So I'm looking into buying a 7.3 non turbo IDI rollback 5-speed. I've driven them before, never owned one or towed with one. I tow trailers everywhere with my 7.3 Powerstroke, and I know not to expect a similiar experience with the IDI. Would I be able to roll on the highway 60-70 ok with say 3800lbs on the rollback and another 4000 behind the truck? Or are there affordable modifications to do to make that scenario better? I also have towed with a fairly stock 460 truck, would it be similiar? I'm glad for any input, thanks!

 

It would be pretty similar to a 460 powered roll back. Not sure what those tip the scales at but grossing 13k-14k isn't bad for my truck(4.10s and 315/75 tires) but 18k is a little much and it struggles up hills.

 

Without a turbo unless it flat ground 70 would be hard. Yesterday I hauled some stuff out to our land gross was 15 k. On Flat ground I could maintain speed. Some of the hills I had to downshift to keep 55. That with 3.55 gears. Starts are slow.

 

it will do ok, but be slow.
add a turbo and open the exhaust up and it will be equal to a first generation powerstroke.

but 70 MPH will be pushing the top of the RPM scale. rollbacks are usually low geared for pulling power instead of speed.

 

Don't the IDI's get really bad mileage pulling on the open road ?

 

A NA IDI would probably perform slightly worse than a stock smog era 460. I wouldn't want to be hauling 8k lbs with one, it'll do it but it will be unpleasant. For it to perform well you'll need a turbo and a higher output pump along with new injectors.

As for MPG, my IDI weighing 6600 lbs with 3.55:1 gears and C6 (presumably similar to a 4.11 gear truck with no overdrive), hauling maybe 5500 lbs has got the following MPG on more or less the same 480 mile route.

7/2014: 10.91
8/2014: 11.01
7/2015: 9.54
7/2015: 9.03
8/2016: 9.52
9/2016: 10.18

The data from 2014 is with a worn out pump and the truck would slow to 30 MPH on most grades. The 2015/2016 data is with a 100cc pump and it would pull the hills much better but still ended up at 30-40 MPH by the top for EGT reasons. This winter I changed from a Banks non wastegated turbo to a newer wastegated Banks and notice at least unloaded EGT is not as much of a problem. Hopefully that's the case when I start towing in about another month. I also swapped to a ZF5, which has given over a 3 MPG increase in mostly around town driving. I'm curious to see what it does purely highway and towing this route I take in the summer, though I expect to still be driving by the pyro unless I get around to doing an intercooler before then. For comparison the same route and load my 6000 lbs 460 truck (lifted, 35" tires, ZF5, 3.55:1 gears) gets 10.5 MPG and will hold 70 MPH the whole way.

 

What year and model is the truck, and what transmission? What diff ratio?

 

It's pretty much as everyone else said:
NA, an IDI will pull anything... just not particularly fast. It'll do it all day long, though.

Once you add a turbo and a decent amount of fuel, you can easily get into 1st-gen PS power levels, and with a bigger pump, I've had no trouble getting 250RWHP out of them... which is above 2nd gen 7.3 PS levels(02 PSD = 250 at the crank, something like 208 at the wheels stock).

Obviously, a powerstroke with a tuner and some added parts can do quite a bit more.

 

Thanks for all of the input. Looks like it'll be fine as long as I'm not in a huge hurry. I'm not really worried about slowing up hills as long as it's not crawling... Basically I buy/fix/sell/trade stuff constantly and I currently use my 7.3 power stroke with trailers to go pick stuff up or deliver. I think that using a rollback would make things much easier for me. I just can't justify buying a power stroke rollback for 2.5x+ the price of an idi or 460 truck. I've been looking at both IDIs and 460s, but I'm leaning toward IDI for fuel consumption.

As as for the specific truck I'm considering right now, 1990 7.3 IDI, 5 speed stick, 4.56 rear. I probably wouldn't be able to run it over 65mph.. not a huge deal I guess.

 

4.56 gears should give you a flat out speed of around 75.

 

You could always add a turbo and auxiliary overdrive. If you can find them both used, you would probably have less than $2k into them and a much more user friendly truck. The aux OD would let your final drive be like a truck with a 3.60 rear end.

 

Typical common auxilary overdrive is the GearVendors unit. It's a good unit in that it's a shift-on-the-fly unit, and you can use it like a gear splitter in a big rig.
Running the numbers... this would be great. You would end up running about 1800RPM at 60MPH in double overdrive, which would get you good unloaded highway mileage.

With a turbo and fuel mods to make some decent horsepower, you could definitely do some towing on flat ground going 70+ in double overdrive; going too slow would drop you out of the power band and require you drop to 5th/single overdrive.

Obviously, hills, load etc will change this, but yeah - GVOD, turbo, crank the fuel up... and let her eat!

 

Gearvendors are pretty nice but pricey if bought new. Not sure what the GCWR is on them, but I think it would be pretty substantial since they are advertised to be used in large motor homes etc.

If your patient and keep an eye out you can find a good auxiliary OD at a big savings. This is what I did. I ended up purchasing a DNE2 OD unit from a forum member. It is a little different than a gear vendor. A gearvendor is designed more like a 2nd automatic transmission. This means you can let it shift itself, of manually engage it. My DNE2 is like a 2 speed manual (gear to gear) that bolts to the back of my c6. I have to manually shift it with a momentary 12v switch. The switch runs an electric motor that loads a shift spring. Then I unload the drive-line by letting up on the throttle and it shifts. Just cruising unloaded I leave it in high. If I am doing a lot of stop and go or am loaded I run in low. I believe the DNE2 is rated for 35K lbs GCWR. The DNE2/US Gear OD's are no longer made.

 

I checked the website - GCWR of 30,000 for non-commercial applications and 25,000 for commercial use.
Pretty much. Full price is ridiculous on these things.

 

I've seen gear vendors units before. Seems like a good option if one could be had used for a decent price.