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Author Topic: 6v92ta verses 8v92ta  (Read 2952 times)
sledhead
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« on: May 10, 2013, 01:41:14 PM »

I have a chance to buy a rebuilt 8v92ta and a 754cr 5 speed or keep my 6v92ta and put the 754cr on it . I just had my 6v92 set up to 350 hp and it run's great with 9.5 mpg (cdn) is it worth the lower mpg for more hp ? What do you guy's and gal's think            thanks dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
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« Reply #1 on: May 10, 2013, 01:49:41 PM »

I wouldn't be surprised if they didn't get very similar fuel mileage if driven the same way, but you would have 50hp or so on tap for "emergencies"...

It's a lot of work to change, unless the 8V92 is on an MCI cradle already.

Brian
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sledhead
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« Reply #2 on: May 10, 2013, 01:56:14 PM »

The complete unit came out of a 1993 mci , I was told about $1500. re and re plus some misc parts.                  dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
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« Reply #3 on: May 10, 2013, 03:38:27 PM »

If I thought the engine was good I'd do it in a heartbeat.  Ain't no prize for going slow...

If I still lived in Ontario I'd take a weekend and cruise on up for a visit.  Opportunity missed, I fear...

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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1972 NTM MK-4 B/SR
luvrbus
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« Reply #4 on: May 10, 2013, 03:46:21 PM »

The 8v92 and 754Cr is a nice setup if you don't want it I know some one that does he pay you a finders fee hard to pass up a extra 125 hp lol with 1400+ lbs of torque, yours a newly rebuilt 6v92 which will serve you well for years I doubt I would do it but we all do strange things
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RickB
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« Reply #5 on: May 10, 2013, 03:49:07 PM »

Clifford

I hope you're thinking of me when you say you know someone looking. I'd sure love to buy that combo if you decide not to.

Keep us informed

Rick
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« Reply #6 on: May 10, 2013, 03:51:58 PM »

I was Ricky lol

good luck
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« Reply #7 on: May 10, 2013, 06:11:59 PM »

I'm having daydreams of a 500hp 8V92 in my 5A, passing sport cars going up Cajon Pass in the fast lane, lvmci...
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« Reply #8 on: May 10, 2013, 06:50:43 PM »

That's not a "daydream" that's an hallucination!!>>>Dan
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« Reply #9 on: May 10, 2013, 06:58:43 PM »

I went from a good 8v71N to a reliabilt 525hp 8V92TA. My fuel mileage is the same.

May be in how you drive.
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Joe Laird
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« Reply #10 on: May 11, 2013, 02:27:56 AM »

Anyone with the 8V-92 @ a high hp running #40 oil, spin the rear main bearing YET?  Prime reason I only ran the #50 oil in my crazy 8V-92 setups, no issues, but the outfits running the #40 are legend for rear main issues.  Just wondering as I also prefer the 8V, but most know why the bus outfits went with the 6V, lack of rear main issues, more miles per rebuild, yes we all have a buddy who is married to the sister of the  mechanic who always gets 2 mil miles from the 8V-92, right ?  Grin

Dave M
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sledhead
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« Reply #11 on: May 11, 2013, 05:20:56 AM »

Now It's clear as mud .   With what I have now at 65mph my tack is 1700 rpm and this is usually the speed I set the cruise at. With the 5 speed I know the final drive is 1 / 1 but to have the extra gear between 3rd and 4th would be all I need to make the set up almost perfect.
Now after driving the 6v92 with little power for the last 6 years. But now with the ddec change with the 350 hp or more  the drive is very relaxing. With the 8v92 I know there will be more power still. But how about the eng heat and reliability and mpg ?      again thanks dave
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1990 mci 102c  6v92 ta ht740  kit,living room slide . home base huntsville ontario canada
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« Reply #12 on: May 11, 2013, 05:52:15 AM »

MCI had great success with the 8v92TA set at 400 hp lots of those still on the road IMO the 8v92 is more durable than a 6v92 a 400 hp 8v92 will do as good if not better on the mileage as a 350 hp 6v92 DDEC or mechanical 

I still would keep your 6v92 with a fresh rebuild over a unknown 6v or 8v the main bearing on a 8v92 has never been a problem for me using 40W oil I guess things could happen
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« Reply #13 on: May 11, 2013, 06:55:52 AM »

I am not a fuel engineer!
I do have a lot of miles in my coach wit the 8V71n, also the 8V92TA. I know what the fuel mileage is. I have kept a record
for 17 years.

If the rearend does 65mph at 1700, it doesn't care what is driving it. It will be the same speed at any HP at 1700rpm, even if a hampster in a cage wheel is powering it.

It takes the same HP to move the coach at the same speed. It is very nice to have extra HP when climbing. With mine, I can blow right past the trucks on climbs.

It uses more HP now when climbing but the time is much shorter. I think it balances out.

I believe if you hot rod a detroit it will not last long. Reliabilt set mine up and I drive it no different than the 8V71.

I also believe the guys that tell you to slam your finger in the door then take it out on the engine never bought the engines.

My 71 was like the rest of them, it ran better at 1800 or above. The 92 seems to really like lower RPMS. It acts like the series 60.
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Joe Laird
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« Reply #14 on: May 11, 2013, 06:18:03 PM »

I have heard from a lot of people that they get 5-6 mpg with an 8V92TA.  Then 7-8 mpg with the 6V92TA.

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Geoff
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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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« 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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« 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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« 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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« 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
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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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« 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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« 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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« 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
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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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« 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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« 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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« 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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« 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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« 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
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« Reply #30 on: May 13, 2013, 01:47:18 PM »

It was called a HT750DR or the HT754CR to differentiate the two. The DR did have a deep 1st gear that was NOT supposed to be shifted up to 2nd while moving. The new 4700RDS also has a deep low added to the 4000RDS that can be shifted full power. Good Luck, TomC
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« Reply #31 on: May 13, 2013, 01:54:59 PM »

Tom, I have the 754 CRD and I can't believe that they would have a lower first gear than this. It is basically for climbing trees, Lol! Seriously, I've never looked at the MPH when I shift to 2nd but it has to be single digits. That's another thing is it win't shift out of 1rst automatically, you have to do it.

Rick
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« Reply #32 on: May 13, 2013, 02:43:34 PM »

Rick as TomC pointed out the 740 and the 754 both have a 1st gear of 3:69 maybe you have a 750DR those are deep a 7:97 ratio almost like crawling basically all the 700 HT series are about the same except for the gearing then you have the V series
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« Reply #33 on: May 14, 2013, 05:09:13 AM »

Rick      I called yesturday but my guy was not in I will call to day and will let you know what eng.s they have                          dave
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« Reply #34 on: May 14, 2013, 07:48:28 AM »

I got a hold of the 5 speed trans. info . It is a 1993 ht755cr atec, it comes with the computer and the key pad . I have a 14 gage 12  wire harness that I can install from back to front.I was told I will need the tps or a tecl, the wire harness connector at the trans.                 Is this a good trans. for my 6v92ta and will I have any problems with the electronics?              thanks again for the help dave
« Last Edit: May 14, 2013, 11:24:11 AM by sledhead » Logged

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« Reply #35 on: May 15, 2013, 08:48:48 AM »

Rick b   I tried to send you a email    well that did't work  so if you could send me one I will respond. here is my email   crane66@hotmail.ca   or call 705  789  8189 

  thanks  dave
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