Early Revcon Diesel Swap

[FEF]

All,

I've got a 'flat nose' Revcon 250 (not GMC) motor home. It uses the second generation Toronado drivetrain, with the Olds 455.

The first question I have is, of the 6.2 or 6.5, which has the least amount of electronics? I'm not afraid of ECU's and sensors, but I'm trying to keep the engine as simple as possible. Do I have any other options, If I'm looking for an engine that's more mechanical by nature?

Assuming it turns out the 6.2 or 6.5 is actually a good idea, it appears I can easily bolt the GM block to the BOP bell housing, with an adapter plate. What I don't know is if the GM converter will slide into the Toronado chain drive unit. The TCI site makes me thing it will bolt right up. I'm not so sure.

What about engine mounts? Are the engine mounting points on the 455 and GM diesels (GM small block?), even close? I don't know anything about the Chevy/GM/BOP differences. Though, the pined thread tells me about the high points of the 6.2/6.5 engines.

The brakes, alt, AC, and all that other stuff, will be pretty easy, after I get the engine mounting details ironed out. Time consuming, but less of a worry, when compared to the engine/wiring details

It's a great tip to buy a diesel whatever, and do 2 swaps. If done right, I might get quite a bit of my money back. Excellent idea, indeed.

Great Forums. Thanks in advance for the help

[BigRabbitMan]

FEF,

Good to see you looking at a diesel conversion to your motor home. I am also and my info is posted in the thread about "converting and early 1976 Motorhome". As you can see mine is an FMC, another of the classic older motorhomes. I came close to buying a Revcon. Great coach. Good luck on your conversion and I hope your questions get answered by those that have the information.

[convert2diesel]

If my memory serves me correctly, the Toronado/Eldorado setup used the THM400, thus the 400 torgue convertor is a straight bolt up if you used the 6.2/6.5. As far as the mounts are concerned, if you can find a late 70s early 80s olds 307 or 350 diesel, they used a motor mount relocation bracket that allowed them to install these engines into any "A" body car or truck. Perhaps this bracket could be used to reverse the process and when used on the SBC configuration it might marry to the BOC mounts. Just a thought.

Another thing you should consider is the use of the 12 valve Cummins, assuming you have the room. This has a mechanical pump and fuel delivery and are reasonably simple to work on. Do a search on this board as this is a very popular conversion. The 6BT and 4BT were used extensively on delivery trucks (Frito Lay) with the THM400 tranny. The adapter plates are readily available (though this configuration may still reguire the BOC adapter as well) and there is lots of stuff available to add power to these engines. Would have to fabricate your own mounts and probably have to play around with gearing but it would seem to me that it would be a better engine to use for this application.

Keep us posted.

Bill

[convert2diesel]

If my memory serves me correctly, the Toronado/Eldorado setup used the THM400, thus the 400 torgue convertor is a straight bolt up if you used the 6.2/6.5 (get the one specific to the diesel for stall speed). As far as the mounts are concerned, if you can find a late 70s early 80s olds 307 or 350 diesel, they used a motor mount relocation bracket that allowed them to install these engines into any "A" body car or truck. Perhaps this bracket could be used to reverse the process and when used on the SBC configuration it might marry to the BOC mounts. Just a thought.

Another thing you should consider is the use of the 12 valve Cummins, assuming you have the room. This has a mechanical pump and fuel delivery and are reasonably simple to work on. Do a search on this board as this is a very popular conversion. The 6BT and 4BT (commercial versions) were used extensively on delivery trucks (Frito Lay) with the THM400 tranny. The adapter plates are readily available (though this configuration may still reguire the BOC adapter as well) and there is lots of stuff available to add power to these engines. Would have to fabricate your own mounts and probably have to play around with gearing but it would seem to me that it would be a better engine to use for this application.

Keep us posted.

Bill

[kaylabryn]

Little info that I know is that the older first generation TH-400's (you have a 425 but they are pretty much identical only different haha" the torque converters were interchangable and I doubt that GM changed that. This is back when GM cared. Here is some links for information about your transmission and some upgrades you might consider while doing the coversion, especially the Switch Pitch portion, I have had a few older Eldo's and it makes a world of difference at both spectrums power/economy.

http://www.remaker.com/caddy/survival.html "Scroll down to the SWP portion"
http://www.california.com/%7Eeagle/SWITCH.html
http://www.bdub.net/tranny/index.html

Hope all goes well and let us know, I have thought about this type of conversion before.

Mike

[FEF]

I think I read the '94-'95 6.5L had a mechanical pump. That appears to be the easiest swap I see. At least the engine should be pretty easy to get.

The Cummins is an interesting idea. Honestly, I'd like to put one in, if they're not too long. It's hard to find info on engine costs, and dimensions. A pont in the right direction would be good, if it's nearly the same cost.

My tranny guy is VERY good. He's been been building odd-ball stuff for me, for nearly 10 years. He's a good guy to know, though not cheap.

This swap appears to be VERY possible, with no nasty surprizes.

It's the Cummins and the 6.5L that are on the scale. WHile the Cummins may be better, the 6.5L will likely be lighter. In this case (torsion bar suspension), I need to keep it as light as possible.

