If someone can help me determine the max RMPs of my 8V71 I would appreciate the effort.
The factors are as follows:
4106
8V71
4 speed Spicer
tires are new Hanook 12R22.5 (I don't know the rolling diameter)
Top Speed in 3rd is 55 to 57 mph (GPS indicated)
I don't know what the top speed is. The fastest I've seen is 78 MPH
I have a replacement engine on a crate that I'm installing N65 injectors, advancing the cam timing, running the rack, etc, and I would like to know what the RPMs are of the current engine. I may be adjusting the RPMs on this replacement engine as it was a NYC transit bus with 7E55 injectors.
Thanks for the help!
There is a variation of opinions on where to set your no load RPM.I do not think I have heard much advocacy for going above 2300 rpm. Mine is set at 2200 rpm, and I have read of some that advocate several hundred lower.
Have some fun with these two speed calculators and decide for yourself how fast you want to spin the engine:
http://www.cwis.net/~mallie/page12.html
http://www.thebouthilliers.com/4106/calcmph.html
The choice is yours. In fire apparatus service, stories are told of 2800 RPM....
Of course, the more you spin the engine, the shorter the lifespan.
happy coaching!
buswarrior
In modern 8V71s, I would expect a high idle setting of 2250 RPM and a droop of 150 RPM, yielding a top speed in the low eighties. Ours will run right at 83 MPH.
Don't mistake the fast idle switch for the high idle setting. The high idle setting is what you get with the throttle wide open with the bus sitting still. The droop of 150 means that you should be able to get a full rack postion until you get to within 150 RPM of the high idle setting.
At eighty MPH on the flats, I would expect you to be turning about 2150 RPM, burning about 12 GPH, and yielding about 6.5 MPG.
While better performance may be pretty important to you, I would stay with the 7E55s and standard timing, partly because the stock power band is much better suited to the four speed standard transmission. With the 65s and advanced timing, you will need to work at keeping the engine RPM up to protect the engine and it will be unlikely that you will be able to maintain the cooling and fuel economy that the stock setup gives.
According to a longtime Detroit man I know, the 55s give the best fuel economy of any of them in the 71.
For what it's worth.
Tom Caffrey
Maybe I NEED a 4106. So what is your MPG if you just conservatively cruise at 55 or 60?
Thanks,
John
Seasons Greetings to you both...by the way
Tom,
I may just leave the engine the way it is. You're not the first to say that I should try it first, before spending $2k on upgrades.
Buswarrior, thanks for the links. I was able to find all of the data and determined that my current engine governs around 2200 rpm. This engine has N60s and runs better going down the road at 70 mph than at 60, or even 65. My only concern is that 7E55 injectors just won't have enough HP to tow my 7500 lbs trailer up and down the hills in New England. I've towed to Indiana and SC and on the flats she cruises just fine at 60-65, but she'll fall flat if there's any type of incline.
For reference, my 4106 with N60s and Spicer will get 10.8 mpg at 65 mph over a 1000 mile drive non-stop. 7.8 mpg same drive at 60 with trailer. I'm happy with the mileage and I'm willing to sacrifice 2 mpg for more HP if it'll allow my to use a cruise control (not yet installed).
Thanks!
Tom,
With our 3.36 rear end, 2000 rpm in the Spicer's 4th gets us about 71+ mph. It would seem the 83 mph would require another gear or a higher ratio.
Quote from: Lin on December 28, 2008, 09:48:23 AM
Tom,
With our 3.36 rear end, 2000 rpm in the Spicer's 4th gets us about 71+ mph. It would seem the 83 mph would require another gear or a higher ratio.
Lin, something doesn't compute here. In my 4106 the stock ring and pinion gear ratio is 4.125 to 1, which is what we would call "short" gearing. The smaller the number the "taller" the gearing which means that the drive shaft in my bus turns 4.125 times for every 1 revolution of the tire. In your bus with 3.36 ratio the drive shaft only turns 3.36 times for every one revolution of the tires. This means that your engine should be turning lower rpms at a given speed compared to my engine.
Mark
Lin, just used the first link that Buswarrior provided. I entered your rearend ratio and the approx tire revolutions for a 12R22.5 tire and your bus should be traveling at 90 mph at 2000 rpm.
Tell us more about your bus and let's see if we can figure it out.
Mark
Something is wrong there. Although my tires are 11R22.5, that will not make much of a difference. Figure 2000 rpm/3.36/500 x 60(to convert miles per minute into mph). My 4th gear, I believe, is 1:1. That would give us about 71.42 mph. Now if I had 12R22.5 tires and a .8 4th gear ratio, as I think some 4106's have, I would be doing 90 mph. I have tried to verify my speed/rpm relationship with my GPS, and it is pretty close. Thanks
By the way, I don't think I want to go 90 anyway.
