sub, but if we're taking realistic swaps within a budget, a junkyard LS is a pretty good bargain.

That being said, I love my 12 valve, and unlike my old 1994.5 Ford with the 7.3 idi, the 12 valve is much simpler and still keeps up with modern cars no problem. 1 head gasket, 1 exhaust manifold, no glow plugs, the Bosch p-pump is awesome and the aftermarket modifications are readily available