Which should/would be the better replacement?
What criterion should one have to decide?
Would the transmission be factored into this??

For most of my life that would have been a diesel almost without exception. Diesel fuel was cheaper, usually better mileage, built to last at least 500K miles, beefer components, and etc. Today, I don't know if any of that is true. In Georgia diesel is $0.60 a gallon more than gas. Modern technology has gas engines that last almost as long. Fuel mileage about the same. Overall horsepower and torque as compared to vehicle weight should be considered when selecting a transmission , not fuel type.

Quess, I certainly wasn't much help! Sorry
Nick

"What criterion should one have to decide?"

Repair: Modern gas engines will run 100,000 miles with basically no maintenance, so the "repair factor" is nil on both.
Routine maintenance on a diesel (fuel filters, oil filters) is significantly more costly than gas and deadly if neglectd; gas engines are more forgiving.
Initial cost: I've never been able to overcome this when a diesel/gas choice is available. No way does a diesel justify the added initial cost.

I wonder what the torque figures are if we were to compare a GM 8.1 litre Vortec V8 gasser with a 8.3 litre Cummins turbo diesel? Both from same year RVs of course.
Wouldn't the diesel give way more torque and better fuel mileage?
I was looking at a newer37 footer with that 8.1 in it here in Bradshaw RV Park and think it must be working hard in a motorhome that size in these Arizona hills.
Don

quote:

Originally posted by Doug Smiley:
Which should/would be the better replacement?

What coach are you repowering? Yours? What is it?

Now would be a good time to mention the merits of the regular practice of listing the coach in the signature line of a post, along with pet pictures, or whatever.

(perhaps I should just let it go at that, but below are some general ramblings)

quote:

What criterion should one have to decide?

For me, it would depend on the weight. When I repowered my coach in 01, I had to choose between a Duramax and a HT502. Both had a little over 500 ft lbs of torque. The 502 had 325 hp at 2800, which is where I drive when not in overdrive. It also appeared that the Duramax would require either a higher engine mounting position or mods to the crossmember for pan clearance. This was confirmed by a Workhorse engineer, who told me that they were exploring that, but there weren't enough engines available due to demand.


I don't have the 5.9 numbers memorized, as it varies widely with version, but the few Breakaways I considered purchasing seemed too underpowered for me to tow a heavy ski boat or 4WD up hills. The later, computerized 5.9s that Dodge uses are pretty decent, though. The later Duramax models also have more power and torque, too.

Now, as far as weight, if I had a much heavier coach, a gasser would not have enough torque. If my coach and its load were lighter, a 454 or 468 or stroker would do the trick. A stroked and cammed 468 is a torquey sonofagun. If a donor vehicle is available, a 454/4L80E combination is nice, and can save a little gas and give better high altitude performance.

quote:

Would the transmission be factored into this??

Not only transmission, but rear end ratio, as well. My preference is the 502 with a built TH400/Gear Vendors. However, the 8.1 with the Allison is a great package because of the locking torque converter. I am not sure exactly what the mileage gains on a MH are, but I really like the idea. The massive torque of my 502 really cooks the converter up hills, requiring heroic cooling efforts by me. The 502/TH400 has the advantage of being way more easily maintained by any competent GM guy, while the 8.1/Allison requires specialized knowledge and testing capabilities, owing to the massive computerization.

I believe the 502 provides a little more useful power over the driving band, as well, but don't have the figures memorized.

The 502 has a bore distortion problem common to Siamese blocks that results in a little more oil consumption. The 502 in my boat has aluminum heads and really good cooling, so the problem was unknown to me when I put the 502 in, or I would have done a torque plate rebore first. And the steel roller cam requires that the melonized distributor drive gear be replaced now and then, but neither is a deal breaker. Supposedly, a composition gear is longer lasting. I will put one in next time, I think.

I am very happy with the 502/TH400/GV, but if I were facing the 2001 repower today, and had a reasonably priced donor vehicle available, the Duramax would tempt me. I could get in there with a plasma cutter and make the crossmember clear the sump, for sure. That would also be a good opportunity to put in a later wide track crossmember and front suspension, which would help handling. There are mods available that would give the Duramax a power advantage. too.

None of this would be cost effective, but, Heck, it's a hobby!

I have had both gas and now a diesel in RV service. My gas rig was a 27' Rockwood class A with a TBI 454 and 4L80 trans. I had the Banks kit on it. Of course it was a puller.

