Update 7-17-2025 - Funny story! Fuel economy related...
Some time ago, I announced here in this thread that I was having Kennedy reprogram Lil Red's ECM to help the truck be a little more "daily driver friendly". I was told that I could have two programs available, and toggle between them using a switch. I asked JK for one of the two programs to be "stock". John sighed a little at hearing the word "stock", but did as I asked - though he added a little twist to the definition of the word "stock".
When delivered, John said that the "stock" switch setting would be a "stock/fuel economy" setting. I guessed injection timing and possibly the fuel rate curve received a tweak. This is what I thought I had been using since the ECM was returned to me - a little more than 4 years ago iirc. The truck felt pretty spunky, I thought, so why add more power if I didn't need it. Plus, I wanted the new head gaskets and injector cup reseal plenty of time to "settle in" before "putting the wood to it".
I had installed a toggle switch on the bottom rim of the dash way back when... not long after JK first began offering EFI-Live programs and I began using one of his ECMs with his big power programming. I knew (or was convinced I did) that pushing the switch toggle away from me would select the "stock" setting and pulling the switch toggle toward me would select the "fun" position (a +100 horsepower setting). Murphy said I had a 50/50 chance of getting it right, if I ever forgot...
Since replacing the head gaskets in Lil Red (in late August 2021) till a couple of weeks ago I left the switch in what I thought was the "stock/fuel economy" position. I thought I didn't need the +100 position... Turns out... All of the Lil Red fuel economy reports I've posted here in this thread these past 4 years were actually with the switch in the +100 position, unbeknownst to me. :eek: Lil Red is 2500-lbs lighter than my crew cab, so I thought the spunk was due to that... till one day... a week or so ago, I thought I'd try the "fun" position... To add a little spice to a YouTube video... Actually, the beginning of this video: https://www.youtube.com/watch?v=nvKLtiGF-50
Much to my surprise, I definitely noticed a change in performance, but it was opposite to what I was expecting. Long story short, I had been running in the +100 position all this time - for at least the last 4 years. Funny story actually, but after considering my mistake for a few minutes a question formed in my mind about whether fuel economy would improve if the "Fuel Economy" switch position was active... So I filled up about 10 days ago, selected the "stock/fuel economy" switch position, then drove the truck another 375 miles over about a week or so - some local and some a little longer distance driving. The prior tank in Lil Red, with similar driving produced just over 20 mpg, which I thought was pretty good for a local biased tank of fuel.
So, what was the result of the most recent tank of fuel? 375 miles, 15.708 gallons = 23.873 mpg.
Maybe there is something to the "Fuel Economy" switch setting after all... I'm looking forward to more Interstate driving to get a better comparison, but for now, it looks like the improvement could be at least 2-3 mpg better... when using the "stock/fuel economy" power setting. :D Would an improvement of 2-3 mpg be a worth losing 100-hp? :confused:
Update 7-25-2025 - OBS Duramax Swap - Oil Pan Mod for the 4WD OBS trucks.
I received the following message the other day asking how to overcome the problem of the Duramax oil pan interfering with the OBS 4WD front axle mount bracket (on the passenger side). The stock Duramax oil pan won't fit into the 4WD OBS chassis without a mod - a fairly easy mod... ;)
Quote:
OBS Duramax swap
From Abe P on 2025-07-21 21:56
Hello, I bought the Duramax conversion motor mounts a few years ago from the diesel page, I'm finally able to start my project, now that I mount the engine to the frame the oil pan is sitting against the front axle bracket, how do you deal with this?
https://www.thedieselpageforums.com/...5&d=1753470000
The above image details the problem. I pointed the camera straight down while standing inside the engine bay (front clip was off the truck). This is the rear portion of the left side (passenger side) mount for the 4WD front axle. The rear of the truck is toward the top of this photo. The red you see in this photo was one of the legs of my engine hoist (that is parallel to the floor).
