Allison 6 Speed GMC 401

[turbobill]

My only diesels are a Cummins B series with a mechanical P7100 pump, an NH series mechanical 250HP engine, a few Oldsmobiles with the DB2 pumps and a 6.5 Turbo diesel with a DB4 pump. All parts are dirt cheap for those engines and they are as simple as a rock. Had a couple of early Power Strokes and they seemed reliable.

I do like BB Chevy's and the 496 would be a good choice. Simpler and cheaper to maintain than a Duramax too. Maybe a 478M will come along or even a 637 V8.

[tommr]

Cummins engines are very heavy and the 6 cylinder doesn't fit. The 4BT fits. HP and torque are not all that impressive though. You are right though on reliability. Bus has 70 year old and 50 year old components throughout. Its the reason it sits in the warehouse. Needs late model updates. Reliability with the Duramax /Allison is excellent and servicing it would be pretty conventional.

[turbobill]

While I believe the 4BT's can be upgraded for more power, the torsional vibration of a big powerful 4 could become a problem with driveline/rear axle components. I recall some years ago, the 4BT conversions were popular in lighter vehicles but the torsional vibration created all kinds of breakage issues.

Years ago when I drove for Greyhound, we had some MCI 12's I believe that had the 4 cylinder series 50 Detroits. Sluggish of the line but held road speed well, even on grades. On the road, it felt much bigger than it was.

[tommr]

Had not heard that about the 4BT. I'm more inclined to stay with newer components. If we were using this only locally you could do minimal upgrading and use it for a long time. We have done 4,000 mile trips in 3 weeks. We need modern serviceable components. Everything needs repair and servicing--even late model. Parts availability is a big issue when you are 1000 miles from home.

[turbobill]

If you eventually pull the 401, I'd still be interested in it and the original Spicer transmission and clutch parts if you still have all of it. In the event you change your mind and decide to turbocharge, I can be of assistance.

[tommr]

Will keep it in mind Bill. Transmission stuff is gone. Remote shift tower went to Australia. Transmission is running a water well drilling rig in IN. Driveshaft and clutch went to MA. Thx.

[bigblockv6]

Originally Posted by tommr

Yes. the BB Chevy engines fit fine. Not all that different than in size to the V6. The 8.0L has made its way into new production school buses and those bus builders have designed a accessory drive system that incorporates an air brake compressor. It makes the BB Chevy an attractive option and crate engine prices are good. That said a Duramax eliminates 85 gallons of gasoline from the bus. 06.5-07 LBZ is the preferred Duramax swap engine. Aftermarket wiring is available new and reliability and parts availability is excellent. The 2012 and later LML/LMM Duramax has very little swap support from the aftermarket. You cant run them without the emissions. An entire body harness is required to accomplish that swap. Not likely a harness and a computer is ever available. But who knows?

What is used in school busses now is an 8.8 litre version not manufactured by GM. Though the block and components are supplied by GM the engines themselves are assembled by "Powertrain Solutions International" (PSI) to their specs and sold to Navistar for school busses. GM is going back into the medium duty truck business but will only market medium duty trucks as Chevrolet's, these trucks will be manufactured by Navistar under contract with GM. They will use a GM cab and powertrain on a International chassis, the Duramax Diesel will be the powerplant not the 8.1 or 8.8 litre V8. Word is GM is coming out with a larger 7.0 gas V8 based on the 6.0 V8, most likely a taller deck block.

[tommr]

Powertrain Integration is using the 8.0l from GM. GM has made it available in crate form too. Part# 19328586. Power Solutions Intl has I'm assuming a modified version of the 8.0. Theirs is the 8.8l. Both have devised a plate system to mount accessories on the front of the engine. Makes hanging an air brake compressor simple. Cheaper gas has made gas attractive again esp with the EPA regs on diesel engines. Diesel engines are expensive and the latest emissions very expensive to service. Fleet owners don't need those surprises and downtime. Both of these outfits have LPG versions of this engine. Its kind of cool how whats old is new again.

[turbobill]

Wasn't aware of those two companies. So I researched it and on the PSI website what do I see?.........a turbocharged big block Chevy. A good read too.

As you can probably tell, I'm a big fan of turbocharged gasoline engines, but their naturally aspirated 8.8L engine looks good on paper too. I hope it catches on as some seem unhappy with the V10 Fords.

At the last job I worked at, we had a fleet of diesel trucks. The medium duties spent a lot of idle and low power time and clogging DPF's was a huge, expensive problem. One new '16 Mack tractor I was driving had constant problems with the urea injection system and I spent a total of a two days on the road in various Mack shops while they tried to figure it out. A '14 Freightliner tractor with a Cummins was trouble free in the 75,000 miles I drove it though.

During my school bus days, regeneration of the DPF was a constant problem. I always knew when the regeneration started, so I'd drop it into 4th and run it on the governor. I never had to do a parked regen but most of the other drivers did, sometimes with students aboard.

You couldn't give me a new diesel today and it looks to me like the big gasoline engines may be on a comeback for medium duty work. Where I live, diesel fuel runs $.60 more a gallon than regular gas, so the fuel cost per mile advantage of a fuel sucking modern diesel evaporates.

[tommr]

I agree on the modern emissions standard for diesels being complex and expensive. I believe domestic drilling and resulting lower gasoline price has made it attractive to the Medium Duty market again. These 8.0 and 8.8 engines from these 2 companies debuted with LPG induction. The gasoline version is the 2nd version. A big thing with bus fleets is the early morning warm up period to get the interior up to temp. Gas and LPG have a lot cleaner warm up period. Have not seen the turboed 8.8. That's a pretty recent offering I think. Will take a look.