sk8r fer life

So I have setup, 406sbc - t400 - 3.73posi, and right now it gets like 8-10 mpg if I changed the gearing to a 3.23 posi how much would this affect the mpg? or would I need to lower it further to make it streetable. Im trying to get away from changing the transmission. How much do rear end gear usually cost and where should I get them from?

Tim

fireturd350

iTrader: (8)

10 bolts are usually around $200-$250 or so for the parts depending on what you get and where from (Summit, Jegs, Randy's Ring and Pinion, etc). If it's a 9 bolt be prepared to pay more I had close to $500 in parts alone for gear and install kit.

Then figure another $250-$700 for install at a shop. It just depends on where you call around. Dealership were quoting me in the $500-750 range while regular mom and pop places were cheaper.

By the time you pay for gears and install you'll probably be in the $500-$750 range. If it's a 10 bolt 3.23s are everywhere. I got one free few weekends back from a board member. You could just grab a used one somewhere.

8-10 MPG seems pretty low. Is it tuned correctly? Normally you want the gears and stuff setup for how well the car runs in the 1/4 or what the camshaft needs to say in the proper range.

Theres an RPM calculator in the Tech Section on the TGO Homepage. You can use that see how much RPMs will adjust. I would expect 300-400 RPMs though at highway speed.

sk8r fer life

I was told its so low because it has a Holley 750 dp and no overdrive gear, and I was told it was all probuilt so it should be tuned right only 700 miles on everything

fireturd350

iTrader: (8)

Well unless they tuned the carb to the motor on a wideband it's not properly tuned. They could best guess the carb jets sizes and etc but it might be running pig rich. Even using a vacuum gauge I was able to get my old 750DP close, but found lean sections once on the wideband.

sk8r fer life

So what would be my best option to do then?
Tim

fireturd350

iTrader: (8)

I'd start with getting the carb tuned up. Carb Board has a Holley tuning sticky.

GTFiero

Could always swap a vacuum secondary carb on such as a Holley street avengor 670.

But in the end, if your worried about gas milage maybe get into hondas?