I snapped the above photo during the very first trial fitting of the LB7 into the chassis. This interference was a problem, but the first step in the solution was pretty easily dealt with using an air chisel and angle grinder.
https://www.thedieselpageforums.com/...3&d=1753470000
The first thing I did was remove the outer brace, which itself was the largest contributor to the interference. I considered that the brace was important, but... just how important, I wondered? This truck has been driven for over 14,000 miles with the Duramax, and has seen many 1/4-mile launches in 4WD, some of those were with up to 600+ horsepower. That front axle bracket hasn't budged. However, if this truck was intended to be used in driving conditions that required a lot of 4WD driving, I might add a new, though flatter, more closely fitting bracket brace - just in case. I don't intend to do that with Lil Red, but it's always an option that can be added later. Of course, those with 2WD OBS trucks/SUVs don't have this to deal with.
https://www.thedieselpageforums.com/...4&d=1753470000
The above shows the scratch that appeared on the oil pan after the above trial fit. That showed exactly where the interference was.
https://www.thedieselpageforums.com/...6&d=1753470000
This was the final step in the solution. I cut out the area using a cut-off wheel, making the cut large enough to provide for a little extra clearance to allow for engine movement. A flat piece of sheet steel (thickness matching the oil pan) was shaped and then TIG welded over the hole. The TIG weld cleaned up nicely, and then the oil pan was painted black. Looks good. Works great! No leaks. And, very little was lost in the way of oil pan capacity. Of course, this modification works with the motor mounts we offer, and this oil pan mod info is included in the printed Duramax Conversion Guide linked below so you can show your welder exactly what you want.
Jim
New Video! August 1, 2025
https://youtu.be/nvKLtiGF-50
OBS Duramax Diesel Swaps & Road Trip - Part II - 57 minutes - This time we discuss some of the history of western Montana as well as the 21 year history of Lil Red, then take you along with me on another road trip. We'll travel through some of the most scenic highways found here in western Montana, and we'll show you just how much fun and reliable a performance truck can be.
Youtube Channel: https://www.youtube.com/channel/UCfR...KC47DfjGKBNJrQ
New Video Short! August 17, 2025
https://www.youtube.com/shorts/yiU5zzOELuM
2-1/2 minute video... Make your OBS/Squarebody Duramax swap easy! We offer professionally produced Motor Mounts that allow for an LB7, LLY, LBZ, LMM, or LML (pre L5P) Duramax engine to drop into into a 1973-1998 Chevy pickup chassis. Thanks!
Duramax Swap Mounts: https://www.thedieselpage.com/form.htm#swapguide
Quote:
If you don't already have a
YouTube account, I recommend that you create one. It's free and easy to register at
YouTube.com, plus you'll be eligible for free stuff here in The Diesel Page. We've begun offering
all member-only online content here at TDP free of charge to those who are subscribed to our YouTube channel.
Our channel subscribe button is located in the lower right corner of every video on our channel... or, click the circle/truck image in the top/left of the above image.
Once you've registered at YouTube, subscribe to our channel, then
send me (using the "Contact Me" link in my signature)
just your YouTube account name. You'll be assigned a new easy password just for use here in TDP. You'll be helping our channel to grow and you get free stuff in return as a Thank You. Easy-peasy!
Youtube Channel: https://www.youtube.com/channel/UCfR...KC47DfjGKBNJrQ
Update: YouTube Video Short - join the team, help with puns...
https://youtube.com/shorts/6Oyo_UEAqy8
After watching a recent video about our OBS Chevy Duramax Swap truck, a viewer asked in a comment, "can it still haul like a Duramax was intended to?". The answer is "YES", of course it hauls "as intended". See if you agree after watching this short video... All in good fun!
Be sure to visit the following YouTube link for more videos about Lil Red and Duramax swaps in general. Be brave - leave a like. Inspire a new video - post a comment. Subscribe - join the team, help with puns... Thank you for watching!
Lil Red Playlist: https://www.youtube.com/playlist?lis...WKA7wgQrN3WEKz
Update 10/9/2025 - Project Planning
I had an email exchange recently with a 1994 Suburban owner who asked a series of questions regarding a Duramax swap. Here is that email exchange:
Hi Byron,
Thanks for your email. Your questions are quite comprehensive, and I thought that they would add value to my swap thread in the bulletin board for Lil Red.
My answers will appear in the bubbles/embedded within your message… Jim
Re: The Diesel Page - Duramax Diesel Conversion Guide
I am considering swapping from a 6.5 to an LBZ in a 94 K2500 suburban. My goal with the swap is we really like the suburban and the diesel, but the 6.5 is just too weak, even with the mods, to routinely tow the things we do without overheating, running out of power before we are up to speed, or both. The engine that is in the 94 should have a lot of life left in it because it only has 150k miles on an Optimizer short block. I upgraded the turbo and tuning, which helps but it is just not enough. Our fuel mileage is 15mpg running empty and slow, and towing at higher speeds drops to 8-10mpg. These numbers seem low to me, but I can't find a problem that is causing it. If I've estimated correctly, and if the mods have done the most they can, the 6.5 is still only 250hp-maybe 300hp at best. Even with major engine rebuilds and major mods, I don't think it will exceed 350hp, while the LBZ starts at 360HP from the factory and has been known to get low 20's in fuel economy.
