M998 turbo conversion

[Mogman]

I am starting to do a GEP turbo conversion on my 1992 M998 I call "Detroit" so maybe some would be interested in the "ride"
Back story:
When I was getting ready to install the 6L80 in Detroit I knew I was going to have issues with my doghouse, I was using a cable driven tach out of a another bigger MV and I needed to add an "inline" RPM sending unit which would extend the place I could reasonably bend the cable under the NA doghouse by about 3 inches and that would not fit.
So I decided because plans were to pick up and install a GEP turbo "some day" I decided to see if I could get a turbo dog house, that would give me room for the tach cable even though I knew that "someday" the tach would have to go because there is no drive on a turbo motor, but heck that would just be "someday" right??
So I put out the want and a guy from NC named Michael Bowen contacted me and said he had a doghouse and was coming to Corpus Christi on some MV business and could bring it with him, so we made a deal and THEN he said is there anything else you need, I said maybe a 6.5L GEP turbo and I will be damned he DID have a GEP turbo, the story is it came out of I think Eastern Metals and had only around 100mi on it, he said it was the last one and he was saving for himself but had decided to not pursue HMMWVs..
I checked with a couple folks I really trust and they said he was a stand up guy, and as it turns out he WAS!!!, delivered everything he said he would.
I decided to install the 6L transmission first before the GEP so I would not be fighting more than one issue at a time.
After installing the 6L I was so happy with the way in performed I have serious doubts I would have spent the money to buy a turbo but that choice has already been made, so here we go...

 

[Mogman]

The GEP
So the GEP had some rather interesting "demil" work done to it, someone took a rather large dia. cut off wheel and made a few passes at the turbo.

So Michael included a couple "core" turbos on the deal and I rebuilt one using an improved compressor wheel.

https://kbdieselperformance.com/

Extended Tip Billet Compressor Wheel for 6.5l GM3/GM4/GM5/GM6/GM7/GM8 Turbos. Inducer: 51.9mm Exducer: 70.0mm 6/6 Blade Design for All Around Performance Pre Balanced Fits: 1992-2002 Chevy/GMC C/K 1500/2500/3500 Trucks, Blazers & Suburbans with the 6.5l turbo diesel.

kbdieselperformance.com

I put the GEP into a shipping container to test run it.

While prepping the engine, since the container came with a "junk" 6.2L (harmonic balancer came loose and destroyed the crankshaft nose) I took the oil pump drive out and put it in the lathe and cut the teeth off of it.

I then installed it without the turbo of course because it will not fit with the turbo and I used a drill to purge/fill the oil system, I had to hold my finger over the oil feed hole for the turbo but managed to pressure up the oil system three times at 30PSI until each time I got tired of holding back the pressure at the turbo feed hole.

Then I installed the turbo added fuel and batteries

And she huffed and puffed and came to life!!
But all was not good in WHOVILLE, see made some disturbing sounds at a certain RPM, but it did not take long to figure out the flex plate was bent! no doubt by some mishandling in her past.
No problem, 10 minuets and it was changed and DARN, THAT ENGINE SOUNDS GREAT!!

So now it gets buttoned up and put outside while I bring in the Detroit and get her ready for the new engine..

 

[Mogman]

I have done quite a bit of research and think I have just about everything I need, seems pretty straight forward.
I am going to do a 1/2" body lift.
I believe I have the exhaust crossover that will allow mt to use the stock muffler back although a muffler delete is definitely in the plans
I hope I have the intake ducting to connect to the M998 air filter
This will be a little different as I will be using the crankshaft sensor and the TPS for the stand alone controller for the 6L80 transmission.
I will be installing a Champion aluminum radiator but other than that am leaving the cooling system (hydro fan clutch) as is of course with the reverse rotation fan..
Other than that as I said seems pretty straight forward

 

[Mullaney]

