looking for the best repower

sledhead · January 22, 2013, 03:06:09 PM

After considering a trade for a newer ss motorhome my wife and I have decided to stay with what we have.After all we built it because of the problems the old ss had as well as a safety and longevity. We have a 1990 mci 102c3 with a 6v92 ta (2 year old out of frame rebuild ) and a ht 740 trans. I installed propane injection on it last year and the power is about 10-15 % better under load. I should be happy with what I have... But I want more power.So what is the best combo of cummins eng. (year , model and trans to fit in what we have without to many modifacations . Or is there some more I can do with what I have. When we get home I will find out the hp and what was installed when it was rebuilt (6v 92 ta ) thanks in advance dave and karen

wg4t50 · January 22, 2013, 03:36:53 PM

I would GUESS, depending on the radiator setup used on your model, the 8V-92 is capable of very good power, but to get away from the 2 stroke, there are a few good choices. Without knowing your coach, I am some what lost. As to the computer details etc.
Me, I would think about a Cummins ISM 450-500 hp, these are computer engines.
It depends alot on your ability to convert it would be my guess, as paying a shop to do the repower would be a large number, My guess anyway.
Know a chap that repowered his 01 Eagle with the DDC 60 Series, but he is a computer control geek and it worked great.
Of course you could be bitting off a large chunk of experience.
Good Luck
Dave M

luvrbus · January 22, 2013, 05:22:13 PM

That bus was offered with a Cat engine also it could be easier for the parts find there is nothing wrong with old Yellow lol

hargreaves · January 22, 2013, 05:24:30 PM

I just put in a series 50 B 400 combo with 3.73 gears. Booted the engine up to 350 hp 1200 foot pounds of torque . Just came down to Quartzsite from vancouver, no trucks beat me on the hills.
Love it. 8.5 miles per gallon at 65 mph 1400 rpm towing a toad. Cheers gerry

PS I now Clifford does'nt like them. LOL

Brian Diehl · January 22, 2013, 06:13:11 PM

I have a Year 2000 ISM @ 400hp & 1450 lb/ft of torque. I love it! I consistently get high 8s low 9s. I do drive it like I pay for the fuel, so YMMV. Plenty of power. It also runs soooooo much cooler. I have intercoolers in front of the stock radiators. Everything keeps up as it should unless it is 105 degrees out and I have it running in 10th gear @ 58 mph. Then it will slowly heat up. all I have to do is downshift back into direct (9th) and the temps come right down. I would not leave home without anymore!

TomC · January 22, 2013, 09:41:11 PM

You could go with a big block engine like a Series 60, Cummins NTC/N14 or ISX15, Caterpillar 3406/C15-but these are all very tall, heavy, engines best suited for big rig trucks (although some do use these engines). My opinion-the best are pre 2002 (no EGR) of the medium sized-like Cummins M11/ISM, Cat C12. The ISM was used in many trash trucks. You can have it rebuilt up to an RV engine that puts out 500hp and 1550lb/ft torque. Either of these medium engines are about the same height as your 6V-92, but of course a bit longer (the 6V-92 is a real compact engine).
Not only will you increase your power, but could get 2mpg more. Good Luck, TomC

wg4t50 · January 23, 2013, 01:33:47 AM

Jusst useless info, the ISM Cummins is the smallest Cummins that theyrate as Heavy Duty along with the 855, N14 & ISX, not to be confused with the B, C or ISL series which are Med Duty per Cummins. Know the L & M Series takes new bearings at 500k and kits & head work at 1 mil. keep getting up. Also Cummins offers the girdle kit when you remove the pan, have found issues after 1 mil miles, why the girdle kit. the ISM500 comes with it. I added it to mine.
I upgraded my 2001 Pre EGR ISM from 450 to 500 with Cummins blessing, they did it for $3,400.00 and the added 100 torque is big, went to waste gate turbo, electric boost sensor control for it and reprogram the ECM, Bingo.
Cheers
Dave M

blue_goose · January 23, 2013, 05:38:52 AM

It may not be the best, but after doing 4 of them it is real good. That is the series 50 and the world transmission. Three of these have been in MCI's and one in a Eagle.
I have just completed the change in my 102C3 that had a 8V92 DD11 and the 755 Allison transmission. I lost HP but so far I can't tell it because of the lower rear end and the 6 speed transmission. I went from a 3.36 rear to a 4.10, that is a big gain in power. With the 2 overdrives it keeps the RPM's down.
Another good reason for this combo is you can get into it for not too much money. There are lots of cheap units on the market. I bought a MCI 12 with everything in for the last change. The ones before that were done from city buses. The city buses will have a world B400 with retarder. The best way is to buy the bus, bring it home where you are going to make the change and use all the parts.
Jack

