Octane for Chevy 283 V8

[HondOtaChOrd]

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?

 

[Chris142]

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?

Thing should have around 9:1 compression. Possibly a little higher. Plus outdated cast iron heads that may cause detonation on lower octain fuel. I'd run no less than 89.
Can you get me a pic of the front of the heads?

 

[hank2]

Yes, when it was new and to the end of leaded regular gasoline in the early 1990's, regular gasoline was 89 pump octane. The economy grade 87 unleaded was brought out when engine static compression ratios had dropped to about 8:1 for emissions reasons. A number of other factors including carbon deposits could affect the need. Unless you know that the valve seats were ungraded for unleaded, it would be wise to use some sort of lead substitute.

 

[The_Jeff]

At least 89. If you can find ethanol free 90 that would be superb.

There's a split between research and motor octane, and the bigger that split is, the more "sensitive" it is (bad thing.)

How ethanol boosts octane is quite different than how lead used to do it, so you'll want a cushion.

Are you still running points ignition? HEI should be your first upgrade, then the timing will at least be consistent.

There's also the chance that in the last 59 years someone "worked" your motor with a hotter cam, different heads, intake, etc so an answer for one 283 may not apply to yours. But generally speaking it was the low-to-midrange V8 offering for the economy minded.

 

[Greasymechtech]

Toptier fuel... grade depends on if you hear it knock or not. Nothing wrong with 87 until it rattles, then move up.


https://www.toptiergas.com/licensed-brands/

 

[HondOtaChOrd]

I plan to go to Costco gas today and get 91. They only have 87 and 91.

Ethanol free gas is nonexistent at the pumps here.

 

[meep]

I owned a 283, and drove it well into the 90s. Mine had a compression ratio of about 10.5:1 stock, per the factory service manual. At one point I sent it off to be machined and then did the assembly myself, as it wasn’t running well, swilled oil, and had compression ranging from 135 to 85 depending on the cylinder. All were bored out .040. After that, it would ping and predetonate and literally stop moving the car on level ground unless I ran 93 in it. I don’t know what the effective compression ratio was after they machined it - they didn’t mention anything about having to shave too much off the block or heads, but mine did not cooperate on low octane gas, at all. On 93, it idled like a Lexus and roared off the line if you put your foot into it.

 

[Chris142]

There's also the chance that in the last 59 years someone "worked" your motor with a hotter cam, different heads, intake, etc so an answer for one 283 may not apply to yours.

This is why I have asked him to take a pic of the front of the heads. So far he has not . If I could see that I would know much more about it. Often the old 58-64cc heads got swapped for 76 cc heads which killed compression on a 283.

 

[jhs914]

Unless you know that the valve seats were upgraded for unleaded, it would be wise to use some sort of lead substitute.

This.

 

[Blinker]

In your application, 87 octane is all you need, assuming it’s stock.

Now if it were a 283 in a corvette with dual quad carbs, then you’d want higher octane. Any of the higher compression versions you should be running higher octane.

The 283 in a C10 series truck was a lower horsepower example and was tuned for truck duty.

Also, do you know if the valve seats have been replaced with hardened seats? If not, you need to add a lead alternative to the fuel everytime you fuel up. Many people I know, including family, use Marvel Mystery Oil on engines with soft valve seats and this prolongs the life of them.

 

[64bawagon]

I run Rec fuel (ethanol free) 89 octane. It runs fine on 87 octane as long as the timing is set right. The 283 does not much care about fuel, now the 327 ? that was an entirely different case.

The short block on mine is a 64 truck 283 with 1957 power pack heads (same heads as used on the 64 2bbl)

 

[bullwinkle]

Back in the day, I used to run Speedway 89 in a mildly worked over ‘72 Skylark Buick 350 I used as a DD-it pinged less & had better power than other competitors’ plus or premium. It might be worth a try, either through Speedway or Marathon. I never used a lead substitute, either, not sure if a ‘72 would have had the hardened valve seats or not. i would be running HDEO in that flat tappet 283 for sure, that’s what I use in my brother’s modded ‘67 283 (he runs 93, 10.5-1 compression).

 

[bullwinkle]

Toptier fuel... grade depends on if you hear it knock or not. Nothing wrong with 87 until it rattles, then move up.


https://www.toptiergas.com/licensed-brands/

The issue with pinging on 87 is-you have to back off timing (retard the distributor) until it stops-and then power, MPG, and driveability all suffer.

 

[CleanSump]

I rebuilt and installed a 327 in a Camaro. When doing the heads, I had the machine shop install hardened valve seats. Didn't cost all that much back in the '80s. I had a '69 Lemans w/350 HO that ate the valve seats in the late '70's/early '80s. Had to have hardened valve seats installed in the heads of that.
Since both were DDs, it was cheaper, at least back then, to take the heads to the machine shop than buy Instead of Lead for every fill-up.
Machine shops were everywhere back then. Hard to find a good one today.

 

[jhs914]

Back in the day, I used to run Speedway 89 in a mildly worked over ‘72 Skylark Buick 350 I used as a DD-it pinged less & had better power than other competitors’ plus or premium. It might be worth a try, either through Speedway or Marathon. I never used a lead substitute, either, not sure if a ‘72 would have had the hardened valve seats or not. i would be running HDEO in that flat tappet 283 for sure, that’s what I use in my brother’s modded ‘67 283 (he runs 93, 10.5-1 compression).

Unleaded gas was common by 1972. Hardened valve seats were used after 1970 because of that.

(Edit): I was wrong. 1975 was when catalytic converters became mandatory and that required unleaded gasoline.

 

[hank2]

Hardened valve seats were used by Chrysler products in the 1973 model year. Most others didn't until 1974 as required. Other than the Amoco premium which was always unleaded, I don't recall any unleaded fuels until 1973-74.

 

[Chris142]

I would think that an engine that old has at least had the heads off for a valve job,seats etc. Not too many around today that are untouched.

 

[CR94]

Unleaded gas was common by 1972. Hardened valve seats were used after 1970 because of that.

(Edit): I was wrong. 1975 was when catalytic converters became mandatory and that required unleaded gasoline.

I think you were right the first time, assuming "after 1970" means starting in with model year 1971. Catalytic converters weren't used yet, but GM knew they were coming.
Catalytic converters weren't specifically required on 1975 model year cars, but that was the first year most cars had them, due to tightening emissions standards. A few Japanese models managed to get by without converters for a couple more years.

 

[Chris142]

I think you were right the first time, assuming "after 1970" means starting in with model year 1971. Catalytic converters weren't used yet, but GM knew they were coming.
Catalytic converters weren't specifically required on 1975 model year cars, but that was the first year most cars had them, due to tightening emissions standards. A few Japanese models managed to get by without converters for a couple more years.

Some ford trucks went into the 80's without cats.

 

[hank2]

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.