Tough decisions, indeed

[a5150nut]

I think I read the '94-'95 6.5L had a mechanical pump. That appears to be the easiest swap I see. At least the engine should be pretty easy to get.

The Cummins is an interesting idea. Honestly, I'd like to put one in, if they're not too long. It's hard to find info on engine costs, and dimensions. A pont in the right direction would be good, if it's nearly the same cost.

My tranny guy is VERY good. He's been been building odd-ball stuff for me, for nearly 10 years. He's a good guy to know, though not cheap.

This swap appears to be VERY possible, with no nasty surprizes.

It's the Cummins and the 6.5L that are on the scale. WHile the Cummins may be better, the 6.5L will likely be lighter. In this case (torsion bar suspension), I need to keep it as light as possible.

Tough decisions, indeed

93 is the last of the mechanical pumps. 94 starts the electronic units. You can put the mechanical on in place of the electronic pump.

[FEF]

The Plot thickens...

I pulled the tranny and had it upgraded. Since you can only pull the engine oil pan when the tranny is removed (front wheel drive), I decided to pull it and take a look. Imagine my surprize when I found pieces of a piston skirt in it.

I'm serious about the conversion, now. But, I must choose my conversion wisely. I'm told that some adapter plates will rotate the engine. I may have room if it rotates to the left (drivers side), but I'm pretty sure the oil pan will hit the tranny if it rotates right.

Will the BOP->GM plate rotate the engine? I'm told the Cummins 12v does. The 6BT may be too heavy for the front wheel drive rig (if it fits next to the tranny), and from what I can tell, the 4BT would be too small.

It looks like the 6.2L or '92-'93 6.5L is where it's at. Sure, it may not be the best engine, but there's a lot to like about a 4 wire install.

Are the Chevy engines if those years so bad? If they will pull at least as well as the Olds 455 that's in there now, it should be fine. Are they compareable?

Thanks for the help

[JeepSJ]

Why would you think the 4bt is too small? They can put out equivalent (or more) power than the 6.5.

[FEF]

Why would you think the 4bt is too small? They can put out equivalent (or more) power than the 6.5.

HUmmmmmmmmmm...

I can't find it now, but that's what I read. If it turns out that it's equilivent (or greater) in HP/Torquepower then the 455, it's back on the list. Though, I'd have to take a close look at one. I'm not sure the 4BT would fit the FWD Toronado/Eldorado/Revcon/GMC morothome drivetrain.

[JeepSJ]

HUmmmmmmmmmm...

I can't find it now, but that's what I read. If it turns out that it's equilivent (or greater) in HP/Torquepower then the 455, it's back on the list. Though, I'd have to take a close look at one. I'm not sure the 4BT would fit the FWD Toronado/Eldorado/Revcon/GMC morothome drivetrain.

There is a link in one of the other threads about a 350hp/700+ftlb 4bt. The issue would be the bellhousing pattern - you can get the Chevy/GM pattern plates for the 4bt, but I don't know about the BOP pattern.

[FEF]

There is a link in one of the other threads about a 350hp/700+ftlb 4bt. The issue would be the bellhousing pattern - you can get the Chevy/GM pattern plates for the 4bt, but I don't know about the BOP pattern.

Interesting.

I think a well built 455 has about 450 ftlb torque. But it has nearly as much HP.

I just found a 12v (Dodge) cummins for $1000. I sure wish I knew more about the BOP->GM-Cummins adapter plates. If I have 2 adapter plates, I may have to shim the torque converter.

It all looks so easy on paper.

[convert2diesel]

A number of years ago I had the opportunity to purchase one the original GM motor homes. Been kicking myself ever since for not reacting fast enough.

Like you I was also looking at converting it to diesel. Having owned a Cadillac Eldorado with the 500 in it, I remembered the volumes of gasoline this thing sucked back. One of the avenues I investigated was modifying an existing 4X4 transfer case and using one of the 4 speed OD trannies. If you used a manual case (i.e. full lock in high) and sealed up the rear drive shaft, then you could use the front shaft only. Your friend at the tranny shop might have some other suggestions (like "that guy is nuts") or has a source of adapters that might work.

Another aspect that might give you some grief is, if my memory serves me correctly, the Caddy had a hole drilled through the oil pan to accomodate the passenger side axle. This would prove to be an interesting fab job unless you could modify the existing pan to fit your new engine. Don't know if yours is the same but it was one of the considerations I looked at.

As far as the engine is concerned, I vote for a full on mechanical 6.5 turbo (this is a GM diesel page after all) but the Cummins is a close second. The Cummins would make for an interesting conversion if you have the room.

Check with Jamie or Benny at the Diesel Depot for the adapters. They do alot of the Frito Lay trucks with the Cummins/400 set-up and should have the plates.

Sounds like a great project. Keep us informed.

Bill

[FEF]

A number of years ago I had the opportunity to purchase one the original GM motor homes. Been kicking myself ever since for not reacting fast enough.

Indeed, they are nice. This one is in pretty good shape for 30 years old. I look forward to actually using it, and not working on it.

