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Turning up DT466 1992 international

petethewicked

Plastic
Joined
May 18, 2006
Location
raleigh, nc
Hi, I have a 1992 International dt466..Its a transit style front motor school bus.

Its turbo, so I believe the HP is 210? (not positive on this) The tranny is a allison MT643. The rear end gear is a 444.

Problem, it pins out at 3000 rpm(governed) it runs 65mph and can't hold it there that solid. What I'd like to do is change out the diff to a either 391, or maybe 373?

Then turn up the pumps/turbos to give it a little more HP and torque. This way I'd be able to run lower RPM at 65 or even run at 70 and still have a little peddle left for passing.

Ideally I should be able to run 70 at like 2300 RPM? right in the height of the torque peak.. (this is a guess, hard to find a chart ;)


What do you all master diesel guys think? Would this be the way you'd go? How hard is it to squeeze some extra power out of this guy?

What do I need to do. Anyone reccomend a shop near raleigh or Charleston SC?

The bus has 190,000 miles on it. We're turning it in to a nascar bus.. 6 bunks, shower, crapper, 15000 btu ac unit on top, 7550w Generac generator on the extended bumper, 12,000# hitch with 3 foot extender (8000# usefullness, not that we'd ever tow much with it, maybe a few motorcycles) The trim work in the inside isnt' finished, waiting for the electrician buddy to wire the 110 boxes


Would be greatfull for anyhelp you could provide!... THANKS!!!

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Rotory or inline pump?

Peak torq is going to be about 1600 rpm.

You need a faster rear end ratio for sure.

Intercooling would make a big difference too. Look at a later model DT466. Air to air is best but hardest to do. Easiest is the water aftercooler. Get one at a junk yard with all the plumbing parts.
 
There are limits to what you can do without upgrading the turbo. You can only get so much air through the compressor inlet hole.
 
As cheap as school buses sell for you could probably buy another one with a road gear in it that you could swap out. Transit buses don't make good RV's for over the road.
 
Inline pumps are a lot easier. I could help you on that maybe if I had a picture of the pump. It should be a fairly standard looking Bosch. Your lucky. That is a really good pump. I'm only really familliar with the Cummins style Bosch but they are all really similar.

You really should put in an EGT gage if you are going to meess with the pump and stay below 1000 deg. EGT.

A nice big clean air cleaner and 4" exhuast really help but you probably already have that. Have you looked at the air cleaner restriction gauge?
 
STOP....STOP

Before you fool with any of that look at an overdrive.

http://www.gearvendors.com/hrgm4s.html

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The engine is in the front right? If so you could get yourself a Brownie box with over and under for cheaper than a GV overdrive. You kind of have to know how to double clutch and I don't know how hard it would be to shift with the Allison in front of it.
 
There is one other idea...

Look for a 2 speed rear axle.

You need the torque that the current gear ratios provide, the overdrive or 2 speed rear will lower engine RPM at higher speeds when the torque is not required.
 
You are correct: it pins out at 3000. If it hasn't been tampered with it will hold at 2750-2800. In most applications the rated speed is 2500 (pulled down from the 2750). I've had several of them in trucks, combines, tractors, and dozers. They can run all day long at 2600 under load, but I wouldn't dare try to sustain at 3000. A DT has a terrible torque curve; its not productive under 1900 rpm in that age bracket.

A DT can generate a lot of power, and it is as simple as a quarter turn of the screw under the cap on either the rotary or in line pump. The governor assemblies are essentially the same. They are both Bosch (rotary is American, in line is Robert). You are adjusting the maximum rack setting when you turn the screw. The stock turbo will easily take it up to 275 and beyond, and intercooling is not a big gainer on DT's. The problem is life and economy. As mentioned, don't jack with the screw without a pyrometer.

