1994 Diesel Suburban Build
 

Hello all. I acquired a 1994 K2500 Diesel GMC Suburban to build up to eventually replace my 2005 Toyota Tacoma.

There were a lot of drivers into this decision. My basic requirement was low long term cost of ownership balancing cost, MPG, maintenance, insurance, etcetera. In addition the vehicle had to have room for my family and friends, able to tow and haul, and had to be 4x4. After significantly overanalyzing vehicle options (understatement) I decided a factory diesel 90s model GMT-400 Suburban was the right vehicle for what I need/want, realizing it will take some work to get it to the MPG I wish to hit.

I am very familiar with this GMT-400 platform having owned and worked on a 1991 K2500 LD truck, and several good parts from this truck will be swapped over (NV4500, NP241, etcetera). The suburban I got has 210k on the clock, but I plan on replacing the powertrain anyway and will eventually rebuild most of the major systems to end up with a like new vehicle. It functions now but I won’t be driving it until I get the powertrain rebuilt and have confidence it is reliable as I have no need for another vehicle until it can replace my Tacoma.

My short term goal is to hit 30 MPG consistently. My long term goal is to hit 40 MPG on most tanks. I think my current plan I will outline in a few posts below will get me at least to the first goal, the second goal will probably take lots of optimization of details beyond what is listed.

Please feel free to comment and offer suggestions, I post to get input and feedback.

http://ecomodder.com/forum/attachmen...9&d=1476453186

http://ecomodder.com/forum/attachmen...0&d=1476453186

Powertrain: (Using best factory options, no exotic swaps.)

Surplus 2010 GEP Optimizer 6.5l diesel long block to replace the factory 1994 6.5l. No swap fitment, title, or emissions issues as this is stock for stock. Brackets off of the 1994 engine will be used to mate the 2010 engine to factory style suburban accessories. DB2 injection pump will be used.

Will use the new engine naturally aspirated not turbocharged. (After analyzing BSFC maps at comparative partial load throttle positions between turbocharged and naturally aspirated 6.5L engines I do not think I would see a significant efficiency gain turbocharging. WOT is another story, but this is not a WOT project.)

Electric Fan conversion. Will upgrade and use controller I built for the Tacoma, but use more powerful fans.

1994 GM NV4500 Transmission with the 6.34:1 first and 0.73:1 fifth gears. NP241 manual shift transfer case.

Eventually will swap the 4:10 gears in the 9.25 front and 10.5 rear differentials for 3.42 gears. (1800 RPM to 1500 RPM at 55 MPH with 32” tires)

http://ecomodder.com/forum/attachmen...1&d=1476453302

http://ecomodder.com/forum/attachmen...2&d=1476453302

Aerodynamics: (After main powertrain has been completed)

Remove factory flares and steps.

Cargo area roof replaced with aluminum “sloping bedcover” style hatchback shell. Body sides will taper in to stepside tailgate. Should look like an Avalanche with an aeroshell.

Aluminum belly pan/skid plates and aluminum replacement bumpers. Bumpers will incorporate a non-destructive “crumple zone” with some give (for safety and durability reasons).

Appropriate grill blocking and engine airflow channeling.

Conveyor belt tire spats.

Probably other rearview mirrors.

Factory smooth wheelcovers.

http://ecomodder.com/forum/attachmen...3&d=1476453371

http://ecomodder.com/forum/attachmen...4&d=1476453371

Other: (Done alongside previously listed projects.)

Reasonably low rolling resistance LT truck tires, either Michelin LTX or a mild all terrain from Cooper or BFG.

Significant weight loss, but only by removing unnecessary weight not stripping the truck bare. Like for like replacements with lighter options will be used heavily. (i.e. DD to GR starter, aluminum to replace steel wheels/skids/brackets/etcetera, swap plush interior panels for plain plastic work truck versions, etcetera.) Remove unneeded weight such as ashtrays, rear HVAC, brackets, etcetera.

Repaint suburban roof with white heat reflective/emissive paint. Add heat rejecting tint in legal levels to all windows.

Swap to work truck grill and use DOT approved sealed beam led headlights. Swap all bulbs for LED.


That is the plan thus far. I will update this thread as I make progress. Anyway, enough rambling from me. I am open to any thoughts or suggestions.

If your running mechanical, try to get smaller pre cups like a 80's c-code 6.2 and then up compression to 21:1 if na.