I now have a 30' Breakaway with a 230 HP 5.9 Cummins and Allison 6 speed. It is a pusher.

I have owned a business that relied on heavy equipment, most of which were diesel with a few gas powered units thrown in.

The main reason I switched to diesel is I wanted a short pusher, 30' maximum, not much choice except diesel power. Only recently have the chassis manufacturers offered gas pushers. There were older FMC gas pushers but--

My gas powered SOB was really quick off the line and would cruise well at 70+ BUT, it drank fuel!!! I know, I know, slow down---can't---. Averaged 8 MPG for four years of ownership. When I bought the rig, it had 60K miles on it and when I sold it was near 100K. During that time I had a radiator replacement, a transmission rebuild and a complete spring replacement. P-30 chassis.

Engine was trouble free but had to watch the temps going up long grades or in the desert with 100+ ambient.

The really downer was NOISE!!!I spent $$$$ with sound proofing and heat barriers, lots better after I finished BUT no where near what I wanted. More noise was created by the Banks kit as they remove some of the noise baffling in the intake to increase the breathing but then you get that full throttle howl. Going up a long grade was not good. The saving grace was that the 4L80E is basically a TH400 with an overdrive added so that RPMs at a docile cruise were low. Fairly cheap to re-build.

Friends of ours had a 454 and they went thru 2-3 exhaust manifolds before they went to a Banks kit, most 454s that I know of don't go much above 130K before needing head work or a rebuild.

On our Breakaway, it is NOT a rocket ship off the line, it is really doggy until it hits second gear, then it goes. Has severe turbo lag and when the turbo overhaul come up I will put on a smaller housing to correct that lag. Pulling power? Hook something behind it and you don't know it is there! Going up grades, I found the best way was to manually shift down as soon as RPM start to fall. Two reasons-keep the engine in the torque sweet spot and the other-most importantly- cooling. On a pusher the only cooling air is by the fan, keep that fan at high speed and the the temps will stay down. I have made some changes to the air flow to keep the hot road air out and draw as much air from the rear side vents as possible. Trans temp has never been an issue. The breakaway will go up the same grades as my SOB did with a 5 mph higher speed. IF, you get out of the engine torque band on a grade, go all the way down in gears and ride it out, you will not get back up to speed easily.

I have averaged 10.5 MPG for 2 years ownership and 30K miles of driving. Haven't slowed down a bit! Allison trans is solid, only had an issue with the throttle position sensor and I corrected that with a small washer. Had a cracked exhaust manifold, but I found out it was cracked when I bought it. The experience I had with our heavy equipment says that diesel power is cheaper in the long run. We had engines go routinely to 270K and many went to nearly 500K before anything major was needed. When you are pulling (or pushing) things that are over 20K lbs, IMHO diesel is a better choice. Go to 30K-50K lbs, no choice, it IS diesel powered for sure.

Breakaway engine noise- when stopped, you hear the engine rumble thru the chassis and up thru the rear floor, NOt bad but it is there, as soon as you move 5-10 MPH, the noise is gone! My wife and I talk in normal living room conversation tones will running down the road 70+. It is so quiet, I hear some wind noise around the drivers outside mirror but that is it! Wouldn't trade that for a gas puller for sure now that I have had both. Some friends that bought a new '07 SOB with 8.1 puller rode with us and couldn't believe how quiet the Breakaway was compared to theirs. (they have had temperature issues with their trans and had some engine related issues also, were covered under warranty. They get close to 9 MPG with their 8.1L BUT he drives 55 MAX!

Fuel costs? Yup, sure is surprising that diesel is so much higher them gas, but, even at a 0.60 premium, my fuel costs are lower then what My SOB costs.

It really come down to personal choice or what is available in the package that the individual wants.

Lastly, diesel fuel is a bit safer then gasoline.

I'm assuming that the diesel engine lasts longer because it's typically running in a much lower RPM range as compared to a gas engine and it has a large oil pan with plenty of oil to circulate. Diesel engines have four piston rings too and probably other advantages that I'm not aware of.

quote:

This Post



Forums Tech Talk Big GAS engines vs Diesels??

I have the 86 regal 28 with the 454 3 sp automatic. 6mpg ouch. I have a bug I can't seem to shake about repowering with a diesel. I have found a doner 5.9l cummins with a 4 sp automatic. The rated hp is 190. Does anyone how this would power the Barth. Thanks, Todd

Todd,

Simple answer yes, it would be what powers similar sized Breakaways.

