8V-71 to 8V92 swap

[Flyingk9]

Ok I have researched this and read quite a few posts on here about the subject and would invite any and all intel on this subject. I currently have a HT 740 allison trans off the 8V-71 and was wondering if it can be used on the 92 ?? the 71 is NA and the 92 is a turbo.
question is will the air cleaner that's there be able to handle the turbo with some mod's to the intake side or would i have to replace it with a larger style same with the muffler.
I have purchased a totally rebuilt 92 with turbo and jakes for 2500.00(yes $2500.00 and long story) and looking to swap out my tired 71 in my MC-8.  So any tip's hint's or pitfall's to watch out for would be most helpful.

[John316]

Flyingk9,

Welcome aboard. Sounds like you will have a fun swap there. I am sorry, I don't know anything about your questions.

However, I will give you some advice. You should at least sign your name, or update your signature. Doesn't have to be a last name, your first is fine. Also, you should mention what kind of bus you have, where in the country you are located (general location is fine), that kind of thing.

The more info you give, the better.

Again, welcome aboard.

John

[akroyaleagle]

You will get many comments on this.
Having done this, here are some of mine.


I changed my 8V71N to a 8V92TA. If going from 6V92 to 8V there are many parts you will already have.

Here is some information for you to consider:

There are a LOT of over the road trucks running around at 80,000
pounds with the 495 converter.
With the 92 your shift points should be:

1-2 1900-2050 rpm
Lockup - 2000
2-3 2025-2100
3-4 2000-2100

The HT740 is part # 6884538. You should recalibrate the valve body
to part # 23040804 Specs.
The 495 converter is 2.391 ratio, 496 is 1.78 ratio.

Upon the advice of a lot of experienced folks I know I did NOT change the
converter. Mine works great but I do not hammer it from a stop. I use the power
to climb.

Here are some of the parts you will need for a truck engine: (If you obtain a coach engine, it will have some of these)

8928605 low profile blower housing (could be 8922167)
5104464 low mount engine bell housing from a Ford Truck with a 6v92 or 8v92
9402015 crankbolts (12)
23045507 adapter hub, flexplate to crank
5143106 Y manifold
8922502 front turbo brackets
E8927027 Garret Turbo A/R .81
5101174 double cooler w/wp pipe

A BIGGER RADIATOR!!!!!!

Be sure to plug the 2 holes (5/8")between the
blower and governor housing!

Drill the lube orifice for the front blower bearing if you go with the optional turbo (front of engine) mount.

Check the the SN of your engine. Silver 8V92TA began with F73594. It should probably have 9G90 injectors.

You will need a much larger air cleaner. Over 1600fpm! Bigger is better! Donaldson helped me with this.

You will need a bigger exhaust system including muffler.

For what its worth, if you patch this engine in, you will probably end up with a lot of money in it and never be happy with it.
 
If we can be of further help, ask.  Good Luck, Joe

[lostagain]

Like Joe said,

you will need bigger air cleaner (1600, 1800 cfm), bigger exhaust (7"), bigger radiators and squirrel cage fans (off of a MC9). Also, the turbo will have to be mounted on the side. There is no room on top, unless you raise the bedroom floor. It is doable, and has been done, but is not as simple as you would think.

JC

[bevans6]

You may need to reconfigure the back of the engine where the accessories live, to match the MCI model.  Power steering pump, 75 degree tilted air compressor, etc.  I thought that on an MC-8 there might be enough room for a turbo on top of the engine, but I can't remember seeing one.  The engine cradle and motor mounts should work between an 8V-71 and a 8V-92, that would save a lot of work!

Brian

[Sam 4106]

Brian,

The turbo is on top of the 8V92TA in our MC 8, but I can see where there wouldn't be room on top in an MC 5C like JC has. In an MC 8 the floor is above the wheel wells, so there is more room than in an MC 5C, where the wheel wells protrude above the floor. Our MC 8 has MC 9 radiators in the normal positions, plus one MC 8 radiator, with a large 24 volt electric fan, in the area where the over the road A/C compressor was. Never overheats. Our MC 8 has the bigger air cleaner and muffler too. There is more to changing from an 8V71NA to an 8V92TA than it would seem at first.

Good luck, Sam

[akroyaleagle]

I am not knowledgeable about MCIs. There may be "The complete Idiots guide to MCIs". Probably more knowledge here on this board.

In the Eagle, the 8v71 motor mounts would not work. That's why you need the Ford bell housing mentioned earlier. You could just do what I did and re-engineer the mounts. That is not for the faint hearted!

