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Author Topic: suitable replacement engines for MC7  (Read 2136 times)
Tin Lizzy
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« on: January 06, 2007, 10:19:34 PM »

I think by this time ( 3 years working on conversion) I should know this but I never bothered to investigate.
When I get a little closer to completion I think I would like to upgrade engine and transmission. I want to put in a 6v92 or 8v92 with either an automatic or an better standard transmission. Can I look at a Kenworth or other Highway tractor for an engine and trans donor?
Any experiences with this type of change?
thanks very much

Tin Lizzy
1972 MC 7
Calgary, Alberta
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« Reply #1 on: January 06, 2007, 10:49:53 PM »

Rebuild your 8V-71 into a turbo engine, add an air to air intercooler, and get 400hp and 1200lb/ft of torque!  Far easier than switching out your engine, and a whole bunch cheaper.  Good Luck, TomC

Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #2 on: January 07, 2007, 01:20:08 AM »

That sounds like a good idea to me too. More power for less money can't be a bad thing Wink
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« Reply #3 on: January 07, 2007, 07:13:24 AM »

Our Prevost was repowered with an 8-92 & 10 sp RR.  The previous owners did the repower & they did a good job.  You are welcome to have a look at it sometime when we are on our way through Calgary. 

R.J.(Bob) Evans
Used to be 1981 Prevost 8-92, 10 spd
Currently busless (and not looking)
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What's behind you doesn't matter - Enzo Ferrari
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« Reply #4 on: January 07, 2007, 08:44:12 AM »

Upgrading from an 8V71 to a 6V92 or 8V92 wouldn't be all that difficult. Both upgrades were standard equipment in most bus applications.
Regarding a Kenworth or Peterbuilt as a donor, finding a two stroke in these trucks will be tedious. You'll also be bidding against the "2 cycle collectors" for such tractors. Most Petes and KWs are powered by 4 strokes.A 4 stoke will be expensive to fit into a bus.
In answer to your question, any truck engine (RH rotation is standard in trucks) will work in a "T" drive bus (MCI, Prevost, Eagle are RH rotation), but would not work in GM which is LH rotation.
However, there are plenty bus donors and recyclers with 6V92TAs. Bolt in conversion. Buy a good takeout with the engine and trans mounted in the cradle. The radiators would be the only item that would require upfit.
As Tom sez, an 8V71T would make plenty of power (equivalent to a high HP 6V92TA)...assuming your engine is in good condition.
Another small issue is that most of the bus 6V92TAs are set at a lower HP than you'll want....something on the order of 280 HP...which is about what you have now. Although the HP can be changed, installing a turbo on your engine would be less work and expense. However, you cannot just "bolt on a turbo" to your engine. There are two schools of thought on the best methods (change to turbo engine components or not) and both turbo conversion systems will reduce your net worth. Altering the engine to turbo specs will significantly lower your net worth.
Expect max of 350 HP from a 6V92TA, around 370 HP-400 with a turbo on your 8V71, and 400-500 HP plus with an 8V92TA (and cooling problems with the 8V92TA if you have an MCI).
An HT740 would be the easiest and least expensive trans conversion...although if you keep your 8V71, upgrading your trans to a truck style trans may give you the granny and OD gears you want. The OD may not be useful with a 2 stroke. A 2 stroke must be kept turned up proximal to 1800 RPM at cruise (especially the lower HP engines) with a max of 2100 to 2300 Redline. The benefit of a 10 speed is that you'll have crawler gears for easing around in campgrounds and tight places, and you'll have gear selections that allows maintaining optimal RPM under most conditions. Most highway buses are geared to give you max RPM v road speed in 1/1. OD would lug the engine.
My thoughts would be to use your bus as it is until you have an idea of what you really want. I wax between wanting a manual and automatic (I have an automatic), but after recently dinking around in Orlando and getting caught in several accident related tie-ups, the auto is cool for now.
An automatic is a definite easier resale item. Auto buses are more desirable and command higher prices.
None of the above ideas are "cheap"...but if you can do your own work and fabrication, it's doable. If you have to pay someone to do the above work, you may be surprised at the expense.



JR Lynch , Charlotte, NC
87 MC9, 6V92TA DDEC, HT748R ATEC

"Every government interference in the economy consists of giving an unearned benefit, extorted by force, to some men at the expense of others.

Ayn Rand
Angola Coach Conversion "Aesop's Tortoise"
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« Reply #5 on: January 07, 2007, 08:56:09 AM »

IMHO, with an MC-7, your best "bang for the buck" would be to rebuild the 8v71 into an 8v71T and mate it to an HT-754 five-speed Allison automatic.

Any "hot rodding" you do to this model coach (including the above suggestion), WILL require increased cooling capacity - the 7s were marginal right out of the factory.

In the meantime, while you ponder, run the darned wheels off the thing!

FWIW & HTH. . .


RJ Long
PD4106-2784 No More
S13406 1978 MC-5C Converted
S14947 1980 MC-5C Shell
Cheney WA
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