Hi guys. I was refered here by the boys over at GrassrootsMotorsports.

Currently I am planning a locost (lotus 7 replica) and I am deciding between the more traditional miata drivetrain and NA FI 13B. Fuel and spark would be via megasquirt.

Is there a good FAQ or place for me to learn more about these engines? Ive heard the 13B does not mate to the miata trans, but the miata guts fit in RX7 trans (still trying to figure why one would do that).

As of today I really like the Westfield-Miata kit, so I would use MX5 (prob 1.8liter parts) brakes/hubs/rear suspension/diff and the powertrain would be RX7. Ive heard of rotary locosts and migets before. Does anyone know of any build diaries online?

Thanks in advance.

 

Why not just use the RX7 transmission? The 13B is a perfect engine for your car. If you really want to be scared put a turbo in it. Don't know of any Lotus build sites but try:
http://web2.airmail.net/atl/Rotary.html
for a build up on a 914.
Pics of my Turbo rotary 911 near the bottom.

 

I have nothing against using the RX7 trans provided it has proper gearing to work with the Miata rear end. Ill have to find some measurements of both to see how different they are in length/girth to ensure fitment into the kit.

Thanks for posting the link!

 

FWIW, the S4 NA trans ratios are as follows:
1st: 3.475
2nd: 2.002
3rd: 1.366
4th: 1.00
5th: 0.711

The s5 NA trans has a very slightly taller 5th at 0.697.
The TII tranny's have very slightly shorter 1st-3rd gears.
S4TII has a 0.762 5th gear.

I hope this helps. Please post pics/writeup if you build this! I really like the idea of this project and would be very interested in how it works/works out.

 

spanks for the gear specs. Ill have to toss those into excel with tire size and final drive ratio to figure RPMs at speed.

The taller top gear prob wouldnt be needed in a locost as they have simply horrible aero.

 

Keep in mind that rotary engines can spin a lot faster than most piston engines. My car has a 10,500 RPM redline. I trapped 95 mph in second gear at the local drag strip.

 

99.99% of rotaries redline a great deal below 10,500.

 

Yes, but 99.99% of rotaries can still out rev a piston engine.
Also, I would guess that he is going to use a rebuilt/built motor in his locost. He has already said that he will use a megasquirt and not a stock ecu. I'm guessing that his engine will be able to rev higher than stock.

 

Currently I am not expecting to build a high hp car. These kits usually use 100hp miata engines, and are quick at that state. Using a 160hp FD motor which should be a little bit lighter should be more than enough powa for this application.

I imagine headers will be required, and removing the A/C, powersteering, and even fitting a smaller alternator should free up some extra power. The megasquirt wouldnt be required IMO, but this would be my first chance to try DIY electronics as my previous cars have been diesels.

Emissions might play a factor in this project, so based on what state Im living in the engine will have to meet the standards of the car it came out of.

 

Exhaust noise and heat are the biggest issues with using a rotary engine. Packaging a decent exhaust and getting enough underhood cooling given the small engine bay dimensions is tricky. Turbo motor would be the way to go I think since the turbo would take some of the sound edge off and with a louvered hood to help keep cool.

For my Locost I wimped out and went with a Toyota 4AGE but rotary would definitely be neat.

Try http://www.locostusa.com as well.

 

Since you're not talking about turbos or turbo power levels and you ARE talking about headers, I assume you don't mean an FD engine. Do you mean an FC engine? A stock S5 NA makes about 160HP at the flywheel. Intake, exhaust and a standalone can give you that much or more at the rear wheels. Passing emissions shouldn't be hard if they don't look too closely at the equipment. (My car puts out about 2-3ppm HC at idle and 2400RPM)
Getting rid of heat is a challenge, especially given the size of the engine bay. How much area do you have for a radiator? A stock radiator (core) for the 2ng gen NA is about 18Hx23WX1"D, for comparison. Header coat/wrap may help as well.