Need Advice- Rear end drive ratio

[wissmannfamily]

I presently have a '84 MCI9 with a 8V71 that I recently replaced with a 8V71T with 80 injectors.  This produces approx. 385HP and I will say that it does run nice down the road.  It has a 5 speed manual transmission and gets approx 5.5-6.0 MPG.  My rear end recently went out and I was wondering if anyone had any experience of running different rear end ratios to increase mileage?  I drive 35K miles a year and with $3/gallon fuel I'm looking for any improvements I can find!

Loren

[Nick Badame Refrig/ACC]

Loren,

Welcome To The New MAK BBS,

Allthough, I'm no expert in gear ratios, I can comfort you in knowing you will get your awnser here!

Thank You for Posting!

Nick Badame-

OK GUY'S, I know you gear heads know this!!

[Busted Knuckle]

Loren need a little more to give you a good answer like what ratio was the old one? What kinda driving do you do(example all Interstate, mostly back roads)? When you say it moved down the road pretty good were you running it against the govenor most of the time? Flat lands, mountains, mixed? Busted Knuckle

[wissmannfamily]

We mostly do interstate driving which is 65-70 MPH.  The bus presently governs out at about 73 mph.  I just found out it had 3.73 gears in it and I have the option to put 3.33 gears in it.  According to our numbers that should govern it out at 80 mph and therefore slow the engine down to 1800 rpm at our normal cruse speed.  If I understand things right that wil put the engine in a more efficient operating range.  It also would put shifting down to fourth gear at about 60 mph which would work well when we do get in mountian country.  I went ahead and ordered the 3.33 gears today so after we get this all put together and running I will give a follow up report to let every one know how this turned out.