turbo-diesel rx7 47 mpg

[Odin]

I had a thread for this once before but i had to delete it for insurance reasons, I didn't realize if you have a car in the states that you don't drive but is registered you still are required by law to have insurance, and i didn't. I got a random insurance check and had to prove to the state that it didn't run and i wasn't driving it (which i wasn't driving it but it did run) just being my paranoid self i deleted everything about this car i had posted in case of a search - once i successfully proved it didn't run and i was out of the hot seat of potentially loosing my license I bought insurance and finished it and took it on the first road test and can freely post my results without worry

1982 Mazda Rx7 originally 1.2l 12a rotary engine
swapped 2.2L IDI Perkins Diesel with a s4 Rx7 TurboCharger

So far my testing has shown 47 mpg @ 55 mph (without a hood)

I am very pleased with these results as my final drive ratio is still far from perfect 3.9 rear with a .825:1 5th 2900rpm @ 55mph when i'd like it to be closer to 2000 rpm at 55 mph
my engines redline is 4100 which doesn't give me much room to work with as i'd like to be able to do at least 70 without over reeving the engine

the car already has been converted to a two tank veggie system and the main reason for the swap in the first place was me wanting to be able to run all my cars on the WVO i collect from my three restaurant grease suppliers, I was getting tired of buying fuel for one of them

first start-

http://www.youtube.com/watch?v=SQySJPEP0Rs

first idle-

http://www.youtube.com/watch?v=JmHcbYk6EQQ

Fist drive! -

http://www.youtube.com/watch?v=VSiqPDJIc4E

[cleanspeed1]

Lookin' good!

You get that thing under 2000 rpms at 55 I wouldn't be surprised if it hits 60 + mpg.

Look into a 8.8 Ford rearend out of a Mustang. More gear options than anything else and the ring and pinions are cheap.

[hondaguy72]

A 7.5 ford rear would be fine as well. I'd shoot for 2.73 gears (stock ratio in most Mustangs). That should get the rpms down. I'd think you'd want cruise rpm to be under 2k personally. 1400-1600 and the motor should be near torque peak.

Here's a guy by you with the 2.73 ford 8.8

CL Link:

Lots of Mustang Parts

[ChrisAE82]

Thats just awesome! lol. I love the RX7, maybe something like this should be my next project

[Odin]

one of my friends has a ford 8.8 with the 3.27 which i think might do just fine, the the length is only an inch longer than stock so thanks for the advice i never would have thought to look under a ford

[hondaguy72]

Just an FYI it's not a direct swap, and most of those rear axles are drum brake setups, so you'd have to do some brake mods to get the bias correct. T-bird turbo coupes have the disc brake axles, but come with 3.73 gearing. It appears you have some options for rear gearing from other vehicle sources too. Not sure if there are gears tall enough for your stock differential readily available. Nice job on the swap!

[Odin]

i've looked for direct swaps but the only ones are above 4 which is the wrong direction and i don't mind modification