Quote:
I’ve thought for some time now that I’d like to do another Duramax swap using a nice OBS (GMT-400) K2500 series Suburban. I really like the design of the OBS. I also like the 6.5, and plan on encouraging my daughter to keep her 1994 6.5TD Silverado Blazer. The fuel economy you’re reporting for your 6.5TD Suburban is in line with my experience and the experience of nearly everyone who has a similar 6.5TD powered vehicle – i.e. 15-18 mpg while running empty during local and/or distance driving, and 10-mpg while towing. A 6.5 reaches a limit in power potential because of fueling and turbocharger limitations. The DS4 electronic fuel injection pump is limited in the fuel it can provide. GM was planning (didn’t quite get there) to increase power for the 6.5 in the 1998+ model years to 210-hp and 440 lb-ft of torque. This is the limit for the 4L80-E automatic transmission, in addition to fueling.
The power potential of the (any year) Duramax is tempting… However, if your intention is to keep the Suburban long-term, I’d recommend keeping it close to stock.
An alternative is to find a 2001-6 suburban and swap in an LBZ, but that seems to be very hard to find and would ultimately be a more expensive swap, even if it would be an easier swap (at least I think it should be easier). Some of the advantages I see is the body should match a LBZ truck, so parts fit up and wiring should be much easier. I wouldn't have to change the dash out, and the interior and body features are more desired. I would think I also wouldn't have as much trouble with differentials, antilock brakes, and transmission fit up. I don't know what other things might be different between the gas suburban and the diesel truck. I also wouldn't be under such a time crunch to get the swap finished, because we would still have the 94 intact to tow the things we do while working the swap.
Quote:
Yes, a 1999-2006.5 GMT-800 Suburban would make the swap easier, but finding a nice one could be a challenge. The 2500s are hard to find, primarily because GM didn’t make that many 2500 series Suburbans. Now, you can make your own 2500 by setting a nice 1500 series body on top of a modified 2500HD pickup frame. Some have done that. It requires some creative metal fabrication because the pickup truck chassis is shaped somewhat differently compared to a Suburban chassis.
Some advantages that I see of my 94 Suburban swap is that I already have an Air Dog boost pump/filter, Hydraulic brakes and power steering, diesel ready suspension, two batteries, and a 42 gallon fuel tank. It also appears to have 3500 front and rear differentials, which appears a little rare based on part's store mismatch problems I've had. Maybe it is a heavy 3/4T.
Quote:
Yes, starting with a diesel Suburban does make a swap a little easier. For one, the diesels get more sound abatement. They usually have the higher rated front torsion bars. The OBS 6.5 Suburbans/pickups have a hydraulic brake booster, that perfectly adapts to the Duramax power steering pump and PS cooler.
For the Duramax, I don't plan on doing much more than minor mods...intake, exhaust, tuning; and reliability upgrades...crank balancer pin, EGR delete, FlowKooler water pump (If i can get them to make one), and anything else to improve reliability and longevity. I figure these things will at most bring it up to 400-450HP, and shouldn't hurt fuel economy or require a transmission rebuild. I'm also considering doing a light rebuild since I will have the engine out of the truck and I won't know its usage and maintenance history.
Quote:
It’s fun to think about aftermarket support for the Duramax, but for a “driver”, I’d personally keep it near stock, except I’d delete the EGR/DPF/DEF if my state/EPA would allow it. The failing crank pins you hear/see online are, in my opinion, more of a problem when these engines are using significant power increases, which outrun the ability of the factory damper to control harmonic vibrations. This leads to pin shearing and maybe even crank failures. Always ask whether the ailing Duramax was running power adders when someone reports pin shearing or a crank failure.
I have quite a bit of experience towing with the Duramax. The factory Allison can handle up to about an additional 100-hp over stock “if you’re careful”. I like to tow with just enough extra power that the Allison doesn’t need to downshift while towing (like on the hilly Interstates of the Midwest). You’ll get a little better fuel economy and a lot less shift busyness. More pleasant…
A few questions you might be able to help with...the 94 suburban has 4.10 differentials which in some ways I would like to keep because I just had them rebuilt last year with a new torsion gear limited slip. Since most LBZ's were 3.73, I don't know how much of a fuel economy loss that could cause for the Duramax. Since it's a smaller diff than the 2006 (10.5" vs 11.5"), is it strong enough for the Duramax at under 450hp?
----------------------------------------------
--continued next post---
