Howdie guys,
I just sold my MC5 that I used for many years with never a problem other than no fuel gauge (I am quite efficient at priming now) Anyway, I recently purchased that 1968 MC5 off ebay last year. The coach is georgeous and was built as a motor home from day 1 and has very few miles.
The new coach only gets 5.8 MPG ??? top speed is only 70 ??? I run out of torque at even the slightest hill...
The only other thing I have to compare it to was my 9.9 MPG MC5 that needed constant feathering of the throttle to keep it under 80 !
Both are 8v71 both have functioning mechanical throttle linkage.
The old coach is a 4 speed spicer
The new coach is a 4 speed allison automatic
No idea on injector size for either
Neither of them smoke (once warmed up)
I hope it is not because it is an automatic - if so, why on earth did I ever change
Automatics have always been known to produce less in MPG! :'(
Ace
Maybe you switched so that you could justify installing that 7 speed all synchro and getting 10.5. Ya think? Lots of things you can do for MPG. Tire selection, tire pressure, alignment, synthetic in differential, syn in trans., insure trans temp is about 180, insure oil temp is about 180. Check injectors and report size. 318 upgrade will kill MPG and increase operating RPM and the 740 would keep the r's too low to get any advantage out of the cam advance.
Were I u I wood be unhapy tu.
John
It has been proven in the trucking industry that with proper training, an Allison automatic should get very close and sometimes better than a manual (especially if you have a driver that doesn't know how to shift and when to shift). The biggest fuel gulping mistake that most do with Allison equipped buses is to just floor it from a stop. If you remember back to your manual transmission bus and feather the pedal so you accelerate as fast as a manual transmission bus, you're fuel mileage will go up. If you have a tachometer (if not, install one-it only takes about a day to do if you have to run the wires), don't do any continuous cruising above 1800rpm. You'll get much worse mileage between 1800-2100, and horrible above 2100.
Try having your engine tuned, and see where you're cruising the engine at when on the highway. I think you should be close to 8mpg with a 5. Good Luck, TomC
Quote from: JohnEd on January 25, 2009, 10:12:41 PM
318 upgrade will kill MPG and increase operating RPM and the 740 would keep the r's too low to get any advantage out of the cam advance.
John -The Allison in this MC-5a, with the 8V71 engine, will not be an HT-740 - it's too long to fit. Most likely he's got an MT-644 bolted to the 8V.
Viento -A 3-mpg drop between the auto and stick is on the high end of average difference. What concerns me more is the lower top speed and lack of power on slight grades.
As TomC suggested, I'd have the rack run to make sure the engine's in top tune, and that the idle speed and governed speed are set properly. I'd also check to see what the rear axle ratio is - you might find it's lower than your old coach (3.70 vs 3.33, for example), which would contribute to the different top speed.
Either way, a 2 mpg loss of fuel economy is about average between an automatic and manual box in a bus.
FWIW & HTH. . .
;)
Maybe it wieghs more than your old coach?
I don't have any experience of automatic transmissions in buses but instinctively it seems very wrong to expect an average 2mpg difference between auto and manual. 2mpg in less than 10mpg is ENORMOUS. I know your fuel is very cheap but I'm sure if I were a bus operator I'd still be desperately upset if my vehicles were using so more fuel than those of my competitors. I cannot imagine bus manufacturers would ever sell buses with automatic transmissions if they represented such a big percentage increase in costs / reduction in profit for operators.
Jeremy
All good points! With my 68 5A i get from 5.9 to 8.1 mpg. 8V71 with an Allison Mt 644. It loves to run at about 1750 rpm in 4th and at 70-75 mph. If i run at higher rpm the mileage drops rapidly. I usually get right around 7 mpg depending on terrain, some freeway driving, a lot of secondary state road driving. My speedo goes to 80 and i have gone faster than that on flat ground and still had lots of throttle left. I was just telling Jim Shepard that i would like to see what the top speed is but not by a cop. :) Maybe Bonneville? ;D There were 2 different rear ends ratios available in the 5s, you have either a 3.36:1 which was standard or a 3.7:1 which was optional. My engine is supposed to have been bumped up to 318 hp but i am not sure if this is true......we get mighty slow on some of the long grades but we just enjoy the view and know we will get there sooner or later. :)
Ps. My bus has gained about 1000 lbs. since we started fulltiming and we now weigh 29,000 lbs. Also if i drop down to 3rd gear and run at 21-2200 rpm instead of 4th and 1750 rpm i am now running at 25% higher rpms.......and using 25% more fuel for the same period of time.
