please excuse this post if this topic has already been covered recently; I did a couple of quick searches and was unable to locate anything.

What is the best fuel to be using in a "stock" 86 N/A 13B?(Mods: cold air box,cone filter, dual 2" long primary exhaust w/cats, 5&6 port sleeves removed, premix )

It is my understanding that high octane fuel burns too slowly and will actually hurt the performance.

Is 87 octane pump gas the best option we have?

My sanctioning body (SCCA -Performance Rally) requires that the fuel be unleaded.

Just looking for something that will perform a little more consistantly and the lowest octane "race" fuel I can find is 95octane.

 

As far as I know, you want the 87 stuff. You're right, the higher stuff will ignite slower and hurt your performance slightly (shouldn't really be that noticable, but everything counts). I'd say, unless you have a turbo, keep it simple. Not to mention cheaper

 

87.. Don't need to go higher unless you're running boost or a high compression boinger motor.

Are you the same Lovell that has the 2nd gen in rally that I see in GRM and Sports Car mag a few times?

PaulC

 

I don't think I am the same Lovell... My first race was in may 2001, my second race was Oct 2002 and my third (and only in the 2nd gen) was last weekend...

My only other racing was off-road and I don't think either of those mags would have covered it.

Matt Lovell

 

87 is the best readily available fuel for the N/A. in the IMSA GTU days racers were using 80 octane "race" fuel for even more power. I have not seen this available at the retail level.

 

80 octane fuel is available in AVGAS, but it is leaded and uses Motor octane only as a rating, so its probably more like 82-83 using the pump method (R+M/2) .

There is a new spec 82UL avgas, but I cant seem to find it for sale yet. Don't know if it would be worth hunting it down for a decrease of 2-3 points...

I guess I was just wondering if there was a "secret rotary fuel" everyone was using. Guess not.

Thanks,
Matt

 

I tried 114 octane leaded a couple times in my n/a (no cats) when auto-x-ing. It did nothing at all for performance. It was just was really expensive. I see you have cats so just run 87 unleaded.

 

Increased octane won't do anything for you unless you have mods to support it (more boost, higher compression, more timing advance). You only need as high an octane to prevent detonation for your particular setup.
The notion that higher octane burns "too slowly" is false. A more accurate statement would be that low octane burns too fast.
Good luck

 

Isn't this a half full/half empty thing?

isn't it true that N/A rotaries have a fairly small amount of time the rotor is capable of producing torque, relitive to piston engines, and therefore would benifit from a "faster burning" fuel?

isn't it true that N/A rotary engines are less prone to "ping" than piston engines (due to the combustion "chamber" shape), and therefore are capable of running a "faster burning" fuel?

of course at some point the fuel will burn "too fast" and even a stock rotary will "ping", but I don't think even 80 octane is approaching that.

I think if I can find a good 82UL avgas it would work pretty well. I would be happy with a 87UL "Race" gas that doesen't change formula as the seasons change...

 

Octane isn't a measure of how fast a fuel burns. Some of the highest octane racing fuels have a very fast burn rate. I attended a demonstration put on by Sunoco a few years back. The guy giving the presentation used Pro Stock drag cars as an example. They run stupid high compression (16:1 or so) and turn some serious RPM for a long stroke push rod motor (9000 or so). They need a very high octane fuel to prevent pre-ignition AND a fast burn rate.

Chris

 

so where do you get information of burn rates of various fuels. I have already contacted Sunoco, they where unable to provide any new information.

 

the octane rating is a number that relates to the resistance to detonation. the test used to calculate octane involves the detection of detonation. burn rates and other engineering type info is not readily available and may not be released by oil companies. again for the rotary engines that are available to the general public the 87 pump gas seems to work best. some have experimented with higher octane and more advanced timing with little to no gains. until the compression can be increased(custom rotors, or spray coating cumbustion area of rotor) there won't be a need for any "race" fuel. try the av gas and do some testing to see what the results are. I would be interested in the results. good luck

 

lol also the best way to really see what the difference is would be on a dyno since if any gains are made from using higher/lower octane fuel and faster/slower burning rates with the octane levels we have at the pump gains or loss in HP would be most likley almost undetectable by just driving the car unless you have some sorta crazy sense and can detect millisecond differences in your acceleration

Am i right or am i wrong?

 

also to see what the burn rate is you can probably just put some fuel from one company and then some fuel from another with the octane level of your choice into a little mettal or ceramic shallow dish and light it up (MIND YOU I WOULDN'T TRY THIS MYSELF AND WOULDN'T RECOMENT IT! SO FOR YOU KIDS DON'T TRY THIS AT HOME!) (DUMBASS!) and see which fuel burns faster .. but i don't even know how fast slower burning fuels burn to begin with so you might even need a camera with some crazy frame rate to time it afterwards..

Also if anyone has no life and has enough time and money and lack of common sense to actually try this and is able to come up with valuable results.. PM me LOL

Just my 2 cents!

 

I don't have any hard Dyno data, but the GT (2 and 3 SCCA) guys have proved that running high octane fuel in a N/A motor does decrease HP. This was a big issue since in the last few years SCCA has mandated fuel testing and some pump gas can fail the test. Race fuel is more safe as far as the test is concerned.

 

I just wonder how about u are runing with Pre MIX 2 stroke oil. do u need to increase ur octane . I am runing pump gas ( 91 with 100:1 2 stroke oil)

 

again it is not the "burn rate" that makes one fuel better or worse, there are many engineering factors that go into fuel formulation(especially for race fuels). lower octane fuel has more potential BTU's available. this directly relates to HP. the lower the octane you can run the more power the engine will make. this can be offset by increased compression, timing, and boost, but you still want to run the lowest octane fuel that will not detonate. unfortunately pump gas can and does vary dramaticly from station to station. so most people recommend you buy from the same place and make sure it is a station with high volume so the fuel is not sitting in the storage tank for long. I have no experience with the different AV gases, so if someone has access to these fuels and can do some testing I would be interested.

 

I have a 90 GTU N/A.. is there any diff. on what fuel and oil i should be using? I'm currently putting 87 octane and 10W-30 for oil. answer anyone?

 

Nvm guys I found my answer... Haha just had look all
over the site. Good stuff.

 

yes, a lot has changed since 2003..

 

Jebus. Just run 87 with some 2 stroke. 1oz per gallon. And you'll be fine. The two storoke lowers the octane some.

 

Not wanting to drag this out, but the only way I could control detonation in my NA was to go to premium (91 octane ) fuel. Using 87 or 89 octane fuels, I had to pull the timing back to about 17 degrees above 7500 rpm to get it to live. With 91 octane or even 94 octane, I am back up to over 25 degrees of timing without detonation. Granted this is on on ITB car with S5 rotors and a wild 1/2 bridge, but we have played and played with the timing and fuels and finally have a setup that works.

The detoantion would only show up on hard long pulls, only over 7500 rpm and only after the ambiant air temps grew to over 65 degrees. This meant that at Mosport I coudn't even pull a 220 hp Nissan when the car was hot. Now a can run with stock motored Vettes.

Interesting.

Eric