# Engine Ping/Knock question



## Bigfoot21075 (Oct 12, 2015)

Hi Everyone,

As some know i just got my 1965 GTO. The car was restored by the previous owner, I got it through one of the mega dealers in the midwest. The car is beautiful and it runs great. It is a rebuilt 389 with stainless headers and exhaust. It starts and idles fine with no odd noises. 

When driving (it is easiest to hear in 4th gear) I hear a fairly loud pinging under light and heavy throttle, it sort of goes away in between. If i cruise at 45mph in 4th and apply light throttle it seems to make the noise the most. At first i was not sure if this was pinging or that noise stainless headers make, but I am pretty sure it is pinging - but again hard to tell. I know the lifters are adjustable also.

I just put in 12 gallons of Shell 93 Octane (10% ethanol) gas. That filled it up, i have no idea how old the gas in the tank was or what it was or how much was in there.

The car now has HEI ignition

I hear no obvious vacuum leaks

Any ideas on what may be the cause? I am hesitant to just knock the timing back as it runs and starts perfectly....


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## oldskool (Apr 26, 2015)

"...Any ideas on what may be the cause? I am hesitant to just knock the timing back as it runs and starts perfectly..."


Could be too much vacuum advance. Try this. Unhook your vac advance and plug the vac source. Then road test and see if that stopped the ping. If it did, then buy an adjustable vac advance. Start at the lowest advance setting and increase it slowly til you begin to hear a slight ping again. Then back it off some, to provide a margin of safety. I reckin you could call this method "Test & Tune".

If unhooking the vac advance did not stop the ping, you may have to "knock the timing back" a bit, anyhow. 

[ame]http://www.amazon.com/Crane-Cams-99600-1-Adjustable-Advance/dp/B000CIO2JU[/ame]


http://www.jegs.com/i/Crane+Cams/27...efDZx7K4PIRyWIjliujO7rmAzNPCh7YcssaAhUO8P8HAQ

[ame]http://www.amazon.com/ACCEL-31035-Adjustable-Vacuum-Advance/dp/B000BW8LSU[/ame]


http://www.summitracing.com/parts/m...kfkGJ-DkSV4idFZlyLh8YvDZCvaoiiTU_EaAgAN8P8HAQ

http://www.summitracing.com/parts/p...EgkBI9u-fmXShzSpS8s32TqdmIfNaMa6QoaAnYk8P8HAQ

http://www.jegs.com/i/JEGS+Performance+Products/555/40003/10002/-1


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## PontiacJim (Dec 29, 2012)

If the compression was not lowered during the rebuild, 93 octane is probably not enough. You can try what oldskool suggested to see if that will help, but dropping your timing back may cause a loss of power and can also cause the engine to run hotter, so if you do retard the timing, just go enough to eliminate the pinging and see how your engine responds. I used to time my cars this way and it always worked, but that was when you could buy leaded gas too.

Do not let the pinging continue as this is a good way to wipe out bearings or damage pistons. You may need to add an octane booster or go with a higher octane gas.


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## Lemans guy (Oct 14, 2014)

bf! i agree with old school and PJ. Likely timing. Does the car have a whiz bang billet racing distributor? With no vacumn advance?

It could be set up, curved all wrong, as it is likely giving you too much timing at say 45mph and light throttle......How? Light springs on the distributor bringing all the advance in.....the wrong vacumn canister in the distributor giving way to much advance......or a distributor with no vac advance for racing.....and bad for street driving....

Start there, if you can run your own timing...8 to 12 base, you set.....say 10...

16 more on the vac can....now 26..... And 26 on the centrifugal weights on the dist....52 degrees bedcovers at light throttle cruise say 65 mph...2,800..3,000 RPM...at 45 not all in as it would be lower, say RPM's at 2000...

Lot's of factors but check that dizzy first....OLD school and PJ are spot on....

Could be other things, just start at dizzy, make it right, then go from there

You will get it! And super 65! Looks Fun!:thumbsup::thumbsup:


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## Bigfoot21075 (Oct 12, 2015)

GREAT points everyone - THANKS this gives me a lot to go on. I should be able to play more with it this weekend. It is running an HEI distributor, I did not look to see what kind, also it may well be a high compression motor. I have a good series of things to try;

- Pull the vacuum advance line and plug the source just to see if it effects the ping
- Try 108 octane boost in a bottle, I have a Shell station not far from me that sells 104 at the pump for an insane price, but I already filled up with 93.
- I will also pull the plugs and see if i can get a read on what is going on there
- Have a look at the distributor and make sure it is "normal"
- If nothing else try retarding the timing

The car seems to be a healthy street setup, it even runs RedLines and it is a Ragtop so a race setup seems unlikely. I am guessing the guy built it hot, and 93 octane, 10% ethanol gas is not good with it. I know the Ethanol gas no longer has any stabilizers in it and has an unbelievably SHORT shelf life. I will also run Marine Stabil (the blue stuff) once I get this squared away.

