The reason is more power. Knock is not 'such a problem' if the whole combination is built to accommodate the power and it's fed and timed to match.
The advantages are real, not perceived. Barry's last post is a dramatic explanation, you will learn a lot from it.

I believe it is now illegal to sell race gas in California to any vehicle with a license plate (non-race car).

So, the race gas option is off the table. Better find another solution if you need it.

That is not 100% true. Unleaded race gas that meets the new state regulations as of January 1, 2010 can be sold from the pump and is being sold at a gas station near me. They can also sell leaded race gas, not from the pump, but you have to fill out some paperwork first and state that you will not use it in a street car. The leaded race gas must be used for race cars on a race track only.

FYI, the 91 octane here in CA may not be the same 91 octane that you get in other parts of the country. Our gas has a "special" formulation, just for us folks in CA.

Sorry man. I didn't mean any disrespect to anyone and I didn't think of anyone in particular other than making a general joke because I've watched guys pick up cars from the dealer and thrash on them right off the lot with new engines and also put them right on the dyno with minimal warm up time. Seriously just a generic statement. The fuel thing is because I don't know too many people that take the time to buy the proper fuel for high performance cars. It's just too inconvenient for most.

My car ran some casual 10 passes because I corrected some of the original install power robbing issues and stuff. Basically it was set up better than how it was delivered.
Fuel delivery with 8AN tank pick up to carb
Aeromotive fuel filter
Properly tuned carb from Pro-Systems
Larger surface air cleaner
Different headers that don't cover 1/3 of an inch width of each exhaust port
Side pipes with a bit more flow
Drag radials to start from idle and have 1.7 or 1.8 60ft time
Different half shafts
Detroit TruTrack rear end with 3.73 gears
Light weight flywheel
1/4 tank of gas for less weight
Lower density altitude
100 octane unleaded fuel on Roush original timing

If anyone can let out a clutch from idle, press the gas and shift through gears they'll run a high 10 on a well prepped track with drag radials, 2450 race weight and 475 wheel HP.

Something that's a common misconception is that a casual start drag pass is hard on the car when in fact a few seconds threw the gears. It's not a big deal on a proper air fuel ratio. Its a few seconds not much different than a romp through the gears entering the freeway. Alternately more damage can occur from things like sustained hard load to store heat and particularly on a lean air fuel along with pinging. Throw in a cold new engine to start and wow. It happens not because people want to cause damage. Generically speaking many just don't know.

No harm Greg. This is a true statement. I just can not condone encouraging a guy to make major and expensive changes to his engine because of 91 octane fuel.

My car is a second off your pace on 93 octane with 465 WHP, 200 more pounds and terrible for drag racing Hoosier T/Ds. Just couldn't put it down -1.9 60 ft. It took half as long to go the last 1/8 mile than the first. 121 MPH was a great top end charge though.

You made smart changes to your car and know how to feed it.

I am running just under 11:1 comp in a Shelby aluminum block with Shelby aluminum heads and Stage II porting, 482ci. I'm here in CA, and the 76 station near my house still sells 100 octane pump race gas (unleaded). It's not cheap. Currently around $8.75/gal. But once I filled my Cobra with that stuff, all was good. Running around 35 deg timing. No knocks, no pings. Just an empty wallet after a 42 gal fillup!!

So you're telling us that your CSX runs great with 11:1 compression and race gas. Cool. :)

... and a fill up costs him a little under 400 clams.:cool:

At our local station the Sunoco unleaded race gas cost is roughly twice the cost of 91 Supreme, around $6.50-ish.

You certainly don't need anywhere near 100% to be filled into the tank. With a 30 gallon gas tank in the Kirkham, I fill up my gas tank the earlier of: a) once a year or when I change my oil and filter. :LOL:

Rick, just kidding around, but it does take a long time to read your posts since they contain so much information. Not like my posts, which tend to have no redeeming value whatsoever. :)

-but all of your posts have a certain lightness about them...;)

I wonder if this is CARB legal gas? The places down here in the San Diego area have been cracked down on, and alot of them wont even sell race gas anymore.

Yes, very legal.

Here's a thread about it with the actual link to the bulletin from the State:

http://clubcobra.com/forums/showthread.php?t=103392

Substance weighs me down. And you know how I want to have a light car.

I know they make CARB legal high octane gas, I was just wondering if the stuff at this station is the CARB legal gas. There are no stations close to me that sell legal race gas, and the ones that were selling non legal race gas have pretty much stopped. I bought 10 gallons recently and had to provide my own cans and had to fill out two pages of paperwork. The places were looking the other way until recently.

As far as I know, no one has tested the gas that this station sells. Is it legal? I don't care. It's the State's responsibility to police the matter. Not mine.

What I do know is that is it legal to sell unleaded race gas if it meets the 1/1/10 CARB guideline. It is also legal to sell leaded race gas to race cars only to be used on the race track only.

This station sells unleaded race gas from the pump, no paperwork needed, and leaded race gas from drums in the service area, bring your own gas cans, which requires paperwork to be filled out prior to purchase per the CARB guideline. They appear to be selling racing gas in accordance with current CA law.

I can see it coming; soon the nazis will have a "smell test" added to the regimen to bust you for using race gas on the street.

Here in KALIFORNYA if 100 octane unleaded is being dispensed at the pump with the various taxes being assesed including road tax then it is legal for use in a "Street" car.

Lots of interesting suggestions and arguments. Unfortunatly, they're all based on too little information.

What's important is Dynamic Compression, which static compression plays a role in. Dynamic compression is the key.

The second most important component is intake valve closing point. The intake valve closes as the piston is coming up into the compression stroke. If it's very late, like 85* ABDC, then the piston doesn't compress much air/fuel. If the valves closes early, like 30* ABDC, then there's a lot of swept volume, and cylinder pressures will be high.

So, do a little more research, and find out what your compression really is. Fortunalty, it's pretty easy. On a warm engine do a compression check. If your cylinder pressures are low, like <170-180psi, you'll be fine on premium pump gas and a good tune. More than that, and you'll have some problems.

Case in point, I run 13.5:1 static on premium pump gas. But the rest of my engine build, and driving conditions support that. My dynamic compression is 8.449:1. When I got to the track, I know cylinder pressures will rise so I use 110 race fuel.

If you have more engine information, you can do some calculations here to see where you're at. http://www.wallaceracing.com/Calculators.htm

Dynamic compression ratio numbers are interesting and directionally useful - but they're decidedly not the end answer. They are really neither "dynamic, nor "ratios" - just a mathematically derived value for comparative purposes. Only a single piece of the puzzle.

There is nothing in the DCR calculation to account for a well shaped and contoured combustion chamber versus a less effective wedge or hemi. Nothing in the DCR accounts for crevice volume, piston dome shape, quench, low lift valve flow characteristics, exhaust back pressure, or a plethora of other things which will definitely have a significant impact on a running engine's cylinder pressure signature or tendency toward detonation.