Series 60 rpm's

Ericbsc · January 30, 2011, 04:01:52 PM

What would be the recommended rpm's for a series 60 between 60-70 for the best performance and economy? I have a 3.73 gear now. I am installing a 60 with an Allison 4000 with double overdrive. Ratio is .741 in 5th, and .641 in 6th. I have a 3.36 available also. The 3.36 is complete and would allow me to upgrade to bigger brakes also. I don't know if it is worth the trouble but I will have everything else out of the bus during the engine swap anyway. According to my calculations I would have the following:

3.73 3.36
MPH RPM GEAR MPH RPM GEAR
60 1548 5th 60 1287 5th
65 1548 5th 65 1394 5th
70 1667 5th 70 1502 5th
75 1786 5th 75 1609 5th

60 1236 6th 60 1113 6th
65 1339 6th 65 1206 6th
70 1442 6th 70 1299 6th
75 1545 6th 75 1392 6th

Any suggestions? Also my entire rear is rebuilt with all new bearings , seals and new dropbox gears. That would need to be swapped also as I don't know the condition of the other one at this

Ace · January 30, 2011, 04:08:46 PM

With a 60 series I wouldn't hesitate using the 3:36 gear. It will have the torque for low end take offs!

belfert · January 30, 2011, 04:12:41 PM

Check with Tom Christensen for sure, but I think the RPMs with the 3.36 would be too low for the tranny unless you're doing 75 all the time. I thought he said about 1,400 RPM is best for fuel economy recently.

lostagain · January 30, 2011, 04:17:17 PM

The S60, 12.7L in the hockey team's bus with 7 speed Eaton-Fuller revs at 1500 rpm at 65 mph. Best torque is between 1200 and 1800 rpm.

JC

rv_safetyman · January 30, 2011, 04:19:09 PM

Eric, something seems wrong with your numbers. I have 3.73 and run 11 24.5 and my RPM at 68 MPH is under 1500 RPM with the same .74 overdrive. Looks to me like you selected a tire RPM that was not correct. For an 11 24.5 tires should be about 480.

Ace, I think the 3.36 would be the wrong way to go. With 3.73 he likely will not get into 6 th gear. Most world transmission buses have something like 4.56 rear end ratios.

Jim

belfert · January 30, 2011, 04:22:03 PM

My bus has a factory B500 and Series 60. It came with a 4:10 rear end. It does 64 MPH at 1,500 RPM in 5th gear. Dina choose to lock out 6th gear. I usually drive 65 MPH so it is a hair over 1,500 RPM at that speed.

rv_safetyman · January 30, 2011, 04:27:00 PM

An added note. While Series 60 engines are said to develop their max torque at 1200 RPM, my seat of the pants feeling is that the engine is not happy at that RPM. That may be a function of engine mounts and some sort of resonance at that RPM, but it just does not feel right at that low of RPM.

Jim

c-coop · January 30, 2011, 04:27:38 PM

Eric, I have a b500 in my mc9 with 3.73 gears. It runs1400 rpms at 70 mph. when it is very windy I usually drop to 5th gear at about 1500 rpm.s This helps out on fuel mileage. I don't think any ratio higher than this would work very well. Chris

luvrbus · January 30, 2011, 04:36:39 PM

If Eric hasn't changed his 05 came with 12R 22.5 tires and wheels the 3:36 gears works good for Mark (Boomer) with his 4060 Allison 9 to 10 mpg is not all that bad lol for a 45 ft x 102 wide bus.
Looking at the charts the torque starts to fall after 1500 rpm on 12.7 series 60 am I reading it wrong ? anyway Eric the brake change over I would do regardless of what gear you use

good luck

Ericbsc · January 30, 2011, 04:43:59 PM

I am running 12r-24 kuhmo ks02 tires. Acording to the kuhmo site they are 517 rev's per mile. I used the caculator on the home page. Would be nice if I were off a little and the rpms were lower. Clifford, What would I have to do to adapt the larger brakes if I didn't change the entire axle out?

lostagain · January 30, 2011, 04:46:19 PM

Jim, I feel the same about 1200 rpm with the S60. If you step on it at 1200, it vibrates and hums till it gets to at least 1300. The sweet spot is really 1400 to 1800 rpm.

JC

luvrbus · January 30, 2011, 04:47:43 PM

Move the brackets for the chambers and the back plate not a major job Eric

good luck

Zeroclearance · January 30, 2011, 06:10:11 PM

With my "slug" I have a 4:10 Rockwell...

Boomer · January 30, 2011, 06:57:21 PM

When I owned new Prevosts, we speced 4.56 diff with the S60, IIRC that was the highest available, and road speed governing at 62 mph which the engine seemed to be comfortable with. They produced good fuel economy, our target was 8 mpg, but in revenue service we usually saw high 7's, especially in the summer. Idling was taboo. Also, when the original 315's wore out we changed them to 12R's because they were much cheaper and we did not need the weight carrying capacity with the H3-45. Now on my Eagle housecar I am running 3.36 which came on the bus and the ISM 450/HD4560 and 315/80R22.5. My cruising preference is still 62 mph and in 5th gear the engine is just under 1,300 RPM, right around 1285-90. Averages 8.8 to 9.3 depending on roads, winds, etc. My weight is 43,000, probably just a little over the H3's with a full load of pax. Peak torque is 1200-1450 for both engines but the Cummins seems to me to run a little better at the low RPM than the S60, just my seat of the pants feel for it. We had our S60's speced at 430 hp by the way. The B500/4000 series transmissions are just fine to run in 5th, I sure wouldn't go to the trouble to switch diffs just so you can utilize 6th gear. Plenty of deep reduction available for starts, hills, etc. Just my experience FWIW.

TomC · January 30, 2011, 10:42:02 PM

Eric- I went to the Kumho tire site and looked up your KS02's. The only 517rpm tires were the 10R22.5 or 9.00R20 (the tube type version)-both of which are too small for your bus. And the 12R-24 that you said you have, isn't listed. The most popular sizes is the 12R-22.5 (485rpm) and the 11R-24. 5 (479rpm). Using 485rpm and 3.73 rear end ratio at 65 you'll be turning 1959 in 4th, 1450 in 5th-which is perfect. At 75 you'll be turning 1673 in 5th and 1447 in 6th-which again is perfect.

The Series 60 produces maximum torque at 1200rpm-but that's NOT where you want to cruise at. 1400-1600rpm is the most economical rpm for the Series 60.

If you're producing 1450lb/ft torque and you weigh in at 50,000lbs, with the 485rpm tires and 3.73 rear end ratio you're startability will be 34%-which is crazy high considering 25% startability is what is required for off road use, and 16% startability for on road use. Stay with the 3.73-you'll love the performance. Good Luck, TomC