First impression towing with 6.9 NA

[Josh Oldenburg]

One big think many seem to forget, the IDI era trucks (83-94.5) the national speed limit was 55, everywhere, including the interstates. So when the engineers designed these trucks, they designed them to work their best at 55mph and below. That’s why 55 is in the 2000rpm range, since that is the general area of peak torque (an IDI is peak torque in the 1800ish range if I remember correctly). So the truck being able to maintain 55 while pulling a reasonable load was the goal. Yes, the 4.10’s do help, but, they are still shooting for 55. My 88 IDI C-6 4.10 likes 60 and under, yes it will go faster, but, it’s much happier there.

Now, fast forward a few years, and the interstate speed limits have been raised, and in my part of the country, the highest speed limit we have is 70. I know there are some states that have higher, but 70 is a good number ina good part of the country. Now, the engineers are designed the vehicles for working well to 70mph and below. Looking at my 03 6.0 Excursion, it was designed with 70 as the goal, which is why 70 is approximately 2000 rpm... same rpm sweet spot as the IDI, but is geared differently and has more horsepower and more importantly more braking power to handle the increased demand to get to, and stop from 70.

So, take a trailer and hook it to an IDI and it will be happiest at 55, but hook the same trailer to my 6.0, and it will run 70, and be happy doing it. But it was designed to run 70 to begin with. The IDI was not.

True, but what happens when someone is tired of the gasser in their 2000 SD and puts in an idi they have lying around? 4.10's and OD and plenty of stopping power

 

[snicklas]

True, but what happens when someone is tired of the gasser in their 2000 SD and puts in an idi they have lying around? 4.10's and OD and plenty of stopping power

Well, if you are putting a stock N/A IDI in a Super Duty, you are still putting the same 185 CRANK horsepower engine is a full size pickup. You are more than likely going to use the transmission the IDI came with, and you said 4.10 axles. So you still have the same power level, and 55MPH / 2000 RPM sweet spot of the IDI drive train. It's doesn't matter what sheet metal is wrapped around it.

My point was the overall design mindset of when the truck was designed.

So the difference in power train and gearing was my point.

An IDI era truck was designed with a 185 Crank Horsepower N/A engine, 3 or 4 speed auto or 4 or 5 speed manual with 3.55 or 4.10 gearing with a designed operational speed limit of 55 MPH, per federal speed limit regulations

My Excursion/Super Duty (03.25+) era truck was designed with a 325 Crank Horsepower Turbocharged engine, 5 speed auto or 6 speed manual with, in the case of my Excursion, 3.73 gearing with a designed operational speed limit of 70, to perform at the speed limit of a majority of the interstates now have.

So to answer you question, your 2000 SD Gasser converted to an N/A IDI with 4.10 axles, is still going to be the same slow **** it was in the Bull/Brick/OBS it came out of, just with better brakes.......

 

[franklin2]

I’m sure mine would but dang do you have to keep yours floored or nearly so? Maybe I’m just expecting too much out of it.

Don't worry, if he is running 3000rpm, has has it pretty much floored. The engine is governed at 3300, so he doesn't have much left. But as he can attest, it does this all day long and it doesn't hurt anything but your ego on the hills.

 

[Hydro-idi]

Don't worry, if he is running 3000rpm, has has it pretty much floored. The engine is governed at 3300, so he doesn't have much left. But as he can attest, it does this all day long and it doesn't hurt anything but your ego on the hills.

If your engine is governed at 3300 rpms, I’m sorry haha. Mine wound all the way up to 3850 rpm and I wasn’t afraid to run it that high either. That was a stock calibrated pump that I bought from Conestoga too.
These engines can take it.

 

[frankenwrench]

My truck seems fairly comfy at 70 with a light foot.. Although my 91 also has a turboed 6.9 in it with zfs-42 and 3.73s in it. Loaded with about 8500 she still absolutely hates hills and will fall to 60 and once even as low as 55. Although I live in Texas so my hills don't amount to what yours do. But on flats will pull at 65-70 all day at 2000-2200 rpm. Empty hwy I get 19. Loaded hwy 15. Anyone have similar set up to let me know if my fuel mileage sounds right?

