James R.

Just out of curiosity I pose the following question. Is the Octane rating scale a linear one?<p>Basically put into a working question it goes a little something like this.<p>Fill half of your tank with 100 Octane and the other half with 92 Octane (in that order so they mix well)...does this result in a composite fuel having an Octane rating of approx. (100+92)/2 or 96 Octane.<p>The reason I ask is I have a Neuspeed 0.8 Bar chip which pings ever so slightly at 4.5~5.5 Grand only while my car is floored in Second gear. So I went down to my local Unocal 76 and bought myself 4 Gallons of 100 Octane Racing Fuel (3.96 a gal...OUCH) and 12 Gallons of 92 (1.89 California sucks when it comes to gas)...so using the above logic I should have approximately the following fuel in my tank .75(92) + .25(100) which works out to 94 Octane...which is what a lot of people up North and back East run...they seem to complain less about pinging than us So Cal drivers.<p>So with this batch of what I assume is 94 Octane I made off to the road for some rough driving. Well I can say I've driven the car harder than I've ever done in the past...not a tick to be heard, just the faint ripping of the turbo and the rush of the wind. Whereas before it would be the faint ripping of the turbo and the rush of the wind disturbed by a few faint ticking and clattering noises from time to time (2nd gear 4.5~5.5 Grand WOT)<p>So basically I'm curious about the linearity of the Octane rating system...I hope it is linear and not Exponential, Log or some other non-linear function. Also I wonder if the fuels are of the same density...or will they separate in my tank...I kinda doubt that because it didn't ping yesterday and it doesn't ping today..unless it mixed enough while I was driving.<p>Thank in Advance.<br>

Math Boy

n

noping

yes, it is a linear mix.. and the stuff will mix completely. gas itself is made up of several hundred<br>hydrocarbons. if you're going to buy 100 octane for ~$4 you might as well buy toluene which is<br>about $3-5/gallon depending on quantity.. it is 121 octane RON and 114 R+M/2... much denser<br>than gas too. and yes, those chipped 1.8T owners running 92 octane have no clue what they're<br>missing, aren't they?

James R.

Is this what is in most of those Octane Booster products? I've been told to stay away from Octane booster because it leaves a powdery red residue all throughout your motor and exhaust system. I imagine the substance you suggest would be poured in then topped off with 92 pump gas? <p>It seems that for the added hassle of the toluene you could just pay a bit more and not have to deal with the gas cans and all Some of those octane boosters use much smaller quantities but yet they make claims of 105 effective octane when used with N gallons of 92 octane gas or something to that affect.

IronMike

Toluene, 6 sided benzyl ring with a methyl substituent group. sp2 hybridiztion in the ring with pi resonance. The methyl is activating and ortho/para directing. I'd say it sounds pretty safe.

James R.

Hehehe uhh anyhow thanks, makes sense to me...well actually I pulled that line outta my ***. I'm not a chem guy...ohh well (I'm an Electrical Engineering guy) but if it's any consolation they do force us to take a fair amount of chem to get an EE degree.<p>I still think it would be easier to pump some 100 into the tank and just whip up whatever octane you wanted by calculating the appropriate ratios of 92 Octane to 100 Octane gas.<p>Have you ever used octane booster??? Do you think it's safe for our engines??? What about the red residue...I've heard it's harmless, but I gotta wonder it's usually the person selling the crap that says don't worry about it...it's harmless.

IronMike

I've never used an octane booster so I'm blank. Never saw the point.

James R.

I guess it's not much of a problem for people who leave their cars stock, but for those of us who modify the boost pressure the added anti knock properties of the higher Octane fuel is appreciated.<p>Boy I guess you must really be burning the midnight oil, me two, alas I can finally go to bed.<p>Studying for a big Chem test are we ?

ChuckH

James,<p>I don;t know if others with the 1.8T are using it, but I add 1/3 of a bottle ($8 per bottle) of the 104+ octane booster per tankful in my 90Q (black bottle labeled for off-road use). I think it's supposed to boost the octane 6 or 7 points for the whole bottle, so I figure I'm ending up with about 94 octane. It really smooths things out for me, and my car isn't turbocharged, unfortunately. :-( So far I have not found any ill effects of using this. My catalytic converter still looks and performs like new, and my emissions test result in no HC or CO at idle, and only 3 ppm HC and .03% CO at 2500 RPM. <p>I'd like to find a gas station near me with more than 92 octane also.<p>If you ask, I bet Neuspeed will adjust your chip programming, if you don't want to use high octane gas all the time.<p>Charles<br>

ChuckH

I think SteveS also uses the 104+ in his 2.8 12 valve. :-)