Cummins swap ?? Need opinions ???

[Rollingmenace]

Ok here goes decided it's time to buy an rv. Instead of spending 10000-12000 on a newer class c to suit what we want the boss has given the ok to buy and restore a classic Winnie .. I'm looking at either a d18 or d20 as its usually only the two of us and we really don't need anything bigger... Also with the current state of economy we would want something that wouldn't cost a fortune to drive, as we make several trips from eastern slope of Colorado to Utah and Idaho every year.. So a smaller chassis would make sense... So here is what I'm thinking a d18-d20 as a solid start and a cummins diesel conversion either a 4bt or 6bt  with some sort of od trans... and that's where I'm on the fence.. I've been watching the 6bt swap in projects section . Here are just some thoughts ...
#1 .. Size the 6 is just about 10 inches longer than the 4 ,and seeing how the conversion leaves everything so packed in I'm unsure . I prefer to try and use a mechanical fan ... As I've had issues with electrical fans before.
#2 .. Power..  The 4 is rated around 110 hp and 265lb ft of torque for non intercooled..The 6 is at 160hp and 400 torque  non intercooled. I would expect to see a 10 - 15% increase in these values with an intercooler.. 
#3 ..  Fuel economy.. I'm looking to try and accomplish 15-18 mpg highway I'd like to shoot for 18+ but I have to be realistic I do have a friend running a 4bt in a ford bronco it weighs around 6500lbs and he is getting between 25-32 mpg depending on how he tunes motor...

Here's what I'm looking for and want some opinions .. I prefer the 4bt to the 6bt Due primaraly size...I'd like to achieve 15-18+ mpg but I don't want to sacrifice power to get that .. I live in Colorado so there will be some highway pulling and some mountain passes.. Primarily just pulling the motorhome and a small trailer with 2-4 sport quads  ocasinaly a flatbed trailer with either my bronco crawler or the 51 ford on there....
What do u guys think will I be able to get what I want and need out of the 4 or do I just suck it up and run the 6bt

[Wantawinnie]

I am the one that did the Cummins swap. Probably not going to have many here with 4bt Cummins experience. As it was used in delivery vans similar in size to what you are considering I am sure it would work alright but not be overly powerful. 318's move these rigs around so a 4bt will too. The aerodynamics of these motorhomes are a big factor so if the 4bt is always being pushed hard you might not see much increase in mileage over a 6bt. Are you planning to turn it up?

You will need to build engine mounts as the 6bt Dodge ones I used don't fit the shorter 4bt. That is not a big deal to some but it does add another complication to the swap. As the 4bt shares all other dimensions of the 6bt there will still be a lot of the same issues to deal with including the exhaust and intercooler.

From a cost standpoint the 6bt's are cheaper as they are more available. They have less vibration as well. I've been in a delivery van with a 4bt and it was loud. They don't have much in the way of sound deadening so that might be better in a motorhome. My rig is 28' long and 12000 lbs. I wouldn't recommend a 4bt for that size as it runs fine with the 6bt but it is not what I consider overpowered.

Have you visited 4btswaps.com? Most guys that pose the question on there get steered toward a 6bt instead.

[LJ-TJ]

My only two cents worth is a 21 footer. Lauren and I are two and the 21 foot Brave is perfect for two. Just the right amount of room. You can wheel it around on a dime..It fits in a single car parking spot. You can park it at any restaurant. I'm sure you guys would love it.

[Rollingmenace]

TJ... I've been looking at the 18 and 20 or 21 I won't have a bunch of money to purchase closer to Christmas .. I've found more of the 18's for sale than 20 or 21 .. I do like the 20-21 due to the fact it has dinette in back and if we were to get one it would be just set up as a bedroom.. I think we will budget about 10000-12000 for the whole renovations .. Including the first order of business the diesel swap...  I like how you re-skinned yours is there a thread anywhere about that...  The route we are gonna take with ours is a diesel powered resto-mod like they do with the older cars ... New motor, skin ,paint , all led lighting.. H4 headlights , and a updated interior

[Rollingmenace]

Wantawinnie.
I've been following your swap.. It seems to be going along rather well.. I will check into the 4bt site and see what they have to say over there.. As far as what I'm really going for I want to be able to cruise down the highway at 65 pulling my trailer with the car or bikes  and get 15-18mpg + . And still have enough power to tote the load up the Colorado mountain passes.

As far as either swap I'm not to worried about the fabrication side of either a 4 or 6 I'm a pretty good fabricater so things like intakes motor mounts bumpers there really easy .. I actually have access to a CNC plasma table for cutting custom parts...

As far as the tune on the motor weather I go with the 4 or 6 I'm basically gonna run it at or close to stock not only to just keep it simple but also reliable but also to try and get the best fuel economy...

Pricing and availability of the 4 and 6 are about the same ... The 4 seems to sell for a few hundred more as the demand for them is slightly higher...
I'm looking for the best bang for the buck without going overboard...

[LJ-TJ]

You should be able to pick up a nice 21 footer for under $2000.00 more likely around $1,500.00 and under. Lauren and I picked up ours up in Kansas for $1000.00. We made going to pick it up a vacation project.

   
• http://fortcollins.craigslist.org/rvs/3941390508.html
• http://phoenix.craigslist.org/evl/rvs/3978611844.html
• http://goldcountry.craigslist.org/rvs/3987974273.html
• This is just a sample of what's out there and remember the prices are asking prices. Hm?

