Recap and real world review of my LBZ Duramax 2003 Suburban conversion

[testdrive]

To All,

Some in the Duramax Suburban Brotherhood followed my upgrade build that involved installing a 2007 Duramax LBZ 4X4 6sp Allison complete drive train package into my 2003 ¾ ton 4X2 8.1L gas Suburban, it is now time to review and update after 10 months and 20K miles of real world driving, mostly pulling a 7500lb travel trailer. All but about 2500 miles were towing miles. 12000 miles were driven in the last 4 months in Canada and Alaska. Remember we travel in the US Rockies, Canadian Rockies, and the Alaskan Ranges. I can’t tell you how many passes and continental divides I crossed in the last 10 months.

Just a short preface…

The reason for conversion was I changed lifestyles from a working guy to a retired guy. That left a lot more time to pursue the lure of the open road. In other words my wife and I plan to spend our up to 6 months a year driving the highways of the US and Canada towing our 7500lb 2006 Bigfoot travel trailer. A requirement from the budget director, was no debt, we could afford this. The upgrade would allow us to extend the usefulness of an excellent tow vehicle. Our GVW on the scales is 15960lbs with myself and wife. This is loaded with fuel and 45 gallons of water. On the same scales in 2011 with the 8.1L and 2 wheel drive we weight in at 14800. The Duramax and 4X4 added about 800 – 850lbs. We are also running tires that about 120lb for the 5 of them.


The conversion went well with the interest and help of the Diesel Place forum members. Notables are theTDIguy (Eric of Duraburb), boisebiker (my interest started with his “at home” trail blazer build) , thefermator, gr8gnzo, CDN111, Skippie, and many others. Thanks to all.


Comparisons of my Duramax Suburban and to my 8.1L gas Suburban. Same Suburban, just a different powertrain.

• On a 35 gal fill up, I can expect to make 475 or more miles. The 8.1L would be lucky to get 325. The DIC will usually show a range of 504 miles when I fill up, the 8.1 might show 310. A bonus of over 4 1/2 miles to the gallon. These figures are towing miles. The fuel tanks are the same.
• I did a solo drive to Dallas (900 miles) at ~65 MPH with a round trip average of 20.9. That has to be 5 to 6 MPG better than the 8.1L. These are hand figured with a accurate speedo. After the computer adjusts to solo MPG the DIC will show range of 700 miles.
• While on the subject of the DIC… The gallons used and the MPG are much more accurate than the gasser. I mean very much closer. The 8.1L readings were never close to accurate. Over the time that I owned it, I put somewhere around 13 thousand gallon of fuel in it. So yes I have some history
• I will address the questions about “towing experience” that some have asked about. To sum it up in a very few words. I will say, it is more relaxed and enjoyable because I do very little shifting and don’t pay much attention to altitude, terrain, wind, and fuel gauge. The downhill braking of the Allison and turbo brake is a nice and save a lot of grabbing the shifter. Remember no transmission braking on my 4l85 4 speed. Sometimes on some long uphill mountain passes (8-10%) I would have the 8.1 screaming and be in second gear with the pedal on the floor for several miles. With the Duramax there are very few forced downshifts even while maintaining near set speed. The diesel seems to level out the mountains and even calm the winds. I guess that the engine and transmission performance was way more than I originally envisioned.
• My 8.1L had good power with good torque, but with the 4 sp trans there was a wide gap between 3rd and 2nd and that would take the RPM way up. I put around 90K towing miles in 48 states on my 03 8.1 and know that it was a solid performer
• All systems including the Autoride active suspension and fuel work just as they did before the conversion.
• This diesel is so smooth. Transition between idle and power is very smooth. Not even a slight hint of dead spot.
• The Allison 6sp transmission is so smooth and well behaved it is almost hard to believe. Simply put, it is graceful. The TOW HAUL with turbo brake works very well in the mountains, almost has the ability to think for itself. Love to silently count the snappy up shifts while in tow haul pulling the trailer.
• I added 4 wheel drive for the off road adventures. We love to visit out of the way places. This was what pushed this conversion into reality. Too many times getting stuck in our own tracks. Eric of Duraburb made it look easy. Easy for him, maybe not so easy for me.
• Lastly, I enjoyed the project from start to finish. I was lucky in so many ways… donor was a big bonus, everything that I could have wished for, I had time on my hands and many of the tools needed and a wife that let me tear apart her daily driver. I had Internet (Dieselplace.com) friends and local friends that assisted and other. Most of the recovery of parts from the donor and the gas stuff sold well and that reduced the total money. One important issue was the fact that my Suburban was a 2003 ¾ ton Genll electronics that works well with the 2006-2007 LBZ engine and transmission.

