i usually always put in 93 on my T2...although i have use 87 once a in a while and it runs just as great...

i use 87 ALL THE TIME on my 91 n/a...runs better that way

 

only 93 or 94 octane in my TII or FD

 

I run 94 if I can find it. When I go to the track I run 100. With 94 on a hot day it will detonate like crazy in fouth at 10psi but with 100 not a single hint of detonation. On long road trips to save money I put 89 in it and just keep out of the boost.

 

Mine is Brilliant Black.

 

what is your car?

I have a white one wish it was black

 

1) Other countries use a different method of computing the octane rating. Basically, subtract 4 from the foreign octane rating to get the US octane rating. It's not exact, but it's close enough.
2) The composition of US pump gas differs by state, region, county, and season. Also, high-altitude regions in the US will add a couple of octane points to their gas because your car's requirements are reduced at altitude, even though the gas is the same.
http://www.exxon.com/exxon_gas/us_fuels_map.pdf
http://www.energy.ca.gov/fuels/gasol..._gasoline.html
3) You have **** gas in Kalifornia because you vote for **** politicians.

 

94 unleaded always. To run any less than 93 is to invite trouble. If you run 91 octane your tuning should be more conservative.

Technically the "best" would be the lowest octane possible that can support the fastest chamber pressures without knock.

The fact that knock can not be taken as "lightly" in a rotary, makes it a different scenario. You can't just "listen to your engine, is it knocking?". If it knocks, there is a good chance that compression has been reduced, or the engine has been blown entirely.

Use high octane gas.

 

I figure that Mazda knows best and my owners manual for my '87 TII recs. 87 octance (regular gas here in VA) so that's what I use. It runs great.

Todd

 

If somebody wanted to they could do some research to find out how to calculate what octane to use based on the mods. Like for example, "If you run X amount of boost more than stock you should bump it up X octane" or "If you do such and such to your engine you must run X octane" you know? That would be helpful. Just a thought tho.

 

Thanks for volunteering!

It should be really easy. All you need to do is take the ambient temperature, humidity, and pressure variables, and then calculate the detonation temperature of each rotor (or just the rear rotor since it is usually the critical one) given the variances in MAP, turbo thermal efficiency vs. rpm and load, intercooler thermal efficiency vs. vehicle speed and airflow rate, compression ratio, engine wear, hot spots, spark plugs and coils, ignition timing, fuel adhesion, etc., and then simply relate that to the MON of the various octane grades of the 18 different types of gasoline sold in the US. Hmm, I may have forgot some variables, but I think I'm close.

I guess you could use charts or spreadsheets, but a Java script program would be easier since the minimum octane requirement will change whenever the temperature, barometer, or humidity changes during a given day. Please post a link when you have it finished so that we know what octane to use.

 

LOL...quit picking on the newbies mod

 

Do you think Mazda took into account the huge increase of airflow possible with modifying our cars? 8.5:1 CR + 5.5psi is not a big deal. I'm sure that's optimal. Running just a downpipe and intake you'll be at around 12psi. Even with conservative fuel tuning and controlled ambient temps, the octane requirements have increased SIGNIFICANTLY.

Go ahead run 87

 

Sorry, I didn't mean to pick, but just trying to explain what is involved. Hey, if he wants to make an octane calculator, then I think it would be great. Wouldn't you like to see a somewhat accurate RX-7 octane calculator on the internet? OK, so it would be rather involved, but unlike an airpump supercharger, it IS possible.

Well geez, of course you would need higher octane with some mods, and the minimum octane requirement is also affected by all the factors in my last post. I'm sure that Mazda put a "fudge factor" into their minimum octane ratings for different driving conditions, and they added a knock sensor for good measure. Also, there is nothing wrong with using higher octane fuel other than the cost. The thing is, if your engine doesn't knock, then you don't need to use higher octane. What is so difficult to understand about that? If you find the mere thought of knocking so terrifying, then don't put a DP on your car, and retard the timing until you are getting about 80hp max, and that should do the trick.

 

How sure are you? Have you done the calculations? If so provide us with some data.

I know the factors that affect minumum octane rating. Here is my point. First, factors such as ambient temp are not static, and unless you are fully confident in your intercooler setup, and have data-logged safe charge temps, this is not a factor to **** around with. The stock top mount intercooler is going to be about 40-50% efficient AT BEST. Combine that with a 100 degree day, and combine THAT with the decreased compressor efficiency at twice stock boost. There are alot of factors to consider. Factors such as humidity of barometric pressure change as well. You can't just assume that Mazda accounted for some "fudge factor", unless you like blowing engines. If you want to calculate out minimum octane requirements for a multitute of different conditions, taking into account mods that affect the engine's BMEP and at what rpm max BMEP is achieved, be my guest. It would be smart to do so for your PARTICULAR setup. Many of the people on this forum do not know how to do so. The stock knock sensor is next to useless. You know these engine's can't take detonation well, so why risk it? Why is it so hard to say "Use the highest octane pump gas you have available?".

To me that is the safest approach to take, short of doing the research and calculations for your particular setup yourself.

My car is modified, and for my particular setup, I know my minimum octane requirements. I run slightly higher octane than what my tuning, and conditions dictate, for added safety.

BTW, if you were to retard your timing that much, you would blow your engine.

 

This thread is for TII owners and my 88 owners manual says to use 91 octane to get the maximium preformance.

 

93 only for me thankyou. anything less would be kinda bad fo engine life. if its kinda cold out ill put in some octane booster too.

 

I've tried all the octanes, and she likes 92 (the highest I can get around here) the best... She's temperamental, so I try not to **** her off.

 

I have a US, 1988, it lists 87 on page 1-4.

I usually run 92. For as little gas as I buy, it really doesn't matter to me from a cost perspective. I would think that more modifications you have, the more warranted the uplift from 87 is though.

Greg O.

 

Will I shoot more flames with 92?

 

After reading all of Evil's BS to see if he said anything important, it's nice to see someone finally ask the real question. So, will it?

 

Hehehe, yes, I must agree with that one. I think that we have too many pot smokers on this forum for anybody to care about technical issues. Shooting flames is something that eveyone understands at the same level.

 

LoL
-------------------------------------
Hey Beavis, FIRE FIRE FIRE!!!
ehehehe ehehehehe

 

why would you add octane when it is cold??? detonation occurs when the air is hot. when it ges cold you should put lower octane in rather than higher...

oooops im sorry this thread is only for TII owners

Justin

 

 

The lower the octane rating the more volatile the gas.
So if you have low compression you want lower octane, if you have higher compression you want less volatile fuel to help prevent detonation.

And with forced induction your compression ratio rises under boost, so your 8.5:1 static compression is actually 12:1 or so at 8-10 psi of boost so you need more octane.

My 87TII which is bone stock will ping with 87 if I am in a higher gear at a low mph and i give it some gas it will ping. If I run 91+ I have no problem. I have upto 94 octane at the pump here in MN depending on the gas station.