Valve knock under full throttle? 68 charger

[Jerry Hall]

.035

 

[Michael_]

im think i should try 93

good idea

What plugs/gaps yall recommend?

Champion

 

[Jerry Hall]

Try some Autolite 85's. They last, which I can't make a Champion do.

 

[pnora]

If blue smoke was a glitch that one time, im think i should try 93, and maybe change the plugs…? What plugs/gaps yall recommend?

If you were smart you would have the timing checked to see what the total advance is. Detonation can cause serious damage. What plug number are you running now? If the timing is ok then try higher octane fuel.

 

[AR67GTX]

The 2 bbl carb 383 was probably designated to run on regular. The 4 bbl carb 383 would definately require premium fuel. Which do you have? Different octane fuels would have nothing to do with any exhaust smoke - nothing.

 

[Michael_]

The 2 bbl carb 383 was probably designated to run on regular. The 4 bbl carb 383 would definately require premium fuel. Which do you have?

But the engine has been rebuilt 6k miles ago so i wouldn't really rely on that.
Given it's not running right on regular i'm guessing the rebuilder probably tuned it for 93 octane.

Well finding out is as easy as putting some 93 in the tank and then floor it (after the remaining regular fuel is out of the tank).

 

[euroz06]

I was at the shop bleeding brakes and found one of the rear lines (before the valve) was clogged, so got stuck in the shop overnight. Put 12 gallons of 93 before i went in. Have new iridium plugs on standby to put in tomorrow. Autozone didnt have a timing tool (neither does my shop).

 

[66 Sat]

But the engine has been rebuilt 6k miles ago so i wouldn't really rely on that.
Given it's not running right on regular i'm guessing the rebuilder probably tuned it for 93 octane.

I wouldn't be guessing anything. Get a timing light, check the timing, adjust as necessary.

Well finding out is as easy as putting some 93 in the tank and then floor it (after the remaining regular fuel is out of the tank).

And if that's the full throttle run that causes a hole in the piston...no smiley face then for the OP.

 

[euroz06]

So good news: put in 12 gallons of 93, drove around a bit, then tried flooring, no more “knocking” and i dont see any smoke! So i assume they “tuned” it for 93… i hope i didnt cause any damage by running regular past 6 years im gonna replace the plugs today with iridium plugs (0.035 gap, right?).
The car is a lot more peppy too! Also fixed my brakes, i guess i was driving without rear brakes, one of the tubes before diverter valve was completely clogged up, so we cleaned everything and replaced the tube.

Next item, i guess i never had hub-centric rings installed (and no shop ever told me i needed them)… any advice on sizes? American racing 17 inch wheels

 

[Michael_]

So good news: put in 12 gallons of 93, drove around a bit, then tried flooring, no more “knocking” and i dont see any smoke!

Congratulations

i hope i didnt cause any damage by running regular past 6 years

This highlights the quality engineering behind these old engines.

Try that (doing something wrong continuously for 6 years in a row) with a modern car.

iridium plugs (0.035 gap, right?).

Isn't there a reason not to use iridium spark plugs with these engines? I could be wrong but i remember "iridium" from when i originally researched which plugs to use.
I decided to go with regular OEM style copper instead.

 

[euroz06]

I actually stayed with stock spark plugs, the new ones were the wrong size. I did inspect all of them, one was a bit loose, adjusted the gaps to .035 (they were .037-.040)

 

[padam]

Congratulations



This highlights the quality engineering behind these old engines.

Try that (doing something wrong continuously for 6 years in a row) with a modern car.




Isn't there a reason not to use iridium spark plugs with these engines? I could be wrong but i remember "iridium" from when i originally researched which plugs to use.
I decided to go with regular OEM style copper instead.

I just put ngk platinum plugs in a Toyota, and they came with a note not to adjust the gap.
Maybe knocks the plating off?

 

[RemCharger]

I just put ngk platinum plugs in a Toyota, and they came with a note not to adjust the gap.
Maybe knocks the plating off?

Just another example of the quality of ngks. They come pregapped properly like they should.
And unlike others.

 

[Geoff 2]

You have to be veeeery careful adjusting the gaps on Plat/Irid plugs. The small electrode end is easily damaged.

 

[mopar 3 B]

So shouldnt be getting blue smoke on 93? I thought these were supposed to run on regular ‍

Stock 383 two barrel engine will run fine on 87 octane fuel and stock 383 four barrel engine has different insides and requires 93 octane or better. Better is good if you can find it.
It's would help if you had posted what rpm the knock occurred at. These engines in stock form were not designed to run over 5800 rpms.
I also suspect it may have a weak valve spring if indeed a valve knock.
Any case you need to find someone that knows what they are doing. Replacement engines are not cheap.