| Author | Message | ||
| Fred Wheeler (Freddie) (209.240.198.60)
Rating: N/A |
I would like to know what top speed I can expect from a 79' 4905 with a 8v71 with a v730 auto trans with stock rear end ratio. I do not know the rear end ratio. Also what MPG can I expect. I am looking at purchasing this type of bus. | ||
| Craig S (65.190.11.25) Rating: N/A |
Hi Fred, I guess most highway coaches would be expected to cruise at 65-70 MPH. I'd say 6-8 MPG. A stick shift would get a little more. They're definatley an expensive hobby, but we love 'em. Go for it and join the rest of us nuts. Craig S | ||
| Craig Craddock (Craigc1) (24.127.59.100)
Rating: N/A |
The 4905 end ratio normally 4.33. They used this lower ratio to pull a heavier bus. Top speed can very, a coule mph or so. Tire size and governor setting will change it a litte. Usally about 72 mph at max. speed. 4905's have large storage bays. Good bus, Have a knowlegable bus mechanic check it out mechanically. In could say you thousands. At least you will know what else is needed $ to but in good mechanical condition. | ||
| Peter (Sdibaja) (64.165.10.70)
Rating: N/A |
I have a 4905 with 8v71 and 730. I do not know what my rear end ratio or governor setting is. I get 6.4 mpg to 7.2 mpg, mostly depending on altitude: higher mpg below 2000 feet. Being in the West I have never had the chance to run out a full tank of fuel on the flats, I always get a combo of flats, climbs, and a coast back down again. I easily run 74 to 76 mph on the flats: sea level or 7000 feet, same top speed. I consume/leak 2 quarts of oil in 2500 miles when it is clean, twice that rate when it is time for an oil change. I am _thrilled_ with everything about the coach except the turning radius, and that is no big deal. Peter PS: speedo (and odometer) verified acurate with my GPS. | ||
| J.L.Vickers (209.34.24.45) Rating: N/A |
P8M4905A Rear-end ratio is 4-3/8:1 V-730 transmission Third gear ratio is 0.875:1 I have a P8M4905A with the V730 installed and it,s a good bus to drive. Fuel miliage is like the other post. Very simple to maintain and parts are not hard to find. I always ask Luke at US Coach repairs and he will always have what is required. Would I buy another GMC Buffalo? You bet I sure would! Good luck with yours. | ||
| Don KS/TX (67.210.119.251)
Rating: N/A |
Back to the original question, the V730 is a lower geared transmission than the original, which in factory settings would only run a shade over 70 as Craig said, so you can expect less speed with the V730 at the same rpm. The REAL answer is how fast to you want to set your governor. Peter obviously has his governor set up (or is running quite a bit taller tires than stock). Based on his reported mileage, he is probably churhing some serious RPM's at cruise. This is common, and the additional RPM never seems to hurt the engine, just gets less miles per gallon, and less torque. | ||
| Johnny (63.159.193.82)
Rating: N/A |
Wouldn't running against a cranked-up governor result in, well, a prematurely shot engine? I know it's possible (I drove an inline 6-71 in a GMC 10-wheeler that didn't hit the governor until 2800 & about 84MPH), but it doesn't sound like a good plan, especially on an engine as expensive to fix as an 8V71 Detroit. | ||
| Mike Eades (Mike4905) (206.148.164.38)
Rating: N/A |
Hi Fred I have the same setup and I get top speed of 70 mph, no faster. I also pull a large closed trailer behind me and if I keep my foot off the peddle I run in the 6.5 to 7.2 mpg average. when I stand on the peddle I drop to 5 to 5.5. I love my coach put close to 35 k per summer. A lot of traveling. I have Luke do almost all my repairs and maintence. One thing I would suggest is to have someone who knows this type coach check the rear structure. I had to replace my bulkhead and my dogbones and part of the rear floor. Be careful. I would do it again. I had large motorhomes and they just would not do the job. | ||
| RJ Long (24.127.74.29) Rating: N/A |
Johnny - Depends on how much it's cranked up. If it's set at 2200, probably not. If it's set at 2500+, probably so. Setting it at 2200 and turning tall 24.5 tires will help overcome the shorter bevel gear ratio in the V-730, bringing it back closer to original gearing/speed, without significantly shortening engine life - at least in RV service. HTH, RJ PD4106-2784 Fresno CA | ||
| Johnny (63.159.193.82)
Rating: N/A |
But cranking a 6-71 up to 2800 is still a bad plan, yes?  | ||
| Don KS/TX (205.187.92.94)
Rating: N/A |
Still depends on who you ask. GMC did NOT want their bus engine to run over 1900 or 1950 as I recall with a standard transmission. When they put the Allison VS2 in a bus, the limit of rpm was 1700. Other bus makers used the same engine and cranked it up a bit, some at 2100 as I recall. In my bus, when cruising at 70 at 1700 the fuel mileage was 8-9 mpg. When I cruised it at 2000 at 70, I was down around 6 or 7. I don't feel that running in that 2200 range hurts them one bit in the type use we put buses to. | ||
| FAST FRED (209.26.115.194) Rating: N/A |
DA BooK for my 4106 uses 1650 Rpm ( a bit over 60 mph) for the limit, I'm not rich enough for a new engine every so often I use 1950Rpm. Many long life gen sets were built ( in the era my coach was built) that cranked 1800 all year, I feel a less than 10% overspeed is OK. Geoff also has pointed out that 1950rpm is about as fast as the 8V will spin and still have some economy. We regularly get over 9 so it seems to be OK. Operating a 1964 engine with the specs of a brand new 35 year newer engine does not make sense to me. I have seen an 8V 71 turn 3100 rpm , in a fire truck , but I sure wouldn't cruise there!!! FAST FRED | ||
| J.L.Vickers (209.34.24.45) Rating: N/A |
Fred always sez by the book. The GMC intercity coaches hand out dated 1976 for the P8M4905A. Sez and I quote P8M4905A 4-3/8 rear axle @ 1900 rpm in 4th gear with a standard transmission road speed is 65.5 mph. 2050 rpm 71.45 mph 2150 rpm 74.93 mph Fred is right turn them slow and the old GM's will last a lot longer. Note this is with a 4 speed Spicer 7145 VK transmission | ||
| Don KS/TX (67.210.119.238)
Rating: N/A |
Thank you Mr Vickers, I had left my copy back in Kansas. As one can see, if it was 65.5 against the governor the way GMC built them, a V730 will barely make 60 mph. Now in the quest for speed, aren't you sorry you put a V730 in yours? | ||
| Frank Allen (64.12.96.235)
Rating: N/A |
Can anybody tell me what rpm the 8/71 is supose to turn set up right??? i see all kinds of speeds and i wonder why i got a 8/71 with a 730 74 mph , no tack . Frank Allen | ||
| FAST FRED (209.26.115.209) Rating: N/A |
Why not just go over to, http://home1.gte.net/res07rfl/, use your tire size and print out the correct answer? I use a copy of the engine speed / rpm table to know the limits for each speed. How many RPM is alowed in first or second coming down a bug hill? The table answers in a second. Eventually I will just stick "bugs" on the speedo to show the max breaking rpm's etc . There are folks that claim 2300 rpm cruise for ever , but NOT ME! FAST FRED | ||
| Mike Eades (Mike4905) (206.148.164.24)
Rating: N/A |
I have a 75 4905 that I repowered and I run 70 with v730. Between 6&7 mpg. I also pull a large cargo trailer. Works for me. Goes as fast as I want to go with the trailer on the back. Mike |