Turbo'ing an 8V71

FolkBus · July 04, 2015, 08:41:42 AM

Hello all,

Thinking about adding a turbo to my MC5A's 8v71. Considering I live near Ridgway, CO at about 6800' it might not be a bad idea. Other then adding the trubo and associated plumbing and hardware. What else should be done?

Thanks in advance for all of the wonderful knowledge on this forum.

--Mike

eagle19952 · July 04, 2015, 08:43:11 AM

change pistons...

bevans6 · July 04, 2015, 11:19:55 AM

Turbo has 17:1 compression pistons while NA is something like 18.5:1. You can overcome that with selection of turbo and boost level control, but older spec pistons and rings, particularly if worn, probably won't last long. The turbo boost significantly increases the temperature of the intake charge and just makes things hotter and nastier inside the combustion chamber, and the rings don't last. I put a turbo 8V-71 in my MC-5C, but I started with an NOS military engine that was already a turbo version and converted it to MCI. The story is in the projects page somewhere. The result is pretty good performance, for a bus.

Brian

Brian

HB of CJ · July 04, 2015, 01:12:49 PM

Might be cheaper just to find another starship. I mean a complete DD MUI 8V71 turbo engine. Just about everything is different. This includes the block, crank, rods, pistons, sleeves, heads, valves, injectors, blower bypass, blower seals, injectors, etc, etc., probably the oil and water pump, plus the turbo and the needed air to air intercooling system with radiator. Yikes!

Lets also consider the rest of the drive train. Water radiator(s), tranny, clutch, u joints, drive shafts, etc.. Where will it all fit? Dunno. How much will it all cost? Dunno that either. A bunch. But ... lots of folks are happy with just adding a soft turbo with not other additions. Just a slight booster. You might find this works great for you and the expense would be much less. HB of CJ (old coot)

wg4t50 · July 04, 2015, 01:26:16 PM

I would go directly to a 6V-92 @ 350 to 450 hp range,, have payed tbe games, the 6V makes more sense to me due to weight, cleaner running engine & power, more joy down the road.
Dave M

Ed Hackenbruch · July 04, 2015, 02:21:17 PM

Unfortunately the 644 tranny isn't rated for more than 300 hp.

wg4t50 · July 04, 2015, 02:59:11 PM

Ed,
No doubt, but the transmission would be a minor issue I think. Having played different engines & transmissions in the MC7.
Just my opinion.
Dave M

chessie4905 · July 04, 2015, 03:41:58 PM

To save money you can just add a turbo to your engine and add a good programmable water injection kit.

wg4t50 · July 04, 2015, 04:45:06 PM

Don't forget, your still stuck with a limited transmission capability. And you need to be above average to put the numbers together for a successful happy outcome.
Dave M

TomC · July 05, 2015, 09:54:26 AM

One of the first things I did was to have my 8V-71NA rebuilt with new liners (bored the block .010 over, but used standard liners to keep the pistons but with new rings). Had 18.7 to one pistons that are 2 piece with the tight transit bus type rings. I wasn't satisfied with the smoke (above 5,000ft with N65 injectors) and the lack of power with bad fuel mileage. I had a custom air to air intercooler made and had Don Fairchild turbo the engine. Because of having high compression, we only went up to 7G75 injectors, used a Detroit Series 60 12.7 liter turbocharger with waste gate to restrict the boost to 15psi, changed the blower to bypass, added fuel modulator to lessen the black smoke from a stop. The power went from 300hp @ 800lb/ft torque to 375hp and 1125lb/ft torque. The performance difference is quite noticable-actually have passing power at freeway speeds. The fuel mileage hasn't changed, but I can live with that since performance and smoke is improved. The MT644 will NOT take this kind of power. In a 5, the best is to convert to a 6V-92TA with 350hp and 1000lb/ft torque (9G90 injectors) with the nearly indistructable HT740 Allison. Which ever way you go, you'll have to increase your cooling. I still have to use misters on long hill climbs on hot days. Good Luck, TomC

eagle19952 · July 05, 2015, 10:12:24 AM

Quote from: TomC on July 05, 2015, 09:54:26 AM
One of the first things I did was to have my 8V-71NA rebuilt with new liners (bored the block .010 over, but used standard liners to keep the pistons but with new rings). Had 18.7 to one pistons that are 2 piece with the tight transit bus type rings. I wasn't satisfied with the smoke (above 5,000ft with N65 injectors) and the lack of power with bad fuel mileage. I had a custom air to air intercooler made and had Don Fairchild turbo the engine. Because of having high compression, we only went up to 7G75 injectors, used a Detroit Series 60 12.7 liter turbocharger with waste gate to restrict the boost to 15psi, changed the blower to bypass, added fuel modulator to lessen the black smoke from a stop. The power went from 300hp @ 800lb/ft torque to 375hp and 1125lb/ft torque. The performance difference is quite noticable-actually have passing power at freeway speeds. The fuel mileage hasn't changed, but I can live with that since performance and smoke is improved. The MT644 will NOT take this kind of power. In a 5, the best is to convert to a 6V-92TA with 350hp and 1000lb/ft torque (9G90 injectors) with the nearly indistructable HT740 Allison. Which ever way you go, you'll have to increase your cooling. I still have to use misters on long hill climbs on hot days. Good Luck, TomC

wouldja be willing to give a cost estimate for such an undertaking ? with any hobby cost isn't he whole reason for soupin up a motor butt it would be interesting to know

