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Author Topic: Trans for a transit and an 8V92  (Read 2895 times)
TomC
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« Reply #15 on: May 17, 2007, 11:06:31 PM »

350hp is the highest I would take a 6V-92TA and keep it reliable.  The 8V-71, on the other hand is very receptive to bumping up the power.  Even my conservative 8V-71 with 9G75 injectors has 375hp and 1125lb/ft torque, which is more than the 6V-92TA.  I would feel comfortable with 9G90's in the 8V-71 with air to air intercooling for a power rating of 450hp and 1350lb/ft torque.  Now that would run with the big boys!  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #16 on: May 18, 2007, 06:55:07 AM »

Ahh... So many options!
The only reason I started with the 8v92 is because I figured that it is more reliable to get 450hp from a larger displacement engine that a smaller one. But Tom explained that the 8v92 will not be an easy fit, maybe impossible. Thanks for that Tom. Thats the stuff you just don't know till your into the project.
So I switched to the 6v92 over the 8v71 because it is roughly 300lbs lighter, and I reasoned that the newer design would be an improvement.
So Tom, you're saying that for durability, the 8v71 wins over the 6v92 at the levels I am reaching for?
Do you know if there is any difference structurally between the newlooks with the 6v71 and the 8v71, or was it a simple plumbing job and cooling system improvements to swap in the 8v71?


Thanks
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WorkingOnWise
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« Reply #17 on: May 18, 2007, 07:11:29 AM »

I just searched the forum and found a great thread on the hot rod potential of the 8v71. So the ?'s about the 8v71 are covered, except for what it takes to get one into a fishbowl the came with a 6v71.

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Keith
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TomC
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« Reply #18 on: May 18, 2007, 07:17:58 AM »

As much as I like the 8V-71, the fact that you have a 6V-71 lends it naturally to replace it with a 6V-92TA since it is exactly the same externally.  You will have to plumb up the turbo, most likely have to increase the radiator, air cleaner and muffler, but then you'll have close to twice the pulling power!  If you have N60's in the 6V-71N you'll have 210hp and 553lb/ft torque.  Switch to the 6V-92TA with 9G90 injectors and you'll have a comfortable 340hp and 1050lb/ft torque!  To me, a no brainer.  Your 6V-71N at best creates gentle acceleration with slow down at any hill.  With the 6V-92TA, you can have a cruise control that will keep up on the hills (it will slow down on the big hills, but going up a 6% grade at 40mph is a whole bunch safer than 20mph).  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #19 on: May 18, 2007, 04:36:18 PM »

Well Tom, you and some others here have sold me on getting the right coach for my wants and needs, and building on that.
When I thought I was kinda stuck with the 6v71/vs2 combo, I was good with turtle pace hill climbs and gentle acceleration. Now that we have soaked in the advice, we are really liking the thought of being able to climb a 6% grade at 50mph or better, so the 450hp mark is where we really need to get. Like I said earlier, I have seen a few 625hp 6v92's, but their like was 500 to 1000 hours tops, and 300 hours wasn't unreasonable. I figure death at 300 hours means they were wot all the time, or maybe 80mph is it were in a properly geared bus and not a boat, so I figure a road life of 24,000 miles. Not a reasonable life at all.
Is the 450hp mark on a properly maintained and well-cooled 6v92 reasonable if I expect 250,000 + miles from it?
In my studies I learned the the 92 series has basically rubber o-rings for cyl. liner seals, where the 71 series has steel, and this is it's weakest link if it ever is allowed to overheat.
At 450hp, is the 6v92 a good choice over the 8v71?
Btw, I really appreciate your time and willingness to share your experience with me/us.

Thanks
Keith
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TomC
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« Reply #20 on: May 18, 2007, 10:47:27 PM »

Just to give you an idea, the Detroit factory guys here in L.A. have built up a 435hp 6V-92TA DDEC for Jay Lenos Flex.  And that's about the highest they are willing to go safely.  Even at that, maybe 200,000 miles might be seen out of it.  The 8V-71 at 450hp will last alot longer than that, but who will be driving more than 200,000 miles over the life of their bus? Very few.  If you want to talk to the guru on hopping up Detroits, call Don Fairchild @ 661-391-4520-he loves to talk high horsepower Detroits!  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
niles500
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« Reply #21 on: May 19, 2007, 12:33:17 AM »

DDEC 8v92 ATEC 755 - dialed in at 515 HP, 1650 ft.lbs.,  108,000 miles - no leaks - less than 1qt oil per 5K miles

A proper maintained DD not abused is a beautiful thing - 46K+ GVW and climbs a 6% grade ACCELERATING -





why would I want to HOT ROD it?


