Gas to diesel conversion

[The_Handier_Man1]

From: bhart70  (Original Message)
Sent: 6/6/2003 10:30 AM

I checked out the link Derrek provided in the Petrol to Diesel thread (fostertruck.com/cummins) regarding the conversion from a gas engine to a Cummins Turbo Diesel.  What a conversion!!!  The guy has done some very impressive work.  Seems like a quality job from the start.  One thing to keep in mind is that this guy was able to do virtually everything himself saving big bucks.  He was also fortunate enough to find a junk at auction with a good engine, tranny, and rear end for $1500.00.

The total cost of the conversion before items added later because of necessity or need was $5081.37.  Granted the pulling power and response is probably incredible, but that seems like an awful lot of money!

Few items to note:  He averaged 7.6 mpg before the conversion pulling 13K.  He now averaged 13.98 mpg pulling 17K.  For comparison purposes, I assumed 6 mpg due to the additional weight (maybe to big an assumption?).  Fuel costs are based on CT prices as of today for 93 octane.

Engine
Total Miles
Avg. MPG
Fuel Used
$/Gal.
Total $

Diesel 4930.5  13.98  352.68  1.71  1116.08 
Gas 4930.5  6.00  821.75  1.93  1585.98 
     Total Fuel Savings     $469.90


Based on the fuel savings of $469.90 over roughly 5K miles, it would take 10.81 years to pay for the conversion at 5000 miles/year.  Some of you guys who travel extensively or year round could probably justify it, but for most weekend/summer warriors I think you would be better served by a rebuild, carb upgrade, headers, larder exhaust/mufflers, maybe a new cam and/or an bore-over and larger pistons, and a shift kit in order to get improved performance.

If you're doing 10-20K or more per year, looks like a helluva conversion!  Keep in mind that more than likely you're going to have to shell out $3000-5000 for the engine, tranny, & rearend rather than the $1500 he did for a junk with good running gear.  And if you're not handy enough to do virtually everything yourself, the conversion can easily surpass the $10K mark!

     I recieved an e-mail from a guy who has done several Cummins swaps in motorhomes and here is what he said his experience has been.

The first swap was done in a '69 Travco that originally had a 318/727 with the 4.88 rear end. In the two years after the swap he put 25,000 miles on it and on a trip to Alaska he got 16 mpg at an average speed of 60 mph.

He sold the Travco and bought an '82 Airstream 310 turbo with a broken Isuzu engine. He installed a '96 Cummins with a 518 overdrive transmission. The Airstream gets 14 mpg at an average of 70 mph.

He said the swap will cost around $4000.00 and is a fair amount of work but he said in the end after doing two swaps the power and mileage increases make the Cummins swap an excellent upgrade and well worth it as far as he is concerned. He said that if I decide to do it he could give me more info. Very interesting. And the #'s are impressive.

     In fuel savings alone a conversion would be hard to justify. The biggest difference would be in resale value providing the swap was done properly and was well documented. For example if you go to NADA.COM to look up the blue book value of a motorhome in the section where it ask the mileage it says right next to it "only enter mileage for gasoline engines"

I also stated in my response that the noise levels would be extremely high in the drivers area. I have since found that this is not neccesarily true. Proper insulation of the floor and the engine cover will reduce noise further than one could imagine. My Apollo has a custom made, well insulated engine cover that was made by the previous owner and even though I have a bad exhaust leak on the passenger side doughnut gasket conversation between the driver and passenger is easy to do even in a normal tone of voice. Once you step outside of the motorhome the leak is very obvious.       Derrek

The other mistake in my response was the fact that the transmission used for the diesel could also be swapped along with the diesel engine.

As you stated performing a swap and deciding whether or not it would be worth it depend on the individual and there traveling habits, what type of motorhome you are planning on doing the swap in, and of course would you own the motorhome long enough to reap the full rewards.

As many already know the main reason for us owning a motorhome is attending NASCAR races. Driving the motorhome to the race track gives us the luxury of relaxing in our motorhome before and after the race while others wait in long lines of traffic trying to enter/leave. Also we do not have to stand in a line 50 people deep for a porta-john everytime we need to use the restroom.

The alternative to a diesel swap would be to buy a diesel truck and pull a 5th wheel. Trying to pull a 5th wheel to a race is unrealistic. Leaving the 5th wheel at a local campground and driving the truck alone defeats the whole purpose.

Given our situation the motorhome is ideal. Being that we attend many races and I could picture us going 5,000+ miles per year and plan on keeping this motorhome for the next 10+ years a diesel conversion is worth at least looking into for us. Who knows maybe I will find it to be unrealistic, but is at least worth doing some in depth research on.

I have also spoke of the aftermarket overdrive/underdrive units as I thought that this may be a good idea. After doing research I have found that this is an expense upgrade that makes very little difference and in the end is not worth the expense. The idea of a Cummins swap may prove to be the same in the end. I have been a fan of the Cummins since Dodge first began using it in their trucks and if it proves to be worth it may have one in my motorhome sometime in the next several years.
 
     Re:Diesel vrs cost benefit.It doesnt really matter what it costs.This is a hobby for most of us,and hobbies cost money.I like the idea of power,efficiency,and dependability.Cost isnt the deciding factor,if I can afford something and want it,I get it.To do it solely as a cost saver probably wont fly unless you fulltime and travel a lot.
So do your conversions if you can and enjoy em for what they are,a really nice upgrade to your hobby.On that line of thinking you will be pleased I think.
Gotta agree,that Cummins is a hot engine.So is the PSD and duramax,have friends with all 3,and all are nice.And loud.And smelly.But thats another rant!And great info on the swap,thanks.
PS,saw a fellow who has a sig that says"The only thing wrong with my Cummins diesel is that its in my Dodge Truck" and saw another that said"When my Dodge falls apart on the side of the road my Cummins will be sitting there,happily chugging away" Folks love that engine.        Boo

 
     We run a half-dozen Cummins Turbo's at work and I'll certainly attest to their power and durability!

If you've got the know-how and the means it is definitely the way to go.  It just has to get put into perspective though.  A lot of guys consider it without knowing all of the costs involved and the amount of time it takes to recoup those costs (I was one of those guys ).

Re: the overdrive/underdrive units, the guy on the fostertruck site basically thought that it was too expensive and un-needed with the Cummins and that it made no noticable difference, infact it even hurt his mileage in some cases.

I would say in your case, by all means go for it.  It sounds like the ideal way to go!  bhart70