What would you replace a 6V71TA with?

[Mex-Busnut]

Dear Friends,

Supposing I was handsome, rich and famous (instead of just handsome and famous!   ) and wanted to replace my 6V92TA with something to boost fuel economy.

I have seen my model bus down here equipped with 335 and 350 Cummins, and L10 Cummins. The latter seems to be one of the more popular installs in these buses. Is the N50 also a viable option? A 3206 or 3208 Caterpillar? Other options? A VW Bug engine?

In my opinion, I wouldn't do it unless I could increase maybe 25% my economy.

As far as space, this bus came from factory with a 8V71TA in it.

Thanks in  advance!

[prevosman]

I would not ever consider changing engines for better economy until I ran the numbers.

At one time I ran about 30,000 miles a year, now less than half that. To justify an engine change for economy I would need to get the engine and installation for a very small cost or drive a lot of miles to justify the cost, or have the price of fuel skyrocket.

Drive slower and avoid rapid starts, reduce the weight of the coach and toad, and minimize the load on the engine by minimizing the use of power robbing loads such as electrical, AC engine driven compressors, etc. Look for the sweet spot where you get the best mileage with a tolerable speed.

FWIW, while fuel cost is a big part of ownership, insurance, maintenance, needed repairs, and in some cases depreciation are the real areas where money can be saved.

[bevans6]

what is your economy now and what is your budget for the swap?  Put another way - how many miles a year do you drive it (or plan to drive it, it don't think you've driven it anywhere yet), what does fuel cost now and for the next five years, and what will the swap cost?  Is there anything terminally wrong with your engine, or do you just think a swap is an interesting option to explore?

If economy is the goal and your 6V92 engine is perfectly fine, then I would de-tune it.  I would put smaller injectors in to bring it down to around 250 hp.  You have a ten speed trans (I think), so you might even get away with it with slower speeds adding to the savings - you won't be able to go fast.  But that is cheap - around $1,000.  I make it around 12K miles if you gain 25% from say 6 mpg to 7.5 mpg and $3.50 per gallon average over the period.  Faster if fuel costs more, i would expect.

if you decide to do a swap, you would want a 4 stroke of some sort to gain meaningful economy.  Using a S50 swap as an example, I looked into that closely last year and costed it at $15K with me doing all the work (I am a fabricator, jack-leg mechanic, decent with electronics and overly self-confident...).    That would take maybe 180,000 miles to pay back based on the same economy factors.

Just some back of the envelope ideas I had.  If I had a nice bus like yours with a good running 6V-92, I wouldn't change it.  BTW, you can do the same thing as swapping to smaller injectors by setting the throttle cable so it only opens the speed lever 3/4 of the way.  Or put a block under the throttle pedal.  And you could also reset the governor to 1900 rpm max unloaded speed.  Those two things would save you some fuel and would be free...  

Brian

[Brassman]

Scratch the Cat 3208 off the list--for sure. The 3206 shouldn't be on the list. If you want a VW bus engine, I'll give you a waterboxer. 

[bottomacher]

Do you have a 6-71 or a 6-92?

[luvrbus]

A 3206 would be a hard find only a few built I saw one on display a V6 the 3306 is a inline 6 cyl good engine I have a friend that has one in his Eagle

[Mex-Busnut]

Thanks to all for your comments.

I currently have a 6V92TA installed. It replaced the factory 8V71NA in 2001, according to the paperwork.

My engine is currently using 50-weight oil, and blows a whole lot out of the slobber tubes, just idling. My truck diesel mechanic guy will do a complete valve and bearings, etc. for 30,000 pesos, which is about $2,250 U. S., which includes labor and machine shop. By the way, he is the mechanic for a friend who has a half dozen big trucks, and my friend says this guy does very good work.

[Geoff]

What are "slobber tubes"?  I can't find that term in my Detroit manual.  Perhaps you are talking about "air box drains"?

[Mex-Busnut]

What are "slobber tubes"?  I can't find that term in my Detroit manual.  Perhaps you are talking about "air box drains"?

I guess I am. Truckers call them "slobber tubes".

[bevans6]

slobbering at idle could be a number of things, one easy thing to check is the check valves - they are supposed to close at slightly above idle speed so the slobbering stops when underway.  If it's not too bad when driving, or it's not using an abnormal amount of oil (say over 1 gallon every 1,000 miles, which would be towards the high usage side of things) then it may run for years for you.  If slobbering is the problem and high oil usages going with it, bearings and valves probably aren't the problem, it's cylinder kit time.   Fresh pistons, rings, liners along with the bearings and valve job will make it like new.  Also taking the opportunity to check the blower out.  But slobbering by itself isn't a reason to do an in-frame.  Just run the tubes into a couple of old oil jugs and the messy part of the problem is solved...


Brian

[TomC]

Round figures on fuel mileage- starting with your 6V-92TA (I assume it is a mechanical engine)-going to a 6V-92TA DDEC electronic engine would be worth another mile per gallon.  Changing to a mechanical 4 stroke engine will have the same mile to gallon change.  Changing to an early electonic 4 stroke engine (pre 1998) will be worth another 1-2 mpg.  So the big question is-are you going to put enough miles on your bus to offset a possible 2-4 mpg increase?  Personally-I would keep the 6V-92TA-it is a very reliable engine.  The number one thing to do is to keep tract of your acidity in the coolant.  Using Nacool typically once a year should do it.  Both Don Fairchild and I just use the standard green Prestone antifreeze with distilled water 50/50% mix.

The best way to get better fuel mileage is to have a well trained loose nut behind the steering wheel.  The 92 series mechanical engines like to cruise in the 1600-1800 range.  Once you get to 1500, power will drop off dramatically-so unless you're topping a hill, it is best to down shift.  Revving above 1900 won't do anything for you except burn more fuel.  So the economical power band is 1500 to 1900 on a 92 series.  Also-92 series do not like to be revved high.  Set your governor at no more then 2,300 no load and don't over rev on a down hill.  Use straight 40 weight and change your oil once a year or no more then 6,000 miles.  I'd keep your engine (and use 9G90 injectors)-get it rebuilt (including pistons, rings and liners) and you'll be a happy camper. Good Luck, TomC

[Lin]

This sort of topic has come up before, but I can not understand the idea of an engine change for economy.  Maybe that would make sense for truckers that are putting on huge mileage and expect to keep the same truck for many years, but I can not see motorhome usage ever getting to a break even point.

[bevans6]

It only makes sense if the existing engine is basically scrap, and you are comparing the cost of an extensive rebuild against the cost of a different type of used engine.  Even then the dollars are marginal.  The real reason to change an engine is because you feel like it, and it will fulfill you in some personal way.  Just like most things we do in life...

Brian

[Geoff]

What are "slobber tubes"?  I can't find that term in my Detroit manual.  Perhaps you are talking about "air box drains"?

I guess I am. Truckers call them "slobber tubes".

I don't think 'truckers' run 6V92's anymore, and I find the term offensive.  If you are blowing oil out your air box drains your engine needs an overhaul.  Catch containers only delay the overhaul.

[bevans6]

Geoff, everyone calls them slobber tubes and have for decades,  Get a life...

Brian

edit:  Ok, that was a little harsh and I apologize.  Everyone knows what slobber tubes means and it's common  usage.  I learned it from a trucker, who was a trucker because he drove a truck.  Many people also know they are air box drains.  It's just so not a big deal what you call them.  DD nomenclature is all over the board - they have a throttle shaft in the governor, for pete's sake!  Ain't no throttle in a diesel engine!

Brian