Hey folks. I have a lifted Jeep cherokee (about 5k) that I'd like to haul to the trail. My Grandpa has an 86 F250 w/th the 6.9 and an ATS turbo. It has 67,000 original miles. It's also got the 4 speed with it seems like 4.10 rear. Right now it has 31 inch tires and you can barely drive it over 60 MPH without over reving it.

Ok now Ive been thinking of buying this from him to pull my Jeep and boat probally 200-300 miles each trip. Or I've been wanting to buy a older used Cummins (96-97). My question is, will this truck with some mods, maybe 33 inch tires be able to pull my toys effectively around 65-70 mph? Or am I wasting my time? I know the newer cummins are going to have more power stock, but I'd rather not have the payments. Are there any more mods that can be done to make it more effective? I know it has a 3 inch exhaust that came with the ATS back in the early 90's but I'd like to improve on that. I hope this makes sense.

 

Makes all sense. The larger tires will help but with the 4:10 rear end you are still going to struggle to get to 65 mph.

The best solution would be to go for an aftermarket overdrive unit (US Gear Splitter or Gear Vendor) to get your engine revs down.

With the turbo you should have plenty of power (of course not anywhere near that of a newer cummins, Duramax or Powerstroke) but plenty to get you around, especially if you turn the fuel up a bit on the IP.

The question is are you willing to spent about $US 4,000 for the overdrive unit installation? Still cheap when you compare to the cost of a new truck.


Seb.....

 

clint_y,
Welcome to FTE and the IDI diesel forum.

Going from 31" tires to 33" tires will add about 5 MPH to your speed.

Right now I figure you are turning 3000 RPM at 67 MPH.
With 33" tires you will be running 72 MPH at 3000 RPM.

Is the truck a 4x4?
You could go to 3.55 gears in the axle and run 33" tires on that.
That would put you at 82 MPH at 3000 RPM, or you could run 70 MPH at 2500 RPM.

Air intake mods, muffler delete mod, add a pyrometer and boost gauge, probably give it a bit more fuel and you should be ready to go.

 

I checked the truck again, It has a 3 inch downpipe from the ATS turbo but is 2.5 the rest of the way. It already has a EGT gauge.

Did 3.73 come stock in these years? If I went to 33's and 3.73 in the axle, am I going to have a problem towing the weight? I do not know the factory numbers (hp/tq) on these engines and this also has the turbo. Yes the truck is 4x4

I do not think I'd like to go with a gear vendors unit. Thats alot of expense for an old truck.

 

The excavator on the trailer weighs 10,000 pounds, the trailer is 3,500 and my truck with the dump bed weighs 8,000.
I live in the mountains of WV and tow that with 3.55 gears and a 6.9 turbo with a 4 speed.

86 model had either 3.55 or 4.10 unless it was special ordered with 4.56 or 5.13.

You probably have 4.10 from what you said above.
If it does not have a tach, how fast will it run?
The engine is governed out at 3300 RPM or slightly more.
On level ground wide open as fast as it will go a 4.10 rear end will between 70 and 75 MPH.
A 3.55 will run 85 to 90 MPH.
4.56 gears will only run about 60 to 65 MPH.

Also check my gallery, I run 6 feet of 3" and then it goes into dual 3" stacks with no muffler. You need to trash the 2.5" pipe and muffler, it is killing your power.

 

Thank you for the response. It does have a tach. Around 65 it's probally around 2700-2800 and I don't feel comfortable running any higher of an RPM. What size tire do you run? What turbo do you have on there?

I would be happy to get 70 out of it at a decent RPM. I haven't touched it in awhile and still deciding what to do. If I do go ahead and run it, I will definetly toss the exhaust for something much bigger.
How big are the climbs you generally run? 6%? To get to any lake around here I've got to climb a pretty steep and long canyon. The boat doesn't weigh much so I'm not as worried.

 

That works out to 4.10 gears.
Diesel engines are governed so it will not run fast enough to hurt the engine unless you overspeed it going downhill or downshifting.
That said, I also have to add that fuel mileage will not be very good running that kind of RPM.

I run 285/75-16 mud tires.
I have an aftermarket ATS turbo.
But I must also say I hauled things like that while it was naturally aspirated, now I just haul them faster on the uphill side.

As far as how steep, WV roads go to something like 14% on the state highways, county roads are steeper. The city street beside my house gains 9.72 feet in 30 feet which works out to 32% in round numbers. It has that slope for about 400 feet before it levels out some. I have to use low gear in low range to park on it and have my truck stay there for a couple hours. I don't know why most people will not drive down that street, could have something to do with the river at the bottom. There are a lot of streets around here that I have to use low range 4x4 to pull equipment up in the summer. Once the blacktop gets hot I just dig it up in two wheel drive.

 

Dave thanks for all your responses they surely are helping.
I drove the truck yesterday, definetly 65 mph @ 2700. How long have you had your ATS turbo? This truck also has the ATS turbo, but seems to take awhile to spool up. I wonder if the bigger exhaust and some intake mods can mitigate this. I've never been worried about pulling the load, it will probally never be over 8500. My concern was just driving at speed on the roads. After all your information, I'm seriously thinking about using the truck.
One other thing, are these 6.9's known for injector leakage? If you stand by the front of the truck you can smell diesel pretty bad. I know he had those worked on once before.

How many RPM's do you turn at 65 and 70mph unloaded and at what MPG? Thanks !

 

While I wouldn't recommend just anyone do it, I have scaled as heavy as 24,500 with my 86, which is 4x4 and has the 4,10 axles. I can haul a car all day without really working the truck. It has so far given a best of 15 mpg empty, 14 loaded. I don't have a turbo though, yet... 77 is the absolute fastest I have run it, and don't plan on doing that one again... the exhaust temps must have been up there, as it formed my plastic mud flap around the exhaust outlet...Mine pulls best at 65-70, have to watch myself or it will climb up there. (not too many speed zones around here over 60, just the interstate)

 

hey Dave, how loud is you truck since it doesnt have a muffler?

 

I bought a reman engine 2.5 years ago that had the turbo on it. I blew up three reman engines and finally got a buyout on the long block since the fuel and turbo were out of warranty by then. But I wound up with an extra fuel system and turbo for about 2200 that I lost on the engine. When I just rebuilt the engine I have now myself, I replaced the turbo with a new one.

I drive a lot of interstate miles at about 75 MPH and very seldom ever burn a tank of fuel without hauling very large loads. When I say I am averaging about 12 MPG it is not what most people are seeing with their trucks. I did burn most of a tank once this year where I was doing a lot of two lane running empty at 45 and 50 MPH, I averaged a little over 17 on that tank. Load it up to about 21,000 gross and run up the interstate at 70 MPH, 9 to 10 MPG is about average.

With the turbo, the exhaust is not really loud, there are plenty of cars that are much louder. The only time it does get rather loud is when I am using the engine to hold a load back going downhill. Between about 2300 and 2900 RPM it sounds just like I have a Jake brake set to high.