Octane for Chevy 283 V8

The US sold cars had to be made unleaded capable by 1974, The first domestic brand cars that had a catalytic converter were the '75 models made in '74. Many of the imports didn't have cats until later, deciding to try to meet emissions otherwise. Also, they probably weren't privy to the technology. Some of the German cars in the mid and late 70's had some thermal reactor exhaust manifolds that glowed in the dark. Some of the Asian brans didn't as well. 1980 Subaru's were the last man standing without a cat. Magazine articles described mashing the throttle on a 1980 Subaru as a barely noticeable on/off switch.

Half ton trucks didn't have cats until 1978 MY, three quarter ton about 1980 MY and one tons about 1983 or 1984 MY.
Interesting that you mentioned Subaru. My mom's 1978 brat did not have a cat.
 
If the engine is original, and that's a big "if" considering its age and that it's a small-block Chevy, the compression would be 9.0:1 according to the brochure linked below. It's interesting that both gross and net hp and torque are listed.

1964 Chevy Pickup Brochure
 
If the engine is original, and that's a big "if" considering its age and that it's a small-block Chevy, the compression would be 9.0:1 according to the brochure linked below. It's interesting that both gross and net hp and torque are listed.

1964 Chevy Pickup Brochure
I'd be very impressed if it still has the original heads on it. Many got swapped for later ones.
 
My 1956 Chevy has the original 265 in it. Honed and Re-ringed almost 30 years ago. Original low compression heads. No need for hardened seats. They did need valve job, new cam, rockers, pushrods and guide plates though. Had to thread in one stud that kept working loose. Never bored, polished, or gasket matched. The alloy in these heads is hard from the factory. Low compression-87 octane just fine. Motor pulls strong for almost 30 years since mild overhaul.
 
If the valves are sunken into the heads, they can be machined for inserts. If I went that far, I would look for aftermarket heads that flowed better.
Regarding octane, that is more about timing curve. You need a shorter curve with less total. And a vacuum can with less advance.
 
Even knowing what cylinder head (Chamber CC) won't tell you the compression ratio, I've seen (Aftermarket/Jobber) pistons sit way down in the bore.

Set the timing at 36°-38° BTDC (mechanical/centrifugal advance all in) & see if it pings on regular unleaded (Ambient air temp will affect this), This assumes the timing marks are accurate.

If you have a stock HEI distributor swapped in.....I can almost guarantee the vacuum advance needs to be limited! I used to braze a limit on them, But adjustable vacuum canisters are available.....Although I've seen them not work correctly.
10-15 degrees is about all you need out of the vacuum advance (Hooked to manifold vacuum)
 

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Perfect. It still has the 283 heads. Now there is a pad I circled. There will be numbers and letters on it stamped into the block. The numbers will match the vin if it's the original engine to the truck. There will also be a letter or letters like an "E" or "AA" etc... What is it? If you can post all you find that will tell us more.
 

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Alright there are some numbers on the right side that start with F. No numbers to the left of that like the photo above. I need to clean it better tomorrow and check. A wet paper towel didn't clean it that well. No E or double A either?

The number and letter combination does not match anything from the VIN.
 
Alright there are some numbers on the right side that start with F. No numbers to the left of that like the photo above. I need to clean it better tomorrow and check. A wet paper towel didn't clean it that well. No E or double A either?

The number and letter combination does not match anything from the VIN.
It could be any letter I just used those as an example. See how in this pic there is an "HE" on the right? Look there.
 

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If there’s no spark knock then 87 octane. If the camshaft has more duration than stock and tight LSA then you definitely can use 87 octane. Most likely a later rebuilder kit was used during the last overhaul with lower compression pistons. Most of those kits have pistons with deeper valve reliefs for sure and possibly dished domes.
 
As @clinebarger posted, too much vacuum lead will ping like crazy. In CA, with our wannabe 91* "Premium", I limit my old L36 Vette to about 10* vacuum advance. Lars Grimsrud and Henry Olsen make a limiter for your distributer.

If I were you, I would recurve your distributer based on load and available gas. I would set base using a vacuum gauge, set to highest vacuum. Same with your carb idle misture. Set total mechanical to about 34*, all in. Add about 10* vacuum advance using full manifold vacuum.

You can play with it from there. Remember, if you have audible ping, you are running too much lead or need better gas.
I am guessing an old 283 in a pickup will never see much RPM.
 
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The truck seems to run best on 91 from Costco. I was far from a top tier station and decided to get 89 again from a standard station. It doesn't get moving as fast, could be a placebo. There is no knocking.

Next time I will put a little 87 from Costco and see how it goes.
 
The truck seems to run best on 91 from Costco. I was far from a top tier station and decided to get 89 again from a standard station. It doesn't get moving as fast, could be a placebo. There is no knocking.

Next time I will put a little 87 from Costco and see how it goes.
I would recurve your distributer. At least figure out where you are...
 
I just bought a 64 chevy C10 with a 283. In my area I can get 87, 89 or 91 octane fuel at the pump. The previous owner put 87 in it.

What do you all recommend?
Is it a Three on the Tree? If there is room get an HEI in there, and eliminate the resistor wire used for points. We used factory L82 curve on 350 rebuilds. Timing 34-36deg all in no vac advance. Too much total, vehicle wont pull top gear.
- Ken
 
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