fuel mileage on big block with od swap

[Montana_k3500]

Hey, All. I would like some real world input. Have any of you done a 3l80/sm465 to 4l80/5sp swap, and what did you see for before/after mileage. Also, if done with the BW transfer case, what problems did you encounter. The basic question is, is it worth it on the heavy trucks. Thanks.

 

[supertrucker1978]

I have contemplated this same thing many times with my K3500, Its a 454 with a TH400 trans. And unless your transmission needs a rebuild I really don't think its cost effective to swap trannys out gain 2-3 more mpg. I also use this truck as a truck (towing, plowing,etc) so I wouldn't even be using the OD most of the time. Here is a math example......

If your truck gets 10 mpg now, and gas is 3.50 per gal, that means it costs you 35 cents per mile
If you added an OD trans and you somehow got 15 mph (which is a stretch)at 3.50 a gal, it will cost you 24 cents per mile. Which is a difference of 11 cents per mile.
Now lets say the swap costs you 1000 bucks, parts and labor (because time is money) you would have to drive over 9000 miles before you break even (9,090.9 to be exact)

Now I know there are factors like the cost of gas, and the ability of selling your used parts but its just a thought.

 

[Montana_k3500]

Thanks, Jason. To counter, I never count my time, unless it interferes with work, i am either making money or wasting time kinda thing. my time is how much i save, make sense? However, not really my point, just kinda a number tweaker. Add to that, as a daily driver, I drive appx 15k a year, maybe more. Recovery mileage is not a real issue. Part of the question stems from my 87 cc dually, (2wd changes things, i know) I get 11-12 mpg with the stock 454 (plus 40 series flowmasters and a flipped air cleaner) and sm465 and 3.73 rears. I am not sure yet the milage of the 89, as the engine is out, but will be temporarily using the 454 from the 87 (the 87's frame and body are wore slap out from being a rodeo stock truck-will be parting it out soon, with most of it going to scrap). The 11-12 seems high (but has been repeatedly verified), but is 15-16 that unreasonable? I am also considering a vortec 8100 swap with a tune, the idea being it wont work as hard as a worn out 454, or stroke the 454 it has in a rebuild, and upgrade the injection/induction system, with a turbo system possible. More power when I do pull, and should be more efficient when I am nice to it. In addition, any thoughts on the 4l80e-six speed planetary set swap? basically the tci 6x transmission you make with your own case....i will find the manufacturer for that for those who are interested. I have too many ideas for this truck, trying to make sense of how to go about it. Thanks, guys.

 

[Montana_k3500]

Also, does the 4l80e bolt right to the BW case on a 475? i would think so, but am not sure. Thanks.

 

[tanman_2006]

I'd guess an NV4500 swap would put you at 14-15mpg w/ a light foot. I like the idea of lowering rpms to reduce cab noise just as much as better mpg's. The Tcase from a 89 should bolt right to an NV4500 or 4l80.

 

[Montana_k3500]

Thans for the tc answer specifically.....that one has been driving me nuts. I tought it would but couldn't confirm. not a lot of info on the bw cases. I drive 70 miles a day round trip, 60 highway. mpgs count. Id rather drive something that won't completely crumple in a fight with a deer/elk/, and get traction in the snow than a compact that gets 40+mpg. That being said, I'd rather not pay everything for those luxuries. That being said a big block at 3500 rpm sounds as good to me as any top 40 song! I am also half deaf......