| Author |
Message |
Bob Damm (216.134.164.38)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 21, 2004 - 12:35 pm: | |
Our Church has just bought an '81 MC-9 with the 8V71 engine, auto tranny and 3.73 rear end. I have read this engine will run 2100 RPM all day but higher RPMs are bad for it. I have figured that the engine should be close to 2100 at 70 MPH, but I know it will go faster than this. So what RPM are they governed for, can I run it up to 75 for passing without hurting it?? |
rodger in wa (64.70.24.205)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 21, 2004 - 3:00 pm: | |
Bob,
You'll get varying opinions on this. Some use the governor as the speed limiter but most of the knowledgeable people I've consulted about this subject agree that 1800 - 1900 RPM is a good cruising RPM from the standpoint of max engine service life and fuel economy and up to 2200 for short bursts won't harm it.
At 1800 rpm my bus w/Allison MT 644 tranny does 60 mph and that's pretty typical. Also, IMO up to 60 is a safe cruising speed for non - professional bus drivers over 65 years of age with slowing reaction times and shortening attention spans. When climbing grades, I run it up to 2100, it seems to pull better at the higher rpms. Mine is governed at 2250.
Downhill, my target rpm range is 1800 & 2000. Downhill is where you're most likely to overspeed it and do some damage. |
Jose (63.190.104.46)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 21, 2004 - 9:30 pm: | |
I@n remove this if it is inapproiate.
Why is it necessary to run a Church Bus over 70 mph ?
Even if You are in one of the 7 western states were it is legal.
A bus load of kids ? With a few adult chaprons.
Church buses are well known not to have the best maintance, funds are used for Sunday School, charitable givings etc,Maintance is generaly a kick the tires, and add some oil, if it has bigger problems maybe a church member has a set of jumper cables.
Jose |
J.L.Vickers (209.34.16.246)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 22, 2004 - 8:27 am: | |
Jose,
You are right about church buses.
The worst used bus to buy is after a church owned it.
I know I bought a PD-4104 many years ago from a church and it was in real bad shape.
I should have walked away and never even looked back.
But the bus hobby was a new thing to me and I had the bus buy it bug.
Needless to say it was in bad shape you name it you had to repair it.
I will never buy a used church bus again.
Church buses get prayer book maintenance.
Let pray it doesn't need to have any maintenance and keep on driving it till it wont go any more!
Sad but true.
J.L.Vickers |
Henry R. Bergman, Jr. (63.224.197.10)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 22, 2004 - 4:22 pm: | |
Trying to get back to your original question, no, it will NOT hurt your mighty Detroit to run all day at 2100 plus occasional blasts up to 2300 or sooss for passing.
Running 70 mph or soosss on the Interstate is NOT going toooss fast. Ever tried to run down Eye Five in California between Sacramento and Stockton?
Unless you are going 80 to 85, you WILL be run off the road, or perhaps get a ticket from the CHP for going toooossss' SLOW?? Maintain you coach properly and go for it. |
Bob Damm (216.134.164.38)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, March 24, 2004 - 12:37 pm: | |
Just to clarify, my question about speed was to know what RPM is safe for the engine, since there is no tach. MPH is the only way to know what RPM the engine is running at.
Our church bought the bus from Gray Line of Seattle (Evergreen Trails), not another church. |
FAST FRED (65.154.176.86)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 25, 2004 - 6:28 am: | |
AN 8V71 was designed for 1800RPM in "forever" generator service.
I overspeed by 10%+ to 1950 road rpm to stay (just barely) in the efficent fuel consumption range.
Da Book used 2100RPM as max rated HP , but for reasonable service life most users derate the engine to 90% full rpm and 80% full load HP.
2100Rpm minus 10% , puts you right back at 1900 or so.
Scream it at your wallets risk.
FAST FRED |
ChuckMC9 (Chucks) (66.167.165.58)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, March 25, 2004 - 4:16 pm: | |
Another reason to not run at full governed speed is headroom needed to accelerate in case of blowout. I hadn't thought of this before. Here's a free Michelin safety video that mentions this - it might be of interest.
http://www.michelinrvtires.com/michelinrvtires/other/RvVideos.jsp |
Johnny (4.174.103.101)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 03, 2004 - 7:03 pm: | |
Not saying this is too bright, but my uncle drove an old GMC General twin-screw tractor with a SERIOUSLY cranked 8V71 (I've seen a picture of the stacks shooting 4' flames--quite a shock at night--his best guess is pushing 450-475HP), governed at 2400. The engine hasn't been apart since an in-frame in ~1989, & has run an easy 800,000 miles since then.
Also, I've seen another General (10-wheeler) with a 6-71 with the governor cranked to 2800 for ~15 years with no ill effects. I have to admit to not seeing the point, though, since it pretty much falls on its face at ~2200. |