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« Reply #22 on: May 19, 2007, 06:05:45 AM »

With the full timing we have planned, we figure we will put on maybe 60k miles per year, so 200k is a bit short for us.
Since the 8v71 did come in the newlooks and it is more durable, I think thats the way to go for us.
The other side is this. I understand that the DD's don't like do be ridden too softly. Most times, we won't come close to hitting max hp. What kind of problems can I expect running a 8v71 too gently, and how can I minimize or avoid them?

Thanks
Keith
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TomC
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« Reply #23 on: May 19, 2007, 09:06:27 AM »

I don't think that will be as much of a problem as you think it will.  While in town, you might be putting around lightly, but you should be flooring it every time you get onto the freeway just to be up to a safe speed to merge.  Even just cruising at 55 will be putting enough heat into the engine with the wind resistance pushing these bricks through the air.  And unfortunately (I know since I have an AMGeneral fishbowl) because of the shape of the fishbowl windshield, it drags extra air compared to a highway bus, so even more horsepower is needed for freeway cruising.  I have 4.625 rears with 11R-24.5 rubber that gives me 65mph @ 2125 rpm-of which the 8V-71 will do that all day.  Granted, it would be better to have the 4.11 ratio that would give me 65mph @ 1,888 rpm, but the $2,500 for the new gear sets says no (if I could find it).  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Dallas
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« Reply #24 on: May 19, 2007, 10:33:12 AM »

With the full timing we have planned, we figure we will put on maybe 60k miles per year, so 200k is a bit short for us.

Thanks
Keith

Keith,
60,000 miles a year? 1150 mile per week? 164 miles per day?
Just a question here....
Are you planning on working as you travel or is this going to be for pleasure?

If it's for pleasure you may want to stop and smell the flowers and enjoy the scenery instead of sniffing diesel and watching the bugs splatter on your windshield.

If it's for work, what kind of work do you do? It sounds like a pretty grueling schedule to keep up that much mileage.

I'm not doubting your figures, but I am interested in the need to put that many miles on a very used, high mileage coach.

Dallas
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WorkingOnWise
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« Reply #25 on: May 19, 2007, 02:51:22 PM »

Yeah, 1000 to 1200 miles per week can be a lot. We know the kind of work we want to do. Technology consulting and teaching to Christian ministries, schools and churches. We are working now to build the contacts and resources to allow us to do that. The way we imagine it, it will be 2 trips per week of up to 600 miles each, all in one day of driving. We will have time to "smell the roses" as much of our work will be in rose gardens. Smiley
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RJ
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« Reply #26 on: May 19, 2007, 07:52:07 PM »

Keith -

Based on your last comment, about what you'll be using the coach for, perhaps it's time to re-consider a few things:

I know you love the look of the Fishbowl.  I agree, they're a classic-looking coach.

However -

Will a Fish really be practical for what you want to do?

Think about that question a little in the context of all the "stuff" you'll be hauling for your consulting and teaching.  I've never met a teacher yet that doesn't haul a lot of "stuff" around with him/her.

Where are you going to put it?  Fabricated baggage bins in a Fish will only be about 18" tall.

600 miles in a day is 12 hours driving time.  That's at an average speed of 50 mph, which is what Greyhound uses for their schedules.  Yes, I know the big grey dogs blow past you at 70+ mph on the freeway, but that's the only way they can maintain their schedule.  With a Fish limited to 57 - 60 mph due to it's transit gearing. . . it's gonna be a LONG day!

Another point:  There is a BIG difference in the tuning of the suspension between a transit and a highway coach, even if they're both air ride.  As I pointed out in another thread, transits, by design, are set up for block-to-block operation, with less consideration given to ride comfort.  OTOH, highway coaches are tuned for ride comfort, as that's where they spend the majority of their time, running city-to-city or town-to-town.  Riders will NOT put up with an uncomfortable ride on a long distance journey.

So here's a suggestion:

Find a highway coach for your major traveling, and keep your Fish for a toy to play with when you get home.  Make a project out of restoring the Fish to like-new condition, then use it for parades, old car shows, etc.

This might be the most practical solution for what you want to do. . .

FWIW & HTH. . .

 Wink
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RJ Long
PD4106-2784 No More
S13406 Now
Fresno CA
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