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Newbie here,
Seems like a dumb question, but what kind of gas should I be putting in my 1969 442? I searched past threads and some said regular gas is fine and some said higher octane racing fuel (which I have no access to) and others said ethanol free (which I do have access to).
If it is original compression ratio I would use minimum 91 or if available 93, non ethanol if available, assuming you’re in U.S. If engine has been rebuilt it is tough to say whether 89 might work or 93 may be marginal. Listen carefully for preignition under load.
You don’t need higher octane than the engine’s requirements but an additional 20-40 cents per gallon for the “good” stuff, with the number of miles the car likely travels, why not play it safe?
Last edited by bccan; April 22nd, 2021 at 09:49 AM.
Your question isn't dumb, it is critical. "Regular" can have different meanings... assuming the engine is at original spec as we don't know otherwise I'd only use 93 octane. The engine required "premium" fuel from the manufacturer but what does "premium" mean today vs 1969? Again I'd use 93 and listen for pinging.
Fuel that is too low in octane will cause permanent damage to piston$$$.
I'll also add that the oil used matters, use something with sufficient ZDDP such as Valvoline VR1 or other oils engineered for flat tappet engines.
I am fortunate to have 94 octane ethanol-free available where I live so I use that and a bottle of Lucas octane boost every tankful and I'm still not able to run as much timing as I'd like. Why is detergent a concern?
I agree with 69442ragtop. I also have a '69 convertible 442. The original 400G has never been opened up and still runs good at 100kmiles. However, I've had to run octane booster at every fill up. Otherwise, pinging.
Lots of discussion on the forum regarding ethanol fuels. I go out of my way to avoid it even though that means I can only purchase 90 octane locally. It'll destroy many types of rubber (and other materials) if they weren't originally designed for it (which our original parts weren't). Many of today's aftermarket parts also don't consider ethanol and you won't know until you see it degrading (e.g. reproduction fuel caps).
By the way, back in the '80's when I purchased the car I ran 93 octane. Soon figured out I still needed octane booster.
I am fortunate to have 94 octane ethanol-free available where I live so I use that and a bottle of Lucas octane boost every tankful and I'm still not able to run as much timing as I'd like. Why is detergent a concern?
I have both a '68 4-4-2 convertible and a '69 4-4-2 convertible with original but rebuilt drivetrains. I use ethanol-free 92 octane gas and haven't had any problems with pinging, misfires or anything of the sort. I was advised when the engines were rebuilt to use ethanol-free gas for best performance and overall maintenance. Both cars get about 12-14mpg.
I’m guessing this isn’t your only mode of transportation. With that in mind, is the extra 10-12 bucks per fuel fill up that big a deal? The cost to repair the damage caused by detonation would pay for a lot of fuel!!!
If your really determined to find the safe limit, start by filling it with the best octane you can find. Drive it under various conditions, in the heat, stop and go traffic, with the A/C on, all the while listening CAREFULLY for pinging. If it’s all good, drive it until the tank is about half full, then fill it back up with the next lower grade of fuel. Once again, go thru the driving cycles under the above conditions. Keep going until the tank is empty, then fill the tank halfway with what you used in the previous fill up. If you hear detonation this time, fill it back up with premium. You know the engines octane requirements are somewhere between premium and the next lower grade. If that’s the case, I’d personally keep running premium. That the safest option, the engine may be experiencing pinging you can’t hear, and not every fuel station has the same quality premium fuel.
Just go slowly, keep dropping octane until you hear pinging, then go back to whatever fuel didn’t make the engine rattle.
I’m only on my first tank of new gas with my 350/310 Cutlass S. So far no pinging, knocking or run on with 90 ethanol free.
Actually I’m shocked and impressed how quiet and smooth this motor runs. Starting to believe the mileage is actually 56k.
This has been discussed quite a bit over the years. I own a 70-442 4 speed, fully restored. I have access to 99 octane and when I choose 93, its a major difference. 99 octane, no ping-runs perfectly dialed in like a 70-442 should, 93 octane will ping all day long upon acceleration. Yes, the 99 octane is very pricey, but I only drive my car a few hundred miles per year and it never goes bad.
The above.
Id say way advance timing? Or carb set up?
Only reason I ask, as I know every engines different.
My 468ci full roller, 10.5 comp
Got a qjet ( forgot through who).
runs like a top on 92 oct.
Car fires up on one click of the key..
But...the w30 carb has the needles out bigger jets..no choke...this carb has much more power..93 Octane was ok..no pinging...just smelt like gas and 4 maybee 7 miles per.
April 22nd, 2021, 05:22 AM
