russell-t

My Oldsmobile 215 V8 has a 10.75 to 1 compression ratio. What is the best

additive available at the parts store to keep octane up to the level I will

need to prevent detenation? The engine has a mild cam with the timing

set at 12 BTDC. I'm hearing some valvetrain noise while driving but it does

not sound like the (marbles in a can) type of noise.

What do you high-compression race engine guys use to add to your

gasoline? I've been using STP additive and I'm curious what others are

using and to what ratio are they mixing it in their gasoline.

bccan

Octane Supreme 130 is the most effective additive I have used. Have used a few "over the counter" brands across the decades along w/ adding toluene & none compared to that product. Search for it on the internet, I believe it is being sold again after death of the company owner (lead poisoning?!?) & being orphaned.

L69

ROGER ON toluene. Turbo 108 I guess is ok but nothing beats mixing in a little sunoco race fuel or AV fuel. Good Luck

ah64pilot

I run a 10% mix of VP C-12 (108 leaded). At $10 a gallon it is comparable in price to the additives and really does bring up the octane. I mix 1 gallon C-12 to 9 gallons of 93.

cutlassefi

I wouldn't recommend Av gas. It's very dry and can be hard on valve guides.

SBORule

Yeah, what he said.
I have been told a cap full of Mystery Oil per 5 gallons will cure that problem.

ah64pilot

Avgas is leaded (100 Low Lead) so I don't know why you would think it was dry. There is essentially no difference in an aviation piston engine and a automotive piston engine.

I think you might be thinking of JetA / JP8 which is a kerosene derivative and is dry, however it is only used in jet engines and diesel engines. You can run kerosene in a diesel engine but for a highway diesel you should mix Marvel Mystery or 2 stroke engine oil so that the injectors get some lube.

L69

All I know is that 100LL is cheap and plentiful when compared to Sunoco race fuel. Also it is leaded which acts as a natural lubricant for the non hardended seat guys and for the guides themselves. I have been using it for over 10 years since I moved out in the sticks next to a small airport and It has never failed me. My current motor is approx 10.2:1 and I run a mixture of 93 and 100LL prob 70% 93 30% 100LL. It has always worked for me.

SBORule

Aviation LL100 gas and even that Leaded 115 gas they make for the old War Planes, lack some lubricating additives that are in all Automotive gasoline's, which includes Racing Gas.

You probably get away with mixing 70/30 mixtures but I wouldn't run straight LL100 without adding some Mystery oil.

And it makes the exhaust fumes smell better.

cutlassefi

Not true. I know you're a military man but a typical airplane engine is vastly different from an automotive one. My brother is a US Air captain, owns several piston airplanes himself and has his A&P license.
Airplane engines are air cooled, run at a much slower rpm, maybe 2750 tops, and require different clearances and materials accordingly.
I still contend if you're going to use avgas you'll need extra lubricant. If you don't believe me just call the guys at AFR, they'll tell you the same thing.

bccan

I have no knowledge of the formulas used in Av fuels but I can say that I ran straight 100LL in a 71 Cutlass (because it was free) & my very high compression 70 Chevelle SS (because it needed it) for years without issue. Was it for a long enough time to get screwed due to lubricity issues? Can't say, but it was for a few years. Used to get all the sump fuel I could take, ran the house on Jet A. With fuel prices where they are I sure wish I still had connections at FBO!