Bill B /bus · July 05, 2015, 01:33:31 PM

New radiators plus adding intercoolers - $8-10K
Engine, assume good, injectors and rack set up - $2K plus engine cost
HT740 - $2-4K
Note that is just purchase cost except for the rack labor.
Friend has a the 8V71 turbo. Had to install custom radiators, intercoolers and scoops to keep his temperature down.

Had the 6V92 turbo/HT740 combo until the Series 50 install. Now one radiator and one intercooler without high temperature concerns.

Bill

FolkBus · July 05, 2015, 09:12:04 PM

Thanks to all. Currently thinking Tom C has the best idea for me. As I have a 5A and live at 6800' and camp mostly above 8000' Liking the 6v92 ht740 idea. Being 35' makes for much better (easier) boondocking.

Again thanks to all.

--Mike

luvrbus · July 06, 2015, 06:02:43 AM

Cheaper to go the 6v92 and 740 route I figured Tom's set up cost him over 10 grand and he didn't even buy the turbo 2-1/2 inch manifolds

bevans6 · July 06, 2015, 07:02:54 AM

FWIW, and I'm only a guy who's done it, been there, got the tee-shirt, etc... My bus has an ex-NATO military 8V-71T that was originally designed for an M110 self propelled howitzer.

You can run a 350 hp 8V-71T in a MC-5C with stock radiators in good condition, and it's fine up to around 90 degrees ambient, in hilly interstate running at 65 mph towing an 8,000 lb trailer. Been there, done that. You can actually do it with 400 hp and N80 injectors, but man does it smoke with those sticks in it! I swapped to N75's.

You can run a 350 HP 8V-71T without an intercooler, after-cooler, charge air cooler or misters, same conditions.

You can run a 350 HP 8V-71T with a non-bypass blower, the way it came stock in the self-propelled howitzer it originally came in.

I know a guy running a 350 HP 8V-71T in front of an MT-64X (I don't know exactly which model, it's a 4 speed auto) in an MC-5C just fine.

I think the keys are - radiators in like new condition and the seals work. With that power, you don't need to be flat on the pedal, hence are running the engine under a little less percentage of full load. You can power up the hills in 4th gear, or run in third at 55 mph just off the governor at about half pedal, no smoke. Maximum cooling, and maintains speed easily.

An MC-5C can be a pretty light bus. Mine is right at around 26K lbs rolling. This improves the performance ratio so the cooling needs are less, and the light load makes the drivetrain run a lot easier. That MT-64X transmission is rated at a certain HP and torque, but there is a presumption that it is pushing against a certain weight of load as well. Lower that load and the transmission rarely actually has to transmit that power to the ground, even if the engine is capable of producing it.

The inter-cooler, etc are great ideas and if you can work them in are worthwhile, but they are in no way mandatory. My engine didn't have one in it's howitzer, doesn't have one in the bus, and yes, I lose around 25 hp and some efficiency, but on the other hand, I didn't have to install the cooler either. Engine runs good without it.

Bypass blower. Not a miracle cure for baldness, just a little valve that equalizes the air pressure on both sides of the blower and basically stalls it out. The blower is still spinning, still taking the power needed to grab chunks of air from the intake side and move them into the air box, you just gain a little efficiency from it not having to pressurize the air. My engine didn't come with one stock, and I wasn't about to buy a new blower once I figured out what the bypass actually did. Which is pretty close to nothing except add a little efficiency. Engine runs good without it.

6V-92TA with a 740 in a MC-5 would be a hoot, but the engine cradle is completely different from either the 8V-71 cradle for the MC-5, or the 6V-92TA/Allison cradle for the MC-9. You would basically have to find the right cradle - rare, the one for the 6V-71NA in the MC-5 would be the one you would need - or do some serious fabricating. You would also have to completely fabricate a new exhaust/intake system, moving the turbo, or raising the fan blower shelf and changing the fan drive system, because the normal 6V-92TA is about 6" too tall to fit into an MC-5 engine bay.

Just some perhaps contrarian thoughts. I obviously smoked over this extensively before I went the military 8V-71T route. Having such an engine basically fall into my lap helped the decision process immensely!

Brian