My impression is you are asking too much from a medium duty motor to push that box 70 mph. DT's are a wonderful motor, but they are just a medium duty engine. It was spec'd correctly to move that bus 45-55 mph, but it is not the correct engine to take it to cruising speeds.
 
You don't think that motor, if pumped up a little... lets say to 250 Hp maybe what, 650lbs? at 2500 rpm couldn't hold the bus at 70mph with a different rear end gear.? Heck my friends 1978 international with a 392 gas motor can hold hit that mark.. Keep in mind, this is towing nothing..


Currenlty its pushing right up to 65.. you don't slow down much on big hills.. I think its got the power... just that the torque curve is real bad at 3000 rpm
 
You don't think that motor, if pumped up a little... lets say to 250 Hp maybe what, 650lbs? at 2500 rpm couldn't hold the bus at 70mph with a different rear end gear.? Heck my friends 1978 international with a 392 gas motor can hold hit that mark.. Keep in mind, this is towing nothing..
Your so called "pumping up the motor" will solve NOTHING... other than a machanics problem of where to get the next customer to pay him a buncha $$$ to fix a screwed up motor.

Your problem is not HP but one of gearing. Fix the gearing and you will let the engine run at a reduced RPM while the torque is not required. On hills you may need the torque and then it will be required to fall back into normal drive ratio.

How will that bus handle at that speed?... certainly it's not designed to go that fast, or is this just a "I wana go faster deal"?

Try doin the math on the diference in time betweeen 55 and 65. See if it's worth it.

Get up earlier, leave sooner...
 
It drives fine at 65... like you said.. I'm just looking to lower the RPM. Will start with the gearing for sure...

One of my partners exclamed,"that thing is so fast out of the whole, I think it would beat my chevy 350 truck" so its got enough pull at low speeds... I'm thinking of doing the rear end gear at this point. I'm still goign to contact what you reccomended and speak with them...

As for tweeking the motor.. if it starts bogging down too much... just want to know what it could get out of it.. from my understanding, its a serverly detuned motor. I'd like to keep it rolling for at least another 100,000.. so gotta get the gearing down.. and if its turned up.. wont' be by much


We certainly dont' want a slow race bus ;)
 
Standard HP/Torque should be fine, I agree the gearing is the problem. A 2 speed box or axle may be what you need. Another approach is a complete different rear axle with the right gears in it from a reliable used parts house. Sounds like you don't really need good low end torque, anyway. 444 is for HD towing/hauling.

You can use one of those laser temperature guns to make sure every cyl is putting out power. Measure the heat being generated on the exhaust output. That will tell you if your injectors are working ok.

I would check the turbo to make sure you are getting good boost. With 200k on the clock, could be some loose fitings. Charge air cooler could help. Does it seem to have more power in the cool morning? Air cooler makes the air more dense for the turbo to be more efficient.
 
The motor was fleet maintained.. have all service records. everything was checked out before we bought it. The motor runs absolutely perfect. I just want to keep it that way.

and no, dont' need low end torque.. just want to cruising speed to be around the torque peak, and save the motor and increase mileage..
 
I dont know if you need the RPM at peak torque for a crusing speed, what do the fellows at GearVendors say?

Here is an example...
I have a 1992 Buick Roadmaster... heavy, comfortable and in perfict condition...
According to the book, it's a Detuned Corvette Engine

At 42 MPH it shifts into the highest gear and the tach says 1000 RPM (little torque there) but plenty to accelerate and go up hills.

At 60 MPH it's about 1500 RPM (maybe a little more torque now)

At 75 MPH it's 1750 RPM ( not sure about max torque there either)

When I pulled the largest 2 axle UHaul Trailer crammed full of stuf, going up hills at 60 ish, it would sometimes downshift to the non overdrive gear if that last gear was in fact an overdrive.

So to summ up, get the right gears and you will be saving the engine from running so fast and extending it's life.

But whay am I telling a NASCAR guy this, thought you fellows knew all about engines and gears and all that stuff ...
 








 
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