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Author Topic: 6v92ta verses 8v92ta  (Read 3257 times)
chessie4905
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« Reply #15 on: May 11, 2013, 06:42:13 PM »

If you have read posts here over the years, you will remember the many posts that start..." I recently installed an 8v-92 to replace my 8v-71 or 6v-92. It has lots of power now that it didn't have before..HOWEVER, it wants to overheat on hills" "Can the radiators be upgraded to larger units? How much will that cost? Will I need to install misters, also?" And on and on. I'd probably go to the larger engine myself, but just remember the other costs that are going to be needed with the engine upgrade.
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luvrbus
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« Reply #16 on: May 11, 2013, 06:47:23 PM »

I hang out some on Jons Prevost board when fuel mileage comes up Jon and the others say with a 14L series 60 pushing a 45 ft 50,000 lb converted bus 5 to 6 miles per gal if you baby it no bs about fuel mileage there  


Weight, hp, gear ratio and the right foot that is where you get the fuel mileage my 8v92 would run in the 7 to 8 mpg range if you took your time (60 mph) anything over 70 it would drop into the 5.5 to 6 mpg

 Cooling is not that big of a deal with a 8v92 in a Eagle or Prevost the MCI will give you fits but it can be over come too
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TomC
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« Reply #17 on: May 11, 2013, 08:50:21 PM »

It will be very difficult for you to get the same mileage out of a 8V as a 6V-92. Why-because the 8V-92TA will be so much fun to drive, you'll be burning up extra fuel for the bigger performance. Just keep in mind, you'll have to maintain more oil at every oil change, service two more cylinders, more expensive to overhaul, and it weighs 400lbs more. If you have a fresh 6V-92TA, I'd keep it and enjoy it for many years.

If you were to do any kind of swap, I'd replace the 6V-92TA with a Cummins ISL or ISM, or even an Caterpillar C12. Then you'd have a pulling machine, AND much better fuel mileage-plus mechanics that would know how to work on you engine. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
wg4t50
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« Reply #18 on: May 12, 2013, 01:21:39 AM »

Both luvrbus & TomC make some great points, for me, having been thru the issues and being a hot rod type, I highly recommend the ISM, (mine is the 500 hp & 1550 ft lb). if/when it comes up for you.
It will not run with the 8V-92 (somewhere between 580-650 hp) I had in the MC7, but is a lot less costly & needing attention.
Today finding a mechanic who knows the 2 stroker that is still young enough to be able to do the fixin up, is getting to be a rare bird.
My experience is that the good mechanics have either retired or move up the line to a paper pusher desk, what is left does not know the little things about my favorite engines.
The ISM500 in my toy is like the family car, check oil every 4-5 k miles or when it is changed.  A hard habit to break after the DDC/MTU babes.
Today I could live with a good 6V-92 setup.  Am not trying to beat myself any more.
Dave M
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sledhead
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« Reply #19 on: May 12, 2013, 11:41:38 AM »

Thanks for all the replies . So I think I will stay with the 6v92 as it has been reliable . I will call the guys tomorow to comfirm the transmission is a 754cr 5 speed . Now what will I need to change over from the ht 740 4 speed to the 5 speed trans. Is the size the same for the driveshaft ? will the tower, cable work ? what else should I need ?    again thanks   dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
luvrbus
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« Reply #20 on: May 12, 2013, 12:56:26 PM »

The 754 is a little over 2 inches longer than a 740 so a shorter drive line is required  it uses a different shift tower the cable and flex plate are fine 

I would not waste the time unless it is a start in 1st gear 754 it gets old shifting manually to low gear and the 6v92 will struggle starting in 2nd gear unless you are down hill call Allison with the serial number they can tell you if it is a 1st gear start or not I think it has to be over the 4000 number
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RickB
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« Reply #21 on: May 12, 2013, 01:06:33 PM »

Sledhead,

I am certainly interested in at least the motor if you're gonna pass on it. Does it come with everything to do the install? Intake and exhaust plumbing, muffler etc/ ?

Also, I have a 2nd gear start 754 and because the folks who owned this bus before me didn't know it was a 2nd gear start they may have damaged 2nd gear by using it in situations where it needed a 1rst gear start.

Sure would appreciate contact info if you pass on it.

Rick
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TomC
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« Reply #22 on: May 12, 2013, 01:29:14 PM »

Stick with the HT740-it is about as dirt reliable as you're going to get with a transmission. The HT754CR is not as beefy-the extra gear added to the rear of the trans can be a problem. Besides-you're not getting any better startability-both the 4 and 5 spd (CR) have the same starting gear. The only difference is that the 5spd has 3 gears in between compared to the 4spds 2 gears in between 1st and final. In my opinion-not worth the hassle of changing the shifter, shortening the driveshaft, etc. The only thing that the 5 spd will get you is maybe 3-5mph faster on a hill pull. Again-stick with the HT740-it works just fine.

