Fuel economy 8V71 vs series 50

[Jerry Liebler]

If anyone has actually swapped a series 50 for an 8V71 I sure would like to know the comparative fuel economy.  Should I keep dreaming of doing this swap?
Regards
Jerry 4107 1120

[Kevin Warnock]

I swapped my 8V71 MCI 5a bus that got 6.4 mpg for a Series 50 RTS bus that gets 10.75 mpg at 60 mph.

[coolbus]

6.4 mpg seems fairly low for a 35' bus. Was the series 50 a fresh engine?

[Jerry Liebler]

What axle ratio does the RTS have?  Also what transmission in both the MCI and RTS? 

[Utahclaimjumper]

If you swapped the whole bus then many other variables are at work, not just the engine.>>>Dan

[TomC]

You'd be looking at 2.5-4mpg better.  But then you have all the electronics to set up.  IMHO-better to turbo your engine for more power.  The fuel mileage savings will not offset the cost of setting up the electronics.  And if you ever have to have the bus towed because of electronics failure (which is highly likely) you completely offset all fuel mileage savings, up and beyond the time wasted.  Properly setup, the mechanical 2 strokers are extremely reliable-probably the most reliable engines ever made.  Good Luck, TomC

[belfert]

How many times do electronics really fail?  Obviously I know lots of people with cars and I very rarely hear of the electronics in cars failing.

TomC, you sell trucks.  How many of those come in with electronics failure? 

Electronicsfailure might be more likely on a engine swap just because of the custom wiring harness.

[tekebird]

I would say it is not some much an electronics failure to worry about........but sensor failure.

I have seen many a new car sitting on the side of the road overheated when the sensor for the fan went inop........thus overheating.

the real question is it worth the time and money..................ANSWER: NO, NEVER.....Unless.......you need the 12 step program for having the need to Futz with stuff

The Cost and Time involved, let alone the possible problems you MAY have will never be recouped.

Similar example:

I want to buy a 3/4 ton pickup......should I get the diesel.......it's a 6000.00 option and will get a few miles per gallon better than the big gas engine.

I went thru this decision once did all the math with the engine cost vs fuel cost at the time.........to realize the fuel savings..........I would have to keep the truck 20 years.........now this did not account for the added resale when selling the diesel........IIRC over 10 years I would have only recouped 3000.00 of a 6000.00 option.........now that 3000.00 I would have lost.........would have served me much better at earning interest in a CD or something

Now this situation didn't also take into account the time and problems involved with the SWAP or problems down the road.


When CA mandadted that some of it's State Subsidized Commuter buses be repowered with the 50, it was done by a company that specializes in such things......and even they had problems with the SWAP.

[TomC]

I see trucks coming in on the hook almost daily.  When I say electronics failure, that can be anything from complete CPU failure to a loose wire to a sensor-but enough to stop that engine.  And that is with any make of truck or engine that is electronic.
When I was driving, the only time I had to be on the hook was for a mechanical failure.  And in 1.3 million miles of driving that was only twice (engine related).  Once for a blown water pump, and the other for a fuel pump.  Otherwise, I was able to disconnect, or jump, or something to successfully get to my next destination (and sometimes run for days-like when my shut off solenoid failed) without interruption.  The ONLY reason electronics were introduced is for smog control.  Good Luck, TomC

[gg04]

 I only know of three people with this swap..none will post here....people on here have told them it won't work is unreliable and too expensive....Just goes by if you can actually do this by yourself...from start to finish...VS 8v71 at least 4 mpg..but better off throttle and useable tq at all highway speeds...A highway geared donor bus still the best way...then you will have something that will run with anything  built....All modern comp controled work so much better than old mui...Can still remember when if you could not fix it for your self setting beside the road you could not afford to drive a bus conversion...now its all glitz and what you can pay someone else to do..go figure..gg04

[kyle4501]

Given the resourcefullness & tenacity of the one who started this thread, I doubt that the electronics will be much of a road block.

I think a S50 would be cool! However, I have pondered this for a while & the thing I keep coming back to is the shaking issues with a large displacement 4 cylinder. They can only be dynamically balanced for a narrow RPM range. Naturally you would want this at normal cruise RPM. That leaves lots of shaking at idle.

Then comes the cost/ benefit ratio. I just can't get there either, not while my engine is a viable means of propulsion.

[Kevin Warnock]

My RTS with Series 50 has a 4:11 rear end, and a 731R transmission. The "R" means it has a retarder, which is really great. The retarder provides about as much slowing power as the Jakes on my old MCI. I don't know what transmission the old MCI 5a has... I think a 642??? 3-speed automatic model.

I don't have other than normal vibration with my Series 50, at any speed, and including at idle. I read many posts before I bought the Series 50 bus about how the shaking at idle would shake my teeth out. This turned out not to be the case. The engine is quieter than my 8V-71, and has no more vibration than that engine did, probably less. The RTS goes up mountains MUCH faster as well, almost keeping up with traffic. The main place it's slower is from a dead stop. There it feels like it takes longer to get up to speed. I think it's the EPA computer keeping me from accelerating faster. I didn't care for it the first few weeks, but I've gotten used to it, and I love the power in the hills, so it's a more than fair trade, particularly since I almost doubled my fuel mileage.

Kevin

[kyle4501]

With a factory install on the RTS, it was obviously engineered properly. It is easy to take the results of a properly designed system for granted.

The natural frequencies of the components involved can be very complex. I doubt I'll be able to do as good a job if I was retrofitting one in my bus - maybe my concern is a result of too much school, the vehicle dynamics classes were rather intimidating.

The vibration issue is real! A in-line 4 cylinder is inherently dynamically unbalanced. The larger the displacement, the larger the vibration. That's why you don't see many in cars larger than 2.4 liters. If you deal with it correctly, no one notices anything. If you get it wrong, the results aren't good. I have been in buses that had a strong low frequency vibration that was so bad, it was making people sick.

The chance of a successful completion of any task is improved if potential problems addressed in the planning stages rather than ignored.

I'd still like to put one in my cruiser. maybe one day. . .

[belfert]

Was the RTS still being made when they started putting the Series 50 in buses?  I thought the RTS buses with Series 50s had all been retrofitted by various companies on behalf of transit operators who needed to meet smog regs?

[TomC]

Kyle4501- I hope I can put the vibration issue of the Series 50 to bed finally.  S50 is the only engine made where the oil pump has to be timed since it drives counter rotating balancing shafts to cancel out the vibration issues.  Granted an 8.5 liter 4 cylinder is not going to be as smooth as a-say-8.3 Cummins 6 cylinder.  But given the fact that the bigger the cylinder displacement is with fewer cylinders means better fuel economy (mainly less friction-and the 8V-71 has a bunch of friction).  I have ridden on S50 transit buses in the back to listen to the engine, and except for a minor amount of vibration at idle (no more than any other 4 stroke Diesel), it really ran well (was in a 60ft transit that was filled).  Personally, I think the S50 is the perfect bus conversion engine-It is reliable, gets up to 350hp and 1100lb/ft torque (like a well tuned 6V-92TA), gets unbelievable fuel mileage, 1 million mile life expectancy, doesn't leak oil or burn oil, is short in length, requires little cooling (on MC8 & 9 Grayhound converted over from 6V-92TA and took one of the radiators out and replaced it with the air to air intercooler-shows how efficient the S50 is).  If I had the room of a 4501, I wouldn't think twice about installing the S50 since you have two radiator mounting possibilities and plenty of room.  Plus-wouldn't it be nice to get 8-10 mpg with an automatic, or 10-12 mpg with a manual?  Good Luck, TomC