I consistently get 7 mpg in my 5A (8v71 & allison 644) I keep the rpm's at 1800-1900 at 65-70 mph. Jack rabbit starts will murder your mileage. I accelerate very gently and slowly.
Also letting off of the throttle and coasting up to a stop light will save fuel and make your brakes last a lot longer too!!!
Hello,
I have to admit, I have it to the floor almost the entire time it is on the road. Only because I am used to racing around with the old bus.
Maybe i should dissable the Jakes and coast more (although they are a hoot)
I am not sure what the ratio is in the rear end but the shift points are exactly the same it shifts at 35km 60km 90km and the top speed is 115km. The old bus top speed was the only difference.
I believe you are correct, this tranny is a 644? The previous owner did the swap and according to Al at "buss's R us" the installer did a great job, even re enforced some cross member that most guys do not bother with?? Is the 644 a good trany?
THe bottom line is the family trip to the ski hill cost $320 instead of $150. It used to be easy to rationalize using the extra fuel and offset hotels and add to the whole event... but now, she just stays parked :(
Al wants $200 per new injector and 12 hours labor to "run the rack?" I have never had a tune up so this is a bit pricey. Do I have to pull the motor? remove the Jakes? my manual does not go into such detail. I have every tool imaginable. all the warm shop floor I could ask for and I am always up for an addventure... I am a little light on the know how.
If you're top speed is 115kph, and figure that is 2250 on the governor, then to get to the magical 1800rpm, then you should be cruising at 92kph. 1850 will be 95, and 1900 will be 97-and go no faster then that-just try it and see. With these speeds, your rear end ratio is the 3.73 ratio. Maybe consider changing to the 3.33 if you're going to keep the bus for a long time-it will be worth it since you sound like you want to drive fast. Good Luck, TomC
It would seem that aside from having a different rear end, the top RPM could be set differently. To go 80 mph with a 4-speed Spicer, you would have to be running at about 2250 rpm with a 3.36 differential. I would not expect the fuel mileage would be so great there either. By the way, do you know for sure that the speedometers are accurate?
Ok - I think I am getting the picture here. It seems that going 55mph is perfectly acceptable in the bus community. I guess I could just live with it... if I must. well, actually that may not work. I remember trying to keep up with busses on the highway all my life - I dont want to be the guy in the "Bounder" holding up traffic sucking fuel at an astounding rate.
The speedo is consistent with the gps.
Quote from: Damn Yankee on January 26, 2009, 07:58:47 AM
I consistently get 7 mpg in my 5A (8v71 & allison 644) I keep the rpm's at 1800-1900 at 65-70 mph. Jack rabbit starts will murder your mileage. I accelerate very gently and slowly.
So Yankee, what is your top speed? shift points? How on earth do you accelerate gently. my tranny shifts at full RPM and down shifts at about 80% of full RPM. I find it hard to not just get going and end all the screeming ASAP.
Ed Hackenbruch, Same question to you...
I have a Tach ready for install - first on the to do list
One more point that may be of note. The old bus I had to sneak up on the start button - just touch ever so gently and it starts every time. The new bus gives me a sore thumb pressing that button!!!
I think you just answered your own question!
DD are known for quick starting.
Your new one doesn't??
Tuneup??
Well, there's a clue. A good running Detroit will start on the first turn in reasonable weather or even in cold weather with a block heater. Hard starting indicates a problem. 55 MPH would not be acceptable to most of us. If the engine is running right and the torque converter is locking up properly then it must be the rear.
When you say tune up are we talking about new injectors and 12 hours labor?
Thank you, by the way...
I just heard back from the guy I bought it from. He says the coach always had that lousy speed and the loss of power was directly related to the transmission. He also told me the injectors are 55s and the motor was gone over when the tranny was insalled.
I have to say that I am still not happy with the performance, there must be something wrong yet. Rear end? tune up?
Viento1 talking with the shop guys they say run from your buddy Al injectors for a non DDEC 8v71 should be about 60 dollars ea and take no more than 8 hrs install and rack adjustments
David
All I can say is, I love our S60 with a Allison B500. It will do 80 up to 85 easy...It accelerates really well too...