Onelapper,
Let me try to re enforce what Tom said above. The reason you really don't want advanced timing is the unavoidable fact that using advanced timing moves the torque peak from 1200 RPM to above 1400 RPM and all the "V" drive transmissions cause the engine to slow from 2100 to 1200 on their last up shift. This is true for the V730 automatic and the 4 speed manuals. The best all around performance will be with N60 injectors and standard timing in a "V" drive bus with an 8V71. Better fuel economy can be had with the smaller injectors but at the expense of some horsepower. Going to N65 injectors and standard timing makes more smoke but actually less power than N60s. If you want more power with standard timing you'll need a turbo. All turbo'd engines use "standard timing". Just what must be changed when one adds a turbo is controversial, with opinions ranging from nothing to practically everything. If you choose to add a turbo you'll be pushing the stock cooling system beyond it's design so you may need to "upgrade" the fan. Several GM buses have been turbo-ed, run with N75 injectors and cooled successfully with upgraded fans.
Regards
Jerry 4107 1120
Quote from: Lin on December 28, 2008, 04:55:40 PM
Something is wrong there. Although my tires are 11R22.5, that will not make much of a difference. Figure 2000 rpm/3.36/500 x 60(to convert miles per minute into mph). My 4th gear, I believe, is 1:1. That would give us about 71.42 mph. Now if I had 12R22.5 tires and a .8 4th gear ratio, as I think some 4106's have, I would be doing 90 mph. I have tried to verify my speed/rpm relationship with my GPS, and it is pretty close. Thanks
By the way, I don't think I want to go 90 anyway.
Okay, with the above info it sounds like you're right on!
Mark
Quote from: Jerry Liebler on December 28, 2008, 05:57:46 PM
Onelapper,
Let me try to re enforce what Tom said above. The reason you really don't want advanced timing is the unavoidable fact that using advanced timing moves the torque peak from 1200 RPM to above 1400 RPM and all the "V" drive transmissions cause the engine to slow from 2100 to 1200 on their last up shift. This is true for the V730 automatic and the 4 speed manuals. The best all around performance will be with N60 injectors and standard timing in a "V" drive bus with an 8V71. Better fuel economy can be had with the smaller injectors but at the expense of some horsepower. Going to N65 injectors and standard timing makes more smoke but actually less power than N60s. If you want more power with standard timing you'll need a turbo. All turbo'd engines use "standard timing". Just what must be changed when one adds a turbo is controversial, with opinions ranging from nothing to practically everything. If you choose to add a turbo you'll be pushing the stock cooling system beyond it's design so you may need to "upgrade" the fan. Several GM buses have been turbo-ed, run with N75 injectors and cooled successfully with upgraded fans.
Regards
Jerry 4107 1120
Jerry, it's diffiicult for me to gauge the performance of my current engine because it clearly has a least one bad cylinder. The other factor is that there is no one clear answer because so many people have some many different setups with varying degrees of success. I've never had the chance to drive another 4106. Heck, I've only seen two others, and they were rolling down the road! Like I said, this replacement engine appears to be a recent rebuild, the compression sounds even when cranking over, it has 7E55 injectors but the original build sheet from DD show it shipped with N60s. Who knows? I do know I want to do whatever work I'm going to do to it while it's sitting on the pallet!
Thanks,
Mark
I have a 4106 and at 2150 rpm it runs just over 80 mph. My previous 4104 did the same. Don't know what gear ratio I have but have 12R22.5 tires. Transmission is the 4 speed spicer.
If you want to make horsepower with a diesel, you need to retard the timing, not advance it. Pittsburg Diesel has alot of info on how its done at their site. I had the 3:36 gear in my 05 and it loved to run 90 MPH. (pittsburgdiesel.net)
Mark,
Actually your present engine is doing pretty good, even with the bad cylinder, judging from your fuel economy data. Don Farchild is the expert on the 8V71s and occasionally is on this board. Don insists the 8V71 can easily tolerate 2300 RPM. In setting up your replacement engine, I'd recommend leaving standard timing, installing N60 injectors, at least for now. If you aren't happy with the performance, you could switch blowers, switch to N75 injectors and add a turbo, drive it a while watching temperature carefully and if needed switch fans all without pulling the engine again. For what it's worth my bus is a bit taller and heavier but otherwise very similar & I get 8.25 MPG at 65, not towing, and 8.0 towing a 5,000 pound towed at 60.
Regards
Jerry 4107 1120
Your address is no good. pittsburgdiesel.net
Mark, Lin, Jerry, Tom, et al -
OK, time for a little refresher on the 4106 powertrain:
Remember, there were an awful lot of slide rules working on this during development, and, since everything's a compromise in some way, shape or form, GM obviously felt that this combination gave the best overall performance for a vehicle designed for revenue service in all types of operating conditions. Thus:
GM designed the 8V71/4-spd powertrain to run 60 mph @ 1650 rpm using tires that turned 495 revs per mile. The goal was also to return 10 mpg at that speed using N60 injectors. When you punch in the appropriate numbers into Mallies's calculator, it shows that the coach should be capable of 76 mph @ 2100 rpm.
