I own a 75 Ragtop that's been tricked out a little...(3/4 race cam, Speed-Pro Hypereutectic Aluminum Pistons, Holly Projection Throttle Body Fuel Injection System, Stainless Steel Flow Master Exhaust system)...Now the question...I run only Exxon Super (93 Octane) and was wondering if these octane boosters are any good or are they "snake oil". :confused:

 

no

 

actually, they should be ok if they are evenly mixed. but there in lies the problem. how are you going to mix it enough so that every injector is getting the same octane?

 

Unless you've raised your compression ratio dramatically, you shouldn't need more than pump premium alone. If your cr is stock, you shouldn't even need premimum. What is it's current cr?. IMO, the octane boosters are more hype and ripoff than anything else. When they adevertise a 4 point increase, they are talking about .4 increase in octane, not 4 more octane.

 

THANKS...I'm not quite sure what my compression ratio is. I believe it is either 9.78 or 10.4. Do you happen to know what is stock for a 350? :seeya

 

toulene works (so I've heard)

 

Use the lowest oct your car will run on without pinging/detonation. Anything more is a waste of $. Oct ratings reflect how fast/slow the fuel burns. The higher the oct rating the slower the burn. Increased oct lets you run more advance at wot or under load without pinging. You can only run so much adv to achieve max power. Once you find that right adv curve, try less oct till it pings, then step back up. Some peopel with high comp and iron head need to run an aditive to allow a good adv curve and not pinging. FI also helps reduce the amount of pinging so you already have an advantage over a carbed vehicles.

 

I think the stock 350 cr is 8.5:1 Your mods probably get it to no more than 9.5. Pump gas should be all you need. :)

 

Actually, through Mountain Motor, I did find and buy a booster that is very good. One quart per tank or pump premium works very well with my 12:1 L88. No pinging or knocking on the street. For extended power runs I use race gas. One quart per tank raises my octane a full 5 points, not .5 points as most stuff will. 92 r+m/2 octane becomes 97 r+m/2 octane.
http://www.kemcooil.com
Lead Supreme 130

Chuck

 

I would like to clarify something about octane numbers. It is not simply a measure of how fast or slow fuel burns. It is simply a rating of a fuel's resistance to knock. While how fast a fuel burns definitly has an affect on knock, there are many other factors involved. One primary factor accoring to John Heywood in his engine fundamentals book, is the ability of a fuel to stay homogenous. A fuel that naturally separates, leaving heavier particles to gather on the combustion chamber, will have a higher tendency to knock.

One way to lower your required octane, is to clean the cylinders and combustion chamber. Reducing the deposits in the engine, will definitely lower the amount the engine knocks. You could do this by squirting some water in the throttle body while the engine is running.

 

Chuck,

The Lead Supreme 130 looks to be interesting. I can understand a 12:1 compression ratio engine needing to boost the octane, but what about something like 9.8:1 and 420+HP? Guessing the same principal would apply... add 1/2 quart and only boost octane 2-3 points? And it's been awhile since I have heard the story behind *lead* in fuel. What was the purpose again?

 

I second the stuff Chuck is talking about. I use it in my 11 to 1 454, and spray another 150 worth of NOS on top of that. I mix it to make 94 octane out of the crap 91 we get in California.

If you are around 10 to 1 with a smaller cam, if you need the stuff, you will not need much. I quart should last a fewl tanks.

 

A little off topic but I'm curious. What is a "3/4 race cam"? I've heard the term used before but never really stopped to question what it is. I appologize if this is a stupid question.

 

bb69,

You are correct that the additive truly needs to bond with the gas in the tank. The stuff I am talking about is a blended fuel additive consisting of tetra ethyl lead. The real McCoy. Lead is the only additive that can in small quantities add octane in significant amounts. Pure tetra ethyl lead would kill you if you even spilled some on your bare hands or arms. Very toxic stuff. Don't use this stuff if you run a catalytic converter. The Supreme Lead is in a diluted form not quite so dangerous for us to handle, but still potent enough to make a very big difference in the fuel's octane.

