Converting early gas MH to Duramax? Possible?

[BigRabbitMan]

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!!

[journeyman]

Any updates?

Are you still converting?

[BigRabbitMan]

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.

[BigRabbitMan]

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!

[BigRabbitMan]

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.

[BigRabbitMan]

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?

[BigRabbitMan]

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.