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Author Topic: 6V92TA vs 8V92TA  (Read 4455 times)
i12fly2medford
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« on: September 09, 2007, 02:04:51 PM »


Hello everybody,

I have been looking through the posts here for a couple of weeks now, and today I decided to join and post.

I have decided to get a bus, hopefully before Christmas, but that depends on the bus.  Cash is in hand and I'm ready to go.  My Grandfather converted an MC8 back in 1992, and he is available for my consultation.  I have my own experience as well, having gutted and remodeled my house, including all new electrical, plumbing, and a 1200 sqft addition.  Anything else I need to know, I'm hoping that's what you guys are here for.   Grin

My question right now is regarding the difference between the 6v92TA and the 8v92TA.  I understand that horsepower and torque are quite a bit higher on the 8v (I believe in the neighborhood of 100 HP more based on MCI's website), but I'm wondering what kind of practicality does that offer?  I travel primarily on the East Coast, but do take trips to the Midwest, and plan to take a trip to Oregon, and Alaska in the next few years.  Very mountainous terrain there.  Will I be looking at a significant speed / power reduction with the 6v in normal fairly flat driving?  Is there going to be an issue with the 6v not making it up certain grades, like a 4 mile 6% grade for example?

I'm interested in hearing from anyone with an MCI 102 with the 6v92TA and 8v92TA with the Allison 740.  What are your experiences with these engines?

I thank you in advance for your input...

Wade Israel

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JohnEd
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« Reply #1 on: September 09, 2007, 02:47:16 PM »

Fly,

Do a search for "8V92 Radiators".  It is a few pages back in the posts.  Knews u can use.

Welcome to the board.  We will be looking forward to learning from you, as well.

John
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« Reply #2 on: September 09, 2007, 02:58:51 PM »

Wade,
Welcome to the board.  I'm afraid I'm not much help with the specifics re. HP, etc. on the DDs, but there is a lot of knowledge and experience here.  These guys are the best!  I'm a wannabe, hoping to find the right bus, already converted, in the very near future.  You've come to the right place for help and comarodary...comoradie...comorody...friendship.
I'm near Roanoke, about 4 hours from you.
Dennis
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cody
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« Reply #3 on: September 09, 2007, 04:35:51 PM »

Hi and welcome, I can't speak to the 8V but I do have the 6V in my eagle with the 740 allison and I have all the power I need for what we do, we travel all over the midwest and some out east, the terrain varies from flat to very hilly, haven't had any experience with real mountains like would be found out west but we can travel at highway speed without any problems at all, generally maintain 70 or so on the interstates without a whimper from the bus.  I would think that either motor would serve you well as long as it had been maintained properly in the past and you service it as needed.  The best advice I can offer is to have a qualified mechanic inspect any bus that you feel would be a good candidate for what you want, it's small money that can save big expenses.
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Jerry32
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« Reply #4 on: September 09, 2007, 04:58:56 PM »

welcome to the group, I have a 8v92 and find that it will not pull the large western mountains in fourth but drops to third and makes about 40- 45 MPH. I live nest to the mountains in the west in eastern Oregon. and cabbage hill is about 30 miles from me. So no matter what either enging will get you over the mountain and none are going to do it at cruise in 4th gear Jerry
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1988 MCI 102A3 8V92TA 740
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« Reply #5 on: September 09, 2007, 06:38:49 PM »

I agree with Jerry ... I have a 8v92ta 475hp with a 6 speed and I have to gear down to 5th on 6% grade end up around 45 to 50 MPH up the hill in eastern BC. A  6v92ta 350hp would be down to 2nd on a 4 speed tranny 30 to 40 MPH
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Nick Badame Refrig/ACC
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« Reply #6 on: September 09, 2007, 06:45:44 PM »

Hi Wade,

Welcome!

And thanks for posting.

I hace a 102C with the 8V92 and 740. Lots of power to climb hills along with enough to tag along my 6900lb Yukon.

Feel free to contact me with any questions.

Nick-
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« Reply #7 on: September 09, 2007, 08:08:57 PM »

I agree with Jerry ... I have a 8v92ta 475hp with a 6 speed and I have to gear down to 5th on 6% grade end up around 45 to 50 MPH up the hill in eastern BC. A  6v92ta 350hp would be down to 2nd on a 4 speed tranny 30 to 40 MPH

Most 6V92s in a bus won't be set to 350 HP unless hot rodded later on or maybe if ordered as a conversion shell.