I am starting to do a GEP turbo conversion on my 1992 M998 I call "Detroit" so maybe some would be interested in the "ride"
Back story:
When I was getting ready to install the 6L80 in Detroit I knew I was going to have issues with my doghouse, I was using a cable driven tach out of a another bigger MV and I needed to add an "inline" RPM sending unit which would extend the place I could reasonably bend the cable under the NA doghouse by about 3 inches and that would not fit.
So I decided because plans are to pick up and install a GEP turbo "some day" I decided to see if I could get a turbo dog house, that would give me room for the tach cable even though I knew that "someday" the tach would have to go because there is no drive on a turbo motor, but heck that would just be "someday" right??
So I put out the want and a guy from NC named Michael Bowen contacted me and said he had a doghouse AND was coming to Corpus Christi on some MV business and could bring it with him, so we made a deal and THEN he said is there anything else you need, I said maybe a 6.5L GEP turbo and I will be damned he DID have a GEP turbo, the story it came out of I think Eastern Metals and had only around 100mi on it, he said it was the last one he was saving for himself and had decided to not pursue HMMWVs..
I checked with a couple folks I really trust and they said he was a stand up guy, AND he was, delivered everything he said he would.
I decided to install the 6L transmission first before the GEP so I would not be fighting mode than one issue at a time.
After installing the 6L I was so happy with the way in performed I have serious doubts I would have spent the money to buy a turbo but that choice has already been made, so here we go...

.
I have bought several things over the past few years from Michael. He has delivered several (down the road about an hour away) and I have picked up stuff too. Darn good guy and as "straight as an arrow" when he tells you what he he has for sale.

Looks to me like you have a project on your hands for sure!
Thanks for the PIcs and the story...
.

 

[Mogman]

Well I have the truck on the lift, doghouse, doors, wheels and hood off,, now the real fun begins.
I installed a Corvette oil pan on the 6L80, it has means to check fluid level without a dipstick so for now I am going to pull the dipstick tube and install the rubber plug in its hole, one less thing to deal with at this time.
Now to dig out my big cherry picker from behind 22 years worth of junk!!

I am going to go ahead and do the 1/2" body lift first, there is almost no clearance between the 6L bell housing and the body and of course I have to be able to pick the engine up enough to clear the motor mount studs so I will probably also drop the rear cross member an inch or so to help give me enough clearance.

 

[Mogman]

Now THIS is a cherry picker, 8000lb collapsed and 4000lb extended and it extends a LONG way.

A little trivia, how many of you remember these? most were made by SUN but mine was made by S/W.

On its way to the scrap pile!

 

[Mullaney]

Now THIS is a cherry picker, 8000lb collapsed and 4000lb extended and it extends a LONG way.
View attachment 864129
A little trivia, how many of you remember these? most were made by SUN but mine was made by S/W.
View attachment 864130
On its way to the scrap pile!

.
Nice and hefty! I never got around to getting one of those pickers. I still have my A-Frame made out of 4 inch round pipe. I inherited it from my uncle, so I painted it and upgraded from the manual chain-fall to and electric. Pulled many a motor with it...

•

I don't have my old scope. Best I could find was an old picture - just so I could say "back in the old days" . . .
Do remember spending lots of bucks to buy it.


.

 

[Mogman]

Well the 6.2L is "on the hook" pull it in the AM.

EDIT, that was the wrong hooking point, ended up moving it forward one ring.

 

[Mogman]

I started the floor conversion this morning on the right side.

EDIT the part numbers for the floor kits are 12469253 and 12469252


The piece I got from HPG is formed in a way that the rivets in red do not need to be removed, all other interfering rivets must be removed including one on the side. (under the first red arrow on the left)
I would suppose that the Commander had some explaining to do about that bullet hole (black arrow)
Measure three times cut once, then radius all the cuts so it does not come back to bite you later.

Tools used


Start with the one rivet that uses an existing hole (arrow) then drill, rivet, repeat,,,

On to the drivers side...

 

[Mogman]

The same applied to the left side, a little zinc chromate primer and a little RAPCO green and Viola along with the 1/2" body lift the body is now turbo ready!

 

[Mogman]

Well we are going to stab the GEP in the AM, so now I need to add the motor mounts to what Mr Johnston's 3rd grade special ed class designed,, WHAT a PITA!!
So the longer alignment dowels are installed and because at the angle the engine is installed the transmission bell housing adapter for the 6L transmission just slides off, I used some gorilla snot to glue the adapter to the back of the engine, will let the bolts stay in until I get ready to stab it in the morning.
I had to modify the adapter because of the turbo, the adapter and also the 6L transmission has a top center hole, some LS blocks have this so I had to do a little "contour" work to the adapter to clear the turbo and will have to do some of the same to the top of the 6L bell housing...

 

[Mogman]

It went in easier than I thought, still somewhat of a PITA to do by yourself..

Now for all the tedious crap.

 

[Mogman]

I had to extend the three body harness wires for the instrument ground (to block) and the oil pressure and engine temp. wires, the battery lead to the PCB and start wire were routed behind the engine instead of in front past the fuel pump for some reason, they were cut so I have to "fix" that anyway so I am going to route it down around the front like the NA harness as there is allot of heat where the turbo harness was supposed to go, makes no sense to me..