THANKS AGAIN for the tips!


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## geeteeohguy (Feb 2, 2008)

Don't bother with 104 or 108 octane boost....absolutely worthless. The only one that works is Octane Supreme 130. If your 389 has stock iron heads and has flat topped pistons, likely your problem is the same one I have with my own '65: Too Much Compression. The only real cure is better fuel (100 octane) or, lacking that, lowering the compression with a piston change or a head change. MANY GTO 'dealers' simply rebuild the engine as-is and don't bother with changing the compression....which is a shame. These cars don't run well on today's poor fuel. I run race gas in my '65 GTO or TEL 130, and in my '67, I swapped heads to lower the CR so I can run 91 octane. Welcome to the GTO forums!


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## Goat Roper (Oct 28, 2014)

geeteeohguy said:


> Don't bother with 104 or 108 octane boost....absolutely worthless. The only one that works is Octane Supreme 130. If your 389 has stock iron heads and has flat topped pistons, likely your problem is the same one I have with my own '65: Too Much Compression. The only real cure is better fuel (100 octane) or, lacking that, lowering the compression with a piston change or a head change. MANY GTO 'dealers' simply rebuild the engine as-is and don't bother with changing the compression....which is a shame. These cars don't run well on today's poor fuel. I run race gas in my '65 GTO or TEL 130, and in my '67, I swapped heads to lower the CR so I can run 91 octane. Welcome to the GTO forums!


I was running 5 gallons of 91 mixed with 5 gallons of Sunoco 110, pricey and all I could do was drive it around town.
I tried 104 and as you stated worthless and a waste of money.
With 150K on it and low oil pressure it was time for a low compression rebuild.
It arrives tomorrow from CVMS between 9 and 1 and now I will have a driver instead of a trailer queen.


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## rickm (Feb 8, 2012)

did you put a timing light on it yet just to see where its at? do that first before changing the settings on anything. what 389 engine is it? what # heads are on it?


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## PontiacJim (Dec 29, 2012)

It is suggested that "hook up the vacuum advance to a ported (no vacuum at idle) source of vacuum on the carburetor."

A little more research into the HEI and I found these 2 articles that may provide some insight.

http://www.angelfire.com/on/geebjen/timing.txt

Changing the Advance Curve on HEI Distributors

:thumbsup:


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## Bigfoot21075 (Oct 12, 2015)

oldskool said:


> "...Any ideas on what may be the cause? I am hesitant to just knock the timing back as it runs and starts perfectly..."
> 
> 
> Could be too much vacuum advance. Try this. Unhook your vac advance and plug the vac source. Then road test and see if that stopped the ping. If it did, then buy an adjustable vac advance. Start at the lowest advance setting and increase it slowly til you begin to hear a slight ping again. Then back it off some, to provide a margin of safety. I reckin you could call this method "Test & Tune".
> ...



Got out to the garage today and gave this a try. The vacuum was hooked up to the primaries on the Edelbrock carb, I pulled the line and plugged the source - PRESTO Problem solved! I have NEVER heard of this issue before on something like this.

I am ordering the part now. I assume it just replaces the one currently on the distributor?

THANK YOU VERY MUCH! This is a huge relief!


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## PontiacJim (Dec 29, 2012)

Bigfoot21075 said:


> Got out to the garage today and gave this a try. The vacuum was hooked up to the primaries on the Edelbrock carb, I pulled the line and plugged the source - PRESTO Problem solved! I have NEVER heard of this issue before on something like this.
> 
> I am ordering the part now. I assume it just replaces the one currently on the distributor?
> 
> THANK YOU VERY MUCH! This is a huge relief!




Yes, it replaces your existing vacuum canister.

BTW, whomever provides the correct answer to any question on the forums, gets a brandy dipped Cuban cigar mailed them from the questionaire or a bottle of their favorite libation. No cash, please. :thumbsup:


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## Bigfoot21075 (Oct 12, 2015)

PontiacJim said:


> Yes, it replaces your existing vacuum canister.
> 
> BTW, whomever provides the correct answer to any question on the forums, gets a brandy dipped Cuban cigar mailed them from the questionaire or a bottle of their favorite libation. No cash, please. :thumbsup:


OH - thank goodness you caught me in time, I almost sent along a case of Laphroaig Scotch to go with those Cigars. Would have been a waste. :jawDrop:


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## Rukee (Feb 8, 2007)

mmm.....Brandy dipped cigars, sounds interesting. :thumbsup:


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