[Wantawinnie]

Your combined towing and MPG goals are going to be a challenge with either engine. 15mpg with just the motorhome will likely be possible with the right setup. Also, I think you will find a 4bt is more than a few hundred dollars higher in cost. You can often find Cummins powered Dodge trucks for less money than a 4bt and you then get the entire drive train if that is the route you want to go. I bought a 4bt a few years ago for $1800 and that was the best price for a good running motor I could find.

Do you have a plan for what transmission you are using yet?  Most of the 4bt's from the delivery vans were Turbo 400 or a non overdrive manual transmission setup. Those setups will not get you to the 65mph goal very well. The towing aspect is what really has me questioning if you will be happy with a 4bt, especially with stock power settings.

I will be curious to watch how your project goes.

[Rollingmenace]

TJ.. That one in Fort Collins is only about 3 hours away.. Ill have to see what kind of money I can scrape together jump on the bike ride up and take a look..

Wantawinnie .. I'm beginning to think the 6bt is the route I will be going just due to power.. I know I could expect 15 I'm hoping up to 18 on the highway just in the coach... Towing the bikes I should see about the same as the trailer and bikes weigh around 1200 pounds. I know towing with my explorer with a 4 liter V6 I see around a 1mpg loss over just driving I would expect the same on the Winnie .. As far as the car hauler with the bronco or the hotrod I know I will see a more significant drop...
I guess the 6 would be the choice just to make sure I got the power I need to get the job done ....

As far as tranny I'm looking at something automatic with a factory OD possible electric shift OD ... I'm not a dodge guy maybe a 618 or 47rh ill have to do a little research to find what will work best...

[Wantawinnie]

The Dodge trannies are a little easier just for the fact the adaptors to the Cummins are much more common and affordable as it was a factory setup. Can't help you much on other makes but there are adapters available if you go that route. 

I don't know if you visited that site I linked yet. There was a 6bt swapped into a Fleetwood Flair a couple years ago that was about 22" long and in the 9000# range, probably pretty close to what a D18-D21 would be. With a 92 cummins, A518, and 4.10 gears he is getting 14-15+mpg with factory power settings over 7-8000 miles of interstate driving all over the country. There is another that is a Class C with a stick shift so that is a little different animal but the mileage is similar. I think that one is in the Colorado area.

I do think you will be happier with the 6BT if towing and hills are in your future plans. You could turn up the fuel and do some other mods to the 4BT to achieve factory 6BT levels.  High EGT's and mpg losses may result from that so hard to say what is the answer until someone actually builds and uses it on the road.

Good luck however you proceed.

[Rollingmenace]

Well thanks guys for all the insight... I checked out the 4bt swaps website alot of great info over there ..... I will probably really start throwing out the questions as the project comes closer to reality....
Some things I learned and a few questions..
I believe the 6bt  12 valve is going to be the motor of choice..
I'd like to find a whole donor truck  for the complete drivetrain.
I've been searching around local best I've found is in the 2000-3000 range does that seem a little high..
What are thoughts on moving motor aft enough to clear a mechanical fan... I still am not sold on the electric fans... I had a bad experience on my bronco rock crawler and it has me nervous.. I'm waiting for more drive reports from wantawinnie
I should expect 15 mpg with sensable driving...
I spotted a d18  to d20 while riding out in eastern Colorado to look at a older class c that some family friends had for sale I would've stopped and asked about the Winnie but it was raining and it gives me an excuse to jump on the motorcycle and take a ride out there
And finally Leslie and myself are really looking foreward to this all coming together... 

[Wantawinnie]

Donor prices vary depending on year and condition of course. I probably have access to more rusted out farm trucks in my area. A 91-93 2wd Cummins with an overdrive can usually be picked up for $1500 pretty easily. Somewhere in the $2-3,000 range is about the going rate for a 4wd around here. The newer 94-95's do bring a little more usually. I have occasionally found all of them in the $1,000 range on Craigslist as some people just don't know or care. You just have to move quickly if you find one.

Keep in mind that in some cases the bus and medium duty engines are setup better to fit in the Winnies. They often have the front sump oil pan drop down exhaust manifold, and some version of a forward facing intake. The Allison tranny often attached to these may or may not be a good option depending on the year. They are bigger as well so that brings more into the swap.

As for moving the engine back there might be a couple options.

1) You will need to drop the engine and transmission down considerably because the transmission bellhousing is almost touching the floor support and floor structure now. Off the top of my head some issues will be the mechanical fan would likely not be centered on the radiator any longer so the airflow may be restricted and at the very least a custom shroud would need to be made, the tranny pan and oil pan may get a little to close to the ground or front axle for comfort, custom drop mounts for the engine and trans, and if you have a midship bearing on the driveshaft that will need lowering. Probably other stuff as well

2) If you want to move the engine straight back without lowering you will need to cut out the step down floor structure, cut out some of the floor directly behind the driver and passenger seat, rebuild all of that and, make a new engine cover. You will loose some floor space in the rig.

I would probably go with the second option.

While I was not crazy about electrics fans (especially pushers on the front of the radiator) they seem to be doing the job. They have yet to run while driving down the road as the temps have never reached close 195. I like the Painless 195 on/185 off setup combined with the 180 degree thermostat and a manual overide. Good or bad most vehicles have electric from the factory now.