Rev limiter + meth injection
 

well I was wondering about increasing the rev limiter of the FD being htat I'm very very new to rotaries and know very little about modding them or their limits . I did a quick search


one of the things I found was that with the FD a meth / water injection is a good mod to have to keep the engine cooler , ( on the top of my list (car isnt running yet ) ) , andhte second thing was increasing the rev limiter .. safely trying to see how high I can get the engine to rev given a standalone ( power FC ) seems to be my target


what do you need to do to a rotary to increase the rev limit ?


and about the rev limiter and meth injection .. I read that with the stock rev limiter the meth may still work thus causing a very lean situation with the fuel cut off and all instead of spark cutoff .

I'm very new to the meth injection concept as well

so howmuch of this is true ? howmuch is myth ? and what have you guys learned from your experiences .

(yes I searched already but didn't really get any concrete answers)

The reason it is suggested to increase the rev limit on the PFC is to avoid hitting fuel cut in case you accidental over rev the engine.

It is not so you can see how high you can get the engine to rev, as you put it.

You still don't want to be revving a stock engine that hasn't been race clearanced beyond the stock redline, as you will most certainly damage the rotor tips / side iron.

ok what is "race clearenced" what do you mean by that ? how do you accomplish that ?

the reason I asked is because my previous car was a miata which i auto-x'd and I planned to auto-x the fd .. increased rev limiter was so that you wouldnt be bouncing off the rev limiter in second on a fast course .. I figured the same may apply to the RX-7 .. on the miata you have 600 RPM you can retune the car to use safely beyond the stock redline .

stock redline is 6900 , but most auto-xers raise it to 7500 .

which is why I asked if tehre was a limit to where I could raise it to safely . in a piston engine well you know you have various things to do to increase the RPM range .. cams and such ..

I was wondering what you needed in order to do the same to a rotary .

and whats this about raising the rev limiter so you WOULDNT hit the cut off ? I mean I'm a little confused now .

is it unsafe to hit the rev limiter on a rotary unlike it is on a piston engine?

Hitting fuel cut @ full boost can lead to a blown engine. That's why it is recommend to increase the rev limit on the PFC, and just pay more attention to your tach or shift light.

Race clearance involves making the rotor thinner.. milling off a few mil's from the each rotor side. This provides a larger clearance from rotor side to side iron, so during rotor wobble / e-shaft flex at high rpms the rotor will not impact the side iron and ruin the side seals.

Their really should be no reason to take a stock engine with stock ports beyond 8krpms.. Power will be falling fast after 8k rpms... if you find yourself needing a little bit more speed in 2nd gear during an auto-X it would be better to just change the rear drive ratio.

While hitting overrev fuel cut is something that should hopefully be avoided, I think you're overstating the dangers. Just about every modern engine (piston or rotary) has it and lots of people have hit it inadvertently without grenading the engine.

Yes, but it will still be falling fast even before 8k. Here are two stock dyno sheets:

https://www.rx7club.com/attachment.p...1&d=1318023728

This was posted on these forums a while back. They are chassis dyno results measured in wheel horsepower. The red lines are from a stock FD, and the blue is form a larger single turbo setup.

https://www.rx7club.com/attachment.p...1&d=1318023728

This is engine dyno information as published by Mazda. The solid line is the 93-95 Rx-7 engine, and the dashed line is from an 89-91 turbo Rx-7.

I agree, while it is unlikely that hitting fuel cut will blow an engine, that is the logic behind people increasing the rev limit on the PFC (at least that is my understanding).

Thanks for the dyno graphs, been years since I have driven a stock port car. Peak power is lower than I expect, but may still prove to be beneficial revving it out to 8k in 2nd gear during an autocross event rather than shift to 3rd only to slam on the brakes a second later.

Very nice information as always Raymond! :icon_tup:

Slightly off topic but people forget that the turbo rotary engines really did not have a complete lack of low end torque, not compared to today's naturally aspirated DOHC 4 and 6 cylinders. The 1st and 2nd gen Rx-7 turbo motors made about as much horsepower as they did torque (when using American units). You'll probably never drive one of those in stock condition but when I drove a 70k miles all original 10th anniversary T2 it felt a lot like the n/a DOHC V6's of the 90s, such as a nonturbo 3000GT or 300zx engine.

Going back even further:

https://www.rx7club.com/attachment.p...1&d=1318031541

dotted line is the early 12A turbo found in the early 80s Cosmo. Solid line was on a refreshed model with a revised turbine wheel. Both had a single scroll configuration with an undivided manifold and undivided turbine housing. The 20B's had basically a DOHC V8 torque curve, what you would expect from a high end luxury car of the day.