luvrbus · January 23, 2013, 03:20:24 PM

Gerry,I don't like any engine that has to use a balance shaft like John Deere,Case or DD but I do admit it brings a smile when you go to S&S or Williams when they replace one and cut a hole in the side of the core and send it to engine haven and then have a old 8v71 they are rebuilding LOL

sledhead · January 23, 2013, 04:09:03 PM

So it looks like I should look for a m11 or a ism cummins or the cat c12. I like the pre 2002 with out the emessions crap. Now what about a transmission.Would the 740 work with my 333 rear end or is it to low? I do have a buddy at home that knows a lot this stuff but me not so much thanks again dave

rv_safetyman · January 23, 2013, 05:17:22 PM

Depends on what speed you like to drive. Lots of folks use the HT740 with a four stroke. Not ideal but it works. See chart below from my engine conversion article series in Bus Conversion Magazine.

The first two columns represent an HT 740 with the most common rear end ratios, while the last two columns represent the impact of world transmission overdrive ratios (or AutoShift with .74 overdrive).

The "ideal" cruise rpm for most four stroke engines is 1400-1500.

Jim

chessie4905 · January 23, 2013, 06:08:36 PM

No matter what you do, in the long run you'd be better off finding a conversion/shell with what you want for an engine. You'll end up spending more money to change it out than you realize. If you like labor intensive jobs, find a shell the same as yours with the larger factory installed engine and swap everything, then install your engine and or trans in the donor shell and sell it.I don't follow MCI's, so I don't know if anything else was available. Or, you could be more patient on the hills.

Brian Diehl · January 23, 2013, 06:33:24 PM

The ISM needs to be behind an over drive transmission. You will get much better fuel mileage if you do.

twostick · January 23, 2013, 07:05:50 PM

If it was me, I would be looking for a DDEC3 S60 12.7 if I was going to the trouble of a 4 stroke conversion. M11/ISM/N14/ISX engines have the same lousy throttle control that the PT pump from the mechanical NTC engines had and they can't touch the DDEC3 fuel mileage in my experience. Lots of people have good luck with CAT but I never owned one that didn't try to bankrupt me. CAT IMHO stands for "Can't afford this"

. I've seen lots of C12's turn themselves into C thrus.

The EGR stuff didn't start until Oct of 03 but the low NoX software started in 98 so for ideal fuel economy/power you would look for a DDEC3 with a MFG date pre 98 that hasn't had the ECM software upgraded to 98 specs. The fleet I worked for at the time saw the fleet fuel average drop by 1 mpg on their S60's when they went to 99 model trucks compared to the 96 and 97's. This was true for all MFG's.

All this being said I have always had a soft spot in my heart for a 2 stroke and an air to air aftercooled 6v92 can get really respectable fuel mileage when driven and tuned accordingly. Hard to get big power and big economy with a mechanical engine tho. You could hot rod the 6V and go with bigger injectors, play with the timing, air to air if it isn't already and step up to a bigger turbo so it doesn't smoke like a freight train but you probably just spent the price of an 8v92 for about the same gain. Torque is your friend and for that there is no replacement for displacement.

3.33's with a direct drive trans preferably with a lock-up torque converter will cruise 64 mph@1700 with 11r24.5 tires. A 2 stroke might be happy there but for a 4 stroke to get good mileage it will want to see a cruise rpm range between 1350-1500 rpm if you are talking pre 1998 specs. More MPH means spending more fuel$$ no matter how it's geared.

If you upgrade your trans to an Allison World you will need an axle ratio of 3.90-4.10 depending on tire size. 4.10's will get you 66 mph@1375 with 24.5 rubber with the World .64 OD or 3.90's with 22.5's.

Here's a handy road speed calculator link

http://www.analysis-inc.com/reference/road-speed-calculator/

Kevin

Brian Diehl · January 23, 2013, 07:51:40 PM

Kevin, what do you mean by "lousy throttle control"? I have no experience with a S60 DDEC 3 to compare to. My comparison is to the 6v92 I had before. The difference in throttle response is night and day better with the ISM. My analysis is the throttle control is great. However, I'm interested in what you mean and how it could be better.

Thanks!