GMT400 6.5 Swap Help

[adventr]

Please don't question my sanity; I do that enough on my own.

I've got a soft spot for the 6.5 engines and also a soft spot for the GMT400 tahoe platform. Was really disappointed that I couldn't just buy a 4dr 6.5 tahoe, so I'm building one.

Found the cleanest 2000 Z71 model tahoe that I could. It has right at 100k miles on it now and is really pretty mint. No issues at all with it, so a good candidate for my swap. I've been driving it quite a bit lately and adding little things here and there while collecting parts/trucks for my swap.

 

[adventr]

Most have suggested that I just toss in a mechanical engine and call it a day. Sure, that would be pretty easy but I just can't do that. I really want this to be as close to a "factory" setup as possible. That means using an electronic engine.

I really don't know WHAT all parts I need in order to make that happen. I assume lots of wiring and modules.

So, I've been collecting stuff that I think might help me out.





Bought this blue truck while back. It's a 98 model with only 115k miles on it. Really nice truck, BUT................ the guy was letting it warm up in his driveway a couple of weeks back and it lost an oil cooler hose/connection and ran all of the oil out before he caught it. Well, it ran 6qts out anyway.
He fixed the hose and refilled it. Drove it a bit, and i'm pretty sure it's toast. Sounds like collapsed lifters for sure at the very least. I'm sure that's wiped the cam out. Probably spun bearings too. It still starts up and drives, but it's rough now. Kinda sad.

I figure since this is a complete, running/driving truck, that it should have everything I need to swap into my tahoe?

 

[adventr]

I also picked up another 98 model just because I saw it pop up on marketplace and I got it for cheap. So I figure if something happens to be wrong with a part on the blue truck, maybe the white truck has it??

 

[dbrannon79]

Welcome to the forum!

Those are nice finds! youll have two complete wire harnesses and PCM's to use. one good engine plus what ever options ether truck came with to work into your tahoe.

 

[adventr]

I know I need a good engine to start with. I do not know the history on the engine in the white truck. Cluster shows it has quite a few miles on it. I was "told" that the reason it was parked was due to some wiring issue at or around the fuse block. Fuse block does appear to be absolutely butchered by someone trying to repair/bypass with butt connectors. Lol


My first thought; Hey, i'll just buy a P400 engine. I remember those from back in my civilian H1 days. People were tossing them in as replacements for the 96-2000 models.
Well, as you all know, you just can't go buy a P400 now.

My second thought; Ok, i'll just go buy a complete optimizer long block to start with. Seems there are a few places selling them.
THANK GOD I GOOGLED THOSE PLACES.
Tons of horror stories out there and lots of carnage pics with extremely low miles. I'm sure you all know what I'm talking about.


I really didn't want to try rebuilding the block in the blue truck, as I'm sure it's probably trashed from spun bearing or something. So, I did the next best thing I could think of and bought a complete GEP takeout engine from a HMMWV.
Appears to be a Navistar 506 block, I really hope its in good shape. Engine looks super clean and almost new on the outside, but you never know until you pull it apart.












I had it shipped to me from the East Coast and it actually just arrived this morning at my shop here in Arkansas.

 

[adventr]

I know from my limited research that I just can't drop that GEP motor in as it sits. And I just can't toss the truck intake and turbo setup on it and go.

So my plan now is to tear it down to the short block, give it a once over, and then build it back up using truck parts.

Does anyone have any suggestions here? Things I should check for? Things that I should address while it's taken down to the short block?
I still don't know if these GEP engines use a reluctor wheel on the crank or not. That's one thing I plan to check.



Anyway, in preparation for all of this, I ordered up a whole bunch of parts from Quadstar. I was also able to track down the very last set of ARP head studs in existence (I believe lol).

