Engine Question!

blue_goose · December 03, 2008, 02:22:14 PM

Forgot to give you the phone number for TKT

1-800-997-4TKT

Jack

TomC · December 03, 2008, 03:50:57 PM

The thing about getting into 6th gear, is because it is a double overdrive, Allison doesn't allow the engine any lower than 1400rpm. When it reaches 1400rpm in 6th it will down shift into 5th. Once in 5th, it can lug down as low as 1100rpm under partial throttle. With 4.1 gearing, you'd have to be at 75mph before it would even shift into 6th, then it would down shift at 66mph. Actually, if you are a fast driver, it should be able to handle it-as long as you have the 4.1 ratio with 12R-22.5 rubber (485rpm). Good Luck, TomC

belfert · December 03, 2008, 04:20:32 PM

For fuel economy, we've been driving right around 1500 RPM which is 64 to 65 MPH per my GPS.

From TomC's reply it would sounds like 6th gear wouldn't really help. The cost of the reprogramming would likely take a while to recover if ever.

Brian Diehl · December 04, 2008, 09:24:49 AM

My ISM @ 1450 ft/lbs torque will allow me to pull 1170 rpm @ 60 mph with no problem. Sure, on a steep grade I need to down shift out of overdrive, but it has no problem carrying that speed in overdrive on level ground unless I have a large head wind. What is it about the B500 that makes doing this on Brian E's bus impractical?

TomC · December 04, 2008, 01:31:01 PM

BD-that works since you have an Autoshift. Allison won't allow 6th gear to go below 1400rpm since it is a double overdrive. Good Luck, TomC

Brian Diehl · December 05, 2008, 11:55:17 AM

Quote from: TomC on December 04, 2008, 01:31:01 PM
BD-that works since you have an Autoshift. Allison won't allow 6th gear to go below 1400rpm since it is a double overdrive. Good Luck, TomC

Technically, what is it about the double overdrive that makes Allison want to keep rpms above 1400?

TomC · December 05, 2008, 02:30:50 PM

BD- It's just what I have found out driving the World transmission, it will not lug down below 1400rpm in 6th-but every other gear will. Just the way they have them programmed. Good Luck, TomC

makemineatwostroke · December 05, 2008, 02:46:36 PM

BD; when the B 500 or the 4070 are in the overdrive the output shaft speed has to be greater than turbine shaft speed and if that is not accomplished it will down shift., with 4.56 gear 1400 rpm would be about right have a great day

Engine Question!

makemineatwostroke