I don't think that helps much. But my point is, I wouldn't like 55mph. It just wouldn't be acceptable for me.
God bless,
John
Do you just let the tranny shift by itself? I manually upshift mine when i hit 2000 to 2100 rpm and i downshift when it drops to 1500 rpm. Don't know top speed but would love to find out ;D....know it will do over 80 with throttle to spare. 55 mph is a real tough speed for me because it wants to go from 3rd into 4th at 55 to 57 mph. If i keep it in 3rd at 55 i am running 2000-2100 rpm and if i shift it into 4th and try to stay at 55mph i am lugging it at about 1550 rpm. I have to get it up to about 62-63 mph before i am running at 1650 rpm. 1700-1750 rpm puts me at 70 to 73 mph.
Quote from: John316 on January 26, 2009, 04:42:39 PM
All I can say is, I love our S60 with a Allison B500. It will do 80 up to 85 easy...It accelerates really well too...
I don't think that helps much. But my point is, I wouldn't like 55mph. It just wouldn't be acceptable for me.
God bless,
John
Dang, thats going to leave a red mark right between the eyes :o LOL John thats funny.
WVaNative
I'll add to the post, heading west on HWY 74 out of Cincinnati last summer I passed two tractor trailers, also East bound a
Indiana State Trooper. I thought when I passed the tractor trailers they were running below the posted 70 MPH. Looked back
and noticed the Trooper was now heading my way with his lights on. Looked again and the trucks were way behind me, and lo
and behold I had a visitor. Long story short.........104 in a 70. Had no idea a bus , especially mine would run that fast. As for
the engine size 8V-92 Spicer 4 spd. Believe it or not it sips fuel at those speeds.
Steve 5B....
Quote from: Ed Hackenbruch on January 26, 2009, 07:57:21 PM
Do you just let the tranny shift by itself? I manually upshift mine when i hit 2000 to 2100 rpm and i downshift when it drops to 1500 rpm. Don't know top speed but would love to find out ;D....know it will do over 80 with throttle to spare. 55 mph is a real tough speed for me because it wants to go from 3rd into 4th at 55 to 57 mph. If i keep it in 3rd at 55 i am running 2000-2100 rpm and if i shift it into 4th and try to stay at 55mph i am lugging it at about 1550 rpm. I have to get it up to about 62-63 mph before i am running at 1650 rpm. 1700-1750 rpm puts me at 70 to 73 mph.
Mr Hackenbruch I believe we have an understanding. Maybe we could have a bus rally at the track?? you know, spice things up a bit.
by the way, I have been letting the auto do the work, It seems to shift at max rpm so manually shifting would not help much.
Quote from: steve5B on January 26, 2009, 08:38:22 PM
I'll add to the post, heading west on HWY 74 out of Cincinnati last summer I passed two tractor trailers, also East bound a
Indiana State Trooper. I thought when I passed the tractor trailers they were running below the posted 70 MPH. Looked back
and noticed the Trooper was now heading my way with his lights on. Looked again and the trucks were way behind me, and lo
and behold I had a visitor. Long story short.........104 in a 70. Had no idea a bus , especially mine would run that fast. As for
the engine size 8V-92 Spicer 4 spd. Believe it or not it sips fuel at those speeds.
Steve 5B....
OK you are not invited to the track!!!
but seriously. Steve just confirmed that I am not loosing my mind. That is some crazy speed but my old bus would just cruise too, I remember before I installed the integral steering I had to keep it at 140km so that it would track
Same questions for you fuel economy? injector size? rear end ratio? shift points?
No matter what the PO tells you I'm not convinced because you still haven't addressed the hard starting.
DDs start on the first crank. If not something is wrong.
Gus, I agree with you 100% my list of things to do is now...
set up tach
solve starting, power and poor fuel economy
figure out as much as I can about what to expect from a tune up and do as much as I can myself.
