700R4 swap question

[sav300]

Ok I know that my questions have been asked alot on here and I did search before posting this, but I'm just trying to get a real estimate.

First off here are my specifics(all of them):
355SB
Edlebrock performer intake (NOT the airgap)
Edelbrock 1406 Carb
Edelbrock Performer cam
Edelbrock Adapter plate (1")
16"x4" Air cleaner
Corvette aluminum heads (58cc chambers)
KB Hypereutectic Pistons (apx. 10.9:1)
Stock rods and crank
Flowtech Afterburner headers
2.5" Exhaust with Summit turbo mufflers
33" tires
3.73 gears with open diffs
4" lift
SWB
TH350 w/NP208
TCI tranny cooler
5260Lbs on the scales

With this set up I get about 9-12MPG in town depending on my foot and traffic. On the highway I can get 13-16MPG and its normaly 15MPG at 55mph (2200rpms).


I am switching my TH350 and NP208 for a completely rebuilt 700R4 and NP208(they have no miles on them). I am buying a 2000-2600 stall lock up converter for it. I would like to hear what you think my gain in milage will be and if there are any mods I need to do to fit this setup; shorten driveline, kickdown adapter, ect. I plan to buy an electric fan for it when I do the swap to help boost the economy a little.

Any and all input is greatly appreciated.



Thomas

[cableguy0]

You are probably going to lose mileage with the 700r4. if your only turning 2200rpm @ 55mph now. overdrive is gonna put you well under 2k rpm which will lug the engine and make it work harder. Overdrive is not the end all be all of getting better gas mileage. It will not work well with your setup. Unless that 700r4 has the heavy duty parts in it your going to break it quickly in that 4x4 with big tires. Overdrive and the lockup clutches in the converters are especially weak because they are tiny. IM not trying to rain on your parade but in my opinion your getting awesome mileage now and your not going to see any improvements regardless what you change. If your goal with this swap is chasing mileage your gonna end up getting worse mileage and having a weaker transmission. You will break the sun shell and burn up the od/lock up clutches its just a matter of time. It costs a ton of cash to get a 700r4 to the point it doesnt break often.

[sav300]

I hear you on the weak side of the tranny and this one is build pretty strong. I'm not worried about this one going out on me because I know who built it and with what parts. I want to do the swap because I can't do 55mph when the speed limit is 65mph and 70mph. At those speeds I can only get 10-12mpg and its hurts pretty bad. That is why I'm chosing to do this.



Thomas

[cableguy0]

I still would think your going to be lugging the engine in overdrive. you should only be turning about 2600rpm at 65mph now. Your only going to be turning 1900rpm at 75mph with the 700r4

[sav300]

Originally Posted by cableguy0

I still would think your going to be lugging the engine in overdrive. you should only be turning about 2600rpm at 65mph now. Your only going to be turning 1900rpm at 75mph with the 700r4

Well I have a set of 4.10 gears that are sitting around. Should I swap trannies and gears??? I'm stuck between a rock and a hard place because with my new work being 35 miles away I'm trying to make due with what I have.

[cableguy0]

I hear ya there. I was driving 30 miles one way for a bit in my 84. 10mpg avg. Your getting awesome mileage now especially for a 5200lb 4x4 with the aerodynamics of brick. I would just hate to see ya go through all the time and effort to get virtually no gain or even a loss in mpg. I would search around for a beater car.They are out there. I found a 96 626 for 200 bucks that needed a water pump. everything else on the car in brand new. These trucks just dont do well when you start racking up the miles on em.

[sav300]

Well you have a good point there. Sucks having to spend money you don't want to. But it will probly pay off in the end. Thanks for your input.



Thomas