M998 GEP 6.5 turbo 4L80 conversion questions

[alpine44]

I recently got a 2-man M998 with troop carrier enclosure from Hill AFB. We have been running this on trails in Montana and Idaho with the troop carrier tarp taken down and our gear stored in plastic tubs in the bed. Overnights are very comfortable under the troop enclosure with an inflatable mattress between the wheel wells.

Overall, I am very impressed with the capabilities and ride quality of this vehicle - especially considering the price. However, the highway portions to and from the trails are a pain with the 6.2L engine and TH400 tranny. On flat ground, the lack of overdrive is annoying and on mountain passes the 6.2 runs out of breath quickly.

I am toying with the idea of finding a GEP 6.5 turbo engine, a 4L80/NP242 combo, and stuffing this in another M998 chassis that I hope to find cheaply with a busted engine or tranny. My current M998 runs so nicely that I am going to use it as is and sell it unmolested later.

Looking at previous post, this drive train conversion appears to be a straight forward. Where are potential pitfalls or challenges of this idea that I am missing?

 

[Dark Night]

From what I have read, the 6.5TD won't fit into a 6.2L HMMWV without a body lift. Also, the turbo needs to be a rear mounted unit, not side mounted. This is to allow it to fit between the frame rails. Replacing the transmission with the 4L80 requires a new harness and controller. There is additional info on it here:

http://www.steelsoldiers.com/showth...-Advice-wanted&highlight=6.5+turbo+conversion

I have thought about it myself... There are also threads on here where you can add a turbo to your 6.2L. It's a bit more involved than just a bolt-on, but it isn't ridiculously complicated.

I have also seen where some have opted for a Whipple supercharger instead of a turbo. There are options...

 

[Retiredwarhorses]

This conversion is my speciality....I have or can get everything you need.

 

[panzerwillie]

Yes you need a complete HMMWV 6.5 turbo engine or one out off a VAN, those are the only 2 options, the block is made for the center mount turbo with the oil feed and return by the block but also the head to intake bolts are 60 degrees instead of 90 degrees on a 6.2L , off course if the engine is electronic you need to change it to mechanical IP not a big deal, as far as the 4l80E you can use a stand alone there are many on the market, the cross member shifter linkages as well of driveshaft need to be change but all can , hope this helps.... before i forget DOG HOUSE needs to change as well...

 

[Action]

you also need to cut the body tunnel top where the doghouse sits. The body lift needed is just 6 spacers between the body and mounts. Contact RTW and see about letting him do it for you.

 

[Iyellkhan]

do this the right way, have someone like retired war horses do it. The conversion is strait forward in the sense that there are specific manuals that let you reverse engineer and upgrade the trucks, along with take out drive lines meant for the ECV hmmwvs that you can pick up in good condition, but there are a lot of random things (big and little) that do make it involved. That being said, doing this conversion made my truck much more fun / drivable, and I'd do it again in a heart beat, but know you're more or less talking about building a new truck

 

[Magyar02]

Where?

This conversion is my speciality....I have or can get everything you need.

Funny that I came across this chain; I work at Hill, and recently got a HMMWV too and want to do the same thing; I love the Humvee but it would be nice to reach freeway speeds with an overdrive. I've seen a couple 6.5 HMMWV naturally aspirated engines on eBay that come with an overdrive tranny; can I just buy the engine from eBay? It's not as great a solution as a Cummings conversion but a lot cheaper. How much would retiredwarhorse charge for the entire conversion or just changing the tranny? And where are they? It would be a long drive to Montana limiting speed to 60. I served active duty for seven years, but I am a submarine nuke, so never worked on humvees, but I am an engineer, and can figure out some things. I am now at the same base that the author of this chain bought his vehicle at serving as a civilian engineer, Hill.

 

[Lionel]

Not including the drive train, I've probably got another $3500 in harnesses, drive shafts, shifter, switches, brake pedal, fuel tank & hardware, etc., etc., etc. There are some great threads out there on this conversion, both here, (Ted's build is like my bible for this project),

http://www.steelsoldiers.com/showthread.php?13063-HMMWV-A2-Project

and on the G.

http://g503.com/forums/viewtopic.php?f=63&t=108962