Time it for low rpm if you can get it as a 2 wheeler

Lots of plans, but the plans look good. Interesting build. :)

Rmay,
The naturally aspirated optimizer that I got has the 20.2:1 compression ratio and the smaller “square” precups. I am not really sure how those compare in size to the single dot or older precups, but I do know they are smaller than the diamonds. Consensus seems to be that smaller precup openings is better for BSFC.

Four wheel drive is a requirement for me, but I would like to eventually change the cam to move my power down low, I prefer to lumber along.

Daox,
Yes lots of plans. :D In my defense I have been planning this for quite a while and will slowly start to make progress. The biggest thing I want to get done is the powertrain rebuild to get it functioning, the other items will be stretched out over quite some time. I like to tinker in my (limited) spare time, so I can’t run out of projects.

The problem with dot approved led head lights is it appears that a lot of the ones from China is they will put junk in a box and slap a "dot approved" sticker on it.
The real dot approved led head lights should run between $100 & $200 for each light..

If I had the chance to get a barn-door Suburban, I'd probably not want to change its body. But anyway, with an old-school IDI Diesel you might be able to try vegetable oils as an alternate fuel.


Turbochargers have been used in Diesels not just for performance and efficiency, but more recently also for emissions compliance.

'Heat reflective' paint is a bit of a myth. Gloss car paint has better emissivity. Just paint it gloss white or possibly do a chrome wrap.

Much like those aluminium foils used for roofing thermal insulation. They might be not so bad at all, are even used to seal gaps in firewalls of second-hand Japanese imports converted from RHD to LHD in Chile and Paraguay.

Also put a bigger turbo on there, unless you are going to be doing nothing but pure city driving.
Highway and towing the bigger turbo always wins.

Oil Pan,
Yeah I wouldn't buy anything that wasn't from a major manufacturer. I was looking at the GE Nighthawks, but I will delay that purchase as long as possible to hopefully let the options increase and the prices decrease.

Cripple Rooster,
To hit my MPG goals, I will either have to change the body or fabricate an add on tail. I like the rear doors, but I would rather lose the doors than increase the length. Honestly as the Suburban is set to replace a truck, a tailgate style rear cargo area would be a better fit for carrying large and long cargo.

Oldtamiyaphile,
Yeah Rustoleum gloss white was my initial thought, unless I can find something that has published reflectivity and emissivity numbers that are both significantly better. I also plan on putting some self adhesive foam insulation on the underside of as well to help cut the heat transfer to the cabin. I know bare metals usually have terrible emissivity compared to painted surfaces.


Speaking of firewall seals I would also like to find a good foil faced high temperature insulation product for the engine firewall. I noticed today the stock stuff which has a black liner is starting to fall apart.

With regards to the turbo, I know this is counter to popular opinions on the subject, but the BSFC numbers I have been able to find in some published military papers between turbocharged and naturally aspirated 6.5L show better BSFC numbers at peak levels but not across the spectrum. The numbers I have seen at low to moderate power outputs weren't significantly different.

Doing the modifications listed should greatly reduce the steady state power requirements to roll down the road so most driving time should be at low levels of fueling, which in a 6.5L engine would result in very high air to fuel ratios. In this scenario, I don't think extra air will help increase efficiency since the air to fuel ratios should already be very high.

If I was using a lower displacement engine thus decreasing the air volume or did not do any load reduction thus using more fuel where the typical air to fuel ratios were lower, I think the turbo would be a better fit. Anyway if I end up dissatisfied with natural aspiration, I can always add a turbo and do a real A-B comparison.

Edit: To be clear I am not making blanket statements above, I understand how a turbocharger typically increases efficiency and how a smaller diesel engine with turbocharger would be more efficient than a larger naturally aspirated engine to make the same power. I would rather have a 3.25L engine running 14 psi boost than my 6.5L (3.25L at two atmospheres ingests the same air as 6.5L at one atmosphere). However since I want to use the 6.5L platform but reduce the load required, I don't think the turbo will benefit that scenario.

Attached is a chart I made to compare between a turbo and non-turbo engine BSFC numbers. Both of these data sets are from freely available publications on military 6.5L engines, and are both done on JP-8 fuel. These are comparing BSFC numbers at specific torque outputs for two RPM levels. As you can see, the efficiency results are very similar at the 2000 RPM level.

Part of me wants to add a turbo to increase maximum torque at low RPMs. The other part of me wants to leave it N/A to reduce weight and complexity.

http://ecomodder.com/forum/attachmen...8&d=1476712445

I am glad you posted this, just goes to show how sad it is that inexpensive NA diesels aren't sold in the US.

