Slight Knock/Ping

[1978 NYB]

The cost of race fuel will probably be a one time test event.

 

[commando1]

Ah! Good point.

Either that, the DIY method of 1 gallon Tolulene to 10 gal. of 92 octane.
Nice cheater trick at the drags w/o racing gas available.

Toulene
R+M/2...114
Cost...$2.50/gal
Mixtures with 92 Octane Premium
10%...94.2 Octane
20%...96.4 Octane
30%...98.6 Octane

 

[1966-300]

Thanks Commando this mixture mirrors others I have seen. I am still going to try to back the timing back a bit more, that and the added octane or some combination will get me close. Thanks again to all.

 

[moper]

My impression is it's just a tuning issue. The carburetor is calibrated for leaded, higher octane fuel. I know where I live its vastly different packages but it's all around 10% ethanol. Also - 383s are no where near their advertised static compression ratio. There are no pistons that can reach it even in the aftermarket, and that's because the blocks are left "tall" in terms of deck heights. So unless you had the block blueprinted, it's closer to 9.2:1 with the 4bbl piston, and 8.7:1 with the 2bbl. So - you need to plot the timing curve for starters.. How much initial, and how much total advance (with the vacuum advance disconnected and the hose from the carb plugged) and when does the centrifical come in (in terms of rpm)? whoever said ping and/or detonation has nothing to do with jetting is mistaken. It's not the only thing, but it's certainly very relevant. With these heavy cars, with milder gearing, and terrible gas, you bet your behind that some deeper carb adjustments are needed and attention to detail in regard to the timing curve setup.

 

[commando1]

"The carburetor is callibrated for leaded."
That's extremely interesting. I would love to hear you elaborate on that further. I'm all ears because I'm new to this carburetor stuff and I want to learn all about them.

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[1978 NYB]

"The carburetor is callibrated for leaded."
That's extremely interesting. I would love to hear you elaborate on that further. I'm all ears because I'm new to this carburetor stuff and I want to learn all about them.

(Sent using Forum Runner)

Interesting...

:sixpack:

 

[moper]

Not sure if you meant to but you didn't quote the whole sentence... The tetraethyllead component was what made that fuel rated for a higher detonation resistance. And the factory would calibrate for the fuel available. It's kind of like early internal combustion engines. They'd run on almost anything flamable because that's what was available - kerosine, gasoline, minieral spirits, alcohol.. whatever. The carbs on these cars are set up for gasoline that was in the ground back then. Only now thery're being run on gasoline with less detonation resistance and in the case of my area (the northeast and some elsewhere) the gasoline is cut with 10% ethanol. Ethanol is alcohol, which leans out the fuel mixture further and does not have the same energy potential as gasoline. The end result is just a tuning issue. The lower power can be addressed via the timing curve, and the leaner mix that can lead to pinging can be can be adjusted with jetting.
You have to keep in mind - cars built prior to the 80s required a lot of regular maintenance and adjustment. Cars of the 60s and 70s required even more and more often. They don't adjust themselves like an EFI system does.

 

[commando1]

You have to keep in mind - cars built prior to the 80s required a lot of regular maintenance and adjustment. Cars of the 60s and 70s required even more and more often. They don't adjust themselves like an EFI system does.

All this pre-EFI stuff is new to me...

 

[1966-300]

Thanks Moper. So what I am hearing you say is that jetting COULD have an impact on the pinging I am experiencing? I had all but dismissed this as a possability and was resigned to increasing the octane of my fuel, and timing. I just had this conversation with my buddy again today and told him I was not going to reject the carb and that all I had heard convinced me it was timing and octane. I guess I am confused as how simply adding more fuel would eliminate pre ignition which to my inderstanding the pinging is. I need a preignition for dummies explaniation. Thanks again to all.

 

[commando1]

What are these things you call "jets" and why are they there?

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[Newp]

Correct ignition timing is the FIRST thing you need to address. It's a Mopar with a Big Block, not the space shuttle.

 

[detmatt]

That's funny Newp! Yeah I would first start with the timing and if it has anything to do with the jetting and how it relates to the lead that is no longer in the gas, then try some lead additive and see what happens.

 

[commando1]

Correct ignition timing is the FIRST thing you need to address. It's a Mopar with a Big Block, not the space shuttle.

THANK YOU!!!
Now we're back on track.
re-jetting.... sheesh

 

[moper]

THANK YOU!!!
Now we're back on track.
re-jetting.... sheesh

Yeah, you always start with timing. Then you move to tuning the carb and might need re-jetting. Always timing first because timing affects carb, carb does not affect timing.