better fuel economy with an automatic

johns4104 · January 31, 2009, 09:57:32 PM

I have a 4104 and I think that if I swapped in a v730 auto trans I could get better fuel economy.
I plan to install a turbo 671. the 4spd has a 1 to 1 angle drive and the v730 has a .875 to 1 angle drive.
I have a 4.125 rear axle and run 11r 22.5 tires.
This would reduce my rpm by 12.5% say 200 rpm.
So my question is will the v730 fit behind the 6L71?
Is the bellhousing in the same location as the 4106?
Looking at the 4106's (without measuring) it looks like the bellhousing may have the same position as the 4104 because the 4106's have the muffler between the radiator and the engine.
Has anyone done this already?

Any thoughts?
Thanks,
John

Busted Knuckle · February 01, 2009, 08:44:33 AM

John,
I don't believe that you'll get any better fuel mileage from the change to an auto! Most auto trannys are far inefficient compared to a manual because the manual is a direct gear to gear drive, while the auto has the torque converter, and clutch packs that lose/use power so even with a slight overdrive on the auto it'll be less efficient than the manual. FWIW

BK

gmpd4104 · February 01, 2009, 09:46:15 AM

1. the V730 is approx 20% less efficient than the Spicer 4 speed.

2. With the instalation of the V-730 you will have to change the rear end as well as the angle of dangle is different

3. With the instalation of the V730 you will have increase engine temp so your cooling system will have to be upgraded

4. With the instalation of the 6-71T you will have increased need for cooling as well

johns4104 · February 01, 2009, 02:59:37 PM

can the v730 use a separate cooler so not to tax the original 671 cooling?
Thanks for the input guys!

JackConrad · February 01, 2009, 04:19:14 PM

Quote from: johns4104 on February 01, 2009, 02:59:37 PM
can the v730 use a separate cooler so not to tax the original 671 cooling?
Thanks for the input guys!

Yes, an oil to air cooler can be installed. Jack

Barn Owl · February 01, 2009, 04:58:06 PM

There is a member on this board that has done several 4104s. I hope he doesn't mind me showing some of his work. Truly exceptional craftsmanship.

4104 8V71TA/730 and one photo of a 671 with a v730.

Barn Owl · February 01, 2009, 04:59:16 PM

The rest:

Barn Owl · February 01, 2009, 05:08:17 PM

Can you all guess which bus nut it is?

johns4104 · February 01, 2009, 07:54:48 PM

Barn owl thanks for the pictures.
I love bus pictures!

John

TomC · February 01, 2009, 08:23:38 PM

They do make a 6-71TA block-but very hard to find. Rebuild your 6-71 into a turbocharged engine with air to air intercooling (mount the intercooler in the transmission door). With 80 injectors (the highest Detroit made from the factory) you can get 300hp with 900lb/ft torque. With the V730-a serious increase in torque-like 50%! The inline 2 strokers are much more rugged than the V blocks since they have just one cylinder running off the crankshaft throw compared to 2 cylinders per crankshaft throw on the V blocks. Personally, I'd feel safe running 90 injectors in a turbocharged and intercooled 6-71 for 340hp and over 1000lb/ft torque! Course you could achieve the same results by using a Cummins ISL through a reverser gear and have 425hp and 1200lb/ft torque, and quite possibly close to 10mpg with it. Good Luck, TomC

roger dolan · February 03, 2009, 04:08:25 PM

John.

When I put an v730 in my 4106 it cost me about 1and1/2 miles per gallon. I have been told that a v730 takes about 35horse power to pull plus generating some heat. But it sure is nice in traffic.

Roger 4106

Bob & Tracey · February 03, 2009, 04:29:42 PM

Hi John,

Our 4104 with a 8V71 and 730 has the transmision cooler outside of the radiator, also the rear end was swapped for one out of a 4106 because the drive angle is different. Doesn't the 730 have a lock-up converter? I would think there should not be an efficiancy difference from a manual when locked up. We averaged 8 mpg in the 3000 miles we have driven it .

Bob

TomC · February 03, 2009, 10:18:36 PM

Yes the V730 has a lockup torque converter, but-and this is straight from Allison- a planetary gear transmission with clutches will always have a drag on it because of the transmission fluid circulating between the disengaged clutches and gears engaged. Granted, on a manual transmission you do have some drag, but the automatic is more like about 20hp with the V730 the worst with its' bevel gear. Even with that, I still think the Allison transmissions are the best for our application-there is no other transmission that will accelerate from 0-40 like a fully automatic transmission with a torque converter. Hence-also alot more heat rejection at all times. Good Luck, TomC

steve5B · February 04, 2009, 06:19:00 AM

johns4104,

This is off the subject, the picture in your post (the black truck, bus behind it) did you at some time tow your bus with that

truck? I remember a few years back seeing this on the road when I was out west! Didn't mean to hijack your thread.

Steve 5B......

johns4104 · February 04, 2009, 04:11:49 PM

Roger, I would be changing the bevel gear from 1 to 1 to .875 to1 I am not starting with the same overall gear ratio as the 4106

Steve5b Yes I did tow my parts bus home from mineral wells tx.

Bob Yes the v730 does have a lock up converter. As mentioned the auto has more drag internally than a manual trans.