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Old 04-17-2012, 11:47 AM   #1
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Cummins 4BTAA

Anyone here that is running or has installed a Cummins 4BT? I'm putting a freshly rebuilt air-to-air intercooled into my shorty and will likely hook it to a newer Allison 6-speed double OD tranny. At 130 hp & 355#'s of torque, it's a lot more motor than either the original Chevy InLine Six, or the 350 transplant that is in it now. Found tons of good info over on 4BTSwap.Com but curious to hear if any other Skoolies might be going this route.

BTW...I've chatted with a few folks who are getting 27-32mpg out of this motor in heavier rigs than mine with just 4 speeds.
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Old 05-13-2012, 10:11 AM   #2
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Re: Cummins 4BTAA

WIll a modern Allison shift behind a mechanical engine? Every one I have seen used a DBW diesel.
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Old 05-19-2012, 10:43 PM   #3
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Re: Cummins 4BTAA

I am currently working with a shop that specializes in Allisons. The tech says "no problem" & not complicated. The 4th gen trannies don't need that much data and can be paired to a non-computer Cummins very easily and will shift just the same including full lock up and a parking pawl. He explained how it works but I couldn't repeat it if I tried.
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Old 09-01-2012, 08:17 PM   #4
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Re: Cummins 4BTAA

Tango,
I have done the 4B with and without the aftercooler...both with the "round" stanadyne, the bosch and the P7100 inline pump.
(The inline pump is the one you want for sure)
You can get 200HP out of one safely If you set it up right. That can be nearly 100% duty cycle too.
(Look up the marine application numbers for that engine...WOO HOO!!)

In a Ford van, it topped out at 27 MPG under perfect conditions. Tried the Clark 5 speed, the New Venture (Dodge pickup trans) and the old Getrag too. The allisons did okay, but unless they were on the highway 90% of the time, they suffered greatly.
Used from a 4.11 rear all the way to a hybrid 2.45 with a gear vendors over/under setup on the stick.
No matter what we did with a 1/2 ton E150, 27MPG was it.

The best ever full sized van MPG ever, was with a Cummins "A" series...otherwise known as an OnanL634 engine.
With the light duty Ford/Mazda overdrive and a 3:50 ratio, we could juuuuuuuuuust eeeek 28 out of it under the best of conditions.
That was at 50 MPH during the days of the 55MPH speed limits.

All this was done for a courier outfit with a fleet of 1400 vans. We were trying to find the best retrofit to make the vans last reliably and get the best MPG possible. The Cummins A was the winner. (Too bad they stopped making that engine as the test concluded. Cummins had bought out Onan and there was a pride thing about selling anything but the B series.)

Full sized buses getting 30+ in real world conditions?
Hogwash.
Even the lighter shorties push huge wind.
When you are playing with a field of vans with each recipe under the hood for 6 month field tests with locked fuel caps and veeder root hubclickers for the mileage records...it is pretty accurate.
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Old 10-17-2012, 11:42 PM   #5
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Re: Cummins 4BTAA

Hey Casey --- lost track of this thread but thanks for the info. Mine is an inline pump and I may look at doing some minor tweaking down the road. The 4BT already puts out almost half again the original buses hp and almost four times the original torque, so I'm gonna' try it there for a while. There are a few crazies running 4BT's up to 800+ hp with as many as four turbos, but they only last for a race or two from what I hear. Nuts what can be done with that little motor.
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Old 04-24-2015, 10:43 AM   #6
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Obviously been a while since I last checked this thread, but...
here's a little follow up on the Allison installation.

To begin, Allisons are available with an SAE 3 bellhousing which will bolt directly up to any 4 or 6BT Cummins.

But the cool part is that the new generation Allisons now have a single on-board computer that allows them to talk to an all mechanical engine via nothing more than a TPS (throttle position sensor). This is a really huge deal since the earlier models were mind-bogglingly complicated to hook up. I've talked to guys who've spent three years trying to get all the programming & wire harness issues worked out and are still having problems. With the new Allisons, it is pretty much plug & play. The TCM (transmission Control Module) does need to be flashed (they come clean from the factory) but there are already folks out there who can flash them by mail or you can take the unit to any authorized Allison shop and they can do it.

All of this means you can now bolt up a state-of-the-art, six-speed, double overdrive automatic transmission to any early, all mechanical Cummins 4 or 6BT engine. For anyone doing gearing/speed calculations, here are the basic ratios:

1st gear: 3.10:1
2nd gear: 1.81:1
3rd gear: 1.41:1
4thgear: 1.00:1
5th gear: 0.71:1 (OD)
6th gear: 0.65:1 (OD)
Rev: -4.49:1

Mine is hooked up, the TCM is off being flashed and I am now working on the shifter and driveshaft.



New firewall & a custom built doghouse are in progress.
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Old 04-24-2015, 01:06 PM   #7
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Looks great.

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Old 04-24-2015, 06:26 PM   #8
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Trans model number ? Cost ? I want one (or two)
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Old 04-25-2015, 10:27 AM   #9
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Mine is a 2200MH (same as HS). If you are anywhere near a Stewart & Stevenson facility (they seem to be everywhere)...they can run all your specs through their system and generate an optimal trans configuration that is customized to your situation. (You can no doubt do the same online and over the phone).

They took my engine specs, gearing, tire size, estimated frontal area, weight and a couple of dozen other factors and produced a 17 page readout for an optimized tranny. It included more data than I could ever have imagined right down to predicted fluid temperatures in every gear under various conditions. Pretty impressive.

Building & buying a new one ain't cheap, but if you are crafting a custom platform for the long haul might be worth considering. And now that this new generation has been out for a few years now, there are probably a few used units to be had. New from Allison they run almost $8 grand minus shifter & wiring harness. Based on other fairly new Allisons, you might be able to find a used unit for around half that. I barely missed one taken from a brand new truck that got damaged on the dealers lot. It was priced at $3800 but somebody overbid the asking price by a grand and got it while I was driving out to pick it up. Ouch. Used, they are in very high demand.
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