IDI Towing

[Oldbrown]

Good morning. New to this forum and considering an IDI for a budget tow rig. I will be pulling 26 foot long travel trailer at roughly 5000 lbs with 1600. Lbs in the bed. I want a manual trans, need super or crew cab and long bed. Flexible on F250 or F350 and 2wd or 4wd. I like the idea of simplicity and that is why I am considering IDI. Everywhere I read people say they will get you there but not fast. I am not a high speed driver but would like to do 65 on flat and 50-55 on the hills etc. I have had 24v Cummins 5 speed and both 454 vortec and TBI with automatics. I know these will feel faster compared to non turbo diesel. Would be fun to add turbo down the road. I would think I should look for 4.10, not the 3.55? Goal is 14mpg empty at 65 and 10-12 towing depending on speed, hills, wind etc. Thanks up front for the feedback.

 

[Oldbrown]

I also know major items are cavitation for 7.3 and head gaskets for 6.9, any other things to look for is appreciated. Thanks

 

[franklin2]

If you expect 14mpg empty, you must get a truck with a overdrive trans. This knocks out all the older rigs unless you find one that has been swapped. 2wd would be a cheaper easier truck to find that will not be all rusted out, but if you go with a overdrive trans (zf 5speed) and are backing a trailer up, you almost need the 4wd so you can put it in low range to back up a trailer without burning the clutch up. That is one of the downfalls of the zf, it has a higher speed reverse gear that makes it very difficult to back up a trailer on a incline.

 

[Thewespaul]

A customer of mine sent me this picture yesterday, he has a factory turbo kit on a studded engine I put together, the turbo is rebuilt and he has a set of my stage one injectors with a 105cc pump. He said he was able to pull the load into a headwind 55 mph up any hill, limited by egts not power since he isn’t intercooled yet. Cruise control easy 70 mph pulling on the flats. When he was non turbo he was crawling up the side of the highway 15 mph in first.

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If you are using the truck as a tow rig, I would only look at turbo trucks or invest in a kit right away. 93 and 94 had factory turbo options and are arguably the best IDIs of the whole production line. I would look at a factory turbo truck, drw, 2wd with a five speed. If you haven’t already look through the tech articles to learn the basics of these trucks

 

[JAKRANCH]

I've towed heavy with both 3.55s and 4.10s and like 3.55 a lot better. It gives each gear more"range". If I hit a hill in 4th and it forces me to downshift 3rd has a top speed of 55-60 instead of 35-40. I wouldn't do without 4wd tho cuz with the higher gearing I need 4 lo to back up sometimes. Also never had a turboed IDI yet but the naturally aspirated trucks fall on their face when they meet a hill towing. Especially if the other morons don't give you room to get a run at the hill!
O ps p.o. put freer flowing intake and exhaust in even before I swapped the 5spd in p.o.s often hit 20 mpg with 3.55s. I've only gotten that good a couple times but I have a lead foot. My average is 17 mpg.

 

[Macrobb]

Turbo really makes a difference. N/A, will always do it... Just slow.
Turbo IDI? Eh, I'm usually limited by EGTs or water temps(no intercooler here either), but only the steepest, longest hills keep me below the speed limit, whatever that may be. And that's hauling a decent trailer(figure 8K behind me when I do this).

Cavitation is... a bit less of a problem than it used to be. Mainly because it happened on succeptable blocks years ago(below 150K miles), and there just aren't that many low-mile blocks still around. So you get 'survivorship bias' now. You still want to use a good ELC coolant like the Zerex G05 Gold or Zerex HD ELC.

6.9s do have head gasket issues(with ancient gaskets and no studs), as do overheated 7.3s - Otherwise, a 7.3 can handle over 15 PSI of boost un-studded, and... a lot more than that if you stud it.

