Hello everyone. I checked the forums and couldn't find any info on this but if I missed something I apologize.

The 425ci engine calls for "premium" fuel. Now to me that's anything 91 octane or higher. My question is......... What is TOO high? Can I run 104 or 105 octane? Where is the danger zone of burning pistons?

 

Higher octane isn't going to "burn a piston" or anything else.

 

Ok, good! But is there a benefit to say 100 over 93? And should I be more concerned with finding a non-ethanol fuel?

 

The benefit will be to the seller who is pocketing the higher per-gallon cost. Look, the reality is that you want to run the LOWEST octane gas that you can that won't cause pinging or detonation. Past that, there is zero benefit. Oil companies have made a lot of money by convincing the public that there is some benefit to using higher octane "top tier" fuel. Obviously, if your engine has higher compression, advanced timing, or other features that require higher octane to make more power, then you need to use the correct fuel, but the octane rating only needs to be the minimum necessary to support the configuration of the engine. Anything beyond that is a waste.

 

Non ethanol fuel is preferred.

You should be fine with a "premium" gasoline sold currently. You don't need racing fuel. Go to some place like pure-gas.org, look up some place with 91 or 93 near you, buy some, then go find a medium hill where you can go up it in top gear at low rpms, like 40 mph or so. See if you have any knocking. If so, get off the pedal, check timing, maybe run higher octane. But, you should be fine.

 

From personal experience non-ethanol is preferred, but 10% ethanol will not harm your engine and will run just fine. Don't be scared of it, just make sure your rubber fuel lines have been changed to later model rubber fuel injection hose so the ethanol won't attack them. With a high compression 425 I'd run 93 if available in your area.

 

In 425 times, "premium" meant leaded gasoline with a 100+ octane rating. Even with Olds' above-average for the times cylinder head efficiency, those 10.25 CR engines liked that stuff, almost demanding it. So did everyone else's high-compression engines.

In my own experience with the Toronado and Starfires, running 100 octane leaded or unleaded fuel compared to 93 octane unleaded turned them into different cars- the roadstormers they were intended to be. If they'd had modern fuel and ignition management systems instead of carbs and distributors, they'd have undoubtedly been very happy and efficient on 93 or lower octane.

I have used a lot of Sunoco 260/280 in my time. Phillips 66 Flite-Fuel and Texaco Sky Chief were excellent fuels too as was Pure Firebird Premium. We also had Amoco White Gasoline premium here in southeast. Esso/Exxon were and are junk fuels IMHO.

 

Aa always, I appreciate everyones input on here. I have worked on "older" cars since I was 16 (I'm 44) but nothing older then 1979. This is my first foray into something from the 60's. As most of you are aware, the 425 Starfire engine calls for "premium" fuel due to it's high compression. I just want to make sure I am doing right by the car and motor and I really am not ready to pay for a rebuild of an obscure engine. I'm not looking to change to fuel injection either. From what I am gathering on here, the pump 94 will be fine but the car will run better on something higher? I priced that Sunoco 260 that was mentioned above....$70 for 5 gallons. YIKES!!!!

 

There is NO point to talking about "octane" if you're not willing to talk about HOW GASOLINE OCTANE RATINGS are determined and advertised.

When these cars were new, the octane rating method was different from what's advertised at the pump in America and Canada today. The numbers are different now.

 

My 67 Vista Cruiser has the "Ultra High Compression " 330 cubic inch engine. Here in Tennessee I can buy 93 octane and it runs fine on that, last fall I drove it California via Route 66 and in a lot of places in Arizona and Cali I could only get 91 or sometimes 90 Octane. On 91 it would detonate on long steep hills, on 90 it sounded like marbles in a coffee can, I really thought it was going to blow up a few times. I bought octane booster at several parts stores which helped a little, I also retarded the timing several degrees which also helped a little. I really don't know if I would drive it back out there for that reason, I was worried about it the whole time.

 

Seems some guys want to jump on me for mentioning octane yet THIS is a perfect example of my concerns. I always get a kick out of these forums........Knowledge is power but you cannot obtain it without asking. Someone said car restoration is not for the faint of heart. Well, neither are online forums lol.

 

Was your question answered ?

 

No one wants to jump on you here, we're straight.

 

I'm your huckleberry

I've been dealing with the inadequate gas situation for years, my high compression 350 is still factory set timing. She is fed a steady diet of premium / super 93 octane plus a 15 oz octane booster every fill up. This is a must for our engines. Double check that the gas stations super is 93 not 91. I've made that mistake before and the car didn't like it.

Even with my preferred combo she can still subtly ping on inclines at speed, occasionally. (maybe one stations 93 is better than another ?)

Many good points were already made throughout your thread. Too low on octane will bother your engine but 100 or even 110 octane will not... ( i've used both blended ) However if an engine doesn't require it then your wasting money.

 

As has also been mentioned there is a difference between 1960's fuel ratings and today's.
I believe our engines require 98 octane leaded minimum. Its my understanding that 98 octane in the 1960's is equivalent to about 95 octane today. Not to mention our engines also require lead for there health.

So either way our engines are screwed no matter what. I have tried several octane boosters and lead additives over the years. Lead additives alone will make our engines run worse.

I highly recommend Lucas 3X octane booster with MMT. 15 ounces per 20 gallons. That will help with octane issues and the MMT helps with lead issues. Its one stop shopping and worth every penny.

PS I love my car and keep a diary on her. I have spent an enormous amount of time trying to keep her running right. I say this so you have confidence in my words.

Yours truly phil

 

Ha! That I can respect!!!!

 

MUCH appreciated. Thank you!!