Reality is NA is just as efficient and only 20% more for the motor than a gasser. (As compared to exponentially more for turbo)

Hope this shuts up the turbo folks.

Diesels don't have to be 600 hp monsters, I guess that is why I own a 6.2

I am very happy with my 6.5 na pickup. It has 4.56 gears and a 700r4, it tows my 10,000 lb Avion just fine. I have three different brands of turbos for it, I have a Banks, an ATS and a factory set. My 6.5 is piston cooled with the improved main bearing caps. I have run GM diesels since the Oldsmobile days, yes they have their problems. I will never hurt my 6.5 if I don't install a turbo! The 700r4 is the fuse that limits the horsepower in my truck.

Put a turbo on it.
If you live in the mountainous part of TN you will really need the turbo.

When I put a turbo on my 6.5 fuel economy increased 10% to 12%.

Rmay and Metro,
Glad to hear your 6.2 and 6.5 are working for you naturally aspirated.

Oil Pan,
There’s a non-mountainous part of TN? :) Your input on the turbo is duly noted. (I mean that seriously, not sarcastically, I am taking note of your input.) I have seen lots of conflicting accounts on this subject, so I surmise there are other factors than just the turbo that come into play with this (driving style?). I am strongly considering starting the project off naturally aspirated (assuming I can round up manifolds and a downpipe) just to get the project going and testing out a turbo for myself at a later time.

Current Update:
Four longer 10MMx1.5 bolts from TSC got my optimizer engine off the floor and up on my engine stand yesterday. I am going to start pulling the accessories and other items I am not going to use off of it to get it ready for the brackets off of the 1994. Then I can start mounting up the new accessories as well as getting a handle on any other small parts I may need to source.

Yeah you can add a turbo later, that is exactly what I did.
I live in a very flat part of NM but really do like having a turbo. I wish it would have been one of the first mods I did.
My fuel economy improvement happened while in NM.

I think GM did a disservice to the entire US diesel market by offering a non turbo diesel truck. When you start trying to do actual truck stuff with them especially in thinner air, really anything above 3000 feet above sea level they really suffer.

As to roof paint. In the Airstream trailer community on Airforums are a number of threads concerning this. Works. The new ones come this way from the factory. Ceramix brand was popular a few years back. (But no one recommends mobile home roof paint on aluminum; yet it might work for you).

Got some progress made on the Suburban. I got a set of factory alloy PYO 16” wheels that were an option on the 2001-2010 8 lug trucks, which are the lightest weight factory wheel option that will fit the Suburban. I want to be able to use the 1992-1994 factory smooth wheel covers with these wheels, but the covers won’t snap fit the alloy wheels like they would the steel wheels because the mounting surface is angled outward. Because of this, I drilled and tapped the alloy wheels to be able to mount some brackets to hold the factory wheel covers in an alternative manner.

One I got all the holes drilled and threads tapped, I took some older tires I had lying around and had them mounted and balanced. So the Suburban now has functioning wheels and LT255/85R16 Cooper Discoverer A/S tires. I took the occasion to start and move the Suburban closer to my garage. I could tell as I changed the tires and drove it that the steering has a bit of play in it, so I will need to check out and replace some of those parts before it gets any road time.

Anyway, some pictures.

I drive that series of truck at work. I have a new pitman arm sitting on the shelf, just waiting for the next service interval to get it on the rack.

Made some progress yesterday, I started to pull the accessories off of the GEP 6.5L engine. I pulled things off, and put them in zip lock bags and took pictures as I went. The brackets holding everything were very heavy; hopefully the Suburban versions won’t weigh nearly as much. I also started taking off some of the cut hoses and other items that were cut off as the engine was removed from the vehicle.

Continued to pull parts off of the engine, got the exhaust headers and a variety of other sensors pulled off. Picked up some engine paint for the block (only doing the absolute necessities of course) and I have been researching and collecting other parts for the swap.

Made a junkyard run with one of my friends, unfortunately they were light on diesels and most of the Chevy and GMC trucks had already been picked fairly clean. I did score some sideview mirrors off of 2003/4 Audi A4s, they looked to be reasonably sized, would fit the factory spot with minimal modifications, and appeared to be fairly aerodynamically designed.

