[shommel]

what type of gas should be used in a 65 a code and why?

[zippyflash]

I have a '66 289 and use the mid grade. Sometimes the low grade gas can create a knocking noise in the engine. Knocking can occur from abnormal combustion of the fuel.

I also use a lead additive. Older vehicles such as the '65 and '66 mustang used regular gas (leaded). Today's gas is unleaded. The lead serves to lubricrate the valve seats. You can buy a lead additive fairly cheaply at almost any car parts or supply store. You add some at every fill up. I keep mine in my trunk and add about .5-1.0 oz. per ten gallons. The bottle will have directions.

[nigel]

Also try to stay away from ethanol. Not good for older cars. Try to buy from a place that sells 100% gasoline.

[Ivy66GT]

The short answer is: Premium. The reason is: Compression ratio (CR)

Ford's advertised CR for the '65 A-code was 10.0:1 compared to the C-code's 9.3:1. That is why the A was called the 'premium-fueled' 289. Premium gas today has less octane than it did in 1965 so its even more of a premium-fueled engine today. A 2009 premium would have only been a mid-grade in 1965 although nobody called anything mid-grade back then. Depending upon its condition, if its been rebuilt or where you drive it the exact octane it needs can and will vary. At sea level it is likely premium and even then you may have to retard the timing to avoid knock. At high elevation, like anywhere in the state of New Mexico, you can use regular. Use whatever it takes to minimize knocking.

When an engine is overbored, if the same piston shape and compression height is retained, its effective CR goes up a few tenths since a larger piston area is compressed into the same head space. That can make the octane requirement even higher. Original Ford pistons are hard to come by today so what the compression ratio, and fuel requirement of a re-built engine might be depends greatly upon the pistons used. I did an A-code rebuild to 0.030 over using common, aftermarket lower compression C-code pistons and the CR still calculates to be 9.56:1. Part of that was the dish of the new pistons was 3 cc less than original but much of it was the 9 cc more displacement for each of the +30 cylinders.

If you live in the USA and can avoid ethanol in your gas these days you deserve a medal. I don't think there is any gas left without ethanol. I couldn't find any driving cross country in 2008 and I am sure its worse now. Many stations try to hide the sign telling your about ethanol because there are people like us who try to avoid it. Never once did I find a station where I didn't eventually find the ethanol sign before I finished filling up. Congress has mandated billions of gallons of it be used and the number of billions will increase much further than today. In many places they are trying to sell E-85 which is 85% ethanol. Its a lousy deal and few take the bait, but its out there if you have a new car capable of burning it and you don't care how much you pay for fuel or how often you have to fill up. Ethanol's biggest problem is it contains less energy so your MPG goes down so you fill up more often while at the same time it costs you more. And that is after the government subsidizes the price of ethanol at something like 50 cents/gallon.

[Ivy66GT]

Originally Posted by zippyflash

I also use a lead additive...

Unless you are breaking the law what you are using is a 'lead substitute' which has no tetra-ethyl lead (TEL) in it. It is illegal in the USA to sell TEL for highway use.

[zippyflash]

You are correct, it is a lead substitute that you add.

[66GT305PS]

A code does need premium, 91 octane, unless you change the timing. You need only be concerned with the lack of lead if you are pushing a load, as in hard acceleration or car load of people all the time. If that is the case, get a top end rebuild with hardened valve seats and valves.

The ethanol will affect your fuel delivery system. Expect to have to replace the fuel pump. Do add some stabilizer to avoid moisture in the fuel since old carb systems are not closed fuel systems like EFI types. Sta-Bil or Seafoam work best as directed. Run the car at least twice a month, with fresh fuel at least once every two months. Ethanol degrades twice as fast as non ethanol fuel. The only places I know to get non ethanol fuel is boat docks and is is about 30 percent more expensive.

[thetvirus]

Looks in the original owners manual. it states MINIMUM 93 octane for normal 289 engines (A and C codes) and MINIMUM 100 octane for 289 HiPo engines (K codes).

[66GT305PS]

True except the octane rating method was changed from when the manual was written. We now have the R+M/2 rating method (r= research octane method, m=motor octane method) so the highest pump gas now is rated at 91 to 93 instead of 92 to 100. For the A Code, the highest premium pump gas is best. Listen to your engine, it will tell whether it is happy or not.

[Sidox]

What about a 66 T code- 200? I never thought to ask about it..

[Ivy66GT]

In ye olden days the pump octane was Reserach octane, the 'R' in the (R+M)/2 formula. R is usually about 10 octane numbers higher than M so the standard rule of thumb is that the 60s octane requirement, MINUS 5, is what today's pump equivalent would be. So if it needed 100 in 1965 then 95 would be the 2009 equivalent. That isn't always true, but usually.

The '66 200 was only a 9.2:1 CR so it was a regular fuel car similar to the C-code 289. So if you take 93-5 that would say 88 octane today.

Ethanol itself absorbs water so its very unlikely you will need anything else to combat water in the fuel.