Here's my parts list that I've ordered from Quadstar:

• New 6.5L Lifters
• New Promaxx Heads
• GM headgaskets and intake gaskets
• Reman'd DS4 Pump
• New Bosch Injectors w/Install Kit
• Fluidampr
• Billet fuel return log
• Valve cover stud kit
• New engine wiring harness
• Ultimate turbo drain kit
• Center turbo drain blockoff plate
• 2.5" exhaust crossover pipe
• Pump timing wrench
• ARP starter bolts
• New starter bracket
• Turbomaster wastegate controller for the GM8

And here's my parts list that I've ordered from RockAuto so far:

• ACDELCO 251-603 water pump
• ACDELCO 131-103 thermostats
• ACDELCO 12557345 crank pulley
• GM 20788261 fan clutch (EV style)
• GM 1580920 fan blade
• GM bypass hose
• New heater hose quick-connect fitting
• New upper and lower radiator hoses
• New gaskets for the 2.5" crossover pipe

Do you see anything else that I should add to all of this? I've never tore a 6.5 engine down before, so I'm kinda going in blind.

 

[adventr]

Complete side note, but I'll be using the Quadstar 6L90e kit on this build. Picked up a low-mile 2014 6L90e and t-case in anticipation of this.
If you guys would like for me to document that in a separate thread when the time comes, I will do so.

 

[adventr]

Sorry for all of the posts/info. Just putting it all out there so that hopefully I can get some good advice. Here's a quick summary of what I anticipate needing help with:

• Engine build
  • Do I have the proper parts that I will need to build the GEP engine from the short block up?
  • Where can I find torque specs for this engine?
  • Would you pull any bearing caps off of the GEP engine to inspect while the oil pan is off?
  • What about priming the engine?
    • I don't know how long it has been in storage. I would HATE for it to spin a bearing at start due to them being dry or something like that
  • I've got my fingers crossed that all of the sensors from blue truck motor can be installed on GEP engine. Anyone have experience with this?
• Wiring ( i know this is gonna be a big one)
  • Do I just use everything out of the blue truck? Or is there engine-specific harnesses I need to swap out?
    • My tahoe has things like power windows/power seats/rear HVAC...etc that the blue truck DOES NOT HAVE
  • I'm thinking I can use the blue truck gauge cluster since it will have the proper tach/fuel gauge and also the glow plug light
  • Should I just swap out the whole underhood fuse block?
    • Will there be any combination of harnesses required since my tahoe has all of the options and the blue truck doesn't?

If anyone has prior experience or info, I'd appreciate it.

 

[ak diesel driver]

Wow keep the progress reports coming. We love to see builds like these

 

[ak diesel driver]

While you have it apart balance it and do gapless rings

 

[adventr]

While you have it apart balance it and do gapless rings

First thing that comes to my mind is that there are literally ZERO machine shops around here that I would trust touching this engine.
A good friend of mine (that helps me work on all my crazy projects) has a performance shop here and I'm constantly hearing bad stories about the local engine builders that everyone uses...

That said, my goals for this engine is near-stock power levels. It will have a really nice fuel system, and a tune from Quadstar. I *may* swap out the GM8 turbo to their Super 54 kit when it becomes available again. But that would mainly be for efficiency reasons.
I'm still on the fence about that one as I don't want a laggy setup with the near-stock power levels. I'm only head studding it because I can't bring myself to put one together with stock head bolts. Lol

 

[adventr]

Looking forward to getting the GEP engine on the stand later this evening. I popped a couple holes in the shrink film and snapped some pics of the block. Got my fingers crossed that it's in good shape.....

 

[Wreckinball67]

I take it the new heads are for a truck configuration (side mount turbo)? Sounds exciting, would love to see pictures as the build progresses. My guess is that your replacement engine will have a reluctor wheel. I believe the mechanical injection requires that while the computer controlled used a optical sensor.

 

[MrMarty51]

Look up the thread that AK diesel driver did on the electro viscous fan system.
In that thread is all the part numbers that can be ordered through rock auto.
It comes with a sensor and controller that is easily adjustable to the temp You want the fan to kick in at.

 

[adventr]

I take it the new heads are for a truck configuration (side mount turbo)? Sounds exciting, would love to see pictures as the build progresses. My guess is that your replacement engine will have a reluctor wheel. I believe the mechanical injection requires that while the computer controlled used a optical sensor.

Yep, I ordered the Promaxx heads for the truck intake. I was actually just doing research on here and it *appears* that my engine probably had a 4L80e behind it (since it's serpentine belt drive and not v-belt). That might mean it has the CPS and reluctor wheel already in place, which would be pretty sweet!
Will know for sure tonight.