Now if you change to the HD4060/B500/4000HS 6spd Allison and change your rear end to reflect that, then you will see both some performance improvement and fuel mileage improvement. But-that World transmission would cost about $20,000 to change to. Again-stick with the HT740. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #23 on: May 12, 2013, 04:03:50 PM »

My coach is 34,000 lbs + toad at 3,500 lbs total about 38,000 lbs . Is there not an advatage to the extra gear between 3rd and final 4th or 5th. I see the 5 speed on most factory built conversions and they usually have 8v92ta's   
I found this on the internet.
One more: Gillig Phantom 552D-15 (?) (Detroit Diesel 6V-92TA engine, 277 HP @ 2100 RPM)
Power band of engine: 1700-2000 RPM
"Typical" stock 4-speed automatic (Allison HT-747): 3.69, 2.02, 1.38, 1.00
"Typical" close-ratio 5-speed automatic for same vehicle (Allison HT-754CR): 3.69, 2.00, 1.58, 1.25, 1.00
 
Shifting from 1.38 to 1.0: 27% power loss (to 73% of the original engine speed which, when executed at 2100 RPM, the engine falls to around 1500 RPM)
Shifting from 1.25 to 1.0: 20% power loss (to 80% of the original engine speed which, when executed at 2100 RPM, the shift achieves nearly 1700 RPM, just at the low end of the 6V-92's power band, allowing the bus to continue accelerating quickly          thanks  dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
TomC
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« Reply #24 on: May 12, 2013, 09:12:04 PM »

Let's look at the speeds of the two transmissions. If you're bus tops out at 80, then the HT740 will have speeds of 21.6, 39.6, 58 & 80. The HT754CR will have speeds of 21.6, 39.6, 50.6, 64, 80. I can tell you-if you were pulling 80,000lbs everyday and driving 120,000miles a year, like a big rig truck, then yes the 5spd will make a difference on your hill climbing and trip times.
But with driving maybe 5000 miles a year and especially since you're not in a big hurry, do you think having perhaps 6 more mph going up the hill is really worth all the hassle and then having a 5spd transmission that isn't as robust as the 4spd?
I'm sure anyone can talk themselves into any kind of equipment with the right argument. Changing from the 4spd to the 5spd will be a plainly waste of time and effort. Spend your money and time on another project. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
TomC
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« Reply #25 on: May 12, 2013, 09:16:28 PM »

One more comment-on my truck conversion, I had a 13spd manual transmission with overdrive. I changed it to the HT740. With my 3.55 rear gears and 11R-24.5, my 65mph cruise is 1830rpm-right at the continuous rpm rating for the Caterpillar 3406B. I used to drive with all those gears but chose the 4spd-mainly for it's track record of being an extremely rugged transmission with long life. I could have put in a 5spd, or even the World transmission, but kept with the HT740. Good luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
sledhead
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« Reply #26 on: May 13, 2013, 05:15:54 AM »

Ok Tom Yes it will cost money but right now when the speed limit is 50 mph like a construction zone the other problem is the trans. will down shift to 3rd at about 53-54 mph then back to 4th then to 3rd and so on it's a pain in the a$@ . The bus runs great on flat ground it's all the hills we drive through that the extra gear would be good. At 68mph with the 1/1 in 4th or 5th and my 333 rear end is right on the 1700 rpm and if I lived in florida were it's flat, life would be good. But I couldn't handle all the heat and humidity. I do like the cold dry winter a little. I will call today to try and find what money it would cost .   

ps I really do like your honest opinion and you're right but in ontario we have lot's of hills not mountians and the plan is to be ready to travel all of north america in the coach in the next few years. Workin on getting the coach ready.     thanks   dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
luvrbus
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« Reply #27 on: May 13, 2013, 05:44:41 AM »

IMO the 6v92 will enjoy the extra gear I never knew of anyone having trouble with a 754 except the second gear start and that was changed after serial number 2600 not 4000 I found out

 You can change the shift points on the 740 to make it work better for you and you can also change the ratios on a 740 except the final 1:1 with different torque converters a little worthless information for you 

The 740 is a proven transmission so is the 754 I know people with the 754 and they like it very much behind a 6v92 then again we all do it our way both transmissions will work for you 

Another point most 754 require a rear support something the 740 doesn't on a aluminum bell housing

good luck on your choice
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TomC
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« Reply #28 on: May 13, 2013, 11:32:08 AM »

Even with my V730, I shift it manually alot of the time. If you're getting hunting between 3rd and 4th, simply down shift to 3rd to hold it in. The 6V-92 will stand up to 2,400rpm for short periods. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Hard Headed Ken
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« Reply #29 on: May 13, 2013, 12:46:49 PM »

IMO the 6v92 will enjoy the extra gear I never knew of anyone having trouble with a 754 except the second gear start and that was changed after serial number 2600 not 4000 I found out

 You can change the shift points on the 740 to make it work better for you and you can also change the ratios on a 740 except the final 1:1 with different torque converters a little worthless information for you  

The 740 is a proven transmission so is the 754 I know people with the 754 and they like it very much behind a 6v92 then again we all do it our way both transmissions will work for you  

Another point most 754 require a rear support something the 740 doesn't on a aluminum bell housing

good luck on your choice

Seems that I remember a 754CR (close ratio) and 754DR (deep ratio). The DR had a really low first gear. Anyone else remember something like that?

Ken
« Last Edit: May 13, 2013, 02:19:49 PM by Hard Headed Ken » Logged

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