Your friend at the tranny shop might have some other suggestions (like "that guy is nuts") or has a source of adapters that might work.

It's a cool idea, but not an option as the tranny's done. It went form a 5 disc pack to 6, boosted the pressure to ~90psi, a few other tweaks, and a small Allison torque converter that I think is from the 5 speed. We're pretty sure it will pull a combined vehicle weight of nearly 20,000 lbs, with the right engine.

I do like the T-case idea. I'll consider it when all this goes belly-up.

Another aspect that might give you some grief is, if my memory serves me correctly, the Caddy had a hole drilled through the oil pan to accomodate the passenger side axle.

Nope. It looks like a standard rear sump to me. All the goofy Diff stuff is a bit lower, were the half-shafts fit in.

Now, one thing that is interesting is that the engine mount is not on the side, but in the front. Imagine a 1/4" plate bolted to the bottom of the timing cover (or bolts on the block around it), with an engine mount on the bottom of a flange welded to the bottom of the plate. The front engine mount sits on a crossmember just in front (but under) the oil pan. This means that I'll have to bolt this plate to the lower front of the engine block. It's no big deal, I'm sure. But it is interesting.
[quote]
As far as the engine is concerned, I vote for a full on mechanical 6.5 turbo (this is a GM diesel page after all) but the Cummins is a close second.
[\quote]
Ya the 6.5, or maybe a banks turbo on a 6.2, will be my first option. I've done a lot of things that "can't be done", but this time I'd rather be driving then have another project.

If any of you have a Drop-in Mechanical 6.5, or a strong 6.2, in the greater Portland, OR area, A PM might be nice. Or, I could use recomendations on where to get (other then Craig's list) a solid used engine.

Sounds like a great project. Keep us informed.

Ya, man. You bet.

[FEF]

UMMmmmmmmmmm...

This may be the most noob question I've asked in a long time.

I remember, in my old ('70) Firebird days, GM and POB had different placement for the starters. One had a high left mount, and the other had a low right mount. If the diesel starter is not on the lower right (passanger) side, That's a show-stopper.

Where is the starter located on the 6.2/6.5? Is it the same place as the early 70's Olds 455?

Thanks again for the help.

[convert2diesel]

The starter is on the lower right (make sure you have the front bracket in place). Having installed the 6.2 in a Buick, I found that using the oil pan from a 4X4 gives you a little more clearance around the front of the engine...just a little flatter up there. Using the front mount would indeed solve a bunch of problems but make sure that your bellhousing bolts are grade eight or better (they are going to be taking up a lot of torque with no side mounts on the engine).

If you do your homework before hand, making a good reliable conversion is not out of the question. Other then a few teething pains, my 6.2 conversion has been my daily driver for 3 years now, has made the Ottawa/Florida trip four times with a trailer in tow (combined wieght of 8,000lbs), been out to the East coast twice, Georgia three times and Iowa once. In a normal year I will put anywheres from 30 to 40 thousand miles on the car.

Little more then normal maintenance in the whole time (oil, glowplugs, filters etc.). Had more problems with the accessories like the alternator, vacumm pump, lift pump then with the conversion. All of this with a known good used engine from Diesel Depot...thanks Jamie. In other words, to it right, do it once.

As many of the others on this forum can attest to, there should be no problems in getting 250 to 275 HP reliably from a good mechanical 6.5 and if you treat it kindly it should give you many years of service. Just choose a good rebuilder and invest the money now in getting the job done right.

Good luck.

Bill

[FEF]

I've run into a snag. The tranny is kinda low and left of the engine. The 6.2/6.5 appears to have a filter in the rear left. That will not fit, as the tranny oil pan is in that area. If it is 'only' a filter, can it be bypased, and moved to a remote location?

I'll get some pics, so you all can help a bit more. Now, the bellhousing is not an issue, but stuff on the lower left side (below the crank center line). Pretty much all that's under the freeze plugs might be fine.

[convert2diesel]

Some of the 4X4 engines and I think the Hummer had a filter that faced forward as opposed to down to clear the mechanicals. That may give you the clearance you need. If not then plumbing a filter into the oil cooler lines may make sense. A standard SBC outboard oil filter kit will work as well (I think Fram makes one) but that would mean the oil will come back from the cooler and then go out again to be filtered before making it back to the engine. Best invest in a real high volume oil pump.

Bill

[FEF]

ACK!!

That's the oil filter, and those lines go to an oil cooler?

This is going to be tough without a model. The last thing I want to do is spend $5k on a crate engine only to find the oil filter hits the tranny, or every time I change it (through a hole like a spark plug) oil drips down the top of the tranny.

Do you know where I can get good pics, with a few views of the engine's left? That would help alot.

I may end up buying a blown engine (or a truck with a blown engine) just to see if it fits.

Or... I spend more money, and try to find a decent 12v Cummins. I don't think there's anything on the drivers side, at crank height.

And we thought it was a 'bolt in" .

[DmaxMaverick]

There are many options for remote oil filters. Both full-flow and bypass. You'd only need room at the oil filter location for an adapter that sticks out about 3/4", with lines running to wherever you place the filter. Put it in the glove box, if you want.