Little more difficult answer, it's more about the chassis being able to handle all that added weight (assuming it will go up front).

Really difficult answer, most diesels have air brakes to make the heavier package safer. This would be more difficult to replicate than the motor swap.

My advice, sell yours and pay the difference up to a Breakaway! The other advantage will be economics when you go to sell an a) FrankenBarth or b) legitimate Barth.

BTW - my 50,000 lb BB WL also gets 6.++ MPG. Shows what a diesel can do for economy anyway.

quote:

Originally posted by todd ryan:

I have the 86 regal 28 with the 454 3 sp automatic. 6mpg ouch. I have a bug I can't seem to shake about repowering with a diesel. I have found a doner 5.9l cummins with a 4 sp automatic. The rated hp is 190. Does anyone how this would power the Barth. Thanks, Todd

To replace the 454, I would not look at the 5.9L Cummins, I would strongly consider a Duramax diesel. They are lighter more compact package that would fit easier then the LONG, HEAVY 5.9L Cummins.

HOWEVER:

I do agree with Corey, unless you are a highly skilled mechanic, and can do most of the work yourself, it will take a long time to get any pay back. The other issue is NOISE! I assume that yours is a 454 puller, if you replace that with a diesel, you will go crazy with the added noise. Will take a lot of effort to insulate the doghouse and surrounding area to make it livable. Further, I would not consider the 4 speed auto, even thou it is lighter, the engine RPMs would be way up during cruise and again much higher noise!!

My 0.02

Merry Christmas everyone!

quote:

Originally posted by MWrench:

To replace the 454, I would not look at the 5.9L Cummins, I would strongly consider a Duramax diesel. They are lighter more compact package that would fit easier then the LONG, HEAVY 5.9L Cummins.

Yeah, me too. When I did my repower, I looked for a Duramax, but they were too new on the market for me to find a donor vehicle in a junkyard. Today, even after 10 years of happy ht502 Barthing, I would still rather have a Duramax. For fuel economy alone, if nothing else.

The Duramax has sump clearance issues, but the pan can be cut and welded to make it fit.

If I were doing a repower today, I would also look at a gas 8.1 with the 6 spd Allison and locking converter.

My hearing does not allow me to be bothered by a gasser's noise unless the fan is roaring when really hot, which is very seldom.

I drive a little slower that Ed, but my mileage is around 7 level no toad, and in the 5s with a heavy 4WD and a lot of climbing. Don't take my figures as gospel, as I do not check it very carefully, and we always seem to be climbing. climbing sucks gas, but there is no payback for going downhill. It seems to be in the high sevens on level no toad, but we don't do enough level driving to really tell. Most of our average figures involve longer trips with climbing.

quote:

The Duramax has sump clearance issues, but the pan can be cut and welded to make it fit.

I used to get a kick out of - early Novas I think - where they would weld a piece of exhaust pipe through the oil pan and the steering arm would pass right through. Now that's what I call Hot Rodding!

quote:

Originally posted by Moonbeam-Express:

quote:

The Duramax has sump clearance issues, but the pan can be cut and welded to make it fit.

I used to get a kick out of - early Novas I think - where they would weld a piece of exhaust pipe through the oil pan and the steering arm would pass right through. Now that's what I call Hot Rodding!

AAAH.............you have fallen for the common misconception on that.

The tube was originally put there to mitigate and oil temp issue. The fact that Chevrolet only installed a splash shield on the driver side caused a cross flow situation with the air underneath. The tubing welded into the pan took advantage of this.

The tie rod thing came later, when some clever person realized the hole in the pan could serve two purposes for the price of one.

I learned something new today! That's a good day.

quote:

Originally posted by todd ryan:
I have the 86 regal 28 with the 454 3 sp automatic. 6mpg ouch. I have a bug I can't seem to shake about repowering with a diesel. I have found a doner 5.9l cummins with a 4 sp automatic. The rated hp is 190. Does anyone how this would power the Barth. Thanks, Todd

The better choice for drop-in would be the GM 6.5L TD; if you already have hydroboost, the brake-P/S conversion would be easy. Better still would be to add the 4L80E transmission, as most 6.5Ls are wired for it. If off a gasser, the orque converter would need changing (that would be the time to get a Sun Coast Converters unit along with the machined spline). The differential gear ratio might need changing as well.

The Duramax is a good choice, but early ones have had injector issues, and a set out-of-warranty ain't cheap.