BlueAdept

Obviously detonation is somthing to be avoided... but since 100 octane fuel is common in Japan... does anyone have any idea if we are gonna have any problem with the lower grades of fuel in various places?

Here, regular is 95octane and Super is 97 or 98.

I also heard that it might on some cars be necessary to reset the ECU somtimes since it will only ever lower it's settings for low grade fuel... never recover with a higher grade used...

Has anyone got any idea, both in general and in how it applies to rotaries?

Gaidin

Blue, I think I read somewhere that a rotary engine doesn't need a high octane fuel. In fact, the article stated that the lower that octane the better. I'm not sure where I found that . . . I'll do a little search and see what I can come up with.

Styjan

I put regular 87oct in my 87 RX-7 and I put 91 premium (Yay for California, 91 is as high as we go!) in my 93 RX-7. The FD needs the high test gas.

Mazda man

Not that I would put diesel in my Rx-8 but can rotary engines run on diesel? Is there a special rotary diesel engine?

fritts

I would want to stay as high of an octane possible, one ping on a rotary and you break an apex seal, which means rebuild. I hope that it is less of a problem on the 8 though but with higher compression rotors it would seem like it would be more of a problem.

BlueAdept

OK, I'll go with that, but if it's got to run on 91 octane in California, and regular is 95 here... I guess I can't go wrong???

red_base 95

To address an earlier concern reagarding the ECU settings - Mnay modern cars have an electronic knock sensor, and this adjusts for lower and higher grade fuels automatically.

How would this work in a rotary though? I'm not exactly sure if you can retard or advance timing in a similar manner to piston engines. Any experienced rotor heads want to have a crack at that? Thanks.

Hercules

What does a knock sensor do? My car has been getting really bad gas mileage as of late, and I know the check engine light is on because of a bad knock sensor.

Could this be a culprit? And how much do they run to replace?

Thanks!

BlueAdept

Well, presumably the knock sensor detects pinking or pre-ignition... so if it's failed then the ECU may just retard the timing as far as it can to be safe... which is likley to play havoc with your performance... (And probably mileage too)

BlueAdept

My issue is not with the ECU retuning for lower grade fuel, but I had heard that on some models it will never return to normal... it never return to the setting for the higher grade fuel without a reset.

Anyone confirm or deny this?

rpm_pwr

On all the cars I've owned the timing comes back pretty quickly after a knock.

Just to clear a few things up:
1) NA rotaries LOVE low octane. When it was available, I knew people running 85 Octane (about 80 US RON) and getting great performance. The shittiest fuel the better. My friends with NA rx-7's all try and fill up on the worst fuel they can find

2) One ping does not equal no motor. It's a common misconception largely held by people who've never detonated a rotary. My 60,000km motor has had about 4 seperate knocks one of them so sickening my first reaction was to see if it could still idle (on-the-fly compression test). 3 of the knocks were my fault 1 of them came from bad fuel.

Think of it like a piston motor, except when detonation get bad enough to lunch head gaskets on piston motors, rotaries can begin to loose apex seals.

BTW a failed knock sensor in most programs = safety mode. You'll get very conservative timing (read:bad mileage)

HTH

-pete

Macabre

That's a good question. It would probably come down to whether they could design the combustion chamber to get high enough compression (~20:1). If you're asking if you could put diesel in an ordinary rotary and expect it to run, no.

Styjan

Here is a link to a diesel rotary engine

Gaidin

So the 8 will run beter on lower octane fuel, right?

wakeech

well, we can't know until the data from the factory comes out on recommended fuel ratings... i DO know though that econo boxes that are DESIGNED for like 87 octane fuel (yay Canada!! :p) NEED TO HAVE 87 octane fuel, otherwise you end up with dirty everything and heavy emissions as 92 octane just won't burn as well in a lower compression motor not designed for it...

looking at the RX-8's RENESIS, and GUESSING (completely; for those who don't know, i'm just a 19 year old econ major in university with a car fetish), because of the 10.*:1 compression, and 9k RPM redline, i'd wager something around 89 or 90 octane recommended...

what's weird though is that i read that stupid article in SCC about the 350Z, and they dyno'ed it with "shitty" 91 octane, and SOMEHOW got a gain of like 1.5 peak hp with another run on gas in the high 90's, or even 100 (can't remember...)... is that bullshit, or just an over active knock sensor??

Hercules

How much to replace it do you think? For the part only, I get labor done cheap from some guy

Macabre

Modern engines are tuned to be pretty close to the edge, mostly for emissions and fuel economy reasons. That's why you don't get much in the way of gains from off the shelf "chips" in normally aspirated engines any more until you start to modify them in other ways - they're tuned aggressively from the factory and even adaptively. On a warm summer day with California's 91 octane, it's no suprise that the Z they tested performed marginally better with a higher anti-knock-index fuel.

BlueAdept

Any idea WHY..... you can say they love low octane... but is there a reason, other than just the design doesn't suffer some of the problems requireing higher octane in piston engines...

Is there a reason wny higher octane fuel is bad?

fritts

I would think that mazda would take full advantage of the use of high octane fuel so that they could advance the timing on the engine and make more power. I was looking over some info on the NA rotaries and found that people advance the ignition timing and then use high octane fuel to make more power, especially down low. Sure enough at stock timing though, the NA use as low octane as they can due to the ease of combustion. My question would be since they have increased the compression on the Renesis and because of the availability of high octane fuels to make power will Mazda use it to make more power. If they have set it up for low octane gas then there will be performance chips available to take advantage of increasing the ignition timing.

rpm_pwr

low octane = faster flame front. Having thought about it I think I agree with fritts - they may go for agressive timing in search of those last few HP and thus you would have to run high octane. If they go conservative then low octane all the way.

Basically the closer you get the engine to grenading the more power. Lower octane = faster flame fronts (more chance of pre-ignition) = more powerful burn. Large ignition advance = more combustion pressure = better burn, but you need high octane gas because of the risk of detonation. It's a matter of wait and see what they do.

-pete

Sputnik

It's neither. 1.5 HP is well within the margin of error for those kind of dynos. Especially since the runs were obviously not done back-to-back, but they would have had to burn through the rest of the 91 Octane, and then some, before they could be sure that they had mostly 100 test. The 1.5 HP measurement basically means that nothing changed.

---jps

wakeech

oh, :D okay sweetness... i had a feeling those guys at SCC were kinda full of it on that, as they are with so much else...

Macabre

It was actually 5hp, or almost exactly 1%. Still within margin of error, but regardless, with modern engine management you will usually get a hair more power with slightly higher octane. You'll also usually get a bit more by simply resetting the ECU, because you'll be running on the "best case" maps even with less-than-best fuel, until it re-learns what kind of crap you're running through it and picks more appropriate tuning.

RedRotaryRocket

I agree completely with the idea that a few HP is complelely within the margin of error on the dyno. The dyno error, heat soak, and other issues make measured differences of a few HP meaninless.

As an example, I had my FD RX-7 on the dyno, and in back to back runs the measured power was different by 10 HP.

fritts

If they reset the ECU between Dynos on the 350Z it could have very well been running on a more advanced timing map. Which resulted in the extra horsepower.