I still get a smile on my face each time I start the engine. My wife has accepted the extra noise and smell (perfume) and that is behind us. In the beginning, she kept asking if the body might turn loose if the bolts got loose. I assure her that I will continue to check the bolts regularly.
The noise level is a little higher because of the hard hitting diesel and the aggressive tread tires. When in TOW Haul I get a little more low speed driveline noise because of the converter locked. I did retain the stock muffler and pipe size.
I’ve had a good number of folks ask about it. Some even demand to look under the hood. Some think that it was just a special order from GM. I had an offer to sell it. While at Haines, AK a diesel Tech from Ft. Nelson, YT spotted it from 200 feet away and came over to check it out. he knew what he was looking at. I tell them if they are interested where they can get one made to suit. Doesn’t have to be an old one it can be a new one also. I am proud to show it off and my wife tells me that it shows, so in every way it has exceeded all of my expectations. On this last outing of 4 months on the road, it saved in fuel about 400 gallons in 11958 miles traveled. The overall MPG figured 13.18. I used 906 gallons of diesel. I traveled nearly the same miles in Alaska and Canada in 2009 and used 1350 gal of gasoline. This year the area we traveled in Canada, diesel was cheaper by 10-30 cents a gallon less than gasoline.

Comments or questions are welcome

[damutt]

wow, i am so glad this worked out ad is ice to read a before/after for this kind of swap.i will have to do this once i get my truck up too. once again, great job :P

[boisebiker]

Great summary, gives the guys who can only dream of this kind a rig a chance to see what it is truly capable of. If you don't mind could you post your actual costs for this build up. I know on mine many people can not believe that I could build a rig like this for $17k from start to finish(including cost of Yukn XL).

Again congrats for the successful build.

[DIESAHL]

great write up. glad everything is working great

[96Sub]

I followed your build write-up with great interest. Glad the trip north was enjoyable, and very interesting to see the back-to-back comparison of fuel economy gas to diesel. At the moment diesel is still tracking about 10 cents a litre less than regular gas so it eases the pain somewhat.
I am located in Calgary AB, if I had known you were passing somewhat nearby I would have liked to inspect and measure a few details of the conversion.
In particular the graduated body lift pucks which you machined for the reverse-rake. If these dimensions are handy I would be grateful to receive them. My FrankenSub is currently 600 miles away from my lathe so it is a little difficult to measure and calculate my own.

[testdrive]

96Sub,
This year I entered BC at Osoyoos and back into the lower 48 at Fortuna ND, however we may come through Calgary next June.
Good luck on your build and be sure to update when you get started.

Actually Skippie was the machinist, he and I did some swapping of needed items. It was all in the Brotherhood, I just gave him the dimensions and a few days later they were on my porch. I had hacked up some temporary ones just for a test period.
My son is the numbers guy so he came up with the math.
I think Eric theTDIguy started the progressive lift several years ago. I am very happy with mine.

Attached is the actual calculations for each spacer and the math. In real world it doesn't have to be this precise.
http://64.185.13.2/images/spacer.pdf

1 = 0
2 = .32426
3 = .52681
4 = 1.0558
5 = 1.5409
6 = 2.0

[96Sub]

This will help considerably, thanks.
Actually I am modifying a project which was semi-completed by the previous owner. He installed a 3 inch body lift all around which IMO was excessive. This lift plus the almost 34" tires makes it a bit of a climb into the drivers seat, even for me at 6'.
So we are lowering this lofty perch, starting with slightly shorter tires, possibly different wheels as well. The reduced body lift will help.
Below are a few photos of where we started in July. Newer photos will be posted when I get a chance to take them. Thanks again.

[damutt]

96sub, is that a chevy HD front clip for like 04? if it is, it looks great

[96Sub]

HD front end was off a 2006-07 HD Classic. Only one problem - what you see in the photos is a 3 inch body lift which puts the bumper and its brackets at different elevations, so the fastening bolts don't all line up, too high by an inch. Will fix that issue soon by dropping the body and bumper down to a 2 inch lift at the front.

[damutt]

ah, it still looks great. whoever chose that front clip had good taste