Alright, I searched and haven't found this question yet and I'm just too curious to not ask. It's a bit theoretical so it might be a stretch to ask.

What octane would be best for a stock S4 N/A?

Now I'm not talking about just what you can get at a pump. I'm talking if you could put ANY octane gas into the engine to burn (ex. 70, 82, 84, etc.).

 

I think the design is to run 86-87 octane with the stock ignition timing and injection for all FC's, in stock trim.

 

some people that i know use 85 to autocross.

 

^^IIRC that is sort of correct. (not ****, the other one... sup ****? )

From what I remember to be a fairly detailed discussion on this, they are tuned to run at most 87. Let me clarify this some, however. I believe the number was actually around 84, but I don't actually remember. I do, however, remember that the "max 87" number (keep in mind I don't mean this is maximum recommended or w/e, that's just a number I know for sure it was tuned to run under) was RON. We use AKI or R+M/2. The difference here in these ranges is generally 3-4 octane.

This means that if it was tuned to run on 87, then here in the states we would use 84 or so octane. If it was tuned to run 84, then 81 or so. I believe the final calculated R+M/2 number that the thread came to was in the 82-83 range but... again... years ago.

I hope this helps.

 

Well I was reading over a post that AaronCake had posted (I think on his website) and he was mentioning that for an S4 N/A best octane is the 87, if you go higher you are going to actually lose power and there will be greater carbon build up. I used to think that if i put 91 octane it would make it run better but after doing some searching looks that 87 is the best for S4 N/A.

 

That is if it is stock

 

All the "use 87" octane posts I've seen are assuming that's the lowest choice. That's why I asked my question in the way I did.

That is helpful, assuming you remember the numbers right.

 

posting up that 87 is the "best" octane for an n/a is like saying stock n/a AFRs are "best" fuel ratio.. and we all know thats not true

 

Was just restating what I read. but what you are saying makes sense

 

I have an S4 NA with an Intake and a RB headers, High flow cat, and a cat back what and I have been using 93 the whole time I noticed a difference from 89octane to 93 it ran smoother but it could of been a placebo(I dont know how to spell) effect what should I be running?

 

Edit ^^^ Run 87 octane only in an NA. As stated below if I could find 80 I'd run it.

Yeah, they run pig rich. I'd run 80 octane if I could find it.

Interesting tidbit though... adding premix lowers your octane. I don't know by how much, but it does. The thread I'm talking about had calcs for it.

I'm positive that these motors are tuned for no higher than 84 R+M/2. 100% guaranteed that number is not higher. I'm pretty sure it's a little lower though.

Or you could just get a fuel management system and wideband, and tune it for whatever you're putting in.

 

Hmm so if I figured out the compressed air temps based on A/F and looked up the ignition temps of 84 octane and 87 octane I could figure out how much to lean out the A/F while still maintaining a good factor of safety. Interesting...

 

^^ OR

You could get a wideband, and properly tune your car. I think for an NA you're shooting for 13-14 AF's depending on condition.

Edit: you also need a fuel controller (SAFC, Rtek, Emanage, or a full EMS like Haltech, Microtech, Wolf3D, Megasquirt).

If you aren't going to tune your car this way (too expensive or w/e) then just fill it with 87 and enjoy. You aren't hurting anything.

 

I made 172rwhp on my nonturbo on 87 octane (no nitrous).

 

This has been discussed before in a big flame war!


Its been proven that lower rate octain provides more power and a better running engine in a NA 13b.

 

Yeah, I tried to find it. It was a mess, but it was an informative one.

There have been a couple messes that I don't even like to mention anymore despite what's in them. I don't remember that one being terrible though. Some of the supercharger wars get downright nasty.

 

I guess you didn't read my post.

 

He did, he just diverged some. The flame fest he was talking about involved people arguing about anything from 80 to 110 octane gas. The argument ranged from which octane is best to the proper or improper calculations for converting to/from RON and AKI or for mixing.

The result of the argument was that 87 was the best to use as far as pump gasses. I know that's not the answer you want, but they came to that conclusion based on optimal being between 80 and 84 AKI. Heck it might have been in the high 70's. I know it was significantly lower than we can purchase at most stations. That is the tie together that he was making with that thread and this one.

 

Mmk, makes a bit of sense. However the "lower is better" statement he made didn't really help me. I'm looking for how much lower. This kind of stems from reading about rotary development and its ability to run on very low octane gas (IIRC the book stated in the 70's).

 

Ok, so... I'm stupid. I'm not very stupid, but... I am in fact stupid TWICE.

I do have a fairly good reason to be stupid though.

I make a partial *** of myself in this thread, because I was at the time misinformed on what the manual said. I had been told at the time that the manual stated 87 RON for a rotary. I was corrected on this. I still don't know what this guy thinks linear approximation means, but... see the last few pages of this thread.

https://www.rx7club.com/showthread.p...hlight=kontakt

According to this next link, the S5 manual states 87 AKI or above. The reason that I've got a good one to be stupid, is that this manual is wrong... ish. The manual means that it will run the way Mazda tuned it (rich) on 87 or higher octane gas. This does not, however, tell you what I thought we were talking about in that thread, and that we ARE talking about in this thread. That is at what octane fuel are you no longer running pig rich.

https://www.rx7club.com/showpost.php...0&postcount=42

Here is another VERY informative thread, that at least touches on octane. It's mostly abouth alky/meth injection, but has some very bright minds.

https://www.rx7club.com/showthread.p...hlight=kontakt

 

^^^ My reply to your PM 5A.

 

Hmm, so I guess I could add some heptane to my gas and see what happens... I guess for clarification though, shouldn't it be (R+M)/2 instead of R+M/2?

Interesting info on the S5 manual. I'll look at my S4 when I get home but I expect it says the same.
That thread makes my head hurt.

Might as well make the info public.

 

Lol... no

R+M
2

LOL... ***.

 

Sorry, I used to be a math major (screw diff eq) and I'm a fan of parenthesis.

 

All 2Gen RX-7's are rated for a minimum (R+M)/2 octane rating of 87 with no more than 10% alcohol. Due to variances in fuel, engine condition, and tuning, Mazda recommends that you stick within these parameters. Much like the stress rating on a bridge, aircraft wing, etc., there is a fudge factor built into those numbers, but it is best to stay within the given parameters for safety and reliability.

The octane rating is only an anti-knock rating. It has nothing to do with energy content, acceleration, deposits, emissions, gas mileage, chi, juju, mojo, or anything else. See here:
http://www.ftc.gov/bcp/edu/pubs/cons...tos/aut12.shtm

If you are looking for a fuel with more power, you need to ask the manufacturer for the "energy content". Assuming the same fuel density and air-fuel ratio, a fuel with a higher energy content will produce more power than a fuel with less energy content.

My car runs a lot better when I use the gas from a particular gas station with a green sign. Therefore, you guys should really be using gas from a station with a green sign if you want your car to run the best. Do you see a problem with that logic? Good, now apply that to the octane rating and you will be at one with reality.