My car is basically stock besides exaust, cai and free mods. Reason being, there is race gas sold close by and was wondering if it would be safe or healthy to mix 93 octane and something higher. Maybe a 75/25 mix low to high.

Feel free to let loose if this is a stupid question. And please don't hold back on your reasons. I asking to learn.

l8r
Finch

 

i used 100 octane a couple of times, it doesnt make any difference on a stock car.....

be sure to get unleaded, the leaded gas will kill your cats and 02 sensors

jesse

 

i had some slight knock on our crappy 91 so i just dumped in a quart of toluelen(sp?) and it went away...
But my car is not stock..

 

There is no need to run race fuel in a stock engined car. Youd only be wasting money. Premium grade fuel will do you just fine.

 

I ran 100 octane a few weeks ago to clean everything out. higher octane isn't bad (unless leaded), but can slow the car down if you go to high (harder to ignite the fuel). The only thing I really noticed was a smoother idle, and a bit smoother acceleration. You don't have to buy race gas though. Go to Sherwin-Williams and buy a gallon of toluene (used as paint thinner, so don't spill it on the car). When you get down to around 4 gallons of gas left in the tank, dump in the whole gallon of toluene. If you're running 92 octane, it should bring the octane up to around 97-98 (I think). I had a post about this awhile back. Just search toluene or xylene in the LT1 tech section. In the post someone gave a link showing how octane differed with different mixes. <whew... takes a breath>

 

Toluene is 114 octane.


Running your example of 4 gallons of 92 octane, plus one gallon of Toluene, you end up with 96.4 octane.

(gallons x octane) + (gallons x 114) / total gallons

(4 x 92) + (1 x 114) / 5 = 97

 

since we are on the topic of octane. I run 87 in my car, I don't feel the need to use any higher at the moment since I'm stock. Car runs fine on 87 so I'll be sticking with that until I do heads, cam, headers, etc.

 

I fill up on Ultra 94 at sunoco basically because it is right at the corner of my subdivsion. If i am an nowhere near a sunoco, i fill up on 91, and it runs like a champ.

There is no need to put higher octane in your car, contrary to popular belief, it will not make more power. Octane is simply how hard it is to ignite. And we aren't running enough compression to ignite pump gas prematurely. Just stick with your 91 and you will be fine.

 

Our cars are recommended for premium octane, they are tuned that way. 91 and up should be fine, below that and some people have had pulled timing due to the low octane. I wouldn't run less than 91 in LT1 or LS1. Yes the car will run on the lower octane, but you are probably losing some power. Anything over 94, etc. won't really give you anymore power on a stock car, but below 91 will probably pull some power. I could tell once when my mom put regular in my old Z28 when she borrowed it a few years ago and filled it up. She wouldnt admit it at first, but then after a while she told me she did use the regular octane.

 

When I bought my 2001 Z28, it was a dealer demo with 3,000 miles on it. Those 3K miles had all been run on the dealer's pump gas ... 87 octane ... and CHEAP 87 octane at that.

That car would ping, no matter how high octane I ran. The dealer had to do a top engine clean (the overnight soak type) 3 times in the first 2 months of ownership. That, combined with several seafoams of my own finally cleaned out the crap inside the engine. Personally, I blame crappy gas.

The car was a complete lemon. GM had agreed to buy it back as a lemon .... when I totalled the damn thing. So, I took my insurance money and bought a 2001 WS6. It's only had 93 octane, with the occasional 91 octane when travelling and that's the highest available.

 

Putting in higher octane would allow you to advance the timing a little bit too though right? - So if I had 96 octane I could add a couple more degrees here and there and pick up a few more ponies...

 

Not necessarily..... the stock ignition timing is already fairly aggressive. Adding timing beyond a certain point can actually reduce power. My 10.8:1 381 was tuned on an engine dyno. We tuned it for 93 octane, then tried 94, and were able to pick up some additional HP. Then we tried 100 octane and it wasn't possible to pick up any more power, no matter how we varied advance and A/F ratio. Then we baselined it on 117-octane C16 for the nitrous tuning, and it picked up 6HP with no changes at all from the 94-octane tune.... so much for the theory that "high octane burns slower" and "you will lose power with too much octane".... that's not the case at all.

Octane refers mainly to the tendancy of the fuel components to break down under the heat and pressure of the combustion chamber, and form other compounds ("end gasses") that will auto-ignite, forming a second flame front remote from the spark-induced flame, and producing excessively high, resonating pressure waves when the two flame fronts collide. It is more a matter of chemical composition, than being related to burn speed or energy content.

A really good reference on Gasoline FAQ... its over 60 pages, but you can find the good info about "octane" in Section 6:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

 

I always run 93 in mine.

 

I've run everything from 87 to Sunoco 94 in my car (only used 94 with the Hypertech plugged in) and have only noticed slight, occasional pinging with 87 in warmer weather. I ran with 87 for the last 2 winters without the Hypertech programming, and almost never heard any pinging because of the colder temperatures. In the summer months I've run at least 91, but again, with the Hypertech programming, it advances the timing to the point where 91 doesn't always prevent a little pinging, so I've run the 94 and had no problems at all.

All that being said, I think running 100 would be a complete waste of money and gas, cause it would cost more, and wouldn't be burned completely either, so half of it would go out the tailpipes as un-burnt fuel. Unless you're running higher than 11:1 CR, I see no need for ~100 octane. Even my dad's '73 is only run on 94, and we've got a set of 11.5:1 pop-ups in it! (although with the current heads, it's only making about 10.5:1).

 

I buy sunoco 94 whenever possible... but I havent noticed a difference between it and 93.