group 31 under gmt800 hood?
- Thread starter Lykos
- Start date
Ducky's Dad
Explorer
Mine is not a GMT800, but I have a '98 GMC. It came with two battery boxes, the second one being for SUVs with rear A/C. I just put in a pair of 34/78s with an isolator. Depending on the batteries used, that pair gives me about 150ah vs 105ah for a single 31 AGM. There is no good place for a 31 under my hood.
rayra
Expedition Leader
You'll have to move the radiator overflow / fill reservoir forward a bit, hard up against the air box. Might have to find a way to move both towards the core support. it will be a very tight fit in the factory Aux battery location. And you'll have to use a side post to fit under the hood at the front by the res. I've got a 78 in there and it pretty much fills the available space. But it's about 2" shorter in height than a 31, too.
Why not in the back? So much room back there. If it's about the mortal perils of hydrogen, that's a bunch of noise.
Here's a low angle shot showing how the leading edge of the 78 is about even with the fender height. Good thing the hood swells up there.
Another idea that MIGHT work, although I haven't paid close attention the to clearances, is stuffing that fat battery in the starter battery location and bumping the starter battery to the Aux mount and just changing the main cabling around. Do it correctly the vehicle'll never know or care.
And one last possibility is a totalyl custom battery tray that will sit flat down on top of the wheel tub. The factory aux tray sits about 1.5" above the tub. But even there I'm not sure you can clear the top terminals. My advice to you is get in there and pull that curved brace out of the way in the back corner by the hood hinge, loose or temp remove the reservoir and tape up the terminals and see if that mother will really fit. Or make a wood mockup so all that dead weight doesn't tear the plastic wheel tub loose.
An old hot rodder's trick for finding out hood clearance is get some of that soft green floral foam and put a slab of it where you think clearance is tight and slam the hood on it. You'll get a mold of exactly how much room you have. Make sure its the micro grain close-cell stuff, not the harder open cell or you'll mess up your hood skin.
eta here's a better pic of how snug a Grp78 is in there.
eta nevermind, there's no way you're getting a 31 in the factory Aux location. Not without cutting down thru the wheel tub and maybe impinging on tire clearance. There's a lot of height under the aux tray at the firewall but almost none at the reservoir.
Why not in the back? So much room back there. If it's about the mortal perils of hydrogen, that's a bunch of noise.
Here's a low angle shot showing how the leading edge of the 78 is about even with the fender height. Good thing the hood swells up there.
Another idea that MIGHT work, although I haven't paid close attention the to clearances, is stuffing that fat battery in the starter battery location and bumping the starter battery to the Aux mount and just changing the main cabling around. Do it correctly the vehicle'll never know or care.
And one last possibility is a totalyl custom battery tray that will sit flat down on top of the wheel tub. The factory aux tray sits about 1.5" above the tub. But even there I'm not sure you can clear the top terminals. My advice to you is get in there and pull that curved brace out of the way in the back corner by the hood hinge, loose or temp remove the reservoir and tape up the terminals and see if that mother will really fit. Or make a wood mockup so all that dead weight doesn't tear the plastic wheel tub loose.
An old hot rodder's trick for finding out hood clearance is get some of that soft green floral foam and put a slab of it where you think clearance is tight and slam the hood on it. You'll get a mold of exactly how much room you have. Make sure its the micro grain close-cell stuff, not the harder open cell or you'll mess up your hood skin.
eta here's a better pic of how snug a Grp78 is in there.
eta nevermind, there's no way you're getting a 31 in the factory Aux location. Not without cutting down thru the wheel tub and maybe impinging on tire clearance. There's a lot of height under the aux tray at the firewall but almost none at the reservoir.
Last edited:
Lykos
Super Trucker
Yeah, I'm about to go there. This post is a last ditch effort to find an alternate methods of getting AH without putting the batteries in my passenger compartment.
You'll have to move the radiator overflow / fill reservoir forward a bit, hard up against the air box. Might have to find a way to move both towards the core support. it will be a very tight fit in the factory Aux battery location. And you'll have to use a side post to fit under the hood at the front by the res. I've got a 78 in there and it pretty much fills the available space. But it's about 2" shorter in height than a 31, too.
Why not in the back? So much room back there. If it's about the mortal perils of hydrogen, that's a bunch of noise.
Here's a low angle shot showing how the leading edge of the 78 is about even with the fender height. Good thing the hood swells up there.
