What octane to use?

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Thomas Baker
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What octane to use?

#1 Post by Thomas Baker » Mon Dec 13, 2010 6:17 pm

I have a source for higher octane gasoline and would like to know what octane rating is best for our cars (I have a '57A with a 912 engine, a 60 Super cab, a '61 Super 90 Roadster and a '64 SC coupe). Is 110 too high?

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Ron LaDow
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Re: What octane to use?

#2 Post by Ron LaDow » Mon Dec 13, 2010 6:45 pm

Thomas,
There is no advantage to a fuel with a octane rating higher than your engines need.
I'd start with half a tank of regular; if they don't ping, use it. If they ping, fill it with premium and use that.
Pretty doubtful that any of your engines need higher than 91 octane. Engines with an honest 9.5:1 CR do just fine on that in the CA formulation.
Ron LaDow
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C J Murray
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Re: What octane to use?

#3 Post by C J Murray » Mon Dec 13, 2010 7:52 pm

Yes 110 is too high. Your street engines will make less power on 110 and use more fuel.
'57 Speedster
'59 Sunroof
'60 Devin D Porsche Race Car - Finally Finished!
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Jim Alton
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Re: What octane to use?

#4 Post by Jim Alton » Mon Dec 13, 2010 8:40 pm

For my 356A at least, the owner's manual says it needs 86 Research Octane (RON). That figure on the gas pump "R+M/2" is the government mandated average of Research Octane and Motor Octane. Motor Octane is virtually always lower than Research Octane so I would guess that REGULAR--with R+M/2 = 87 is typically about 89 RON.

To get the octane rating a 356A needs one might try mixing some kerosene or diesel with regular gas. Having said that, I use Premium (R+M/2 = 91 in California) for insurance in case the ignition winds up a little advanced or the engine's a little too hot.

110 Octane racing gasoline probably has other attributes which might make your car run better and make more power (and which are prohibited by the EPA for street use) but the same would be true of 100 Octane racing gas or even lower octane racing gas if you could find it.
 
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Ron LaDow
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Re: What octane to use?

#5 Post by Ron LaDow » Mon Dec 13, 2010 9:01 pm

Jim Alton wrote: ...110 Octane racing gasoline probably has other attributes which might make your car run better and make more power....
Jim,
The opposite is true. Gaining octane rating means trading off some energy content. The lowest octane fuel you can use is the best for that engine combination.
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Re: What octane to use?

#6 Post by C J Murray » Mon Dec 13, 2010 9:02 pm

110 Octane racing gasoline probably has other attributes which might make your car run better and make more power (and which are prohibited by the EPA for street use) but the same would be true of 100 Octane racing gas or even lower octane racing gas if you could find it.
Please explain.
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Re: What octane to use?

#7 Post by Ron LaDow » Mon Dec 13, 2010 9:20 pm

Thomas and Jim, this has been discussed before and some very competent folks have commented on it; look here:
http://www.porsche356registry.org/resou ... -need.html
Last edited by Ron LaDow on Mon Dec 13, 2010 10:06 pm, edited 1 time in total.
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Re: What octane to use?

#8 Post by C J Murray » Mon Dec 13, 2010 10:01 pm

Ron- I love your link but You may want to correct it anyway.
Cliff
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Re: What octane to use?

#9 Post by Ron LaDow » Mon Dec 13, 2010 10:07 pm

C J Murray wrote:Ron- I love your link but You may want to correct it anyway.
Cliff
Probably a good idea; Barry might look askance....
Done.
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Re: What octane to use?

#10 Post by Carl Zapffe » Mon Dec 13, 2010 10:45 pm

Here is a quote from Ron's corrected link:
Just remember that for an SC engine the recommended octane rating in 1964 was 96 RON which in today's terms would equate to about 92 octane.
I would assume that the same octane rating would apply for S-90 engines as SC engines as both have the higher compression. I use premium gas, which in the Midwest runs about 93 octane, and it works just fine in my S-90 Roadster.
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Barry Brisco
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Re: What octane to use?

