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Diesel Conversions Convert gas to diesel, or convert to a 6.2/6.5/Duramax/Cummins/Navistar/Isuzu/Perkins/Detroit/or ... diesel engine. Go here to see completed projects, works in progress, share your conversion or ask the experts.

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  #21  
Old 09-28-2007, 07:29 AM
BillCarry BillCarry is offline
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Join Date: Mar 2000
Location: Sylvan Lake, Michigan, USA
Posts: 42
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I have a 6.5 TD 30 ' motorhome which I bought new in 1994 (one of the first 6.5 front engine units built by Georgie Boy and perhaps the industry). Loaded it weighs around 15,000 pounds.

I just passed 150,000 miles.

I have accurately calculated mileage on four or five trips from MIchigan to Florida and back and I consistently get between 11.5 and 12 mpg. I drive 60-62 mph on the interstates. With three previous, slightly smaller gas motorhomes (one GM 454 TBI and two Dodge 440 carb) I consistently got 7.5 to 8 mpg. My oil consumption has not changed since the engine was broken in and runs a quart about every 1800 miles. The over the road performance feels about the same as the gas jobs.

I'd say if you can pull this off with the Duramax you'll be real happy with what you get.

Bill Carry
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  #22  
Old 09-30-2007, 10:36 PM
BigRabbitMan BigRabbitMan is offline
FMC Cruiser
 
Join Date: May 2007
Location: Dixon, CA
Posts: 83
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Bill,

Thank you for the input. As you did, with the 440 I am getting 7.5-8.0 mpg and would expect it to go to about 11-12 mpg. That lines up with your experience. I will get it done, but I do know that it will be a long involved project. That is why I went ahead and got a replacement 440 installed so that I can use the coach while I am gathering all of the parts.

What I am looking forward to is the expected improvement in general performace particularly in the mountains. That is where I expect to havest the benefits of the higher torque of the Duramax linked to the gearing of the 6 speed Allison through my 4:62-1 rear end.

Once installed it will be off to Mexico and Alaska!!
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Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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  #23  
Old 12-09-2007, 03:57 PM
journeyman journeyman is offline
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Join Date: Jan 2005
Location: Kazan
Posts: 27
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Any updates?

Are you still converting?
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  #24  
Old 12-19-2007, 09:44 PM
BigRabbitMan BigRabbitMan is offline
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Join Date: May 2007
Location: Dixon, CA
Posts: 83
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Yes, I am still converting, but the time line is probably fairly long. As it turns out , the shipping damage was minimal - tough engine! I am looking to continue the project by aquiring an Allison 6 spd in late spring and look towards making the install happen in mid to late summer.

Due to a pinched nerve in my upper back (since October) that is only getting better very slowly (typing still bothers it!) all physical activity is on hold. I am going to contact the mechanic son of my neighbor an see if we can take the engine down to his shop and, with it on the stand, identify what parts are missing, locate them and have him install them on the engine.

He drives a Duramax powered unit so he will be able to use it to help identify the missing accessories and bracktry etc..

I will have more time after the end of Febuary as that is when I semi-retire to about 25% time.
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Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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  #25  
Old 06-30-2008, 09:06 PM
BigRabbitMan BigRabbitMan is offline
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Join Date: May 2007
Location: Dixon, CA
Posts: 83
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Well, semi-retirement is just now happening, but am now supporting wife's schedule to assist daughter when granddaughter arrives in July. Then it will be preparing for spending most of September in the Philippines and then back to MY projects. I am looking for a forum that has the Allison transmissions as it's main subject as I need to start the searching in that area. I have solidly decided on using the Allison 6 speed as it will give me 1900 rpm at 65mph with no rear end modifications.

Does anyone have any suggestions on forum(s) for the Allison transmission?

Here is a mileage report by the present owner of the conversion to an LB7 of an FMC motor coach like mine that was previously covered by The Diesel Page. He will be making a 5000 mile trip in September and will do a more complete report at that time. He will record results at different speeds, etc.

"Pulling a 3500lb car at 70mph we got approximately 11.8mpg. Without the car behind, we got about 14.5mpg at varying speeds at mountain elevations.