My Series 60 is only 350 HP and I'm not looking forward to some of the grades on I80 through Wyoming, Utah, and Nevada.  I do have more torque than the 6V92 so that is one redeeming thing.
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TomC
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« Reply #8 on: September 09, 2007, 09:14:02 PM »

The nice thing about Diesels, as compared to gasoline engines, is that if you drive a large engine at the same speed as a small engine, you'll get very close to the same fuel mileage.  But with the large engine, you'll have the option of pressing harder on the accelerator if you want to make some time. 
The buses were originally equipped with 80 injectors that would get you 300hp and 900lb/ft torque for the 6V and 400hp and 1200lb/ft torque for the 8V.  80 injectors are a good economical size, that could be driven with your foot on the floor all day and not hurt the engine.  Most like to increase to the 90 injectors that will give you 340hp and 1050lb/ft for the 6V and 450hp and 1350lb/ft for the 8V.
My bus weighs in at 31,000lb and pulling my 3750lb car, with my 375hp and 1125lb/ft torque from my turboed 8V-71, I am quite pleased at that power output.  But personally, if I were in your shoes, I'd find a bus with the 8V-92 with the original 80 injectors-that would be a good set up.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #9 on: September 10, 2007, 04:12:05 AM »

I personally would go with the 8V92. When I bought my bus I picked it up in Reno Nevada and drove I80 all across the country in March of 2005 back to Connecticut. Even though it was not converted yet and all the seats were gone we cruised over the mountains of Salt Lake city in 6th and had no problems. Mine is equiped with a six speed Spicer standard as to compaired to the 740. The 740 would have been great also but I have finally learned to do some clutchless shifting with the spicer which makes it easier once you learn to play with the rpm's.
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Steve Canzellarini
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« Reply #10 on: September 10, 2007, 02:01:16 PM »

Stephen(scanzel),

Everybody, or nearly so, has gone on record recommending the "automatic" strongly.  I have read a couple of posts over the years by people that did convert and their feeling was that they would not have converted if they had known what a serious hit they were going to take in the mpg department.  Only a couple, now mind you.

A couple questions, if you will.  What is your top speed?  How many mpg do you get on average?  What is your max speed in first?  Is you 8V92 a mechanical or DDEC?  I assume you don't have an air to air intercooler between the turbo and intercooler.  How much boost are you getting at full throttle?  I think your data will be of some interest to many people besides myself.

Thanks,

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
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« Reply #11 on: September 10, 2007, 04:21:08 PM »

Stephen(scanzel),

Everybody, or nearly so, has gone on record recommending the "automatic" strongly.  I have read a couple of posts over the years by people that did convert and their feeling was that they would not have converted if they had known what a serious hit they were going to take in the mpg department.  Only a couple, now mind you.

hi john
when you say "serious hit" are you saying there is a big difference between the automatics and the standard transmissions??....in the m.p.g.... and how big..
what can i expect to get with either??/
im just still in the looking stage,but had my mind set for a automatic ,but if theres a big difference and all this talk about trouble going up some hills ...maybe it would be better to buy one with a standard transmission...any comments
thanks
scottie
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RJ
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« Reply #12 on: September 10, 2007, 10:39:56 PM »

Wade -

All else being equal, you'll be happier with the 8V in the long run, much "fatter" power curve than the six.  Has the torque to maintain speed on minor grades (freeway overpasses, for example) that the six will slow somewhat on.  Generally will pull most grades one gear higher (3rd vs 2nd) than the six, too.  Both will provide satisfactory RV service when properly maintained and driven.  The six will return slightly better fuel economy.

Here's an example of the difference between a 6V92TA and an 8V92TA, using the 300-mile run from Fresno CA to Reno NV.  The first 180 miles or so is flat up the valley to Sacramento, then east on I-80 to Roseville.  Just east of Roseville, you start climbing the Sierras, foothills first, then increasingly steep 4, 5 and 6% grades for 70 miles until you crest Donner Summit at 7,229 ft elevation, before dropping down into Reno.  The 8V92TA-equipped coach will pull into Reno all of maybe 10 minutes ahead of the six-powered coach, and burn about  5 - 10 more gallons of fuel in the process.  BTDT, lots of times.