#11 Post by Barry Brisco » Tue Dec 14, 2010 1:31 am

Hi Cliff,

Tell me what needs correcting in the article at http://www.porsche356registry.org/resou ... -need.html and I can do it.

Thanks,
Barry
C J Murray wrote:Ron- I love your link but You may want to correct it anyway.
Cliff

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Re: What octane to use?

#12 Post by C J Murray » Tue Dec 14, 2010 7:46 am

Barry- Ron did an edit...it is good now. Cliff
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Michael Eker

Re: What octane to use?

#13 Post by Michael Eker » Tue Dec 14, 2010 9:14 am

In the UK you can purchase 95(RON) and 99(RON) fuel..

Here is what Shell say about their 99 (RON) "V-Power" offering.

High Octane
Shell V-Power is a high octane unleaded petrol (99 RON). This enhanced octane rating is designed to help provide improvements in power delivery and to help drivers achieve maximum performance from octane responsive engines. And even vehicles designed for standard octane levels may benefit.

There is a presentation here:

http://www.shell.co.uk/home/content/gbr ... /benefits/

M.

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Re: What octane to use?

#14 Post by C J Murray » Tue Dec 14, 2010 9:44 am

Michael Eker wrote:In the UK you can purchase 95(RON) and 99(RON) fuel..

Here is what Shell say about their 99 (RON) "V-Power" offering.

High Octane
Shell V-Power is a high octane unleaded petrol (99 RON). This enhanced octane rating is designed to help provide improvements in power delivery and to help drivers achieve maximum performance from octane responsive engines. And even vehicles designed for standard octane levels may benefit.

There is a presentation here:

http://www.shell.co.uk/home/content/gbr ... /benefits/

M.
Nice marketing program!!! "octane responsive engines" In other words, 356s with short cams over 10:1 compression or longer cams and higher compression. You determine if you have such an engine by experimentation. No 356 near stock needs 110 octane or 100 for that matter. "And even vehicles designed for standard octane levels may benefit." MAY? It will not but the marketing guys gave themselves an out. No law suit here...please move along.
'57 Speedster
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'60 Devin D Porsche Race Car - Finally Finished!
'63 GS 2133 coupe
'64 Elva Courier mk4T
'67 911 S Original Owner

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Re: What octane to use?

#15 Post by David Jones » Tue Dec 14, 2010 10:03 am

Michael;
Your efforts at educating the 356 clan are somewhat late. This subject has been discussed ad nauseum and also the advertising hype you attached is just that. The link aforementioned discussed in detail the difference between octanes and I would add that unless your engine has been set up on the dyno for a particular type of gas then the advantage gained would be lost when you switch to another gas unless the jetting were changed to accomodate what are very likely to be significant changes especially in fuel density. This is not material for modern vehicles but critical for carburreted engines.
My Boxster 6 cylinder high performance water cooled engine (205 hp)mandates "premium" gasoline while my Subaru 6 cylinder (250 hp) water cooled shopping cart recommends "premium". Do you know the difference? By the way if I go to Denver then my 93 octane premium gas is now 91. You do know why of course.
I have attached a chart showing the difference between the various octane ratings. By the way did I mention that I work in an oil refinerry?
I also raced aircooled cars for 30 years and can say without fear of contradiction that for a normal street car you will never notice a difference in performance between one make of gasoline or another because in essence the gasoline you buy could be from any of the refineries near you. This means that the Shell hype means that the additives in your gas were added by the Shell tanker driver according to his manifest and that is the difference (maybe) between the Shell gas and the local supermarket brand.
Trust me on this I do know of what I speak.
Attachments
24 hour 91 octane.jpg
If I had known I would live this long I would have pushed the envelope a little harder.
Cymru am byth
David Jones #9715

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