JIM BRAMHAM wrote:

As far as I know in the late 60s to present Cummins has used the B, C, N, M, 555, and 903's in busses. The B comes in 4 or 6 cylinder, in line 3.9 liter and 5.9 liter respectively; so it is a 4B or 6B. If turbocharged, add a T; if after cooled, add an A. So a 6BTA is very common in late units. The 6B comes from 150 to 240 Hp. You find the 4B in bread trucks, potato chip vans and some small busses. The 6BT and 6BTA 150-170 hp is the engine Dodge has in pickups. In its 240 hp configuration it powers numerous school busses and is one of the engines Cummins has coverted to compressed natural gas (CNG) and propane.

The C is 8.3 liter and the same T and A apply. It is only built in 6 cylinder in line so no prenumber is needed. The C engine is very popular with the Big diesel pusher motor home crowd. At 310 hp on diesel it moves anything under 60,000 lbs very well. It is also used in CNG and propane

The underfloor Crowns and Gilligs used mostly N blocks. They where all inline 6 and came in two sizes small bore at 743 ci and big bore at 855 ci. The 855 block came with a bigger cam after about '77. The small bore had a taperd nose on the crankshaft. The small bore came 180, 220, 240, 280 and 335. The 855 block came 220, 240, 270, 290 310, 335, 350, 380, 400, 444,and 475. I have never seen anything larger than a 290 in an under floor. The N is followed by HH for the 90 degree mounting and side pan. The T and A mean the same as above.

Cummins made a K block 1100 plus ci, 450, 525, and 600 hp. I don't think they ever saw bus use. The M engine is 11 liters, hp from 300 to 425 and are used in some big tour busses.

Cummins built two V engines 555ci and 903ci. The 555 or "triple nickle" as it is known with 170 to 260 hp was popular in pusher Gilligs. This same engine pumpimg out over 400hp is what powers the Army's Bradly Fighting Machines.

The 903 was big and short lived. It put out about the same power as an N block. It was hard to fit in some trucks and couldn't be laid on its side. I saw one in a tour bus once but I doubt Gillig ever used them.

Both the 555 and 903 have been used in truck and tractor pulls; they put spark plugs in the injector holes feed them race gas and hope they live 20 seconds. A 903 ci engine turning 5000 rpm with flame 5 feet out the stacks WILL move a pull sled nicely.

Detroit Diesel built three series of engines, each based on cubic inches per cylinder, 53, 71,and 92. They made them from 1 to 32 cylinders, in line or V, all had blowers some also had turbos. An 8V92 would be 8 cylinders, V configuration, 92 ci per cylinder. A 671T would be a 6 cylinder, inline, 71 ci per cylinder, with turbo. Crown and Gillig used the 671 in many underfloor busses. The 8V71 was the workhorse of Greyhound in the late 60s to 70s, then replaced by 6V92s and 8V92s. These engines are a two stroke design, they are messy and inefficient. They also require more frequent overhauls. Their sales in trucks and busses dropped in late 80s. Detroit then bought out John Deer's four stroke engine design and called it a 60 series. I have yet to see one in a bus but they are a great truck engine.

As for Fuller transmissions, the RT is for Roadranger Transmission. Next is no O, or O or OO. No O means the trans is 1 to 1 direct in high gear. One O is overdrive high gear and two Os means two overdriven gears. Next is the input torque rating; 66 = 660 ft/lbs, 95 = 950 ft/lbs, 125 = 1250 ft/lbs, 146 = 1460 ft/lbs, and 185 = 1850 ft/lbs. Next is number of speeds 9, 10, 13, 15, 18 etc. So a RTO12513 would be an overdriven, 1250 ft/lbs, 13 speed. You will see a few 6610s and 6613s in big gas and small diesel trucks and busses. An N block puts out too much torque for a 66 series trans. 95 series work fine up to 325/350 hp, 1250 units to 425 hp, 1460 units to 500 hp, 185s are a must with the 525/600 hp that most new trucks are coming with.

All transmissions are the repeat pattern low and high side. The overdrive units shift with 4 and 5 reversed, fourth is full right back and fifth is full right foward. There are different ratios in some models but are generally pretty close.

10 speeds and 15 speeds are the same except the 15 has a double reduction unit so the pattern repeats three times not twice. The low low side is for very heavy loads or starting on grades. They would be of no use in a bus.

A 13 speed is a 9 speed with an over / direct splitter on the back. In both, first is a Low that is not repeated. You split only the top four gears in the 13 speed. This makes them 200 to 300 rpm gears and helps keep the engine speed near max torque. Because the splitter is an overdrive, more road speed can be had with the same axle ratio and tire size. If you use an overdriven base transmission in a 13 speed you get a double overdrive = lots of road speed with low engine rpm. Hope this helps JIM