| Author | Message | ||||||||||||||||||||||||||
| bill chisholm (Billybandman)
Rating: N/A |
I am looking for ACUTAL proven data about top speed/RPM in GMC coach. With any of the following trannies, VS 6, VS 8, v730, and a 4.125 what is your speed, mileage and rpms | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
The highest speed will without a doubt be the VS2-8, simply because the bevel gearing makes it that way, followed by the VS2-6, and then the V730. I had the VS2 in my 4905, hi tred 24.5 tires, top speed if you had a very steep downhill grade and a furious tailwind would project to be way over 100mph with the governor tweaked only a little. Actual conditions worked out to a steady 9 mpg, while cruising in the 70's, loafing along at about 1700 rpm. The bad side of course, this would not have been a good machine for mountain climbing pulling a trailer, as it "unlocked" around 25 mph, and starts making LOTS of heat in the hydraulic mode. I also drove a 4106 with a VS2 from Charleston SC to Topeka KS on one tank of fuel, AND had enough left over to go half way back to SC! It loved to cruise in the 70's also. | ||||||||||||||||||||||||||
| HondoJoe04
Rating: N/A |
60 mph @ 2000 rpm 72 mph @ 2350 rpm V730 trans w/ 4-1/8 gears. I think I may have the underdrive 730 trans that is said to not exist....fwiw joe | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
HondoJoe you did not say what size tires you are using, but that sounds about the same as all the V730's that I have been around. Most people tell tall tales, but a brand new GMC 4106 as delivered from the factory, 4 1/8 gears, would not go but 60 mph with the standard transmission. That is taken from the 4106 advertising brochure, GM did not want that engine to turn over 1650 RPM! The V730 of course lowers that top speed, so people turn up the governor to attain RPM's that GM never intended the engine to run at, reducing longevity and increasing fuel consumption. | ||||||||||||||||||||||||||
| TWODOGS (Twodogs)
Rating: N/A |
the MAIN thing to keep in mind...90% of all transmissions are "one to one" in high gear.. if you want more top end speed...you either have to go to an Overdrive trans. ....OR....lesser rear-end ratio... | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
But he is talking V drive GMC Two Dogs, that stands for General Motors Corporation you know, and severely limits both the differential ratio choices, sometimes to only one! The V drive transmissions all have a bevel gear ratio included, so none are actually one to one, and there are virtually no big choices of bevel gear ratio. Pretty much the way the GMC'ers do it is by turning up the wick on the governor, and changing tire size. Now you are going to tell me that a "Heinz 57" type Eagle who just bolted together all different makes of components allows this, yep it sure does. | ||||||||||||||||||||||||||
| TWODOGS (Twodogs)
Rating: N/A |
stick & staple...stick & staple .....  | ||||||||||||||||||||||||||
| TWODOGS (Twodogs)
Rating: N/A |
hey Don...remember that guy that had the vibration at 12,000 r.p.m. ??? | ||||||||||||||||||||||||||
| RJ Long (Rjlong)
Rating: N/A |
Don - Just a little FYI - in the 1978 GMC 4905 brochure I have, GM upped the rpm settings: 4108: 65.5 mph at 1800 rpm w/ 4.125:1 axle 4905: 65.6 mph at 1900 rpm w/ 4.375:1 axle These numbers are with 12.00x22.5 wheels/tires. Bill - Daris Boutillier has a GREAT little calculator that can answer your question about speed/rpm on his website. Here's the main URL, then click on the "MPH Calculator" in the LH column: http://www.freewebs.com/darisb/ Mallie Lennon, another fellow busnut, has a calculator that's slightly different, but just as useful, on his website: http://www.cwis.net/~mallie/page12.html As Don already mentioned, GM set up the 4106 to run 60 mph at 1650 rpm on 20" tires that turned 495 revs/mile. That coach will return about 9 mpg in that configuration. Problem with an '06 is that they like to run a lot faster, w/ subsequent fuel penalty! With the V-730 and the 4.125:1 rear axle, installing 11R24.5 tires that turn 470-475 revs/mile will bring you back to nearly the same road speeds as the original 4-speed, altho the fuel mileage will be somewhat less, especially with increased city usage. IIRC, Bill, you have a 4107. That coach, if the rear axle's still stock, will be the same as the 4106's and 4108's ratio. HTH, RJ PD4106-2784 Fresno CA | ||||||||||||||||||||||||||
| FAST FRED Rating: N/A |
"65.6 mph at 1900 rpm w/ 4.375:1 axle" This is accurate with the 4 speed , we have had the "mountain gears" in our '06 for about 5 years . Much over 1950 rpm and the fuel milage stats to suck, so we mostly settle for just under 70. The milage is about 9.5 , but we just towed a small trailer with a lawn tractor down to Fl . and only got 8.5, AMAZING! as towing a VW rabbit does not seem to hurt the fuel milage a noticable amount. $2.25 for diesel (or $1.80 for heating oil) makes traveling a bit more painfull than usual. FAST FRED | ||||||||||||||||||||||||||
| John Rigbyj
Rating: N/A |
Don/RJ, Do you guys have any infomation on the 4104/671, original info from G.M. etc. Thanks John | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
I don't, but I bet you RJ does, how about it? By the way, RJ and FF, you are right on it as usual. | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
By the way FF, I noticed the same strange thing, my overgeared 4905 actually seemed to get BETTER mileage when the slightly over 2000 lb Saturn was in tow. I became convinced that the airflow is BETTER with a toad (maybe), since I was usually cruising at higher than normal speeds. | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
Two Dogs don't get too smart now, remember that I am the one basking in warmth and sunshine, YOU are the one with the shivers and a snow shovel in hand in Amarillo! | ||||||||||||||||||||||||||
| Tom Caffrey (Pvcces)
Rating: N/A |
