| Author | Message | ||
| Henry 96A3 (Hank)
Registered Member Username: Hank Post Number: 66 Registered: 11-2005 Posted From: 69.129.124.111 Rating: N/A |
From what I read it sounds like all the DD 2 strokes are governed. Is that true? I don't have a tach but I've taken my 6V-92 MUI as far as 55mph in 3rd (HT740) and by that time she's really screaming and I dare not take it any higher. In 4th, I've had no problem getting it up to 80mph but I don't like going that fast and I am too chicken to go any faster. I am about to install a tach and I'm curious what the "red line" is-or are they always goverened? I don't know what the axle ratio is or how to determine that. Thanks, Hank | ||
| Jerry Campbell (Jerrync)
Registered Member Username: Jerrync Post Number: 38 Registered: 7-2006 Posted From: 76.182.44.149 Rating: N/A |
2100rpm | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1118 Registered: 12-2000 Posted From: 67.181.163.170 Rating: N/A |
Henry - The most common rear axle ratio on MCIs is 3.73:1, unless it's an 8V92, which often used a 3:35:1. There should be a tag on the axle housing with the ratio listed on it. (But DON'T crawl underneath to look w/o blocking up the coach body - squished busnuts are not a laughing matter!) Jerry's right, 2100 is the normal governed RPM on a two-cycle Detroit such as your 6V92TA. BTW, you should determine the maximum road speed in 2nd & 3rd, in order to improve performance when climbing hills. By marking the working speedometer, you'll then know when to downshift smoothly. The Allison will perform much better when climbing if you downshift manually rather than letting the transmission do it by itself. FWIW & HTH,  | ||
| Stephen Fessenden (Sffess)
Registered Member Username: Sffess Post Number: 666 Registered: 1-2002 Posted From: 67.142.130.11 Rating: N/A |
2250 RPM on my 8V7TA | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 39 Registered: 10-2006 Posted From: 4.235.204.27 Rating: N/A |
Detroit used to govern to 1600 rpm for the Hound fleet. A bit over 60mph with good fuel economy. Most folks feel over 1950rpm will add hugely to the fuel bill , so distance cruisers like my self set the gov there. There is little use for a Tach on a slushpump coach, simply go to Darris Site and the computer will give the road speeds in every gear at whatever RPM you choose. FAST FRED (Message edited by fast_fred on November 28, 2006) | ||
| Bobh (Bobh)
Registered Member Username: Bobh Post Number: 11 Registered: 8-2006 Posted From: 204.116.186.20 Rating: N/A |
2800 RPM on my 6V53 | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 943 Registered: 12-2000 Posted From: 64.231.9.193 Rating: N/A |
Hello Henry. Yes, by design, all the engines are "governed" so that they will not spin faster than the maker intended. Without the governor to automatically restrict fuel delivery, it would be incredibly easy to over rev the motor and damage it. So, the governor itself is a good thing. What RPM it is set at might need an adjustment to suit the owner! Fleets would set the governor at a chosen engine speed to limit top speed, in an effort to keep a leash on the hired help (drivers). Since we are our own leash holders, we may want something different. In an MCI with the 3.7 differential gear, 2100 RPM will give you 70 mph road speed with the usual 495 rev per mile tires. and just around 50 mph in 3rd. Also, remember that it would be best to suspect the speedometer reading until you have checked its accuracy. Old story from long ago, in the infancy of auto travel, the way to cure an owner's complaint that his car was showing a slower speed than his neighbour's? Change out the gears in the speedo so it looked like it was going faster! Ignorance is bliss? As RJ suggests, these older transmissions drive a lot smoother and performance is improved if you shift it yourself. The tranny shifts up too early and shifts down too late, and hunts roughly between gears if you roll along at the "wrong" speeds. Co-pilot is not going to be happy at all the banging and jerking. May be a big reason she doesn't like the bus, and she'll never come out and say it. Let the tranny take care of the 1-2 shift. So, with a 2100 RPM governed engine, it would look like this: 0 to 35, shifter in 2, 35 to 50 in 3 and 4th 50 to 70. As speed is dropping off, shift down 2-3 mph ahead of the shift point on the way down to hit max RPM. Each one is a little different, fine tune the points to suit your coach. Knowing exactly where the tranny will force its own shift gives you the flexibility to hold the gear just long enough to get over the top of what you are climbing instead of shifting down only to shift up again in the next few yards. The goal is smooth shifts, good driveability and above all else, happy passengers! happy coaching! buswarrior | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 48 Registered: 10-2006 Posted From: 4.235.205.94 Rating: N/A |
If it works this is cheap enough for most tool freeks. FAST FRED Our TC802 Hand held Laser Tachometer is perfect to calibrate your speed readings. Simply place a small piece of reflective tape on the pully on the main crank shaft. Turn on your engine, point the visible laser light at the target and the non-contacting laser tachometer will accurately display your speed from 2.5 to 99,999 RPM with an accuracy of 0.05%. The tachometer is supplied with a leather case, reflective tape, batteries and instructions manual - only $49.95. Additional information and secure on-line purchasing can be found at: http://www.reliabilitydirectstore.com/Reliability-Direct-TC802-Large-Display-Tachometer-p/ rdi-tc802.htm TC802 Laser TachometerDave G. www.reliabilitydirectstore.com |