Here's a link to Rons' new website. A call to him can solve a lot of problems at very reasonable cost.




http://www.ronthebusnut.com/

[TomC]

8V-71 and 8V-92 are basically the same block on the outside. But-the 92 has the big front vibration dampner that will put the lower pulleys that power the overhead blower out of alignment. Most just move the engine back the approximate 2" to compensate.
Turbo can be mounted most anywhere. You could reuse the low profile blower inlet if you want.
You will have to change to a larger air cleaner-8" is suggested. If you have a 5" exhaust system, that's enough-just change the muffler to a turbo rated muffler.
Largest radiators are needed. Is your Allison cooler built into the side of your 71, or is it a separate shell cooler.
Keep in mind the 8V-92 is the hardest to cool.
The HT740 will work well with the 8V-92TA. I would just use as is, possibly changing out the torque converter.
It will be alot of work-I would just turbo your 8V-71 and be done with it, but you're doing the work. Good Luck, TomC

[RickB]

Tom C,

I was under the impression that the 92 block is longer and taller than the 71 I seem to remember that it is a little over an inch longer and nearly the same in height.

FlyingK9, I have researched this extensively and unless you buy a motor that came out of an MCI you better be an advanced mechanic or a man of great means who can pay alot of money to have someone do the changeover for you. If the bellhousing is not the correct one for the MCI alternator,power steering pump and compressor you will either have to find an adequate belt driven alternator or you will have to change out the bell housing, one of the camshafts will need to be pulled and replaced with a camshaft with a gear drive for the alternator. The bellhousing changeout is a fairly difficult undertaking for experienced DD mechanics and lastly I believe there is a change you may have to make to the gear drive on the rear of the engine. If I'm correct about the length of the motor then you will need an 8v92 MCI cradle as well. If you're going to use the 740 you will need a dual oil cooler on the drivers side of the block (it dissipates the added heat that the transmission generates) which are spendy and hard to find. These things are all doable but they are difficult and they do require solid mechanic skills and tools and great attention to detail.

For the above reason's I have narrowed my choices for repower to an existing rebuilt or low mileage 8v92 that is already equipped for the changeover. Or a deal like yours that I save so much money on that I can take the motor to my friend Curt at Central Truck here in Minneapolis who can do the retrofit in his sleep and provides a solid warranty as well.

If you've got a shop full of specialty DD tools, a lifetime of mechanic experience and some real time on your hands I 'd be all in if I were you but after researching this deeply I have decided I will keep looking for a repower that I'm capable of with my tools and my experience.

I bought an 8v92 a couple years back, stuck a bunch of money in it and it basically blew up in a shop and we hadn't even begun to address the retrofit issues which were in the $3500-5000 range

Good luck and keep us informed

Rick B

[robertglines1]

If new low cost $ motor is military you need to do your home work.  A member just did it and was high dollar labor intensive job.  If not bus engine simple things as Oil pan depth can be a high dollar cost;some if new over $1,000. Not to mention  air compressor and alternator fit. Does your new engine come with computer that is compatable with change over? or is mechanical.  If it was one of the recent gov engines in Ga search back post for what had to be changed to do job.  Was a lot of post about it and a great out come. CK Bevans6  if memory serves me correctly.   Bob

[Flyingk9]

Yes it is a pre computer motor complete with starter,28 volt alt, air compressor.The power steering  hole is there but not the pump.  It is a military rebuild for truck app.. as for everyone's concern I am a skilled mech. and to give you an Idea I just pulled a 8v71N out of a mc-7 parts bus in 2 1/2 hours by myself. I also can weld and fabricate and machine part's as required. So far as i can tell my biggest problem is locating a bigger air cleaner, Bigger radiators and muffler.

Robert     

[robertglines1]

Follow what others have learned and you will be ok with your skills. Past mistakes by others save you $$$.  I learn something new every day.   Plus they have the referance for the change over parts.  Share your experiences. Bob

[luvrbus]

The 8v92 block is longer than a V71 the  vibration damper takes a little more room also but a 8v92 does fine without 1 as long as you stay under 425 hp

1000's of the 8v92 in service without a vibration damper so if you need the space without 500 hp they do good without a vibration damper


good luck 

[HB of CJ]

Excellent answers already given way over my head.  About the only thing I can add is that we have not yet heard much about the necessary large air to air intercooler.  And, what is the rated set HP of your rebuilt mighty 8V92T?  Are you going to be happy forever with that power?

One experienced answer suggests you may not be.  How about just changing out the injectors to something more appropriate, (like much larger) a turbo change and consider a large air to air intercooler.  I think, (dangerous) you can might leave the HT 740 convertor alone.

Will a proper conversion support over 600 hp?.  Maybe.  My point is that if you are going to go to all this work, why not make it pay off?  Don't set yourself up for a big disappointment.  Intercooler, vib damper, injectors, boost, intake, exhaust...and radiators.   HB of CJ (old coot)

[bevans6]

My adventure with a military 8V-71 may have some relevance to your project, maybe not, but I like to get people to read it anyway    http://www.busconversions.com/bbs/index.php?topic=21836.0

Man, not a single person ever replied to it, that makes me feel a little silly for posting it.   

Anyway, point I wanted to make is probably obvious to you, but it the power steering drive gear and coupling isn't there, you have to remove the rear engine plate along with all the drive gears to install it.  That means you get to install a new crank seal and gaskets, plus all the sealing washers on the bell-housing, which is probably not a bad idea anyway.  It would be neat to go to a belt drive 50DN alternator too, if you are taking the back off anyway.

Brian