 

[towcat]

My truck seems fairly comfy at 70 with a light foot.. Although my 91 also has a turboed 6.9 in it with zfs-42 and 3.73s in it. Loaded with about 8500 she still absolutely hates hills and will fall to 60 and once even as low as 55. Although I live in Texas so my hills don't amount to what yours do. But on flats will pull at 65-70 all day at 2000-2200 rpm. Empty hwy I get 19. Loaded hwy 15. Anyone have similar set up to let me know if my fuel mileage sounds right?

take it out of 5th when you hit the hills.
night and day difference.

 

[frankenwrench]

I usually have to. I just never have been a fan of running my truck above 2400. It's a 2 year old rebuild but I'm afraid of running it higher than that. Never got a clear answer on safe rpm range on this truck but it just sounds raunchy above 2400 to me so it feels like I may blow it up. If I'm incorrect, well I guess it just goes to show what I know. But I got ALOT of money tied up in this old girl

 

[Cubey]

Day 2: I had it floored at one point in 3rd gear. Admittedly it was a very hilly stretch of US highway with a still 55 limit. I have it nearly floored most of the time though except when going downhill.

Oh and there is a little smoke at idle. Fuel probably, not oil. Oil consumption is way down with the Lucas oil stabilizer I think.

It never quite reached 200*. It’s probably running at 3000rpm when it’s screaming in second gear but my inaccurate tach shows 2000-2300. It downshifts fairly often if I have it open too much so I have to back off just a tiny bit at times.

It’s getting really terrible mpg though. Possibly as low as 10. I don’t see any ********* clouds. I see a grey one taking off. Harder to see at highway speed from the mirror if it’s not rolling coal.

 

[Cubey]

Oh and it dropped below 35 on a couple of those really bad hills. One for sure had a truck lane. I can’t remember if the other time did or not. No one road raged amazingly. Only one biz pickup passed me.

 

[Hydro-idi]

I usually have to. I just never have been a fan of running my truck above 2400. It's a 2 year old rebuild but I'm afraid of running it higher than that. Never got a clear answer on safe rpm range on this truck but it just sounds raunchy above 2400 to me so it feels like I may blow it up. If I'm incorrect, well I guess it just goes to show what I know. But I got ALOT of money tied up in this old girl

3850 rpm is the redline. No need to be scared to use your engine what it was designed for. My $6k engine build saw redline rpms about 30 minutes after starting it for the first time. They are designed to be run in hard. Baby them, and they will be a oil drinking **** with lots of blowby because you never got rings to seat.
Sold my truck to father in law but he’s racked on about 20k on the engine and so far so good. Zero blowby coming from CDR and no oil usage.

 

[oregon96psd]

I just never have been a fan of running my truck above 2400.

An idi won't pull a sailor off your sister at 2400 rpm, wind that pos out.

 

[Thewespaul]

And from a mechanical point of view, it’s harder on an engine to load it up at lower rpms than st higher rpms

 

[Hydro-idi]

An idi won't pull a sailor off your sister at 2400 rpm, wind that pos out.

Or a greased string from a cats ass.

 

[Runningaford]

I pull my 5'er in and out of storage yearly, it's a big one; empty it's just under 13k, but I've got probably another 1,400 pounds inside of it. The truck is under powered, but it does it!

There are some more engine modifications beyond just the turbo I've done, but I think in regards to better towing power, I'll add an auxiliary transmission first before any other upgrades; let the gears do the work.

With the ease at which a man can work on these rigs, unlike the new 'expensive electronic' trucks; it's the best truck I've ever had.

 

[Fudd]

I’ve only had my IDIT for about 5 months now and I haven’t towed any more than 5k behind it, but I thought it did pretty good. I towed about 2500 up through snoqualmie pass and never had trouble keeping up.

I never towed with my old NA 7.3, but I did haul some seriously big loads of wood with it, about 1 full cord of green wood. It was a dually with a big service body on it, so I had a lot of cargo space. I’m guessing those loads were in the neighborhood of 2500 lbs, and it never had trouble going 60 uphill fully loaded.

If you really want to see a gutless tow vehicle, I drove a 98 Tacoma with a 2.7l 4 cylinder for about 4 years, and I hauled some big loads with it. I never really worried too much about how gutless it was. Yeah, it was slow, but I was WAY more worried about sway and braking.

Many years ago, I used to drive an International Traveller with a NA 3.0 diesel in it. Now that was an absolute slug. Driving up the pass, it literally could not go 55. I towed a buddies car on a dolly with it once and we could not keep up on the freeway even on level ground. It did get close to 30 mpg however.