Minnesota Focus Owners Club

its how the fuel goes boom . the higher the octain the higher the inital light off temp has to be . that why high compression needs hihg octain, the sqwish will light off lesser fuels. a low comp non adj valve traine engine will see zero benifts in perf. its not hot enough to reap any thing from it.

focinite wrote:its how the fuel goes boom . the higher the octain the higher the inital light off temp has to be . that why high compression needs hihg octain, the sqwish will light off lesser fuels. a low comp non adj valve traine engine will see zero benifts in perf. its not hot enough to reap any thing from it.

Well said, my young padawan learner.

focinite wrote:its how the fuel goes boom . the higher the octain the higher the inital light off temp has to be . that why high compression needs hihg octain, the sqwish will light off lesser fuels. a low comp non adj valve traine engine will see zero benifts in perf. its not hot enough to reap any thing from it.

Pretty sure you're just not writing it out correctly. I'll help.

Compression ratio is just that, a ratio of compressed air volume vs air volume at atmospheric pressure.
As any liquid (air is a liquid) is compressed it gains heat. This is in part to the molecules being packed tighter and rubbing against each-other, friction (research "mean free path" for more).
So naturally as air is compressed more and more it will heat itself more and more.

Gasoline/isoOctane has an "auto-ignition" temperature (which is also based on pressure).
If the temperature of the compressed air is too close the fuel will ignite and explode rather that burn very quickly.
This is where ignition timing comes into play. It's only purpose is to ignite the fuel and allow it to expand slow enough so that the highest pressure is a few degrees after top dead center; too little ATDC and it results in more negative work, too far ATDC and you can get some very odd problems,,, piston speed outrunning the flame and extinguishing it (something F1 had to overcome way back when).


In the old world of mechanical ignitions compression and Octane were more important than they are today. Electronic ignitions allow us to be able to control the timing at virtually any load/rpm. That means you can run a low Octane fuel and high compression so long as you reduce the lead time of the ignition. Using hotrodder tech, lets say your SBF ran great with a 12* base on 91; on 87 you'd probably want to back off to 10* to get the PPP near the same ~13*ATDC.
The physical burn rates of the Octane variances don't change enough to necessitate more or less fuel being used / BSFC remains almost constant. Which also means that once timing is set for one fuel, tuning for another shouldn't be any more difficult than changing the base timing.

iminhell wrote:As any liquid (air is a liquid) is compressed it gains heat.

Anuder qualifier: While air is fluid, it is not a liquid. Air is matter in its gaseous state. There are four states of matter: liquid, solid, gas, and plasma. In any event, for the most part, liquid cannot be compressed - or compresses very little (infinitesimal).

iminhell wrote:

focinite wrote:its how the fuel goes boom . the higher the octain the higher the inital light off temp has to be . that why high compression needs hihg octain, the sqwish will light off lesser fuels. a low comp non adj valve traine engine will see zero benifts in perf. its not hot enough to reap any thing from it.

Pretty sure you're just not writing it out correctly. I'll help.

Compression ratio is just that, a ratio of compressed air volume vs air volume at atmospheric pressure.
As any liquid (air is a liquid) is compressed it gains heat. This is in part to the molecules being packed tighter and rubbing against each-other, friction (research "mean free path" for more).
So naturally as air is compressed more and more it will heat itself more and more.

Gasoline/isoOctane has an "auto-ignition" temperature (which is also based on pressure).
If the temperature of the compressed air is too close the fuel will ignite and explode rather that burn very quickly.
This is where ignition timing comes into play. It's only purpose is to ignite the fuel and allow it to expand slow enough so that the highest pressure is a few degrees after top dead center; too little ATDC and it results in more negative work, too far ATDC and you can get some very odd problems,,, piston speed outrunning the flame and extinguishing it (something F1 had to overcome way back when).


In the old world of mechanical ignitions compression and Octane were more important than they are today. Electronic ignitions allow us to be able to control the timing at virtually any load/rpm. That means you can run a low Octane fuel and high compression so long as you reduce the lead time of the ignition. Using hotrodder tech, lets say your SBF ran great with a 12* base on 91; on 87 you'd probably want to back off to 10* to get the PPP near the same ~13*ATDC.
The physical burn rates of the Octane variances don't change enough to necessitate more or less fuel being used / BSFC remains almost constant. Which also means that once timing is set for one fuel, tuning for another shouldn't be any more difficult than changing the base timing.

yeah, shits not hot enuff!!!

12.1 :O , begs the question how hard would it be to tune for 87 with 10.2.1? svt compression but not an svt, zetec would be much easier in the tuning department I would think since the svt is a pain in the ass to tune I hear

End of debate.

You can have your girls. I like my women.

What can i say... i like em young. haha

Stilz wrote:

End of debate.

I agree, 87 octane will clearly be easier on your pocket book.

bflesher wrote:

holy fugg that ish is fuggin funny haaaaaaaaaaah haha

iminhell wrote:


You can have your girls. I like my women.

i just like boobies and round tushies. as long as she is leagle and has a brain in her head and the fore mentioned goodie parts i am game.oh wait i thought we were talking fuel? howd i git vagina in my head?