Anyway some pictures.

http://ecomodder.com/forum/attachmen...5&d=1478608828

http://ecomodder.com/forum/attachmen...6&d=1478608828

http://ecomodder.com/forum/attachmen...7&d=1478608828

http://ecomodder.com/forum/attachmen...8&d=1478608828

http://ecomodder.com/forum/attachmen...9&d=1478608828

http://ecomodder.com/forum/attachmen...0&d=1478608828

Subbed.

Sorry I haven’t posted an update in a bit, I have been super busy working on other household priorities. I am still researching and getting parts for the Suburban, picking up a few things at a time especially if I can find items I need on sale. Rock Auto had a wholesaler closeout with some Fel-Pro gaskets and other random nonsense so I got some of those items. I also watch for amazon deals on used/returned items.

Unfortunately because of this type of mentality my garage-workspace is getting to be tight quarters with a bunch of supplies for household and other projects. I am in the process of insulating, sealing, and enclosing the attic space over my garage, which will free up some space to work in the garage as well as help normalize the temperature swings of the garage a bit. So while this isn’t direct progress on the Suburban project, it will help enable future progress.

I drive a 03 ram 2500 diesel, 6 speed. 35x12.5 17 mud tires and 3.73 gears. Best I ever got was 600 miles at 28 mpg with a 12 foot noat sticking out the back. I can get 40+ mpg upto 40 mph, by 50 it's just over 30, at 55 it starts dropping and it's all downhill from there, gets to be 17mpg by 70. Really not aerodynamic. When looking at the gallon per hour display,, I see a sudden increase at about 1700 rpm - cruising rpm- when the turbo starts spooling. If I could get some lightweight street tires, larger diameter, I might gain a few more mpg. Forgot where I was going, it's late

No the project isn’t dead. Finally got the garage cleaned up and organized enough that I can work out there again.

Pulled the cover off the injection pump last night, the GEP optimizer 6.5 came with a DB2 injection pump, unfortunately it’s fuel shut off solenoid was 24 volts like the Humvee it came in. I had ordered a 12 volt version, and I got everything ready to swap over. One thing I don’t have is the cold start advance solenoid, it is 24V so I will need a 12 volt version of it as well.

Anyway some pictures.

http://ecomodder.com/forum/attachmen...9&d=1484830977

http://ecomodder.com/forum/attachmen...0&d=1484830977

http://ecomodder.com/forum/attachmen...1&d=1484830977

Made some more progress on the new engine. Got the 12V fuel shutoff solenoid swapped, and put the cover back on. I did not change out the other 24V solenoids on the injection pump as they are for cold engine idle/timing and not 100% mission critical, I thought about running a small 12V to 24V converter as that would be significantly less expensive than replacing the remaining solenoids. The converter would be downstream of the sensor, so it would only be powered up when the engine was cold, not the whole time it is running. Anyway if they don't work right I can always change them out later. Besides if they don't work, the engine will still run and drive just fine, just will run rougher when it is cold.

Flipped the engine upside down on the stand, found a bit more oil and coolant that hadn't quite been drained out yet. Pulled off the Humvee oil pan which won't clear the differential, and test fit the truck style oil pan, which I had purchased as a cheap new takeoff item from a boat engine company. As my research had already indicated, I ran into clearance issues with the Humvee style oil pickup. Instead of replacing the pickup tube, which is the typical fix, I simply adjusted the bracket holding the pickup tube to move it down 3/8 of an inch (down on an upside down engine). Then I clearanced the tray that divides the oil pan in half to allow the pickup to pass by it.

After pulling out the glow plugs, I was able to turn the engine over by hand and check out the engine bores. Everything looked nice and clean, no visible scratches or issues. Since the bottom end looked so nice, I decided not to pull the heads, to not have to replace the head gaskets and torque to yield bolts unnecessarily.

I picked up some permatex sealant, so I hope to get the oil pan reinstalled and back on the engine this evening, so that I can flip it back upright. Getting close to time to pull the old engine out of the engine bay, and start to swap over accessories and brackets.

So yesterday I cleaned up and deburred the oil pan, wire wheeled the oil pan mating surface down to bare metal and sanded it with 1000 grit sandpaper. I scraped and cleaned the block and gave it a light pass with the sandpaper as well. I picked up some permatex sealant and pulled out one of the fel-pro gasket kits.

I put in the rear main seal with only a drop of sealant on each end per the directions. I decided to use the oil pan gasket with a light coating of permatex above and below it. I have read so much conflicting information on gasket vs rtv I just decided to go the belt and suspenders method. The army technical manual stated you could use both together, and the fel pro gasket kit instructions said to use a light coating of sealant with the gasket.