Keeping combustion chamber clean, as you said, is very important. As a matter of fact, GM anticipated combustion chamber build up to raise the true compression of most of its v8 engines 1/2 point of compression. This was the explanation given to me for the 11:0 rating on the Chevy pistons from the dealer's parts counter and catalog while the manufacture of the pistons, TRW, listed them as 10.5:1. Unleaded does keep chambers cleaner. Water, carefully applied, can clean combustion chambers. A little too much water can lock an engine, bending connecting rods. Water is not very compressible.

bgrice,

Using a pint or less instead of a quart per tank would probably be just fine. As was posted elsewhere, too much octane is a waste of money. Way too much can even hurt because you don't have enough cylinder pressure to facilitate a complete burn of all the fuel. Might be like the same thing as dropping your engine's compression to only 6:1. Less power and less than complete combustion even with regular gas.

You really don't need high octane for most driving. Even 91 octane will work in the L88 if I don't put my foot very deep into the throttle, or for very long. A quart of the supreme 130 allows even full throttle passes through 4 gears without any problems. If I were to do this repeatedly, especially on a hot day, I would start to hear that annoying hammer within the block. For such track work/play, I will fill up with 114 racing gas. I have taken many measures to help my engine live on less than 100 r+m/2 octane specified. Polished combustion chambers and piston tops, oil shielding below intake manifold, cold air hood, MSD ignition to assure complete burns and reduce rate of deposit buildups, slightly rich mixture, large aluminum radiator to engine at as close to 180 degrees as possible. (concerned that any colder might cause incomplete burning at highway cruise), aluminum heads, headers. It seems to have worked. The cooler air and engine reduced the octane requirements by about 4 numbers. The very long cam duration helps too. Below 4,500 rpm I probably don't make any more cylinder pressure than a 10:1 motor. But above that :D

NOX RATT's is a very good testament. His engine is certainly a challenge to pump gas. Probably more than mine.

Chuck

 

Bence,

When I was in high school, nobody really quoted numbers like lift and duration for cams. They were either full race or grocery getter. I would probably have called a factory LT1 cam a 3/4 race cam. Back then, when roads were just being paved, cam design was limited to rather tight parameters due to metallurgy and machining limitations. My L88 cam with .540/.560 lift was considered outrageously tall in the mid and later 60's. A small block cam with lift over .500" lift was astonishing.

So your cam choices were rather limited. A stock cam or a race cam or something kind of in between. I never did hear the term 1/2 race very often, although JC Whitney used to list them that way. 1/2 race, 3/4 race, and full race.

Chuck

 

When I had my '69 Z-28 with the 11:1 compression ratio 302, it pinged like crazy even on pump premium. Retarding the ignition slightly would lessen the ping but I lost a lot of power and it also is hard on the exhaust valves since it raises exhaust temps. I used just about every octane booster that was commonly available with ABSOLUTELY NO improvement.

The one thing that WORKED: AVIATION GAS!!

Since the airport wouldn't let me drive the car onto the tarmack to fill it, I would drive the car to the airport parking lot and carry two 5 gallon cans out to the pumps. Then I'd carry the cans back to the car and add the AVGAS to a half tank of unleaded premium. Using the factory spec spark advance the car had LOTS of power and absolutely NO spark knock.

The additives that are supposed to contain lead weren't available at that time so I've never tried them but I can swear by AVGAS.

 

Chuck, thanks for all of the details. With 11:1 on the LT-1 and a best of 91 octane available, I have had to compensate with reduced timing as well for regular use. Ther power loss at 4000 rpm (what should be peak torque) on 91 is unreal. I generally mix 100 octane available at one local station to help. At $4.29 per gallon it hurts the wallet. I will have to give the stuff you mentioned a try.

 

AVGAS was formulated for optimum performance at high altitudes, but it'll work