| Author |
Message |
Steven Braud (65.132.36.110)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 5:35 am: | |
I had read somewhere on the net about the best r.p.m. range for DD 8's and 6's. The gist of the article was that if you wanted more highway speed it was better to change the transmission and/or the rear end rather than run your engine at a high r.p.m. I can't find that article now, does anyone out there have any info on this? |
Nick Morris (Nick3751) (65.117.139.135)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 7:41 am: | |
I've always heard the best way to drive a DD is to slam your hand in the door and drive it like your made at it. My 671 proved that right bringing it home last week. If I tried to baby it I couldn't get over about 40 and hills were a joke, but if I ran the rpm's up prety good and shifted to 4th I made it to interstate speed. I have heard that DD will wear out quicker due to the higher rpm's you have to run to make power but I don't know how kind of time we're talking. So basicly from what I've always heard your DD won't give you the power if your not running the rpm's up there. |
DonTX/KS (66.82.9.42)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 9:21 am: | |
Well, you might have been referring to the discussion about 8V71 speeds and torque. An 8V71 as set up at the factory for most buses developed maximum torque at 1200 rpm, and drops off to lower than that as the RPM increases. The factory setup for maximum rpm was usually around 1900-1950.
Fuel useage increases with rpm dramatically in these also. In the archives you will even find an RPM/Torque chart from the GMC 4106 sales manual.
The post by Nick mostly reflected the useage of the "318" DD in trucks, which was designed to run with different specs. In addition, the typical trucker was being paid by the mile, and time was money to him. If the company truck engine flew apart or wore out quickly or used amazing amounts of fuel, he certainly did not care as long as he got in an extra few miles to be paid for in the days time.
I think we all decided that nobody is going to live long enough to ever notice the difference in wearout times.
The fact remains that if you can put up with some shifting, cruise at lower RPM certainly reduces wear and increases fuel economy.
A lot of it is just personal choice. I prefer to run low rpm, long engine life (as well as the other spinning things on the engine). Others prefer to scream along at 2200 or so, fuel burn makes no difference to them, and engine life don't either. Mostly they live in the hills, I used the flatlands mostly. |
Larry (208.18.102.78)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 9:49 am: | |
Ran these in our trucks for years (30 to be exact) never blew a one. We always run them in an RPM range of 1850-2100, on the v6 screaming Jimmy we ran them at 1850-2450, they slip right into gear no clutch used when moving, (Also never lost a clutch). Never bulg the old gal, keep her wound up.
I know all the experts will pull their hair out on this one. |
Joel (64.142.48.67)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 9:58 am: | |
DD are very self-destructive when lugged. Their pistons swell, seize the cylinder liners breaking them at the air inlet ports and pulling off the top flanges. This in turn allows the cylinder to move within the block cylinder walls.
As a general rule of thumb on any diesel:
1. If it will not accelerate while going up hill, shift it down.
2. Do not let it over-rev while going downhill. |
Geoff (Geoff) (66.238.120.44)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 10:42 am: | |
The only people that have a problem with running the engines at top rpm are the people that have low ratio rear ends, like commonly found in transits. It is not good to get on the freeway and mash the pedal down to get a top speed of 55-60 mph, at this speed your are up against the governor at 2300 rpm. You can run the 71 and 92 series at 2100 rpm all day long without hurting it, but not at 2200-2300. Now if you can run the rpms lower than 2100 without lugging it you will get better fuel milage. I never run mine lower than 1600 rpm.
--Geoff
'82 RTS CA |
mel 4104 (208.181.100.111)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 11:39 am: | |
here on the west coast of BC they use a lot of the 6-71 in the boom boats in the log sorting areas, these engins are gov. for 2450 rpm and are souped up to 450 HP and the companys as the opeeators just love the and the get 1,000 hrs out of the engine before they are taken out for rebuild regardless of how it runs. |
DonTX/KS (66.82.9.28)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 11:49 am: | |
If any of this sounds like disagreement, it isn't. We are comparing apples, oranges and avacodos in the same basket. "Lugging" is an imprecise term, and has never been defined by DD to the best of my knowledge, and I believe it is a different definition on different engines DD made over the years.
The ORIGINAL configuration 8V71 with VS2 would not and could not be shifted down until rpms reached approx 1100 rpm. Allison and DD cautioned against changing this speed setting to obtain higher rpm downshifts. THAT engine was deliberately designed and operated at hard pulling speeds of 1150 or so, for long hills if necessary. This engine setup was NEVER used in trucks to the best of my knowledge. For my use, mine cruised at 1700 rpm, at 75 mph, and consistently obtained 8-9 mpg while pulling an overweight coach and a toad. It also ran SO sweet at that gearing and rpm, and yes, on a slow hill, you would have to let it shift down. Big deal.
I would never run an engine like Geoff has at that same rpm load, and his torque and hp specs are a lot different too, right Geoff? |
ken Turner (198.81.26.45)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 12:08 pm: | |
HEY Mel
I used to work on steam tugs around BC. 1940's.. Towing logs,up to 70 sections from queen charlotte sound to Vancouver.
They wound up the engine to 90 RPM !!
1.1/2 knots was really truckin !
SEA LION....and the PRESTIGE
www.pipesusmc.com |
Ken Turner (152.163.252.163)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 12:44 pm: | |
Am getting OLD ......
my web page should be... www.pipesusmc.net
I was a good Tugboat man tho |
Geoff (Geoff) (66.238.120.44)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 12:59 pm: | |
Don, 1100 rpm shift point? My fast idle is at 1100 rpm!
--Geoff |
Jose (216.229.92.25)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 1:00 pm: | |
Ken;
You are getting old,I only worked on the old
Direct Reverseing Enterprise Engine ( 180 max.RPM) Boats !
You could count the revolutions by the exhaust & vibration |
DonTX/KS (66.82.9.11)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 1:51 pm: | |
Geoff: Yeah, crankshaft RPM downshift point! I was going to crank it up a bit, which can be done, but the book cautions specifically against doing that. Anyone with a VS2/8 manual can confirm what I say.
I found it worked very well actually, and with a VS2 in original config, all you have to do if you find yourself pulling a looooooong hill at 1180 or so, is let up on the throttle a little bit, and it slows down to the shift point and ups the rpms enough to make us all feel better, and will stay there until you get too lead footed and get the rpm back up to the high rpm shift point of 1700! |
John Fitzgerald (Johnfitz) (209.179.168.15)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, January 12, 2004 - 2:28 pm: | |
Steven,
This might be the article you saw:
http://users.cwnet.com/~thall/clarke_echols.htm
In case I messed up the link I found it in
"Coach Conversion Central On Line", in their "articles"
section by author Clarke Echols
-John Fitz |
Steven Braud (65.132.36.48)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 15, 2004 - 5:27 am: | |
Thanks John, that's not the same article but it is the info I was looking for. Thanks again and Happy Bussin'
Steve |