The owners manual in my 83 12a says to use no lower than 91 octane yet I have heard multiple times that the rotary motors benefit from a lower octane. Is that correct? What is recommended?

 

I've always used 87 in my 82 GSL. I too have heard the lower the better.

 

Anyone know the compression ratio of a 12a or 13b off hand?

 

9.6, if I'm not wrong

 

What is the benefit of the lower octane in Wakel motors? Are they incapable of having "pinging" like a piston engine?

 

In my case, the benefit is the $.10-.20 I save on every gallon of gas I buy. I use regular unleaded, to answer the thread question.

Read this for reasons not to buy more octane than you need:

http://members.ij.net/mrmazda/cfaqtext.html#ROCTANE

That site is about the most comprehensive repository of rotary information available online.

 

Unless your engin is specifically designed to burn High Octain fuel (or you have some wacked out custom motor where detination is a potential problem) there is ABSOLUTLY NO NEED to burn high octaine fuel. Save your money.

 

There's a very long thread on this in the 1st gen section.

 

i use 87, But in my turbo cars, its all about 92. Unless the 12a has really messed up timing, it shouldent ping, so just use 87.
However, boosted rotarys, cannot handle detonation under any circumstances. Most stock boosted rotarys will only handle detonation a few times befor they blow, So thats why 92 is required in T2's and Fd. or any other boosted rotary that may be driven hard and not want to blow.

CJG

 

I use 95, but then again, that's the lowest I can get in Belgium anyway. There's no way you could get less then that. In some other EU countries 91 is still available, but that's getting less common.
You don't benefit from using lower (or higher) octane with these engines, so I think keeping to Mazda's specs is rather good. There's a lot of talking about octane, but for us it's not all that important. Once you go turbo it might be intresting to play safe and go for good quality fuel (I'll use 98 once the car is up and running again)

 

I ran an 85 12a for 14 years/214 kmiles on 87 octane--never a problem. I'd really like to see the owners manual that says 91 or better.

In my boosted T2 engine I run no lower than 89. Last fill up was Shell Vpower 94 octane. Oh and the 88 Turbo owners manual says you can run 87.

 

Yes, 87 is fine.

 

I don't have my manual in front of me, but when you look at recommended octane you need to pay attention to the calculation method specified. There are two different methods used to calculate octane ratings. I think 87 == 91 when you look at equivalent octane ratings across the two methods.

 

So we've determined that higher octane is used for boosted rotaries.... probably a stupid question, but what about ported motors?

 

i'm sure the owners manual is refering to a completely stock setup. i would never risk that.

 

I think we've determined that it doesn't matter unless you got boost

 

Yes, for a boosted car, that has a couple mods done and is driven agressivly, you need to run the highest pump grade. Its very good insurance from detonation.
For NA, ported or not.
My beliefe is 87. especially for stock ports and street ports.
For bridges and PP. You have 2 choices, you can run high ignition advance and high octain, or you can run lower advance and lower octaine, they are about equal as far as performance. Plus most pp race engines burn premix 100:1 or so anyways, which also reduces the octain rating.

CJG

 

87 for the REPU. 15.6MPG last tank.
89 + 1oz Castrol 2stroke per gallon for the bridgeport. I want the extra octane for detonation protection with the 28* total advance and hot temperatures @ the track burns 6 gallons every 20 minutes

 

Around here the only gas that isn't "oxygenated" is 91+ (premium)

I'm afraid to put ethanol into my old cars...

 

87 in all my four port 13Bs.

 

With the price of gas I can only wish that I could get mine to run off of ****. Drink a few beers and fill 'er up!