We've seen a similar effect in boats. An increase in the length of waterline increases hull speed and can add quite a bit to the displacement of a vessel without increasing fuel consumption for a given speed. Air and water are both fluids, so it makes sense that there would be some similarity between them. Adding length should reduce wind resistance some, but the added weight when towing increases rolling resistance and takes more energy to get up to speed. Haven't you noticed that many short motorhomes get lousy mileage at even less than half the weight of our buses? Whenever the increase in rolling resistance is more than the reduction in wind resistance, fuel mileage will drop, and vice versa. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher | ||||||||||||||||||||||||||
| RJ Long (Rjlong)
Rating: N/A |
Well, let's see if I can get this to work. Using GM's published data and Daris's calculator, here is what I come up with for the three most popular GMCs. The RPM given in this table is all based on using the original 495 rev/mile tire at a standard 60 mph, rounded to the nearest 50 rpm. B/R = Bevel Gear Ratio and R/A = Rear Axle Ratio. 4107 and 4108 owners can use the 4106 stats, while 4103 and earlier owners can use the 4104 numbers. I'll even throw in the stock MC-9's rear axle ratio for comparison, as well as a V-730 Allison. Here goes:
Now you can see why two folk running down the interstate together at 60 mph, one in a 4104 and the other in a 4106, can almost get identical fuel mileage, even tho the '06 is running the 1/3rd larger 8V71! The heavier and longer 4905 will be pretty close, too. . . Obviously, YMMV, based on the amount of "stuff" on board, terrain, tires, driving style, rain, sleet, snow, boot size and so forth, but this is good campfire trivia anyway! Does that help, John?? RJ PD4106-2784 Fresno CA | ||||||||||||||||||||||||||
| RJ Long (Rjlong)
Rating: N/A |
And for those of you who only receive these messages via email, in order to see the table that I developed, you're going to have to log into the BBS. RJL | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
RJ, what RPM did GMC limit to on the 6-71 in the 4104? I don't have a chart for them, do you also know the rpm/torque curves? | ||||||||||||||||||||||||||
| jim wilke (Pd41044039)
Rating: N/A |
Your 4104 chart should include the optional 3.55 ratio too. My copy of "Da Book" says the engine should turn 2100 max. But don't forget that the bus & the book were developed to provide best possible fuel economy at yesteryears highway speeds. You couldn't sell highway coaches today that didn't do at least 70. The Detroit engine is capable of happily running at 2350 for an hour or so here & there but your fuel economy will suffer greatly. Trucks were set up as high as 2500. | ||||||||||||||||||||||||||
| RJ Long (Rjlong)
Rating: N/A |
Don - The Technical Sales Brochure I took the 4104 info out of only gives the HP and torque figures for the engine: 211 hp @ 2000 rpm 574 ft/lbs @ 1600 rpm In the transmission/rear axle section, it gives a road speed figure of 57.8 mph in 4th gear. Using Daris's calculator and the tire/rear axle ratio info, 57.8 comes up at 2000 rpm. The similar Technical Sales Brochure I have for the 4106 has more info in it. In one section, it says: "Standard engine governed speed is 1650 (recommended)." Three pages later, it says: "BHP @ 1650 rpm (Governor Speed)(std). . 235" "Torque (max. ft.lbs. at 1200 rpm). . . 770" Two pages after the above, there's a performance data chart, dated July 1, 1960, that shows the output as 272 hp @ 2000 rpm, same torque figure. And when you go to the transmission road speed page, that table shows: 60 mph @ 1650 65.5 mph @ 1800 (same as the 4108 data noted above, btw) How's that for conflicting information? My best guesstimate is that on the 4104, the 6-71 was actually set for 2000-2100 by GM, and that the 4106 was purposely set low at 1650 to provide similar fuel mileage to the six. The company that originally owned my 4106 set the governor at 1900, which is 72 mph with the 12R22.5s that are on it right now. Isn't this hobby fun!! RJL | ||||||||||||||||||||||||||
| RJ Long (Rjlong)
Rating: N/A |
Jim - You're right, I do have the listing for the optional (and rare!) 3.56 axle. I didn't include it because they're just not that common. So to keep Don happy (LOL), it gives a top road speed of 67.8 mph for the 4104 with that axle. I totally agree with the different time and era comment, too. The 4104 and Scenicruiser were both developed before the Interstate system, back when most major highways were still two lanes and 60 mph was considered "fast". So the performance curve matched the operating conditions of the time. Time to go to work. . . RJL | ||||||||||||||||||||||||||
| Don/TX
Rating: N/A |
OK RJ, you passed that test with flying colors, now lets see what the 3751 was like. I AM aware that it also had two rear axle ratios, known as "mountain gears" and "flatland gears" by the old timers. My brochure lacks that information. | ||||||||||||||||||||||||||
| L. R. Taft (Larryk2lt)
Rating: N/A |
HBS... Has anyone tried using a towed as a pusher for the long mountain climbs and better takeoff in traffic? I need to look into the controls of doing this with an automatic and a few simple actuators for shifting into drive, brakes and throttle. Railroad locomotives do this all the time. I ask because I would like to get a 4106 with a V730 to replace the wornout (155,000 miles) Itasca 454 that has served faithfully for several years but is at the end of its road life. As I said, a Hair Brained Scheme.... Larry | ||||||||||||||||||||||||||
| John Rigbyj
Rating: N/A |
RJ Thanks to Richard and his son we were able to test your infomation using satelight tracking. My 4104 developed the following. RPM MPH 1500 55 1600 57 1700 60 1800 65 1900 70 2000 75 2050 77 The RPM info could be off as it runs of the alternator. But it sure is nice to know the exact speeds John |