I understand that what octane meant in 1971 no longer applies. Just received a set of owner's manuals purchased on eBay for my 1971 Mustang. The book says I need 99.8 octane. Where do I buy that? Do I need to go to a local hardware store and buy some toluene to pour in the tank?
mike
You only need enough octane to prevent pinging. Lots of factors involved there. Start with premium pump gas. If it pings, add toluene. If it doesn't, try mid grade. If it doesn't ping with mid grade, try the "cheap" stuff.
You can adjust (re-curve the distributor) or replace (electronic distributor) your ignition system to run your 1971 Mustang on today's (low octane) pump gas without pinging.
Toluene is some nasty stuff. I looked into using it but decided not to after reading up on it. It's not something I would want in my garage, especially if there are kids running around.
Unless the compression ratio is in the 11.0-12.0 range he should be able to adjust the timing to keep it from pinging with Sunoco 94 octane. Also, carbon buildup on the pistons can cause big detonation problems.
maybe somebuddy elses memory is better than mine, because this goes way back:
there were once two different octane rating methods (seems to be they were "Motor" and "Research") in use......can't remember who came up with them or why, but one had a much higher number range that went to like
110 for fuels available at retail. At some point, retailers went to "Pump" octane which is the average of the two ratings and is the nuber you see displayed on pumps today.so......it's possible to have an owners manual for an older car that is referring to 100+ octane that really translates into 89 - 92 in today's lingo. not that new gas isn't crap, but you should be able to run about anything on modern premium.
anybuddy else old enough to remember buying gas at airports to get "aviation" octane? for conspiricy theorists: no doubt the lower "pump" ratings were implemented by the evil oil companies to get us to buy more octane than we need......and how many other dumb kids like me dropped the big bucks to put Sunoco 260 in some old roach that hardly had any compression left and probably would have run on kerosene, lol.
I found this information on the internet: STRAIGHT TALK BY JAMES HALDERMAN
Halderman: The gasoline rating used today is an average of two methods used to rate gasoline - the Research method and the Motor method. Today, regular is 87 octane (R + M/2), midgrade or plus is 89 octane, and premium is 91 or higher. In the old days (1970s and older), gasoline was rated using the Research scale, which gave a higher reading. Back in the 1970s, regular was 91 or 92 octane, midgrade was 94 or 95, and premium was 99 or 100. Therefore, regular 91 grade gasoline in 1970 is equal to our 87 octane using the newer method.
Wheels: Does this mean that older engines can use 87 octane as posted on the pump?
Halderman: For most older vehicles, the answer is yes. However, if the older engine has high compression, a higher octane rated fuel will likely be needed. If there is a concern, you can start by using premium (91 + pump octane) and see if the engine runs knock free. If so, then maybe midgrade or regular (87 octane) may be used.
Note: Many European vehicles specify that 91 octane or higher is required. However, this is specified in the Research octane rating system and is equal to regular 87 octane rated at the pump.
Not sure exactly what engine you got in your Mustang or how well it's built, but I've got a '71 Cougar (351C) that I put a few hundred miles on per year. I will run on 91 octane with no problem but if I'm going to get on it a little bit, 93 can be used. If you need higher octane, which I doubt, you can mix some racing gas with it and blend it until you find your best mix.
If it ran good with pump gas before you got your manuals from ebay, why would that change now?
What I am getting from this thread is, if the engine runs without pinging at
89 octane, using 91 octane will not improve performance. If the car pings with 91 octane, tuning the engine to run on 91 octane will likely improve performance. The engine is a 351C 4V, but with the Edelbrock parts, it is not stock.mike
I put Aussie heads on a 351C and haven't installed it yet, (fenders off and painting the engine bay right now). I always thought you need to run 104+ octane booster for that application. Am I wrong? Can I run premium, I have forged pistons with bronze valve guides and hardened valve seats. Keep in mind, I haven't even started this engine yet (can't wait!!!) Dave
I run 1971 open chamber four barrel heads (351 Cobra Jet) on the four bolt main 351 Cobra Jet Block. I started with a custom arched Duraspark electronic ignition system, and switched to a Mallory Unilite and Mallory Hi-Fire IGNITION BOX. Both ignition systems worked well with no pinging on pump premium gas.
Today gasoline octane is given in (R+M)/2 format. An average of the research and motor octane numbers. The manual is probably giving you one or the other. 99.8 RON sounds really high, sure there isn't a typo?
91 RON = 87 (R+M)/2 95 RON = 91 (R+M)/2
The highest at the pump, what other choice do you have? It still depends on your ignition system...
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