| Author | Message | ||
| chris cole
Unregistered guest Posted From: 68.119.229.238 Rating: N/A |
what kind of mpg could one expect a 40' bus to get with a dd8v71 with a allison v731 trans. @65mph. | ||
| Bob Greenwood Unregistered guest Posted From: 65.150.47.23 Rating: N/A |
6,7,8,9 | ||
| Ron Daniels
Unregistered guest Posted From: 71.111.214.187 Rating: N/A |
I JUST RETURNED FROM A TRIP ON MY mc-R W/ dd8V-71 W/ aLLISON V731 @ 55 MPH WHILE ALSO RUNNING KUBOTA dIESEL GENERATOR FROM SAME FUEL TANK. i AVERAGED 6.5 MPG. | ||
| Arnold J Molloy (Ayjay)
Registered Member Username: Ayjay Post Number: 34 Registered: 10-2005 Posted From: 151.203.117.214 Rating: N/A |
I run a 8V71 TA in a RTS and believe the 730 and the 731 both have a 0.88:1 3rd gear, with a 4:10 rear end and towing a Ranger P/U I average 5 to 5 1/2, mixed city and highway (65-70 MPH.) Straight highway about 6 1/2. AyJay | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 978 Registered: 12-2000 Posted From: 71.195.113.23 Rating: N/A |
Clarification point: The V-730/731 does not have an actual 0.88:1 third gear ratio. Third gear is 1:1, just like 4th gear in an HT-740 or fifth gear in an HT-754. The misnomer comes from the fact that this is a V-drive configuration, and there is a set of bevel gears between the engine and the torque converter to change the drive angle. It is the bevel gear ratio that is 0.875:1, not third gear. OTOH, if you're talking about effective gear ratio, especially the effective final drive ratio, then you must multiply (the bevel gear ratio) X (transmission gear ratio) x (rear axle ratio) = overall effective final drive ratio. In the case of the V-730/731 with a 4:10:1 rear axle, the numbers are (0.875:1) x (1:1) x (4.10:1) = 3.587:1. For those still running manual gearboxes in their GMCs, the math is: 35-foot coaches: (0.808:1) x (1:1) x (4.125:1) = 3.333:1 40-foot coaches: (0.808:1) x (1:1) x (4.375:1) = 3.535:1 Clear as mud? Ok, now to answer the original question: "It depends. . ." The heavier the right shoe, the poorer the fuel mileage. Buses have the aerodynamics of a brick, consequently, the harder you push them, the thirstier that Detroit becomes. Weight is also a mileage-killer - the heavier the coach, the more fuel burned. Keep the coach around 60 mph, and you'll get close to 7 mpg. 65 will yield in the 6.0 > 6.5 range. 70+ will drop into the middle > upper 5s. All of the above for typical flat-land running. Deduct 1 - 1.5 mpg if you're doing a lot of mountain work (I'm talking West Coast mountains, not the speed bumps back east. . .  ). Better with a tailwind, too. Headwinds and cross-headwinds are like driving uphill. FWIW & HTH (PS: BTW, the stock final drive ratio for MC-7/8/9 is 3.73:1, so 8V71- & 6V92-powered V-drives will outrun "the big dogs", assuming that the coaches are running 12R22.5 tires and the governors are set for 2100 rpm. Of course, we all know what happens when you "assume" something, so don't take this as gospel!) (Message edited by rjlong on July 15, 2006) |