What Octane gas should I use?

d00mbuggy

d00mbuggy

Registered User
I Own a 1990 SC with 108,000 miles on it now. Bought it in Feb '06 with 93K miles. The car had been VERY well taken care of over it's lifetime,(original owners, old couple, garage kept, kept all reciepts including window sticker, wife drove it, no BS). So of course I blew the head gaskets only 4 months after I bought it just by GETTING ON IT on the freeway a couple times. This was before I knew about the "Head Gasket Blowing" problem, and also what made me an immediate member to SCCOA, because I wasn't about to give up that easily on such a beautifully kept SC.
ANYHOO... I replaced the head gaskets, along with a few other parts that were in need of replacement while I was at it(with MUCHO help from a member here), got my baby running strong again, and ever since I've been ALWAYS using 91 octane fuel(CA), and rarely floor it out of fear if it happening again. I've listened for engine knock when going up steep hills, and haven't heard any yet, but I still am cautious. So I just wonder if I'm wasting money on 91 octane gas, will I be safe with cheaper 89 or 87 octane, or why risk it for a few cents per gallon?
Sorry about the long post, got carried away.
Just looking for what you guys think.
Thanks!
Chris
 
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Run the best gas you can (Is there such a thing in Cali?) I have a 98 Crown Vic that I ran with 87 and got about 21mpg highway. I started using 91 just to compare and I was getting 24mpg highway. I then filled up at Chevron and I get 26mpg driving from Boise, Id to Sacramento, Ca. Not bad for a 2ton car and a V8 that rides like your on you sofa at home. Here in Boise we can get 93 at some pumps, but you can also get 85 so look out when in the area.
 
d00mbuggy said:
I Own a 1990 SC with 108,000 miles on it now. Bought it in Feb '06 with 93K miles. The car had been VERY well taken care of over it's lifetime,(original owners, old couple, garage kept, kept all reciepts including window sticker, wife drove it, no BS). So of course I blew the head gaskets only 4 months after I bought it just by GETTING ON IT on the freeway a couple times. This was before I knew about the "Head Gasket Blowing" problem, and also what made me an immediate member to SCCOA, because I wasn't about to give up that easily on such a beautifully kept SC.
ANYHOO... I replaced the head gaskets, along with a few other parts that were in need of replacement while I was at it(with MUCHO help from a member here), got my baby running strong again, and ever since I've been ALWAYS using 91 octane fuel(CA), and rarely floor it out of fear if it happening again. I've listened for engine knock when going up steep hills, and haven't heard any yet, but I still am cautious. So I just wonder if I'm wasting money on 91 octane gas, will I be safe with cheaper 89 or 87 octane, or why risk it for a few cents per gallon?
Sorry about the long post, got carried away.
Just looking for what you guys think.
Thanks!
Chris
Click to expand...

I have the same thing here and run 91. I can only get the higher stuff if I drive into the city, and from the gains I've got running '94 on a stock motor I think was more my imagination than anything else. Even going into WOT the motor doesn't ping or detonate. Do not run anything less than 91 though unless you pull the octane plug, or you could end up replacing those gaskets.

I was like you at first. Nervous about putting the hammer down just after I replaced the gaskets. Well, I'm not so nervous now 10000km's later. I'm easy on the car till she warms up, I run 10w30 mobil 1 and even when she's hot at 200F oil pressure is 65psi at 1700 rpm's cruising, and holds steady 24 psi at idle in drive, and hits 45 when she hits 800rpm's. So far running like a champ.
 
91 or better

d00mbuggy said:
I've been ALWAYS using 91 octane fuel(CA), and rarely floor it out of fear if it happening again. I've listened for engine knock when going up steep hills, and haven't heard any yet, but I still am cautious. So I just wonder if I'm wasting money on 91 octane gas, will I be safe with cheaper 89 or 87 octane, or why risk it for a few cents per gallon?
Sorry about the long post, got carried away.
Just looking for what you guys think.
Thanks!
Chris
Click to expand...
The SC requires Premium Fuel because of the supercharger. The forced air induction raises the compression ratio when the compression stroke is under boost. The cost of using Premium fuel is very little compared to the damage that will occur to the engine if you use lower grade fuels. Rule of thumb is “Just Don’t Do It and Use the Best Fuel You Can Get At The Pump". In New England I get 93 octane and my motor runs fine. Octane ratins depend on you altitude so if you live in a high elevation your ratings could be lower.

Also changing your coolant ever 2 year will extend the life of your head gasket and keep it from eroding.

Another highly recommended action would be to install a better exhaust system. You can start with a better resonator and ported exhaust manifolds.
 
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