10spd in my MC7?

[DuaneMC7]

 I am just getting started on my MC7, now I know I want to get rid of that 4 spd gear grinder and install something that will get the most out of the current 8v71 and be a good match for a possible engine up grade later on down the line. Would like to hear from anyone that has done this swap and find out what needs to be done.

Thanks for any help with this, Duane

[NCbob]

I'm sure it's been done...and you sure make my mouth water at the thought of it...   but inasmuch as I own an MC5A (a great bus) it ain't in my future.   Oh! (dreaming) Lord , give me just 4 more holes!!!!!! 

Ncbob

[TomC]

In reality, torque is torque and the 8V-71N with 65 injectors only puts out 800lb/ft.  No matter how many gears you have, you're going to slow down on the grades.  What a 10 speed will do is allow you to select from more gears to go up the hill, but at best may increase your hill climbing by 5-10 mph (and that's being very optimistic).  What would serve you better would be to either turbo your engine (more or less a complete overhaul for full turboing) or install a 6V-92TA with 350hp and 1050lb/ft of torque.  That 4 speed is rated at a minimum of 1200lb/ft capacity.

I am most likely going to have Don Fairchild in Bakersfield install a smoke turbo with a one injector increase from 65 to 70's.  What we're going to do is I am going to have a custom air to air intercooler made (13" of space in front of the radiator), Don will pull the two piece pistons and replace the rings with turbo style rings (but keeping the same two piece pistons at the higher 18.7 to one compression ratio), install a waste gated turbo and keep the boost around 6-8 lbs (instead of 25-28 lbs on a full turbo). I figure this will increase my power from 318hp to about 350hp and the torque from 800lb/ft to about 1000lb/ft.  But most importantly will maintain that power in high altitudes without smoking (the politically correct thing to do) since any black smoke is fuel wasted rather than turned into power.  Besides, how many hills have you gone up with the bus slowly loosing speed (just doesn't fall on its' face right away-compared to trucks that slow down quickly to grind up the hill) to find yourself having to go up with the trucks about half way up? Personally I know just a little more power would maintain the speed.  Will keep you posted, but not going to do this till the end of the year when it is cooler in Bakersfield.  Good Luck, TomC

[TomC]

A follow up- if you want to really increase your performance, have an Allison HT740 installed.  While it won't increase the speed going up the hills, the acceleration on the flats is second to none.  The pleasure of driving is outstanding (this coming from a truck driver that drove nothing but 13 speeds [still a great transmission-over the 10speed anyday] for 21 years and 1.3 million miles worth) and then anyone can drive your bus in a pinch.  If you don't believe me, drive a bus that is similar to yours with the
automatic in it.  Granted you mileage might go down a bit, but just how many miles will you put on it over the entire time you're owning it?  Good Luck, TomC

[DrivingMissLazy]

Is there such a thing as a heavy duty 740? When I had my 6V switched to an 8V, the shop dong the work  informed me, after they had installed the larger engine that they were going to have to install a heavy duty 740 because of the increased hp. Since they screwed over me so bad on other things, I am just wondering if they screwed me on this also?
Richard

A follow up- if you want to really increase your performance, have an Allison HT740 installed.

[TomC]

Richard- the HT740 had a heavy duty version called the HT748-mainly for the transit and trash trucks that were making hundreds of starts and stops a day.  They had a hardened input shaft and tuffer material on the clutches, but if I remember right was just about all they did to the trans.  Your standard HT740 was rated to around 1,400lb/ft for continuous use.  I could see them having to install a different torque converter with a lower numerically stall ratio since the 8V puts out much more torque than the 6V and the torque converter will only transmit a finite amount of torque before blowing.  Good Luck, TomC

[DrivingMissLazy]

Thanks, Tom. I was just curious. Probably another screwing. I went in with an $8,000 estimate to switch out and everything needed and it ended up over $25,000 before I got out of there.
Richard

[rv_safetyman]

I think Duane posted a few more details on the BNO board.  One of his goals was to select a transmission for a future change to a four stoke engine. 

The HT740 is recognized as one of the most durable automatics ever produced.  It has been used in some large truck applications for loads up to 80K.  However, it has a 1:1 high gear.

If a person is going to go to a four stroke they really should have an overdrive transmission (cruise at 1500 for a four stroke vs. 2100 for a two stroke).  Generally the gearing can't be accomplished by rear end ratio and has to be done with the transmission.

On BNO I had suggested that Duane consider a truck overdrive transmission to replace his 4 speed.  Lots of gears, easier to shift and he would have the overdrive.  He did not get much response over there, so made this posting on MAK to see if he could round up a person who has done this conversion.

Bottom line, I agree that the HT740 would be great for his present bus.  It would be a fairly expensive conversion  (maybe 4K?).  It would not be the ideal transmission for the later four stoke conversion and he was looking for options for only one transmission conversion.

[DuaneMC7]

Thanks Jim, nicely  put.

[TomC]

Just to give you an idea on the realistic use of a HT740 with a 4 stroke engine, I believe you can get a 3.08 rear ratio drive for the axle.  If you have 11R-24.5's (478rpm), you'll have a 65 mph rpm of 1595; 70mph @ 1717rpm and 75mph @ 1840rpm, which is not to high considering all big gensets run at 1,800rpm.  If you have an engine that is putting out 1,450lb/ft of torque, based on a weight of 45,000lb, then your startability will be- 32%!  At Freghtliner, we want the turnpike startability to be 14%, on road 16%, on/off road 20%, and off road to be 25%.  So you'll be fine
For some of you that want to play around with startability, here's the formula.  First, take what you think is the heaviest your bus will ever be in pounds and multiply that figure by 10.7 and put that figure into memory.  Then take the starting torque of the engine (with automatics it is pretty much full rated torque since the torque converter can pump up to 12-1400rpm on starting), multiply by first gear, multiply by torque converter ratio, multiply by rear end ratio, multiplty by tire rpm and divide by the figure in memory and that's your maximum startability in percent of grade. So in this case it'll look like this:
1450 X 3.692 X 2.0 (torque converter) X 3.08 X 478 Diivide by 481,500 = 32.74%.  Good Luck,TomC

[coachcrazy]

kinda on the same subject( i didnt want to start a new thread) with all this talk about different trannies, engines and what not.  I was wondering is it in common practice to upgrade turbos and add  "twin" turbo or more setups and run propane injection on buses?  i ask this only because an aquantance of mine works at a deisel shop and they do these type of upgrades all the time to full size pick up and ocasionally tractor trailer rigs.  Deisel motors love working hard and are capable to tremendous amouts of prower with little effort, im surprised to see that more "busnuts" aren't taking advantage of the raw power hidden within the powerplants in your coaches. 

[MC7S50]

Duane

I have a 10 spd in my MC-7.  The first one was a RTD (direct top gear), and the current one is a RTO (overdrive top gear).  I can give you details if you want. 

John

[oldmansax]

John,

Please publish or send the details. I have a 7 & am thinking about the swap also.

Thanks, TOM

[belfert]

70 MPH at over 1700 RPM in a 4 stroke is really going to suck down the fuel.  They like to run a lot closer to 1,500 RPM for best fuel sipping.

Edit: My Series 60/B500 will run at 1650 RPM at 70 MPH.  I wish the RPMs at that speed could be a little lower.  For some reason, Dina speced the B500 as a 5 speed and had the second overdrive locked out.  I talked to a Dina engineer (now employed by MCI) and he claims it was done because the RPMs are too low with the second overdrive.  I don't understand it,  but I wonder if this was done due to lower driving speeds in Mexico or something.

Brian Elfert

[kyle4501]

The estimates I have gotten to swap my 4spd to 740 auto have started at over $5000 in parts only!

Where do I go for the $4000 install?