The project creeeps forward!
__________________
Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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  #26  
Old 08-23-2008, 11:06 PM
BigRabbitMan BigRabbitMan is offline
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Join Date: May 2007
Location: Dixon, CA
Posts: 83
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Here is the report of the mileage for a trip from S.D. to VT and back: "We averaged 61.2 MPH (according to "Miss Garmin") even with lots of road construction and slower speeds in the mountains and we averaged 13.8 MPG." This was a 3800 mile round trip. This is the coach that is the same as mine and was featured in an article in The Diesel Page several years ago and was discussed above. He normally tows a BMW.

That is the kind of results I would like when I eventually do my conversion with the LBZ that I have in the garage.
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Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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  #27  
Old 03-31-2009, 08:04 PM
BigRabbitMan BigRabbitMan is offline
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Join Date: May 2007
Location: Dixon, CA
Posts: 83
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Well I am back to having conversations about my project (the '06 LBZ is still in the garage!). I just talked with a used engine/transmission reseller here in the local area and he has a number of different model Allison's in stock. I have been looking at the 2550 as it has the lower gear ratios in 1st and 2nd and the parking pawl. Allison didn't allow parking pawls in new units if they were over 22,000 lbs. Mine is 14,000 plus an tow vehicle which could take me up to 18,000 lbs gross weight.

The question of the day is whether I should go with a 5 speed or a 6 speed. With my present rear end and wheels, which I will not change, the 5 speed would put the Duramax LBZ at about 2200 rpm at 65mph. The 6 speed would put the engine at about 1900 rpm.

To all of you Duramax folks that run with loads in that range a lot of the time, where should I target my RPM? Reasons?
__________________
Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

Last edited by BigRabbitMan; 03-31-2009 at 08:14 PM.
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  #28  
Old 04-01-2009, 11:56 PM
BigRabbitMan BigRabbitMan is offline
FMC Cruiser
 
Join Date: May 2007
Location: Dixon, CA
Posts: 83
Default Conversion to 5spd or 6spd better for Duramax?

Quote:
Originally Posted by BigRabbitMan View Post
The question of the day is whether I should go with a 5 speed or a 6 speed. With my present rear end and wheels, which I will not change, the 5 speed would put the Duramax LBZ at about 2200 rpm at 65mph. The 6 speed would put the engine at about 1900 rpm.

To all of you Duramax folks that run with loads in that range a lot of the time, where should I target my RPM? Reasons?
Have changed the title to reflect the current question.
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Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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  #29  
Old 04-03-2009, 10:08 PM
BigRabbitMan BigRabbitMan is offline
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Join Date: May 2007
Location: Dixon, CA
Posts: 83
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Based on the discussion in this thread http://www.thedieselpageforums.com/t...ad.php?t=34258, the decision has been made to use a 6 spd.

Now to find an Allison 2550 which is the model with the lower 1st and 2nd gear ratios.
__________________
Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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  #30  
Old 12-27-2010, 09:12 PM
BigRabbitMan BigRabbitMan is offline
FMC Cruiser
 
Join Date: May 2007
Location: Dixon, CA
Posts: 83
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It is time to update this thread - the action begins!

Today I aquired a 2006 GMC Sierra 4x4 with an LBZ and 6 spd Allison (47,000 miles). So now the project goes into high gear utilizing the time and talents of two people: myself and a fellow FMC coach owner. The conversion will be done at his house as I have no room at my house. He is also very talented mechanically, electrically and with control systems.

I still have the LBZ in the garage, but we decided that it would be best to get a "roll over" donor vehicle so that we could utilize the maximum number of other systems instead of the minimum number of other systems. It is now our intention to integrate the compete GMC dash module into the FMC dash including physically. We will disable any unused functions, but will otherwise have a stock gauge/dash module in the FMC.

Right now the biggest unknown is the transmission issues I have discussed above.
1. Will a Duramax ECM function as well with a non-GM TCM as it does with a GM TCM?
... or,
2. Will a GM TCM work with changed gear ratios in the Transmission?

If you can give any help or direct me to a source of information on these two questions, I would greatly appreciate it.

Wish us luck as I pick up the donor vehicle in a day or so. The LBZ in the garage will be sold when we are sure we don't need anything from it as well as all excess parts of the roll over donor GMC Sierra 4x4.

Stay tuned,
__________________
Stephen H.
BigRabbitMan
1976 FMC Motor Coach #1046
Formerly 440, now LBZ
Rear engined w/4 wheel independent suspension.
Tow car: 1987 Subaru Brat 4x4
http://www.fmcowners.com/mbbs22/phot...asp?albumid=77
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