| Author | Message | ||
| pat young
Unregistered guest Posted From: 71.138.18.189 Rating: |
Howdy folks My friend has a Crown with a 855 Cummins, and 4.88 rear gears. What would be the better ratio to keep torque/climbing power, but get about 8 more mph? Would a 4.56 be better, or a 4.11. You can answer off board if you want. Thanks a lot Patrick in Fresno WheelchairBusProject@yahoo.com | ||
| Bob Greenwood Unregistered guest Posted From: 63.232.252.52 Rating: N/A |
there is NO way to keep power & torque if you go for more speed,it's a sacrafice,only way is with a bigger engine | ||
| Ed Jewett (Kristinsgrandpa)
Registered Member Username: Kristinsgrandpa Post Number: 248 Registered: 2-2003 Posted From: 64.24.212.10 Rating: N/A |
http://www.cwis.net/~mallie/page12.html This will help figure top end speed. HTH, Ed. | ||
| Dallas Farnworth (Dal300)
Registered Member Username: Dal300 Post Number: 98 Registered: 3-2006 Posted From: 172.144.184.252 Rating: N/A |
An 855Cummins What? NT? NTC? BCI,II, III, IV,? SCI, II, III, IV? NTA? NTB? if it's a 220 drop a new motor into it, or turn it into a 250 by putting a split manifold on it, turn it into a 270 by increasing the air flow and putting a turbo on it. A 335 would require an inframe major. Bob, ya gotta admit, the 855 was the most used motor cummins ever came up with, probably equaling the 2Cycle Detroit. Once you get the power to run a transmission, rear gear and tires, then you can figure out how fast you want to go. There is a caveat. The lower the gear ratio, the less climbing ability. conversely, the lower the gear ratio, the faster on the flats. Good Luck! | ||
| pat young
Unregistered guest Posted From: 71.130.76.20 Rating: N/A |
All pre 1990 Crowns buses run the NHH series of Cummins, or Detroit 6-71s, both horizontal models. Crown got away from thier classic bus in the early 90's as far as I know, and started building quite ordinary rear engine buses. A 220 is a 743 cubic inch motor, the turboed version is a 262, and the 250-400 hp Cummins are the big block 855. The 250 is naturally aspirated, above that they start turboing them. I know there is a compromise when you change differntials, but does anyone know how much difference a change from 4.88 to 4.56 or 4.11 will make? That was the question. Patrick in Fresno | ||
| TomC
Unregistered guest Posted From: 66.218.33.156 Rating: N/A |
If you have 11R-22.5 (500rpm) then I would suggest the 3.70's. You'll still have enough startability and then a cruise speed of 65mph at 2000rpm (I assume you still have the 5 speed box?) Personally, I'd switch the box to an overdrive 6 or 7 speed, then won't loose anything in climbing performance. If it is an 855 block (easy to tell- NH block has external injector lines, the 855 does not), you can add an aftercooler for an easy 350hp. Good Luck, TomC | ||
| Henryof cj
Unregistered guest Posted From: 74.32.168.91 Rating: N/A |
Pat, my '74 Crown 10-wheeler,(VIN 37317) has the non-turboed 855 Big Cam 2 250 mill with 3.7 rear gears along with the RTO-910 with a .82 10th gear. Tires are the usual 12R X 22.5's. Top end works out to right at 80 mph at 2100 observed. Whoever did the last mill overhaul set the injection pump just right as the Cummins seems to pull best between 1600 and 1800. Tenth gear (the overdrive) is good down to as low as 55 mph at 1400 rpm under perfect road conditions with no wind or grades. However, any hills or breezes ahead or aside require at least one downshift and sometimes two. What kind of tranny do you have now? IF..it is the 910/1100/1150 family you MIGHT be able to simply swap boxes to the .82 RTO or even the rare RTOO .66 version. Would be a simple R&R. MY plans began with uppowering the 250 into the 400 using used factory parts. Now sidelined due to $budget$ considerations. And...my CROWN may be available. Good luck and CROWNS FOREVER!!! |
