Zonzo

Hey everyone, I recently inherited a 1969 Olds 442 that has a fairly hot engine, though the info I have on it is 2nd hand for obvious reasons.

Cylinders are .30 over so displacement I believe is 461ci
Probe pistons from Mondello, supposedly 12:1 though that seems incredibly high so IDK
Edelbrock 77cc aluminum heads and intake
Engle Cam, 230 intake/240 exhaust with 110 ls

Could anyone guess at what the compression might be on this thing? It's supposedly been fed 105 most it's life, but it's supposed to run well on 100 as well. Could anyone tell me how much the timing could be retarded to bring the octane down without making it run poorly?

Thanks in advance for any answers. I don't know anything about Oldsmobiles so if the info I've given sounds off def let me know, I'd like to run this thing right.

OLDSter Ralph

Of course people can guess at things, but that doesn't do you much good. Have you actually measured anything ? Unless you have, or someone else, has measured things, you are just guessing
Oh, and .030" over 455 would be 461.
I am dropping a link to help you calculate compression ratio. Fill in the blanks.
https://butlerperformance.com/n-1287...alculator.html

cutlassefi

If it’s their 3cc piston, and the heads haven’t been cut, then you have a bit over 11:1, not 12:1.
That’s still high for pump gas though. See if you can grab a tube camera to verify one way or another.
And a side note, Mondello sold stuff to people they never should’ve sold to. Amazing.

Zonzo

My intention right now is to mix my own gas at home, which I've done for other cars so it's not a problem. At around or over 11:1, what kind of octane do these engines like? When I deal with the lawyers and get the car next week I'm going to take apart as much as is reasonable and find out more about the engine, but it'll need to be driven around 500 miles home haha.

66SportCoupe

If you have a small municipal airport near you run 100LL fuel in it. It will handle your compression. I run it in a 13:1 BBO.

cutlassefi

ALL of the aftermarket cyl head manufacturers I’ve ever talked to, tell you to NOT use Avgas. It’s a very dry fuel, too dry for automotive use.

oldsrush

Add 4 oz of Marvel Mystery oil to every 15 gallons of AV gas and it will be good to go. Been using it for decades.

randy442

I gotta chime in here on this. I've been an aircraft mechanic for over 20 years and mostly all piston powered type, (Only a couple kerosene burners) and thus I have easy access to avgas. In fact i work for a guy who has a bunch of planes and quit a few nice older cars ranging from 1930s to 1970s. All get a steady diet of avgas and love it. Zero problems. My 442 also runs on it at 10 to 1 comp with no complaints.
And no, you dont have to add marvel mystery oil to it.

CANADIANOLDS

you know the cam that’s in it. if it’s really 12:1 with that little cam installed @110 or usually +4, your cranking compression will be sky high… like 200+

do a simple compression test and let us know what you get. You’re just guessing now. Adding more octane than the engines needs, hurts performance