to make a long story short, I have a slipping 700r4 and I need to replace the tranny, I will be replacing it with a TH400.

With my 700r4 I was getting around 30mpg with a Holley Stealth Ram on an otherwise stock 350 with a good Megasquirt tune.

My question is how much will losing an overdrive gear affect my MPG?

If it makes an difference (and i know it will) I will be upgrading to a 427sbc, 210cc alum heads and a medium duration solid roller turbo cam.

Like i said before I have a Megasquirt with a Wideband O2 sensor, so I can run it fairly lean for improved mileage.

Mileage is very important to me because I NEED to drive it 2000 miles to get it to my new home. After I get it there, MPG is no longer important.

Thanks.

EDIT: I should mention that for the trip I am going to run a really tight convertor. Summit has a 1700-2100 stall Convertor for $99, hughes makes a "Fuel Mizer" TQ for $189, but I dont think that TQ will save me $89 worth of fuel compared to the summit.

http://www.summitracing.com/parts/HUP-GM5FUEL/

 

depends on the gearing. My turbo car has 2.73s currently and with 26" tire it drives around very nicely... but overdrive would be great to have. If you have steeper gears like 3.42's or more, which are common for n/a motors, then you will be turning lots of rpm at 55-65 mph cruising speeds and its gonna suck on mileage.

motor combo also will determine mileage

 

dbl post...

 

I think it has 3.23's in it right now, i could throw in some different gears in the rear end just for the trip, but would it make enough difference to justify buying new gears?

I am looking at some Trip cost things on the internet, and getting 20mpg would only be $250 based on current gas prices. 15mpg would be $333, but I have a feeling I can squeeze 20mpg out of it with a good tune.