set up my bus similar to my new friends so I can enjoy similar performance
change all my fuel filters
change my air filter
replace light bulb (not that exciting but on the list non the less)
Viento - you really should have a jake switch - If your jakes are always on your losing some coasting ability there - HTH
55 injectors are going to give you the best fuel mileage. With careful driving, you could change to 60 injectors and still get about the same mileage with the added bonus of a bit more horsepower. Change to 65 injectors, and you'll have more power, but with a definite fuel mileage loss and possible smoking. 55 injectors will give you 257hp and 677lb/ft torque. 60 injectors with give you 280hp and 738lb/ft torque. 65's will give you 304hp and 800lb/ft torque. 70's (with proper timing) will give you 318hp and 860lb/ft torque-and that's about the end of injectors for a none turbo engine. Turbocharge and aftercool the engine and the same 65's will give you 325hp and 975lb/ft torque, 70's will give you 350hp and 1050lb/ft torque, 75's will give you 375hp and 1125lb/ft torque (this is what my engine in my bus is set at and the performance is quite noticeably better-fuel mileage about the same [5-6]), 80's will give you 400hp and 1200lb/ft torque-and that's the last factory setting that Detroit had with the 8V-71TA. You can go with 90's that will give you 450hp and 1350lb/ft torque, but I doubt the engine would last much past 200,000 miles (course, that could be a lifetime of driving for some of us). Good Luck, TomC
I only drove it twice last year and I'm not positive on the shift points but I think it shifts to 2nd at 15 mph, 3rd at 25 mph and 4th at 45 mph. not sure of the rpm's but I rarely get to 2100. The PO didn't set the governer to specs, I have had it up to 80 mph at 2500 rpm (down hill & daydreaming) Going up hill it will upshift on it's own at 45 mph. problems with detent cable adjustments or trans governor are common.
Gracius Amgo Viento,
Sounds like blocked fuel filters, Thow the old ones away, buy new ones say for $25.00 then whos the hero you,
Olay
John
My -5A with 8V71 and 4 speed has N70 injectors and it gets between 5 and 7 depending on if i'm towing the car and if i'm keeping it at 2000 - 2100 rpm which is where it seems to like to run. That produces about 72 to 75 mph according to GPS. It also starts immediately down to about 50. From 40-50 its bump and run. Below 40 it takes ether. I have two group 31 start batteries and i run straight 40.
I had the rack run last winter and it took about an hour and the mechanic charged about $70.00. Of course I had the engine on a dolly, not installed in the cave. It made ahuge difference on how it sounds, and how much blue/white smoke it produces when started. Running the rack is simple if you know what you're doing and have the Detroit issue curved wrenches. Otherwise, pay to have it done becuase its touchy.
Definitely replace fuel filters and check air filter before spending any money.
I don't know how anybody gets more than 75 mph out of a spicer equipped MC-5 unless they have the RPMs turned way up.
FRED
Wow, I have seen so many outrageous claims on mpg I thought there was something seriously wrong with my bus. I also have N70 injectors with my 8v71 and V730 and am happy if I get 7mpg. Up and down these mountains it is more like 6 to 6.5. I plan on having my rack run as soon as I can find someone locally that I feel good about. I hope that helps with my starting because mine is difficult unless warm and seems to have injectors that have difficulty waking up the first few seconds. I don't have any blue smoke but too much black if I get into it. Thanks for sharing Fred.
Fred,
I had /have a 4104/671 which was always hard to start cold until I found out that the one way valve holding the prime in the head was allowing the fuel to drop back,not holding the prime good enough. Once I change out the valve no problem.
John
Quote from: johns4104s on January 28, 2009, 05:27:45 AM
Fred,
I had /have a 4104/671 which was always hard to start cold until I found out that the one way valve holding the prime in the head was allowing the fuel to drop back,not holding the prime good enough. Once I change out the valve no problem.
John
Hi Johns4104s. I hadn't noticed there was a one way holding prime in my 671, is it under the valve cover? Need to look at da book again I suppose.
If you have a mechanical 6-71, 8V-71, 6V-92, or 8V-92, a trick to starting the engine in cold weather is to start it from the back by the engine. What you do is to turn on the ignition, then hold the stop lever on the governor shut with your fingers. Then start turning over the engine-after a count to five slowly release the lever over the next 5 seconds, and the engine should start. This works because, first you're turning the engine over without fuel preheating it, and the shut off lever on the governor retards the timing to make starting in cold weather easier. I've done this several times both in the past with my truck with the 8V-92 and my bus with 8V-71. So far, I've only used ether when the weather was below 0. Good Luck, TomC
Tom,
I am a little confused. Are you saying to reach around or in the middle of the fan belt to hold the fuel lever shut? I am really shy of getting near that belt when it is moving. If I aired up with the electric compressor first, would holding the rear stop button do the same thing?