Anyway I snapped a few pictures during the process. Time to flip the block back right side up.

Continuing to plug away at this. I got the block back right side up and began scraping off the remnants of the intake manifold gasket from the engine and the intake. I would love to gasket and port match everything, but that is a later down the road project. The intake gasket has a good sized gap on all sides of the intake and head, but I did a paper traced overlay to compare the head to the intake and it was actually closer than I had seen in online photos, perhaps the GEP quality control has tightened that up a bit.

I did notice on the intake manifold there were a few casting flaws where there was a slight edge to the intake manifold that formed sort of a shelf. I chucked up a sanding tool in my dremel and ran it around the intake manifold ports on all sides. I intentionally didn’t really take any meat off, just got the casting flaws gone and smoothed it out just a bit.

The rest of the intake has a “sand” finish on the inside; I don’t think it is necessary since no fuel/air mixture is traveling through there, just air. I don’t know if I will smooth it out, probably another later project.

Anyway, some pictures of the intake “porting” work, notice the before and after of the runner with the worst casting flaws.

Might not make much difference, but as expression of principle in ones determination I know it felt great to have done it.

So last night the patient got wheeled into the operating room in preparation for brain surgery. Current plan is after removing several smaller items from the engine bay is to pull the transmission and transfer case from below and then the engine from above out of the Suburban. Then I would pull the Suburban out of the garage and wheel in my older pickup and pull the NV4500 transmission, clutch, etcetera out of it and pull it back out of the garage.

I would then get all the brackets and accessories swapped over to the new motor and get all the prep work I can do in advance taken care of. Then I will wheel the Suburban back into the garage and drop the new engine in and new to it transmission into the Suburban.

I know I will probably have to order a few more little things along the way, but I think I have 98% of all the parts I will need on hand.

What rear end gears were you going to run?

Oil Pan,

Stock the Suburban came with 4.10 gears, so I will be running them for a bit, but the eventual plan is to run 3.42 gears. That is the highest ratio I am aware of for the stock 10.5 14bolt/9.25 IFS differentials. With 6.34:1 first gear on the NV4500, taking off shouldn’t be a problem even with the higher 3.42 gear ratio.

Stock 4.10 with 0.73:1 overdrive and 31.8” tires equates to 1800RPM at 55 mph and 2300 at 70 mph. Stock 3.42 with 0.73:1 overdrive and 31.8” tires equates to 1500RPM at 55 mph and 1900 at 70 mph.

You might be able to find 3.23 or 3.21 gears for it.
Try nitro gear.
They had the impossible to find 3.21 gears for my 10.5 inch 14 bolt full float axle. They were impossible to find because only nitro gear has that ratio for that diff.

Oil Pan,
I looked on their website, but I didn’t see anything taller for the 9.25” IFS differential. I had looked a while back for something taller than 3.42 that would fit the IFS differential but came up empty. I daydream about axle swaps, but it will be several years before I could pull something like that off, plus I like the idea of keeping it mostly stock.

So last night I did the first of the prepwork for pulling the engine. First I got the batteries disconnected and out of there. Next I disconnected the air intake back to the turbo. I pulled the relocated PMD and extension harness. I pulled the stock skid plates and splash guards off the bottom front.

Next I started trying to drain the antifreeze, (without making a mess in the garage) but the drain port that you hook a hose to was pointing straight down into the lower radiator support, so no luck on that front. I started trying to siphon the antifreeze from the top radiator port, and got several gallons out. Ran out of time, but I will have to start pulling hoses off the bottom to finish getting the coolant out.

Continued to plug away at disconnecting things from the engine bay in my spare time. Got the coolant hoses disconnected and the fan and radiator removed. It looks like the radiator has been re-cored, as the insides look new and the top and bottom flanges have been cut apart. The coolant hoses feel soft, I am thinking I will go ahead and replace them. Also need to get an appropriate coolant temperature sensor and housing to go in the upper radiator hose to trigger my custom engine fan controller.

I drained the oil and began applying wd-40 to several of the bolts on the exhaust and frame that I will have to disconnect. I also assembled a cheap engine cradle to set the removed engine in, so that I can roll it around and it will be safer to work on and remove parts from. It was a $35 cheapo stand from a big auction site, not too terrible of construction and welding but I did replace the bolts that connect the three frame pieces together with larger better rated ones.

Tomorrow I have help coming and I am going to devote an entire day to working on the Suburban, hopefully I will make lots of progress.