IDI's in Medium Duty Apps

[philadelphia]

i guess im the outsider..
My flatebd s1600 uhual pulls fine empty at 10200 lbs and still pulls good with 7800lbs of truck on it.. gets 11 mpg loaded..

tops out at what says 65-70 on the speedo. pulls hills fine( i mean its a truck not a drag car)

id like to get more power from it but thats being greedy.. all ive done is exhuast with a stack and opened up the air cleaner at the engine inlet.

 

[ameristar1]

i guess im the outsider..
My flatebd s1600 uhual pulls fine empty at 10200 lbs and still pulls good with 7800lbs of truck on it.. gets 11 mpg loaded..

tops out at what says 65-70 on the speedo. pulls hills fine( i mean its a truck not a drag car)

id like to get more power from it but thats being greedy.. all ive done is exhuast with a stack and opened up the air cleaner at the engine inlet.

No outsider here. I like to see more of this.

 

[1320Cummins]

I just ordered 4.56 gears today so I will finally get to see how the truck performs with "normal" gearing. I also found out today that at some point it seems someone thought it would be a good idea to install a under drive fifth gear in my trans. Looks like the trans is next on the list...
Fingers crossed on not breaking any more wrist pins with the taller gears

 

[ameristar1]

I just ordered 4.56 gears today so I will finally get to see how the truck performs with "normal" gearing. I also found out today that at some point it seems someone thought it would be a good idea to install a under drive fifth gear in my trans. Looks like the trans is next on the list...
Fingers crossed on not breaking any more wrist pins with the taller gears

That's a pretty big jump, are you sure it won't be too much for the little guy?
From what's been shared so far, a 5.13 is a good compromise, unless that 2 speed rear can boost it up on the low side.

 

[1320Cummins]

Turns out the truck had a 5.57 but because of the underdrive top gear that I did not know about I thought it was a 6.50. The trans is geared plenty low in the low end with a very small 4-5 jump. I hope this explains the situation.

I figure if its too much its a good reason to mate it with a 466 and 7spd OD

Edit: These are my gear choices- High/Low 4.56/6.34, 4.89/6.80, 5.57/7.75. I am almost wishing I had gone with the 4.89 and put 5th back to 1:1

Edit: It looks like 5th gear is about a 1.17:1 just great.

 

[ameristar1]

I did a quick check, and the 4.56s will drop the cruise rpm a good 600 or so rpms. I am basing it on a 36" tire running a direct top gear, since I don't have the info to your combination. Guessing at 65 mph you'll be spinning at 2800 rpms with the current transmission.

But a compound turbo'd Cummins or DT will need 3.55s and you'll need a "get out of jail free" card!

 

[1320Cummins]

I am running 42" tires.
5th gear 1.17:1 and 4.56 rear- RPM
2000 - MPH 46.9
2500 - 58.6
3000 - 70.3
3350 - 78.5

5.57 rear- RPM
2000 - 38.4
2500 - 48
3000 - 57.5
3350 - 64.3

5th gear 1:1 and 4.56 rear- RPM
2000 - 54.8
2500 - 68.5
3000 - 82.2
3350 - 91.8 - if it has the power!!

5.57 rear- RPM
2000 - 44.9
2500 - 56.1
3000 - 67.3
3350 - 75.2

Here is what I have to play with...

 

[ameristar1]

That third option sounds like fun, either that or a 4.30 with the existing trans. If you weren't concerned about blowing that 7.3 up again, you could hit her with 25 pounds worth of boost.

Then you could say, " I break wrist pins, connecting rods, crankshafts.............."

 

[1320Cummins]

4.56 is the tallest gear available for my G175T Spicer axle. I am already concerned about my soft ground issues at 34,000lbs+ Poor little truck will sink in a second so you gotta have some RPM on tap (1900+) incase the situation turns bad. I am thinkin that torque cam is sounding good.
I am wanting to try the removed glow plug thing to lower CR. I dont even have them hooked up any way. I figure a late model 7.3PS intake heater will get me by just fine.

 

[ameristar1]

You think the grid heater from a 5.9 might work?

Elsewise the poor little truck will need that transplant.

 

[1320Cummins]

Here is how the trans is geared from Spicer...

1st 7.22
---------86% step
2nd 3.88
---------75% step
3rd 2.21
---------76% step
4th 1.26
---------26% step
5th 1.00

Reverse 7.22

The 26% 4 to 5 step seems about right. I hate getting other peoples projects!!

 

[1320Cummins]

You think the grid heater from a 5.9 might work?

Elsewise the poor little truck will need that transplant.

I would like to use a 5.9 grid because I have a few laying around but it would need to go pre turbo in the 4" intake tube. I just traded a complete 02 7.3 I shoulda got the heater from it.
I am gonna get good doing in frames on this 7.3!!

 

[ameristar1]

I am considering one other combo that hasn't been discussed, and I don't know why I didn't think of it sooner. An Allison MT643 4 speed auto with lockup in third and fourth. I like the Allison, but never liked the super loose convertors that normally get specced.

Somebody was saying that Suncoast Transmissions has upgrade kits for these things, so I'm thinking shift kit, extra clutches, override switch for the lockup, and a huge cooler.

And you know what an auto can do with a hot turbo diesel.

 

[1320Cummins]

A decently loose converter in a MT643 or MT653 (manual low 1st) would be perfect to keep the IDI in its power band.
The school bus had the AT545 4 speed direct non lock up converter.
I believe the loose converter is the main thing that made it decent to drive. In my opinion a 5spd manual direct would have been hell in that beast!! youd have to run to red line every shift if you wanted to build any speed.

Edit: I just read all of your post and noticed what you said about the loose converter. I am pretty sure thats to make up for the lack of gears and still allow a decent cruise speed.

 

[ameristar1]

The convertor can be decently loose with the lockup, even help with using a bigger turbo. I am thinking 1600-1800 rpm to get it into the torque band and then lock that sucker up once she's moving good.