Now, some numbers to ponder:
Rear Axle Ratio: The stock rear axle ratio in the 4106, 4107 & 4108s is 4.125:1
Transmission Ratio: The stock "high gear" ratio in the manual 4-spd and V-730 automatic is 1:1
Bevel Gear Ratio: The stock bevel gear ratio for the manual 4-spd is 0.808:1 (the 4104 and earlier models have 1:1). The bevel gear ratio in the V-730 is 0.875:1. (Supposedly there are some V-730s out there with a 1.04:1 bevel gear ratio, but this may be an urban myth, as there is not listing in the parts book for them.)
Overall Final Drive Ratio: This is computed by multiplying the rear axle ratio times the bevel gear ratio times the transmission gear ratio (for each gear, if you want to get all techie). Thus, for the 4-spd in fourth (1:1), you get (4.125) x (0.808) x (1:1) = 3.333:1. The V-730's numbers in 3rd (1:1) yield (4.125) x (0.875) x (1:1) = 3.609:1
Thus, for any given engine rpm, with equal-sized tires, the manual gearbox coach will be going faster than the automatic, due to the "taller" overall final drive ratio. Better fuel mileage, too.
Now, back to Mark's original question:
All of the various literature pieces that I have in my collection regarding the two-stroke Detroit's indicate that the normal setting for maximum rpm is 2150 no-load, and 2100 loaded. Fire apparatus specs are a little higher, at 2500 loaded, but that's the exception, rather than the rule. Again, being a compromise, Detroit most likely specifies these settings to give the best overall performance and engine life for a revenue service vehicle. Since we're now dealing with a non-revenue service situation. . . well, you decide.
The literature also agrees with what Jerry & Tom have said - that advancing the timing shifts the torque peak UP the rpm scale. With N65 injectors, you gain all of 30 ft/lbs. of torque (800 vs 770), but it's at 1600 rpm, not 1200, like an N60-equipped engine. This is fine, if you've got a 10- or 13-speed transmission behind the 8V, so you can keep it in the power band. But with our widely-split 4-spds. . . not so good!
If you're into the Tim Allen Syndrome (More Power!), the turbocharging with the appropriate injectors is the way to go. Stock 8V71T with N-75s gives 350 hp and 990 ft/lbs. If you can find one of the rare 8V71TAs, they produce stock 370 hp w/ 1064 ft/lbs. of torque using 7C75 injectors, with which your coach wouldn't even know the trailer's behind it climbing RockyTop.
With the crate engine you've got sitting on the pallet, it's entirely possible that you could put a low-boost "smoke" turbo on it with N60s "as is" and have a dependable, fairly fuel-efficient powerplant. Suggest you give Don Fairchild a call, and ask him how to check to see which pistons you've got in the crate engine - that would help determine if you could turbocharge it or not. Maybe Dale (Songman), if he's following this thread, can ask Don and forward the info, too. Don's office number is 1-888-473-3626.
Sorry for the long dissertation, but thought it was appropriate to review this info again.
FWIW & HTH. . .
;)
RJ,
I believe that I have C60 injectors. What is the difference between N60's and these.
Lin,
The difference between C injectors and N injectors, as it was explained to me, is that the C injectors were used in city that had smog concerns. The injector tip design was supposed to reduce black smoke at throttle tip in. N injectors are the most common used for truck and industrial applications. 7E series were common in coaches for fuel economy.
Mark
RJ, thanks for the info. How would I find a copy of some of the literature you have? I love reading technical paperwork!
BTW, I did forget to factor in the vee drive bevel gear ratio. Oh, and the tech manual I have says the 4th gear ration is .808, same as the bevel drive gears. Is this a typo? Third is 1.21:1. If fourth is 1;1, then the ratio split between third and four would be very close. Which it isn't.
It sounds like a N60s is the best all round injector according to your specs.
Thanks,
Mark
Quote from: RJ on December 28, 2008, 07:52:11 PM
Mark, Lin, Jerry, Tom, et al -
OK, time for a little refresher on the 4106 powertrain:
Overall Final Drive Ratio: This is computed by multiplying the rear axle ratio times the bevel gear ratio times the transmission gear ratio (for each gear, if you want to get all techie). Thus, for the 4-spd in fourth (1:1), you get (4.125) x (0.808) x (1:1) = 3.333:1. The V-730's numbers in 3rd (1:1) yield (4.125) x (0.875) x (1:1) = 3.609:1
OneLapper, the ratio given is the combined result of high gear and the bevel gear; they just didn't say so. If you look ant the transmission section of your service manual, it should be obvious that there is no overdive within the transmission.
If you think about it for a minute, there would be no reason to put an overdrive inside the main box and every reason not to. The final ratio could be set anywhere they wanted it with just the bevel gear; they wouldn't want to pay for it twice. In any case, the transmission needed to be short, and an added overdrive would add some unwanted length and weight.
I see that RJ's explanation shows a droop of 50 RPM. If that's the case, I've probably forgotten it. I thought it was listed as 150 RPM.
Good luck.
Tom Caffrey