Changing engines: 8V71 to 8V71T in MC8 with HT740

[ChuckMC8]

 As most who follow the board knows, I have engine woes in my MC8.  At this point, I am considering all options, so I would like to increase HP if I have to change engines. Prices that I see for 8V71T and 6V92TA Silver are close to the same. I figure that the 8V71T would have slightly more hp capactiy (370) vs the 6V92 (350) and be an easier swap since I have the 8V71N now.
What would be involved in swapping in the 8V71T? (I have HT740D) Will the rads that I now have (GC) cool the turbo engine? Thanks

[TomC]

6V-92TA would be a nice swap.  But personally, I don't like the 92 series (even though I had an 8V in my first truck-lots of preventative maintanence required).  The 71 series is a much less stressed engine and I like that it has dry cylinder liners that can't leak or weep when left sitting for long periods of time. 

A couple of things you can do to an 8V-71.  First, like what I'm going to do-add a turbo from an early Series 60 that has a waste gate, adjust the turbo to only put out 7-9psi, change the piston rings to turbo rings (seal better under pressure), add an air to air intercooler (already have it), increase the injectors just one size to 70's (either N70's or 7G70's that have more injector tip holes for better dispersion pattern for a bit more efficiency), then you'll have about 345hp and 900lb/ft of torque.  This I'm doing mainly for smoke control and maintaining horseypower at high altitudes.
Second is to rebuild the engine to full turbo specs-either using your exsisting block with it modified to the big bearing bypass blower with either the air to air intercooler or with another block that has the aftercooler in the valley of the engine below the blower-commonly called the TA block.  With this setup, you can get a comfortable 400hp with 1,200lb/ft of torque.  I think Don Fairchild (who is going to do my modifying) has his 8V-71TA pumped up to around 550hp.  Now that would be a runner!  Personally, as you said, it will be much easier to stay with the 8V-71-or maybe use an 8V-92TA set up around 400hp?  Many ways to go-none that are really wrong-none that are completely right.  Good Luck, TomC

[Ncbob]

Hi Chuck,  I'm going to jump in here, not because I have a lot of first hand knowledge to offer, sometimes playing Devil's Advocate can move a problem a bit faster toward a solution.

You have an engine which would be classified as a good core. Your coach should have enough room and be receptive to an 8V71T.
Like Tom, I don't like wet liner engines...don't care who builds them.  Wet liner engines have an "O" ring at the top and bottom of the liner which is surrounded by coolant.  Every time a cylinder fires is places tremendous stresses on the liner.  It flexes outward pushing the coolant outward as well..but once the internal pressure is removed the coolant smacks back against the outside of the liner.  I'd equate it to a bolt of lightning passing through a cloud.  That creates a space and the resultant thunder we hear is the displaced air colliding with itself at the speed of light. The pitting of liners, and ultimately fractures causes too many engine failures

A dry liner engine, like the 8V71, has precision fit liners to a solid, cooled block.  That is why the 'liner to block' fit is so important. The dry liner can't and won't flex as much as the wet liner because it's backed up with solid cast iron.  And if the fit is correct there shouldn't be cooling problems or vertical motion of the liner.

No one asked my opinion but I'm going to offer it anyway.  Wet liner engines are cheaper to build than dry liner engines!  Front wheel drive cars and trucks are cheaper to build than rear wheel drive vehicles.  They sold us a bill of good on that one too!
Can anyone imagine a horse...with front drive?  Or a Mule?  Or an OX?  The animals which provided the power to settle this great land!  If they were re-engineered we'd still be back in the Fontier days!

Manufacturers base their decisions on cost of product..not how well it will serve the end user.  Look at what we've been stuck with!

I am confident, Chuck, that there is much more valuable information out there with the specifics of bringing your dream to fruition and I will repectfully bow to their superior knowledge on the nitty gritty of you situation.

I'm sure you find the ultimate solution and I hope you share your sucess story with the rest of us.

Bob

[ChuckMC8]

Looks like I found a decent deal on a low mile 6V92. How much problem would that be to swap in where 8V71 was? (MC8, 740HD) I know the lower pulley must line up to run the fans. I assume that the engine is shorter, so does that mean that I would have to find a longer driveshaft? Other problems with this swap? The 692 and 871T are the same price..............hmmmmm.....but the 692 is local and the other is 700 miles away.
   It's not an emergency, the bus is in my yard. (I am truly grateful for that. It could be in a parking lot somewhere) I'm considering my options and kicking around ideas. Main thing is to have a trouble free result without reinventing the wheel and would like to have a little mo power. (More than a 7V71......8V minus 1 cylinder)
thanks for the advice. ;-)

[NJT5047]

The 6V92TA would make a better choice...dry liners have their limitations too.  While dry liners are simple, they don't transfer heat as well.    6V92T MUI would be more dependable compared to a high HP 8V71T.   No one can argue with the dependability of a 6V92T.   They are great engines. 
A 6V92T MUI will make an excellent, more efficient repower.   When compared to an 8V71T, a 6V92TA at 330 or 350 HP may be less stressed...it was designed with the turbo.  The 8V71 was not originally designed for a turbo, and the pistons and liners should be changed to lower the compression to utiliize a turbo..not everyone agrees with this, but??
A 6V92T is a shorter enigne...perhaps a longer drivehsaft?  Move motor mounts to accomodate...or buy a 6V92T cradle and driveshaft...maybe the donor bus has these items.  You're correct that the engine pully must align with the blower drive. 
An 8V71T would be fast, and if it's pumped up, would outrun a 6V92T, however, if such performance is used, your transmission will suffer, and the engine would be difficult to cool in an MC8.  A 6V92T may require more radiator than you have if your rads are OEM MC8.   Both engines will fit into your engine room with factory fittings....exhaust. etc.
No problem with the turbo on top of the engine.
Gotta go, JR

[Beatenbo]

My MC8 was 8V71 my 9 was 8V71 My 96A3 was my first 6V92 and my C3 is the same. I will take the 6V92 any day.A friend of mine lost an engine in his 9 , 8V71.  Detroit Diesel in Denver put him in what they called a new engine. I didn't know they made a new 8V71. I later saw it was 8V71 Turbo. They replaced all every thing but radiators. Charged him 22,000. and he cannot drive over 60 mph without overheating. The 8s and 9s had radiators designed for the 55mph speed limits in those days. BE PREPARED TO REPLACE YOUR RADs Good luck.

[Stan]

It would be a lot less work to put in the 8V71T. You would have some pipe work with the air intake and the exhaust, but this is pretty much non technical work.

  If you want to run your bus with higher HP (either engine) you will have to incease the cooling capacity. MC-8 buses are marginal cooling with standard engine so you may have to change to bigger rads and/or bigger fan.