Does Higher Octane Fuel Burn Cooler?

[Smokin04]

You already answered the afr question.

So I know people run anywhere from 15-25+* of timing but what would be the result of running too little timing?

Thanks again!!

A safer spark event, but less than optimal power, but generally more top end power. As RPM increases so does piston speed which means your incoming air charge (mixture) has less time to burn. Which means at higher rpm, the sooner the plug ignites, the more time the flame has to "travel" per stroke resulting in better efficiency. Also undserstand that is a very general description and does not encompass all situations as every combination/engine is different.

 

[03snakeminated]

Perfectly fine. A/F at idle and cruise should fluctuate from rich to lean constantly, it your O2 sensors dialing in optimum fuel consumption.



Yes 11.5 will produce lower chamber temps than 12.0. "Burnable material" just refers to volume, not octane. So you're right the answer is no.



Think of the term "stoich" as optimal. AFR can be altered by the tune, but is not related to the fuel you are burning. AFR is a product of fuel volume and incoming air which is controlled by the PCM. What octane you're running has no effect on the PCM (unless programmed to know it's running a higher octane). That is why you SHOULD re-tune your PCM when running race fuel because the stoich (optimal) required volume is different than pump gas. But simply adding race fuel, wont hurt anything, but you won't pick up any HP either; unless you add boost or timing.

Clear as mud?

great info :beer: so lets say if you are running 19-20 psi of boost (on a twinscrew) when its cold outside even if you are tuned with an afr of 11.7-11.8 and do couple of street/highway "spirited" driving could you be detonating due to the fact that is too much boost for 93 octane ??(lets say timing is not too agreesive @17-18 deg) if you had a splash of race fuel in the tank would that help vs detonating?? so far i understand detonating kills motor and thus an engine can run it will kill power, am i in the ballpark?:shrug:

ps: i've seen up to 21psi on extremely cold nights...

 

[03snakeminated]

damn, i just saw the date of this thread but w/e....;-)

 

[Smokin04]

great info :beer: so lets say if you are running 19-20 psi of boost (on a twinscrew) when its cold outside even if you are tuned with an afr of 11.7-11.8 and do couple of street/highway "spirited" driving could you be detonating due to the fact that is too much boost for 93 octane ??(lets say timing is not too agreesive @17-18 deg) if you had a splash of race fuel in the tank would that help vs detonating?? so far i understand detonating kills motor and thus an engine can run it will kill power, am i in the ballpark?:shrug:

ps: i've seen up to 21psi on extremely cold nights...

I kind of having trouble following what you're asking. Yes detonation is harmful and it can happen quickly on a boosted motor...but most of the time, it's audible and you can hear it and save the motor by getting off the throttle.

On a night where you see more boost do to colder (denser) air, if the tune was pushing the limit of timing to make max power at 18 psi, adding 3 psi will certainly cause it to detonate. Adding octane will help, as will retarding timing, but the proper way would be to reduce the psi back to where it was tuned by changing pulleys.

Read post 12, it should clarify.

 

[Red Poison]

Smokin, you really know your stuff...

Reading all that made my head hurt.

 

[Smokin04]

lol...thanks man.

 

[04sleeper]

Grest posts Smokin04! :thumbsup:

The lower stoich point of E85 (9.765) is one of the reasons it resists detonation so well. One of the reasons I choose to run it. The higher octane rating of E85 is also a nice addition. :rolling: