The stock 3.909 rear end gearing is wayyyyyyyy to short! Freeway travel kicks my mpg down from 24-26mpg to 18-19mpg, first gear is useless, and the right lane is getting old. I just spent 5hrs searching for the fabled 3.308 ratio gears from the diesel B2000/ford courier truck with no luck, then I set my sights 3.636 gears from the 79-82 626 only to find a $500 aftermarket copy. Our Rx-7 can share ring and pinion gears with 94+ miatas and I can't find a single set for under $450 that goes under 3.909. Any of you guys have any thoughts as to where I should look next? My plan is to call the all the bone yards in the area to see what happens, also I have filled out a part request on car-part.com as well as their English, Australian, Irish, new Zealand, and Canadian counter parts. some thing has gotta give I can't be the only guy out there seeking a lower ratio!

 

You've already basterdized the engine so why not basterdize the rear axle assembly too? You're no stranger to modding things in the engine bay to fit an engine from a domestic. Why not the rearend too? Plenty more gearsets available, but I'm sure you already knew that.

Ask peejay. He's always never happy with the rearends in these cars for whatever reason. Good luck with your search!

Are bigger tires on the table?

 

I'm running 205/70-15 tires on the street to cut the revs down. The bridge port likes to be loaded down under cruise, which is contradicted by the 4.78 final drive that allows me to use three gears when rallycrossing and cuts down on the right-side wheel lift problem that solid axles have.

With the tall tires and 4.78, revs are only 10% higher than stock. Good compromise, I'd say. They fit the wheelwells with no issues.

No overdrive with the 302? Can you adapt a GM transmission or (gack) use an AOD?

 

I just switched to 3.7 from a RX-3 SP which has the same pinion shaft lenght as the pre-86 RX-7. Im heading to vegas car meet in may so the close to $4.59 per gallon dont hurt my pock. I was running 4.44

 

taller tires or get a real engine....

 

Just stuff a different rear under the car, could probably do it in a weekend. And pick one designed to handle a V8 and you'll find the gears you're looking for. You should be able to loaf along at about 1600 rpm on the highway with that engine.