Geoff & Clifford: 350 hp vs 350 hp OR 8V71 vs 6V92

[RJ]

Geoff & Clifford -

Am looking at two different 4106s, both with interiors that would work well for me.  Price for each is w/in $1K of each other.

One has a documented rebuilt 8V71T, tuned to 350 hp, and the OEM 4-spd manual gearbox.

The other has a 90% documented 6V92TA, also tuned to 350 hp, mated to a V-730.  (This powertrain came out of a transit, and the repair order for the rebuild is torn w/ the piece missing.)

Obviously, I know the arguments for/against the transmissions, but I'm curious as to your opinions about the two engines, since they're both tuned to the same HP specs.

TIA, guys!

[TomC]

The power maybe the same, but it has been proven that the 6V-92TA will get better fuel mileage. But-in this case since the 8V-71T has a manual and the 6V-92TA has the V730, the fuel mileage may nod to the 8V-71T.  Even though I have an 8V-71 turbo in my bus, I would get the bus with the 6V92TA and the V730.

As I've told some of my trucking friends, I've driven just about every type of truck transmission- 5spd, 6spd, 5spd with 2spd rear axle, 5x4 twin stick, 7spd, 8spd, 9spd, 10spd (both regular and Super 10), 11spd, 13spd, 15spd, 18spd, 10spd Autoshift, 10spd Ultrashift, 11spd Ultrashift Plus, 12spd Mercedes auto, 12spd ZF auto. But there is only one transmission that always brings a smile to my face, and that is an Allison automatic.  Nothing performs off the line (except for another torque converter automatic-like a ZF or Voith) like a torque converter automatic.  Now when Allison finally releases the new TC10 10spd twin countershaft transmission with torque converter and continuous power-that will be a winner!  Get the economy of the twin countershaft transmission with the performance of the torque converter continuous power shift transmission.  Good Luck, TomC

[buswarrior]

Someone have the torque curve charts for the two?

Somewhat academic, a 4106 with 350 HP is going to move out with either transmission or engine.

How's your left knee likely to hold out into the twilight years?

Which is going to move off with the greatest power with the least smoke, after everything has been adjusted to compromise the unintended attention that those infamous black clouds will attract today?

I'm thinking the belching cloud and the pull off the line would be high on my decision list between these two.

happy coaching!
buswarrior

[luvrbus]

The 6V92 is the better choice I doubt the 350hp  8v71 has any type CAC or aftercooler it would need to be later 8v71 block to accept a after cooler 

A standard 350 hp 6v92 or a souped up 8v81 for 350 hp should be a easy choice lol

[Utahclaimjumper]

I have favoured the V6 over the years for good mileage,,but they are sensitive to overheating,, if the cooling system is up to par then its a no brainer.>>>Dan

[Geoff]

I have favoured the V6 over the years for good mileage,,but they are sensitive to overheating,, if the cooling system is up to par then its a no brainer.>>>Dan

Actually, the 8V71T is notorious for overheating and cracking heads.  The 8V71TA with updated heads is a better choice, but it still gets less fuel milage than the 6V92TA.  The Silver 6V92TA with by-pass blower and MUI at 350 is bullet proof if mantained with an adequate sized radiator.  The 350HP does not overstress the 6V92TA in any way.  I'm very happy with my 92 and never hurt it in those few instances where I didn't reach for the radiator water sprayer early enough when going uphill while towing and the engine safety shut-down did what its supposed to do.

Can't wait to see you on the road, RJ!

--Geoff

[Lin]

Merely the choice between a standard and auto transmission would make it an easy decision for me.  We change out the Spicer for an Allison and, expensive as it was, I feel it paying me back every time I sit in the driver's seat.  If you buy the standard, there will definitely be many times that you will think to yourself that you made a mistake.  You will never b e driving an Allison and wishing you had bought the Spicer though.

As far as the engines go, they are both good.  There are many with preferences for one over the other, but no one could call either on a sub standard engine.  One possible disadvantage of the 8V71T in this case, would be the question of whether everything was upgraded to turbo spec parts.  I suppose the receipts may be able to tell you that.

[luvrbus]

Like Geoff said the 350 hp 8V71T was not that great it smoked and heated like crazy with the N75 injectors, the 370hp 8v71TA was a good engine it used modern injectors ,different blower, different heads,valves and water passage

good luck

[Boomer]

692/Allison.....and install a Stone Bennet shifter as soon as possible.

[luvrbus]

A wise man I love the Stone Bennett but electric over air but not the hydraulic


good luck   

[HB of CJ]

While nothing sounds better than a good 2-stroke Detroit, some Detroits just sound better than others.  A V8 Detroit just SOUNDS soos much better than the six.  Kinda like the difference between some foreign mill and an American V8.  I'm also wondering how they cool that 3 speed automatic?  Damm that clutch wear...full double clutching ahead!  HB of CJ (old coot) (who loves to shift for himself)

[twostick]

8v71t 968 ft/lbs @ 1400 RPM vs 6v92ta 1020 ft/lbs @ 1200. the 52 ft/lbs won't make a lot of difference but that 200 RPM difference in peak torque will make the 6V92 feel like it has a bunch more power and should be good for a mile or 2 to the gallon if driven with mileage in mind. Gear it to cruise at 65 mph @ 1600-1700. Neither one of those transmissions will do you any fuel mileage favors but there aren't a lot of options there. Does that 730 at least have a lock up converter?

The 8v71 if tuned properly will have that unmistakable eat nails and $h!t barbed wire snarl that the V6 can't quite pull off.

My first new truck was an 87 Freightliner with a 3406 that wouldn't get out of its own way. I took it back to Cat and they said they wouldn't even look at it until it had 100,000 miles on it. I told them it would have a Silver engine with 2 valve covers on it long before that. At least it would sound like it was trying lol.

Kevin

[chessie4905]

will a 6v-92 tolerate running all day at 22 to 2300 rpms? Something to consider if running the v730.

[luvrbus]

Since it started to drift anyway I try to discourage people souping up the 8v71 it makes no sense to me you take a 8v92TA set it at 350 to 400 hp it will out preform and get better fuel mileage than the 8v71 or 6v92, the 92 series don't mind 2200 rpm all day the 2500 rpm they don't care for that much

good luck

[RJ]

I try to discourage people souping up the 8v71 it makes no sense to me you take a 8v92TA set it at 350 to 400 hp it will out preform and get better fuel mileage than the 8v71 or 6v92

Clifford -

Good advice for T-drive buses.

Much, much harder to find LH 8V92TAs for the GMCs.

FWIW & HTH. . .