 

[jayro88]

I tow with my 7.3 NA IDI. IT has a c6 and 3.54's. As it sits I gross a little over 14K lbs fully loaded. I installed and auxiliary O/D (DNE2 unit) for when I am running empty since the van is also my daily driver, but the O/D is useless when towing on anything except flat ground. If all I used it for was to tow and I was going to stay NA I would want to swap in 4.10's. However, I have a turbo I will be installing so I plan on keeping the 3.54's until I see how it does. With a manual I would think you should not have any issue hitting your MPG goal. Unloaded I can average in the 16-17mpg range unloaded and I am above 10mpg towing (10-13mpg). That is with a c6 which isn't the mos efficient transmission choice. Just plan on sinking some $$ into it since it will be older and have age related issues to address.

My suggestion would be to find a turbo truck or plan on putting one on shortly after the purchase. You can definitely get where you are going in NA form while towing, but the turbo would make it less tiring. I have to constantly watch my EGTs and I try to keep an eye on how my smoke I am blowing as well.

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[Oldbrown]

Thanks guys, this is the kind of feedback I was looking for. The reverse gear ratio in the5 speed sounds like a major design flaw. Hoping I can find an elderly rv hauler instead of a kids mudder.

 

[Duke57]

Turbo really makes a difference. N/A, will always do it... Just slow.
Turbo IDI? Eh, I'm usually limited by EGTs or water temps(no intercooler here either), but only the steepest, longest hills keep me below the speed limit, whatever that may be. And that's hauling a decent trailer(figure 8K behind me when I do this).

Cavitation is... a bit less of a problem than it used to be. Mainly because it happened on succeptable blocks years ago(below 150K miles), and there just aren't that many low-mile blocks still around. So you get 'survivorship bias' now. You still want to use a good ELC coolant like the Zerex G05 Gold or Zerex HD ELC.

6.9s do have head gasket issues(with ancient gaskets and no studs), as do overheated 7.3s - Otherwise, a 7.3 can handle over 15 PSI of boost un-studded, and... a lot more than that if you stud it.

Is there any issues when adding a turbo to a NA engine due to the higher compression ratio? Someone told me the NA's were 22:1 and the factory turbo IDI's were 17:1. Is that true?

 

[jayro88]

Is there any issues when adding a turbo to a NA engine due to the higher compression ratio? Someone told me the NA's were 22:1 and the factory turbo IDI's were 17:1. Is that true?

I believe the compression etc is the same between the NA and Turbo engines.

The turbo rods are stronger, but NA rods are fine except at pretty high boost levels. I think the turbo blocks may have some extra webbings, but NA is fine except at the extremes.

Or this is what I remember from my research.




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[austin92]

I can only reiterate what everyone else has said although I built a 10.25 with 3.73s. My truck is a na 6.9 with a zf5 2wd. I want an intercooled turbo with water ****, sick of towing and looking at the pyro more than the road. I also want to get a 4wd trans and tcase just for low range backing a trailer. My driveway is slightly up hill, maybe 60 yards long and it sucks backing my trailer up. Towed about 12k last weekend, it moved it but kept getting up past 1100* if I went much past 55. Its got the ass to move it, just gets too hot


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[Duke57]

I believe the compression etc is the same between the NA and Turbo engines.

The turbo rods are stronger, but NA rods are fine except at pretty high boost levels. I think the turbo blocks may have some extra webbings, but NA is fine except at the extremes.

Or this is what I remember from my research.




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What are the compression ratios of the idi's by the way? I noticed that when I turn of my engine it always has a sharp shake at the emd of crank rotation. I assumed it was due to good compression.

 

[snicklas]

Very early 6.9's may have been 22:1, but most IDI's 6.9 and 7.3 including the Factory Turbo in 93.5-94.5 was 21 or 21.5:1.

The 7.3 PSD in 94.5, which is a Direct Injected, Turbocharged engine that is designed completely different than the IDI was 16 or 17:1, because they were designed with a turbo in mind.