Another example, and this one really is more dramatic.  On the 400-mile run from Fresno CA to Las Vegas NV, the 8V92TA-equipped coach will arrive almost an hour ahead of the 6V.  The reason here is that there are lots of long shallow grades on I-15 between Barstow and Vegas.  These are just steep enough that the six will have to drop from 4th to 3rd, and stay in 3rd for miles on end at 50 mph, whereas the 8V will keep on running 65 -70 without hardly breaking a sweat.  Interestingly, on this run, the 8V gets better fuel mileage.

Doesn't matter if it's a stick or an automatic, running times are about the same.


John -

Using only STOCK MCIs as an example, both the 4-spd stick shift and the HT-740 automatic max out at about 15-20 mph in first, 30-35 mph in second, 45-50 mph in third, and around 75 in fourth.

Obviously, tire sizing, rear axle ratios, and different gearboxes will change these numbers, but this is a good, general guideline.

FYI, it's the GMC V-drive folk who take the biggest hit, fuel-economy wise, when switching from the OEM 4-spd stick to an automatic.  Due to the design of the V-730 automatic, between the different bevel gear ratio and only being a three-speed, the combination combines to drop the mileage anywhere from 2 - 3 mpg vs the stick shift.  This is not as much of an issue with T-drive coaches.


Scottie -

Fuel mileage is sort of a moot point when you're talking about a vehicle that has the aerodynamics of a BRICK!

However, based on my 25+ years of experience in the bus industry, I can tell you that most 40-foot, three-axle coaches with OEM two-stroke Detroit powertrains get between 5.5 - 6.5 mpg overall, regardless of whether its a stick shift or automatic.  Those folk who run only in the flatlands will do slightly better, those of us who have to deal with Rocky Top will get slightly less.

You will always wish you'd bought the automatic when you get stuck in rush hour traffic, find yourself on city streets with poorly timed stop signals, or trying to wiggle your way into a campsite.  For overall driving convenience, you cannot beat the automatic, even if the fuel mileage suffers somewhat (about 1 mpg city, 0.5 mpg highway).



Wade, Scottie, and other newbies/lurkers -

You must change your mindset about driving habits/styles when you get behind the wheel of a bus, because it's completely different than a car (or a stick 'n staple RV, for that matter).

Remember Aesop's fable about the Tortoise and the Hare?  This little fable becomes an excellent analogy when it comes to operating a coach.

If you expect Hare-like performance out of a bus, you're going to be severely disappointed.

OTOH, if you treat the experience like a tortoise, you'll have a GREAT time.


FWIW & HTH. . .

 Wink



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RJ Long
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« Reply #13 on: September 10, 2007, 11:37:00 PM »

Scotie,

I think Russ covered it in his excellent post.  3 mpg is a "serious" hit.  I don't remember that it was a V drive.  My memory is that the "T" drive guys were talking about a 2 mpg reduction.  I am not contradicting Russ as he has first hand experience in many coaches over many years.  I can say that the mpg reported by different people would lead you to believe that they are driving different airplanes.  Big spread!  6 to 7 is what I hear about the 8 most of the time.  If I had one and couldn't get 7, I would be trouble-shooting.  Met a guy with a Sceinic Cruiser with an 8V71 with a three speed stick that swore a holy oath that he got right at 10 mpg and he was a trucker by profession and equally amazed.  No matter what you have, your driving technique will impact mpg performance dramatically acording to everyone.

Here again, from the professional drivers to the ther rest of us the advice is to get the automatic.  I think the ultimate bus transmission weapon is the "select shift" for a manual engine and "Auto select(?)" for an electronic engine.  10 or 13 forward gears from a Road Ranger and a slot for every occasion and 10% better mpg over a standard shifter.  You won't find that as OEM equipment...you have to do that one.

Food for thought.

Good luck,

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
—Pla
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« Reply #14 on: September 11, 2007, 04:22:28 AM »

thanks guys
thats what i figured,i just wanted to hear it from the pros!!
scottie
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