| Author | Message | ||
| marc schlabach Rating: N/A |
I have a 1982 mc9. The rear end is geared fairly low. I run about 74 mph at 2250 rpm .is it a major task to swap it out for one that is geared higher? It would help my mileage if it was geared higher. Any thoughts ? Marc | ||
| TWODOGS (Twodogs)
Rating: N/A |
do you know what the ratio is now ? it's ususlly on a tag on the rear end...also find out the make of the rear end...usualy either rockwell or eaton...I think there is a eaton 373 for sale on the "E" place.. | ||
| John Rigbyj
Rating: N/A |
If you change to a higher ratio you will be very slow on the hills. John | ||
| jimmci9 #2 Rating: N/A |
mci-9's came standard with a 3.73 ratio.... its a rockwell design... but proprietary for mci applications.... | ||
| Marc Bourget Rating: N/A |
John, Not exactly, depending on the ratio chosen he might be able to drop a gear and be in a better position with regard to the powerband of the engine. | ||
| dave4106 Rating: N/A |
how come everybody needs to go 75 mph? is it a macho thing or what. drop 10mph and watch your fuel milage increase and your torqe curve rise. is ten minutes an hour really that important? thought we were doing this for fun and relaxation. | ||
| Phil Dumpster Rating: N/A |
I don't know about everyone else, but I would like to have 75+mph gears mainly because it would improve fuel economy at a more reasonable 60 miles per hour. | ||
| RJ Long (Rjlong)
Rating: N/A |
Marc S - What you're describing sounds like the stock 3.73:1 rear axle ratio for MC-9s with 8V71s or 6V92TAs. Later production MC-9s with the optional and more powerful 8V92TA came with 3.35:1 axles. It's VERY hard to second-guess the factory engineers when it comes to the BEST compromise between performance and fuel economy. And it IS a compromise! The worst part of the equation involves the weight of the operator's right foot, which is the unknown variable. One change you could make that would have some effect is to install 11R24.5 tires, at least on the drive axle. The stock 12R22.5s turn around 490-500 revs per mile, depending on the manufacturer. Bridgestone makes an 11R24.5 drive axle tire that turns 470 revs/mile, about a 5% difference. Not much improvement, but a whole lot less work than changing out a rear axle pumpkin!! You'll spend around $2K, give or take a little, to swap in a taller rear end pumpkin for the current one. How quickly would this pay for itself if your fuel mileage went from an average of 5.5 - 6.0 up to 6.5 - 7.0?? What's the payback point? The cheapest way to improve your fuel mileage has already been pointed out to you by Dave.  FWIW & HTH, RJ PD4106-2784 Fresno CA | ||
| FAST FRED Rating: N/A |
how come everybody needs to go 75 mph? TO KEEP FROM BLOCKIN TRAFFIC is ten minutes an hour really that important? AFTER A 12 HOUR DAY THOSE 10 MIN ADD UP TO A FRW EXTRA HOURS thought we were doing this for fun and relaxation. FINE IF THATS "YOUR WAY" , SOME ARE NOT MERLY CAMPING FAST FRED love that 75 cruise , and STILL get over 9MPG. | ||
| TWODOGS (Twodogs)
Rating: N/A |
I sure don't ...I get 9 m.p.g. at 60...if I go to 70 it goes down to 7 m.p.g. | ||
| TWODOGS (Twodogs)
Rating: N/A |
Buses are beautiful....but,...they have a flat front...it's kinda like pushin' 3 or 4 sheets of plywood thru the air(resistance)..the faster you go,the more resistance...I had an old man,tell me..."if you can't afford to go,...ya' need to stay home"... | ||
| John that newguy Rating: N/A |
You sure the governer is set at max and your tach is correct? | ||
| Marc Bourget Rating: N/A |
2Ds, It isn't so much the size of the front, it's the corners that really affect the "Q", (aerodynamic quotient) Keep in mind a 747 has a lot more frontal area than a bus and it travels (indicated airspeed-wise) about 3-4 times faster! It takes about 9-16 times as much horsepower (ignoring induced drag from lift vs velocity) but, then, a 747 stops flying long before it gets to 70 mph. The flat front of a bus wouldn't/doesn't make that much difference if the corners had a 12" radius. [The 747 stuff isn't properly presented, being much more complicated, but I used it to illustrate the "corners" thing] Onward and Upward | ||
| TWODOGS (Twodogs)
Rating: N/A |
try this test...nail and bolt 4 sheets of 3/4 plywood together....get in a 70 m.p.h. wind...phone me from whatever state you wind up in..... | ||
| Jim Bob Rating: N/A |
Thank You, Marc. The antique, outdated 4104 was designed by GM with a 12" radius on the corners as the best compromise between interior volume & aerodynamics! By the way, mine will do 74MPH with a 170 HP 6-71 non turbo and gets 9.9 mpg at 65. Jim-Bob | ||
| Brian Brown (Fishbowlbrian)
Rating: N/A |
I'm getting anxious to see what mileage my new 4106 with stock rear and 12R22.5 tires will get @ 70-75mph. My Fishbowl gets 6mpg @ 70mph and the MC8 got about 7mpg against the gov. @ 65mph. As much as I'd love to "toodle" where I'm going, it's usually a 13 hour slog across three states to get from Point A to Point B. I'm 25 years or so from retiring when I WILL be able to go 60mph and not care when I left or when I'll arrive. Tis MY way... for now. I'd try RJ's tire idea. Rear end swap seems expen$ive. Or try out a 35' GMC parlor coach. ;-) Brian Brown Longmont, CO USA http://www.browncowpro.com/bus/4106/photos.htm |