Putting a turbo on an N/A engine is not an issue. Keep the boost reasonable 10ish in a 6.9 12ish in a 7.3 and it will hole up well. Many IDI's had a turbo kit added to an N/A engine, including mine. decades ago and are still running well with tons of miles. Now, wanting big numbers, then there is work to be done. My truck, has been worked most of it's life, is has ~150,000 miles, and has an early Hypermax Turbo on it, and the biggest problem with mine is electrical, not mechanical due to the turbo. Then engine needs a water pump, and the engine electrical fixed, and tires. The engine would go anywhere I wanted to go, if I could keep coolant in it and the tires not blow (yes they are that bad).....

They will tow well, just not necessarily fast. I remember back in the day, when these were still fairly new and we didn't have the improvements Mel. Russ Justin and Wes have made, hearing an N/A IDI will tow anything at 35, and one with an added turbo and the 2 flat recommended increase in fuel at 45. These speed were at max loads, not towing a lawn mower.

One other thing to remember, these trucks were designed when the national speed limit was 55. I've seen may posts with people saying my trucks seems to work best in the 55-60 range, it doesn't like 70-75. Well, 55 was what it was designed for. The newer trucks were designed for 65-70 speeds limits. The RPM's my IDI runs at 55-60 is what my 6.0 runs at 70-75. But the 6.0 has a different gear ratio, larger brakes, and more power to reach that goal. An N/A IDI was 185 at the crank, a 6.0 was 325. The statement of my truck won't keep up with the new trucks..... well, it wasn't designed to. Not saying you can't make them run that well, but like Wes @Thewespaul said in one of his threads, he was towing a fairly heavy trailer at 80 with no problem with is shop truck, but look at what he has done. You can make an IDI a solid tow truck. But keep in mind, you are dealing with an engine that was originally designed in the 70's, and put in with a goal of running at 55 MPH.

Please don't think I'm knocking the IDI, I'm not. I like them, and the trucks they are in. My oldest just picked up another one for a song. But keep in mind what you are dealing with. Not just in these trucks, but across the board. The fastest, big V-8 muscle cars that were in the 400 Cubic Inch range, and were the fastest things on the road in the 60's 70's and early 80's would have their a$$ handed to them today by a 4 or 6 cylinder. Just think, the "big 3" are now in the 400hp range factory, up from the 200 range in the IDI's and 7.3 PSD.

 

[Thewespaul]

Very well said Scott, couldn’t put it better myself. Like he said, these trucks can be made to pull very well with some work. A turbo is the first big step, then after that it’s goodies that take it from “good enough” to “I need another set of rear tires again” the shop truck has a good bit of work done to it, but fairly cheaply. It’s still a stock bottom end, stock junkyard turbo and injection pump with just some upgrades added on to maximize the stock components (like an intercooler) without forking out big money for a bigger turbo or pump. As the truck sits now, I have about $2200 in the engine and the upgrades, and I am very happy with it.

 

[laserjock]

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Here’s my rig. It’s a 26 bhw. It’s right at 30’ tip to tail. Whole works loaded pretty well for bear (less a tank of water) was around 12.5k lbs. I think my specs are in my sig. but I’m an N/A block with turbo (albeit not a stock setup) and a 100 ish cc pump. 3.55 gears. I get right at 10 mpg towing. 14-16 (sometimes more) empty.

She will pull as fast as you want to go on flat ground. In the mountains I’m water temp limited. I’m cool spring weather I can pull any of the mountains out here at 60-65 without working the truck too hard. If ALL I was going to do was tow, I’d put 4.10’s back in it. With the 3.55’s 4th gear is totally an option clear to 65 (more if you want to push it to the governor). The 4.10s would let me hold 5th longer mainly because I could make more boost at a little slower speed. In 5th to make “full boost”, I’m way faster than I’d like to be to have enough RPM to make the boost.

Talking to a couple guys who also bought motorcraft fan clutches from rock auto I’m wondering if they just were no good out of the box. That’s really my only power problem.

Hope that helps.