Another idea that MIGHT work, although I haven't paid close attention the to clearances, is stuffing that fat battery in the starter battery location and bumping the starter battery to the Aux mount and just changing the main cabling around. Do it correctly the vehicle'll never know or care.
And one last possibility is a totalyl custom battery tray that will sit flat down on top of the wheel tub. The factory aux tray sits about 1.5" above the tub. But even there I'm not sure you can clear the top terminals. My advice to you is get in there and pull that curved brace out of the way in the back corner by the hood hinge, loose or temp remove the reservoir and tape up the terminals and see if that mother will really fit. Or make a wood mockup so all that dead weight doesn't tear the plastic wheel tub loose.
An old hot rodder's trick for finding out hood clearance is get some of that soft green floral foam and put a slab of it where you think clearance is tight and slam the hood on it. You'll get a mold of exactly how much room you have. Make sure its the micro grain close-cell stuff, not the harder open cell or you'll mess up your hood skin.
eta here's a better pic of how snug a Grp78 is in there.
eta nevermind, there's no way you're getting a 31 in the factory Aux location. Not without cutting down thru the wheel tub and maybe impinging on tire clearance. There's a lot of height under the aux tray at the firewall but almost none at the reservoir.
Yeah I'm afraid I'm stuck. I was pretty sure it's a no go but wanted to ask one more time...
Ducky's Dad
Explorer
This post is a last ditch effort to find an alternate methods of getting AH without putting the batteries in my passenger compartment.
You asked about the engine compartment, but the other alternative is to mount one or more batteries under the truck, on the frame rail. I did this on my Power Wagon, with a G31 in the engine compartment and a G34 under the cab. I later upgraded to a pair of 34s under the cab to provide better support for my Indel B 50L fridge in the desert. I'm not sure how much space there is under the cab on the GMT800, but you should be able to work something out. Space is tight under the PW (pics to follow if I can find them), so I went with 34s, but in hindsight I should have tried to fit 24s or 27s because there are a lot more choices on those sizes. There was no good way to fit a 31 under the PW.
Another possibility would be to find a battery relocation kit to hang a battery inside the rear fender, drag racer style. You might be able to get a 6V inside each rear fender, but might require exhaust mods.
The PW, with batteries tucked up as high as they would go. Boxes came from Summit Racing, reinforced with some angle iron.
You asked about the engine compartment, but the other alternative is to mount one or more batteries under the truck, on the frame rail. I did this on my Power Wagon, with a G31 in the engine compartment and a G34 under the cab. I later upgraded to a pair of 34s under the cab to provide better support for my Indel B 50L fridge in the desert. I'm not sure how much space there is under the cab on the GMT800, but you should be able to work something out. Space is tight under the PW (pics to follow if I can find them), so I went with 34s, but in hindsight I should have tried to fit 24s or 27s because there are a lot more choices on those sizes. There was no good way to fit a 31 under the PW.
Another possibility would be to find a battery relocation kit to hang a battery inside the rear fender, drag racer style. You might be able to get a 6V inside each rear fender, but might require exhaust mods.
The PW, with batteries tucked up as high as they would go. Boxes came from Summit Racing, reinforced with some angle iron.
rayra
Expedition Leader
Another idea for power storage which I've long been considering was the addition of several small 10Ah batteries for wheelchairs. They'd cost more for a given amount of storage, but they are small and can be arranged and tucked in just about anywhere. My own design intent was to tuck four of them in my rear power box in my Sub. I used some wood block mockups when I was figuring out the interior layout.
These were $71 for 4 (40Ah total) ~3yrs ago, they've gone up a good bit. But they are small and SLA.
https://www.amazon.com/dp/B00LRUGE0...colid=QWZ1BSZYG6VW&psc=0&ref_=lv_ov_lig_dp_it
How I was thinking of positioning them. Figuring to wire them on the general and solar charging circuit, but isolate them from backfeeding / general discharge and using them to supply a few power ports in the rear interior. Those that would be used while sleeping in the vehicle.
These were $71 for 4 (40Ah total) ~3yrs ago, they've gone up a good bit. But they are small and SLA.
https://www.amazon.com/dp/B00LRUGE0...colid=QWZ1BSZYG6VW&psc=0&ref_=lv_ov_lig_dp_it
How I was thinking of positioning them. Figuring to wire them on the general and solar charging circuit, but isolate them from backfeeding / general discharge and using them to supply a few power ports in the rear interior. Those that would be used while sleeping in the vehicle.