 

[Mogman]

Well it is starting to look like a Humvee engine bay again, decided to replace the hose to the fan clutch as the original was leaking a little, unfortunately I did not have any 3/16" hose in stock but did have all that was needed to build a 1/4" on hand so there you go, 5600 psi working pressure so I think it will have an easy life, I decided not to go with the quick connect because with the serpentine belt you do not have to remove that hose to mess with the belt which removes 90% of the reason I normally had to disconnect the M998 hose, now I only hear about folks having to replace the leaking quick coupler so...


no big surprises yet has real happy to see the ECV air horn and the M998 air hose playing so well together.
Going to build the stack tomorrow..

 

[Mogman]

So we are getting close, getting M10-1.5 X 65 studs made mating up the exhaust SOO much easier, pre-installed some #8 screws and nuts so it will be easy to install the shields!
The studs also double the chances of being able to remove the pipe many years down the road..

Some were advocating using a gasket between the manifold and down pipe, I did not like the way it choked off the exhaust so we are going to try it the way the factory did it first, of course longer studs would be necessary which we already have on hand, JIC

The heat shield on the down pipe only clears the 6L80 pan by about 1/8" which is fine, so that worked out good!!!!

I picked up some 5mm brass tees to tap in the "new" PS reservoir vent and they were too large, so I ordered some 4mm tees and they were not as tight as I would like, a few high quality panduit (makes a difference) ties fixed it up...

So now I can re-install the right engine side panel and the fuel system, then it is VAROOMMMM

 

[Mogman]

I have the TPS and the engine speed connected and calibrated to the TCM, now to install and calibrate the tachometer (I lost my M35 mechanical tach because there is no way to connect the cable on the turbo motor)
I am going to do some more work to the fuel system then it will be time to install the hood and tires!!

 

[Mogman]

Got the tach installed, it would not read off of the alt, in fact I could not get a good reading of CPS (hertz for you young folks) with my Fluke meter, so I paralleled the signal lead with the crank sensor to the TCM and programmed it for 4:1 and it works OK, not as responsive as the old mechanical tach. though
So in the morning I will install the hood and wheels and give it a spin!!
I need to find something to jack up the hood pivot mounts 1/2" to match the body lift...

 

[Mogman]

BTW there was no detectable exhaust leak at the down pipe so I am happy with that decision.
The only thing holding me up is I cannot find that dang hood support rod and bracket, spent a couple hours doing laps in the shop, will try again in the AM.
It's ALWAYS something!!
But I did find some 1/2X1 1/2 aluminum stock to make the hood risers out of while I was doing laps...

 

[Mogman]

Got it all together but the doors (poor mans AC) and took it for a drive, I did not expect much difference going from 160HP to 190HP but it is noticeable.
Having the batteries turned off the TCM had lost all of its adaptive programming so it will take awhile before the shift points settle down.
I was busting a 20 MPH headwind on the first leg and I could still get it into 6th at 70 MPH no problem, before it was much happier running in 5th with a headwind, when I turned and headed down wind I was buzzing along at 80 MPH before I knew it so I am a happy camper, now to get the EGT gauge installed (if and when I can find it or buy another) and then TURN IT UP!!
GEP says this engine with the mechanical DB2 IP is good to 205HP, I am assuming the GM engine was only good to 190HP thus the backwards compatibility of the GEP.
I see several references to a 2.5 ton military truck using a 205HP IP but have no clue what that would be except for possibly the 16000 lb GVW HMMWV I have seen references to....

 

[MattNC]

That sounds awesome especially with the 6 spd. I have the BMI turbo and a 700r4 and the kit had me turn it up 3/8 of a turn from stock. If in OD and bogging under a load it throws a little smoke but otherwise super clean running. Max egts so far were 900 at 12psi boost and it was ripping up a hill with 4000lbs of loaded trailer and 4 passengers and gear. I try to use the accelerator to keep it under 10 psi and plan to adjust the waste gate down to 10 from 12 psi. I’ve loved it so far and the vast majority of the time egts are 400-700. It takes a lot to make it get up to the 850-900 range.

I have a feeling from my seat dyno the turbo adds more than 30hp. On hills with the trailer I was lucky to hold 35-40 mph. Now I’m holding 55 easy and getting on the highway is a totally different experience.

I’m looking forward to seeing your experience especially with extra gears.