Engine Knocking?
 

hi, ive been lurking around these forums for awhile now. this is my first time posting anything. anyways, i just had a question in regards to using low octane gas and engine knocking. i did a few searches and couldnt find anything in refards to this. so...

its a known problem for many piston driven vehicles that when using lower octane gas than recommended causes engine knocking. in order to get around this problem, many cars nowadays are equipped with knock sensors. do rotary engines experience knocking if u use lower octane gas? and if so, is it equipped with knocking sensors? and would lower octane gas prove to detrimental to the rotary, or does it just reduce performance? thanks a lot guys, look forward to any responses.

note, im not being stingy when it comes to gas, im just asking out of curiousity ;)

Re: Engine Knocking?
 

Yes RE's have knock sensors, crank angle sensors etc etc !

Inregard to your question on fuel we have 96~98RON Fuels avaialible and I have never used anything below 96RON.

I had two 1st Generation RX-7's, and I do not ever recall hearing "knocking". I started to use premium, back in the days that it was 89 cents a gallon! But I mostly used regular unleaded, and that included Colorado's winter blend. Never had any knocking. The rotary sounds so pretty that maybe I ignored it. I had a friend (in FC) who had one of the two rotary's in his RX-7 go out... he was still able to drive it to the Mazda dealer!

wow, now thats reliability.
________
Post-Traumatic Stress Disorder Advice

He didn't get over 30 mph, but he was able to drive it. Rotary's are great!

Back in the day my dad had a RX4 and ran out of gas while camping. The only fuel around was kerosne, so he put some in and drove it to the nearest gas station. It didn't run well, but it ran. Now that is amazing.

Wow! That's something.

I would stick to premium. Thing is a piston engine tolerates knocking much better than a rotary. The knocking will put all of the stress on the apex seals and can prove fatal to the engine.

I thought knocking was caused by the valves in a piston engine. A rotary does not have valves, so what's to knock?

Any tech-heads out there?

you're thinking valve bounce, and that's from the valve (yes) bouncing off the heads as they come up to close...

knock is the sound of the engine when the fuel detonates instead of combustes in a controlled manner...

edit: well, acutally yes, hot valves can pre-ignite the fuel as it compresses (or at least contribute to the preignition)... ping or knock can happen in any internal combustion (i have crappy spelling toda) enigne. (<- see??)

Knocking has nothing to do with valves. Knocking is pre-detonation, which is when the air-fuel mixture ignites too early (normally by itself). The "knock" is the sound of the predetonation, which is discernible because it isn't as powerful as a normal detonation, sometimes comes in multiple detonations, and occurs when the piston/rotor is in a different position, and if bad enough is causing damage in the engine. For example, knock at low-rpms (which isn't completely destructive) sounds like someone is shaking a can of paint.

The damage comes because the rest of the engine is trying to push the piston up (or rotor around), while the explosion is trying to push it down, and something has to give. The more extreme the pre-detonation, the worse the damage. In piston engines, piston rings, head gaskets, and sometimes connecting rods are the first to go. In rotary engines, the apex seals are by far the weakest point, so they're the first to go.

Apex seals aren't "fragile", that's a misconception. They are simply the weakest point. In fact, top of the line tuners are finding out more and more that rotary engines can handle a little bit of pre-detonation after all, just like piston engines. It's just a little harder to hear it yourself in a rotary, so it happens more often than people realize. It's the big pre-detonations that you normally hear, which normally blows the apex seals. Just like a single big pre-detonation can also kill a piston engine (via the piston seals, normally).

---jps

OK, Here's a thought...

What do people here get in terms of octane ratings on your fuel?? You are all saying high and low octane, but I don't think it's the same everywhere...

Here, the standard stuff is 95 and "premium" is 98...

The 13b-rew in my last rx-7 had clearly audible detonation on five separate occasions and still kept motoring along :) The 7m-GTEU in my supra pinged once and luched a head gasket - again :(

-pete

By design, the rotary engine does not knock.. unless its a mistuned turbocharged one.. which is why they also run better than piston engines on hydrogen fuel. N/A rotaries also like to run on low octane fuel as well..the RENESIS on the otherhand it would be safe to follow Mazdas guidelines on what octane rating would be for gasoline.. but they did also say not to use synthetic oil in the engine, yet their own race teams use it.

Isn't that partially because they run at higher temps than the RENESIS will? I mean, those race engines have much higher redlines! :)

????? Factory Mazda Race engines have had Dry sumps ??

12APP
13PP
13JPP
20BPP
R26B

All have dry sumps.