I want to drive around for a week with some race fuel in my 68 coupe 289 stock, im just curious. my question is, how high of an octane should i get? i dont wanna cause any problem. 100? 120?

i drive around normally with premium (91) in it as we speak, but im just curious how it would drive with some higher grade fuel

 

it might make it up that hill with out pinging.

if your engine is about stock and is indeed pinging on 91 then the timing needs to be retarded a few degrees. high octane like 100 120 wont cause any problems that im aware of but will cost more than a timing light.

*Edit* I saw your other post and it looks like you got it figured out.

If it runs great on 91 dont waste money on higher octane....In this case do the opposite. run regular and see if it makes any difference at all...I bet not...other than saving money.

-Gun

 

Running higher octane than an engine requires is BAD for the engine. Higher octane gas burns slower and colder, and unless you increase the timing to compensate (which will only help so much), you're going to be leaving carbon deposits in your combustion chambers. The only reason you should be running gas at that high of an octane is if you have a very high compression motor (which a '68 289 is not) that needs it. Otherwise, you should be running the lowest octane you can without pinging while accelerating under heavy load.

 

+1 on what starfury said, I used to run 91 now I run 89 only difference is that my wallet is slightly heavier and its giving me lower back pain :P

 

True...

 

Spammer?????

 

Yeah that octane is seems to be just a waste. I run regular in my stock 289 without a pinging or rough running issue at all. The only reason I can think of really running premium is an engine with forced induction like my Lightning causing the high compression like Starfury said.

Your profile says SLO. I think I have seen your car on the freeway a couple times.

 

I had to run 110 in my car for a while with the 408 cause I had the timing off. It was only a temp fix, but it enabled me to enjoy my car for a few monthes before having to seriously mess with it.

Talk about fun though... mixing 5 gallons of 110 with premium... 110 was $6.59/gal.

 

I have always heard that racing gas (i.e. c12 108 octane) is a leaner fuel. When you run racing gas, not only do you need to adjust the timing, but you also need to adjust your jetting. It is not something to just throw in and try. If you want octane booster (i.e. mixing 108 with 91), just buy some additive that will boost your gas 10 points or so.

 

I was putting booster in my car. 351 Cleveland 4v - higher compression pings on higher rpms.

Can't really tell difference. I read fine print and the 10 point increase is equal to 1 higher octane rating (i.e., 89 to 90).