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H3 - motor/trans swap vs tow rating

crwalkerasla

Well-Known Member
Messages
313
Location
Corinth, MS
Looking for a little advice... Down to the point where something will have to be done.

Love my H3 except for the anemic ability to haul a trailer up hills. Been seriously considering a 6.0/6.2 LS and trans swap, but need to know how it will affect the trucks ability to haul a trailer through the mountains. (Getting ready for future travels). From what I have been able to find out, the tow ratings is a multiplier that includes engine hp/torque, transmission capability, frame strength, and axel load strength. You then add a little pixie dust, jump in a circle while patting your head and then some attorney in Detroit whispers in GM's ear what the number will safely be.

For those of you who have done the engine swap, what sort of results have you found?
 

Jeepwalker

Well-Known Member
Messages
857
Location
WI
I haven't done the swap and I can't give you towing fugures, but I have a Jeep GC with an I-6, and another GC with a 4.7L HO engine. The 4.0L I-6 makes for a good DD, but the 4.7L has way more power and snort. I've dusted off quite a few vehicles at stop signs over the years with that thing. It moves it around effortlessly, and will pass any vehicle w/o downshifting. I've towed a full-sized (tilting) car trailer with it many times with equipment (snow plows, skid steer backhoe, skid steer buckets, but not vehicles) on it ..and it leads the trailer around with no problems. That's the only way to go. My suspicion is the V8 would give you the same results. Hopefully someone can chime in on trailer specs.

What you could probably do is sort of triangulate the capacity by looking at the specs of the V8 Hummer, and compare to the tow specs of a regular cab long-box Chevy pickup with the V8 engine (probably similar weight), and similar gear ratio of your H3 ..of about the same era of the V8 engine you are considering. You should be able to find the tow specs online or from a brochure ..they're usually published in brochures. If you cross reference them, that should give you a pretty good idea of what the tow capacity would be. You could also look at, say, a Tahoe too, and subtract the weight difference and add that back to your capacity. A newer V8 Colorado, maybe like the Bison, might be one to compare as well since the frames will be of similar 'weight' and engines more powerful than the older Colorados. That should put you in the ballpark.

How heavy of a trailer are you going to be towing?
 
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Gpcalero

Well-Known Member
Messages
234
Location
SW Florida
Looking for a little advice... Down to the point where something will have to be done.

Love my H3 except for the anemic ability to haul a trailer up hills. Been seriously considering a 6.0/6.2 LS and trans swap, but need to know how it will affect the trucks ability to haul a trailer through the mountains. (Getting ready for future travels). From what I have been able to find out, the tow ratings is a multiplier that includes engine hp/torque, transmission capability, frame strength, and axel load strength. You then add a little pixie dust, jump in a circle while patting your head and then some attorney in Detroit whispers in GM's ear what the number will safely be.

For those of you who have done the engine swap, what sort of results have you found?


What are you trying to tow? Why are you considering a trans swap? Are you trying to tow more than the vehicle is rated for?

Few different items to consider...

I towed my track car to & from the drag strip with my Alpha T. The stock 5.3L V8 didn't seem to have a problem at all here in Florida, yet there are no hills here. The chassis capability is the most important, and you should not expect it to haul more with an engine swap. Adding more power will definitely help it from being "anemic" feeling, but you shouldn't expect it to increase your towing limits, only to help make towing up to the limits easier on the existing limit.

I have swapped to a built LS3 engine & built 4L60E transmission, and added rear air bags to assist with the tail end height. It tows more effortlessly now, but I still won't go over the manufacturer ratings.
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
What are you running right now? I have the 5.3L and it will haul 6k pretty well, even through hills. Just don't expect to win any races up the mountain passes. I pulled my 16 foot 6k car hauler with a 2008 Dodge Charger on it which combined is right around 6k pounds.

The tow rating with the Alpha's (5.3L) is limited to 6K. The wheelbase affects tow rating as well so don't discount that and think that by putting a 6.0L and 4L80e in you can tow the same amount as a 1 ton full size pickup. I doubt the frame and suspension can really handle more than maybe 7k at the bumper, but even 6k is quite a bit for a vehicle this size.

With the shorter wheelbase we have I think anything more than 6k is asking for a lot of trouble. When I towed that much I was really, really wishing I had a load equalizing hitch at least with some sway control while on the highway at 75mph. The wag the dog effect was a little too much for my comfort and if I had to do any emergency maneuvers I would have been screwed unless I was extremely lucky. The extra length in wheelbase a full size truck has makes bumper pull at the higher loads much safer.

Could I haul an 8k load at 25mph? Sure. But I wouldn't want to go much faster than that due to lack of stability. 7k at maybe 35mph, 45 tops. 6k at 65mph isn't bad, but get up to 70, 75mph? Get's interesting when there's other vehicles on the road with you, especially semi's.
 

650Hawk

Well-Known Member
Messages
480
Location
SoCal
The Alpha has a tow limit of 6K (with a WD hitch; 5K without), and the rear axle rating is 3200 (or 3250; I've seen both listed). But there is a lot that goes into determining tow ratings; engine & trans is just a piece of the puzzle. Axle rating, brakes, tires, chassis strength, curb weight, etc. That rating is also based on the weakest link, and I don't think that the engine/trans is that weak link.

Ultimately, as others have said, you're not really going to increase your tow rating, but will make it easier to tow it.:thumbs:
 
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crwalkerasla

Well-Known Member
Messages
313
Location
Corinth, MS
Everyone, thank you for the responses. Currently, she's an original I5 with somewhere between 280 & 300K, but 3rd trany and it's getting suspect. I currently have a 16' double axle trailer that gets moved around on occasion, but I am planning to get ready for retirement and a lot of overlanding. To keep the wife a bit happier as we travel, I am thinking about a solid offroad trailer. Not close enough to selecting anything yet, just knew that the I5 was having fits just trying to keep up with traffic on the interstate when driving through Denver without a trailer. Can't imagine how far traffic would have been backed up behind me with one.
This will be the deciding factor as to whether I keep her and completely rebuild, or trade for a 2nd gen Raptor/King Ranch.
 

crwalkerasla

Well-Known Member
Messages
313
Location
Corinth, MS
Just did a little further looking, the weight for the type of offroad trailer that I'd like will be between 3,500 and 6,000#. Considering it would be a constant load from Mississippi, up into the rockies, guess a Tahoe would be a better bet than the H3.
 
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