Tom C,
Your last post is some real good info on starting in real cold weather. I'll try it next time I fire the old girl up. Our temps here
in Indiana rarely get extreme as others around the country, but here of late, we've had our share. Back to the post. my 5B
has a 8v-92 and it sips fuel at 75-80 for what reason I can not explain. May be the gear ratio? at those speeds the engine
seems like it's hardly running!
Steve 5B.....
Steve - how in the world does an 8V92 fit in the hole an 8V71 fits into with about 2" of clearance? After personally removing and re-installing my 8V71 i can't imagine how that mill would fit. And secondarily, how does it stay cool? I have to drive with the temp gauge when the weather is above 80 degrees. Did you install that mill? Can you send pictures of the motor mounts/rails?
Fred
Fred,
I have that question ask all the time, when I bought my bus out of Canada from Trailways they re powered their units from the
71's to the 92's natural. If I knew how to download pic's of it I would. As mentioned the fuel mileage is fantastic, power is
awesome. It fits in there without any problem. I guess because it doesn't have the turbo. The only thing that is noticeable
is that it seems to have larger heads from what I can tell. Never had a heating problem!
Steve 5B....
Steve 5B, What does sipping fuel equal in MPG? Thanks Tom Y
Tom,
What I will state, and have no reason to fabricate the truth, she will get 10-11 MPG. I use special products in the engine,
Trans, and the rearend. There will be a lot of controversies over this statement but that is the truth. I have mentioned
this in previous post. One being the higher CETANE of the fuel the better the performance and fuel economy for starters.
As for the heating issue as formentioned, I use pluronic 60 mixed in the radiators. Cuts heat by 25plus degrees.
Steve 5B....
Steve,
I tried to see what you were talking about and came up with pluronic L61 and a product called Kwick Kool. Is that what you are using? Do you know of any independent lab work on these things?
Lin- I have a V drive with no belts (everything is gear driven) so I can access my governor without getting near anything spinning.
The 8V-71 and the 8V-92 are exactly the same dimensions externally, except for the addition of the vibration damper (what looks like a small flywheel) behind the crank pulley. As to cooling, the 8V-92TA is THEE hardest engine to cool-except if you had an even larger 12V-71 or 12V-92. This is why, converting to a 4 stroke with air to air intercooler will be less strenuous on the cooling system. Good Luck, TomC
Lin,
The product that was formentioned is the chemical name. This product is in alot of the water cooling products.
Usually the amount is around a fifth of an ounce per 12 ounces of water when you buy off the shelf. As for products
I am a chemists, I have the knowledge on different products in these type of applications.
Steve 5B......
Tom,
Well, maybe I am not as much of a wimp as I was suspecting. If you have ever looked at an MCI fan belt, it is pretty intimidating in motion. I will probably try your start method using a rod to hold the lever though. That's what I do to shut the fuel off when the air isn't up yet.
Steve,
Sorry to be dense here, but are you saying that you buy the pluronic 60 itself and use it instead of buying a commercial additive?
Now this is getting interesting. Anybody got a good 8V92N to trade for a good 8V71N?
FRed
ZubZub,
The valve holding the prime is located just as the return line exits the head)you do not need to pull the valve cover) It is only a small 90 degree fitting that is one way, meaning the fuel flows one way back to the tank but is not allowed to flow back to the head, which holds the prime on the head.
John
Quote from: viento1 on January 26, 2009, 08:40:34 AM
Hello,
I have to admit, I have it to the floor almost the entire time it is on the road. Only because I am used to racing around with the old bus.
If you have it floored, you probably aren't in top gear, like when you floor it in your car.
You need to come off the pedal a bit and see if it shifts again. Remember, you get LESS torque at top RPM than you do at 2000.
I think I know what you are after, I am doing a 800 mile trip this weekend and I replaced the fuel filter and air filters. I will give an accurate accounting of my progress.
Thank you
Quote from: steve5B on January 30, 2009, 06:45:46 AM
Lin,
The product that was formentioned is the chemical name. This product is in alot of the water cooling products.
Usually the amount is around a fifth of an ounce per 12 ounces of water when you buy off the shelf. As for products
I am a chemists, I have the knowledge on different products in these type of applications.
Steve 5B......
A question for the Mad Chemist - I have heard from a quasi reliable source that putting ATF transmission fluid in the fuel - it is as good as that $120 a bottle stuff the WURTH sales guy gives me... ??? thoughts ???