 

[adventr]

Look up the thread that AK diesel driver did on the electro viscous fan system.
In that thread is all the part numbers that can be ordered through rock auto.
It comes with a sensor and controller that is easily adjustable to the temp You want the fan to kick in at.

Yep! I read thru all 17 pages yesterday, and that's where I got the part numbers! Great info in there. I'm a sucker for stuff like that. My background is in electronics, so I plan to integrate the control system for the EV clutch into my vehicle PC that I'm building.
It does stuff like handle the air suspension i'm adding, and also handle the CTIS for the portal axles that I'm using. Kind of an oddball build for a OBS tahoe, but it'll be different.

Info for all THAT stuff can be found in my main build thread for the tahoe, here:

Portal Axle Tahoe Build Thread


Hopefully that link works for you guys. If cross-posting isn't allowed just let me know and I'll delete it.

 

[MrMarty51]

With the pan removed, check the block for cracks.
I’m sure that You most likely already know that.
I was at a machine shop over in Billings, picking up the rebuilt head and cylinder for the 74 T-150 Triumph Trident. I told him about the aluminum T-150 head that I had messed up. Told him the welding shops here could not weld the dings and have the welds to not fall out. Not enough of a bead to get penetration.
He told Me that He could pin the dinged spots then machine the head down. He told me that he has pins for aluminum, cast iron and steel.
He said that He pins a lot of 460 Ford blocks.
I got to talking about the GM 6.5 problems of cracking. He said He has repaired quite a few of those and they are still running.
I told him if I ever have a need to rebuild the engine in my truck, if the block os cracked in the main webs, I would be bringing it over to Him.
I guess I should do a search and see what this pinning method entails.

 

[MrMarty51]

Be nice to pull the rotating assembly and get it balanced too.

 

[Will L.]

Welcome.
Question your sanity- not needed. You are as nuts as the rest of the group! Haha

All the posts makes this thread flow perfectly. Don’t apologize.

Make sure you are legal with your dmv to convert gas into diesel and that you can use older engine in newer truck.- many places made it illegal to do either one.

Decide what you are gonna do about the dash gauges because the two won’t interchange.

Rip optimizer down. It is not a new engine and the stories they all get changed by mileage is flat out wrong. Too many guys were the wrench turners that can disprove that. That looks like it was opened up- that is not from GEP. So could be that hack outfit in NY had their hands on that one! I know 2 guys, 1 Army & 1 USMC that were up in the chain dealing with hmmwv fleets- they had a certain amount of the NY specials sent to them automatically snd the failure rate was so high they just set them aside and paper whipped that the install was done- then send the reman to auction. they slap in 1 set of bearings and don’t use the select fit or nothing on 2 that I opened up. Your lucky to get 5,000 miles when that happens and the block/rods/crank can all be junk afterwards. Not opening them up is a HUGE MISTAKE!

Inspect for main webs cracked #7 or #8 cracked cylinders, etc. Then all New bearings, gapless rings, balance the lower rotating assembly. GEP is horrible for cast flashing- do that work and flush the oil journals. Throw away that hummer thermostat crossover. Replace the hmmwv 2 wire cps with truck 3 wire. Save that sensor with the db2- folks want that stuff.

Leroy rents a primer tool, or buy a moroso unit that you can prime before every start.
I would get p400 heads over promax for sure! Not that much more expensive.

Getting the lower assembly balanced is worth the cost of shipping it to a shop- that balance makes a huge difference in longevity of the engine. Where are you at and maybe someone here can Recomend a machine shop not too far away from ya.

If you are 100% you are never going to go for big power- rethink the head studs. I have put together hundreds of 6.5s using NEW factory bolts and had no failures so long as boost was kept under 14psi. If you stick with the head studs- make sure you read up on options for sealing them from leaking- to many people learned the hard way the arp sealant tube goes in the trash.

 

[93detroit]

Just ditch the stock turbo. No Hx35 variant (Super 54) spools slowly. Your engine will run freer, cooler, and last longer.