# Spark Knock, 65 389



## SLSTEVE (Dec 8, 2020)

Took my almost finished 65 GTO for a short trip into town to get the front end aligned. Only a couple of miles. 80 degree outside temperature. Had a few issues but my main concern is what I would describe as excessive spark knock on acceleration. I’m running ethanol free regular unleaded, 9.5:1 compression, 389 bored .030 over, M 20 Muncie, 3.55 Safety Track, and around 8-10 BTDC timing. HEI distributor. Spark plugs are gapped at .040. Water temp was right around 190-200. What do I do to remedy this situation? Premium unleaded? Racing fuel mixed into premium unleaded? Timing? Less gap on plugs? I’m open to any and all suggestions from the Pontiac experts here. TIA.


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## Baaad65 (Aug 29, 2019)

I'm certainly not an expert here (and Army will concur) but by regular do you mean 87 octane? Maybe the combination of that and the higher engine temp and the wider plug gap all created the perfect storm. Most things I read here state to keep the gap a .035...idk again just throwing stuff at the wall.


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## ponchonlefty (8 mo ago)

maybe try a 160 thermostat. take a look at the spark plugs see if it may be running lean. it would be safe to assume premium gas would be what you will have to run. where im from i can only get 87 ethanol free. the 93 is blended. i hope this will help.


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## pontrc (Mar 18, 2020)

I would go down to the 035 gap. But first try premium fuel. Lucas fuel products help out the pinging detonate problems. I think today’s fuels are getting worse. And recheck timing


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## armyadarkness (Dec 7, 2020)

SLSTEVE said:


> Took my almost finished 65 GTO for a short trip into town to get the front end aligned. Only a couple of miles. 80 degree outside temperature. Had a few issues but my main concern is what I would describe as excessive spark knock on acceleration. I’m running ethanol free regular unleaded, 9.5:1 compression, 389 bored .030 over, M 20 Muncie, 3.55 Safety Track, and around 8-10 BTDC timing. HEI distributor. Spark plugs are gapped at .040. Water temp was right around 190-200. What do I do to remedy this situation? Premium unleaded? Racing fuel mixed into premium unleaded? Timing? Less gap on plugs? I’m open to any and all suggestions from the Pontiac experts here. TIA.


Your timing is fine, assuming that it's accurate. Did you mod the dizzy with weights or springs? Vacuum advance? What kind of coil do you have? If your gap is set higher than 35, then you need a coil that can jump the gap and plug wires that are meaty and fresh... Spark will take the path of least resistance.

What kind of plug looms do you have?

I would start by verifying the health of your plug wires and vac advance and drive the car. If it persists, set the timing back to 6 degrees BTDC and see if it stops. If so then you know for sure that it's a timing issue and not something else. 

If you run 93 e10 in your car, you should be fine. It's all I ever use and I have 670 heads.


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## armyadarkness (Dec 7, 2020)

The only thing that high octane will do is to help you avoid knock on advanced timing, but 8-10 degrees should not be an issue. Is this a new dizzy?


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## AV68 (Aug 18, 2021)

O.P. is running an HEI distributor so .040 is not a big gap by any means, try 91/93 octane gas to start


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## armyadarkness (Dec 7, 2020)

AV68 said:


> O.P. is running an HEI distributor so .040 is not a big gap by any means, try 91/93 octane gas to start


Agreed, but my concern is that if he were to be using OEM style wires or crummy looms, that the spark would/ could jump to ground, before reaching the plug.

On my Davis DUI, I had the gap set at 45, and with MSD wires with less than 1000 miles on them, the spark was jumping to the wire looms. So, just trying to cover all of the bases.


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## SLSTEVE (Dec 8, 2020)

armyadarkness said:


> Agreed, but my concern is that if he were to be using OEM style wires or crummy looms, that the spark would/ could jump to ground, before reaching the plug.
> 
> On my Davis DUI, I had the gap set at 45, and with MSD wires with less than 1000 miles on them, the spark was jumping to the wire looms. So, just trying to cover all of the bases.


Jimmy,
I used the MSD wire kit with the 8.5 or 9 mm wires and cut them all to length. Using OE wire looms. How do you tell if the spark is jumping? Fire it up in the dark?


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## AV68 (Aug 18, 2021)

did that test once when i was kid, changed the cap and rotor and the car ran worse opened the hood at night and the light show at the distributor explained everything


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## armyadarkness (Dec 7, 2020)

SLSTEVE said:


> Jimmy,
> I used the MSD wire kit with the 8.5 or 9 mm wires and cut them all to length. Using OE wire looms. How do you tell if the spark is jumping? Fire it up in the dark?


Yeah... when I did my cam recently, I was revving it up and my buddy says, you're arcing under there. Glad he was watching, because my performance had been terrible, and with new MSD wires, who would suspect?

But MSD does give an ohm rating, so you can test them urself. Might not be the issue, but it's good to do so that you can eliminate any suspicions.

*Coils and Spark Plug Wires Trouble Shooting*

There are not a lot of things that you can check to confirm that the coil is operating. Also, due to the number of different coil variations available, it makes it difficult for specific specifications.

If you have an ohm meter, you can check the primary and secondary resistance of the coil. First, be sure to have the ignition turned off and the coil disconnected from the ignition. The primary resistance is measured with the probes on the positive and the negative terminals of the coil. This value will vary between coils, but a rule of thumb on MSD’s coils would be between .03 - .7 ohms.

Secondary resistance is measured between the coil + terminal and the secondary tower (where the spark plug connects). This reading also will vary between the make of the coil, but it should be somewhere between 200 – 14,000 ohms! Quite a range. The important thing to look for is that there is not an open or a short in the windings.

Spark plug wires can easily be visually inspected for tears, burns or black spots that may pinpoint a voltage leak. Close inspection of the boots and terminals should also be checked. You can also measure the resistance of each spark plug wire, but like coils, values may vary between wire brands. MSD’s 8.5mm Super Conductor Wire will measure about 50-ohms per foot of wire while the Street Fire brand wires have about 500 ohms per foot. As an example, if you have a 4-feet long Super Conductor wire, the resistance should be about 200 ohms. The important thing to check is that the resistance values of your wires should be consistent throughout the entire set. Lengths will vary the values, but they should all be within a similar value.


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## armyadarkness (Dec 7, 2020)

AV68 said:


> did that test once when i was kid, changed the cap and rotor and the car ran worse opened the hood at night and the light show at the distributor explained everything


Im lucky that I did mine in a dark garage and had a buddy watching.


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## armyadarkness (Dec 7, 2020)

SLSTEVE said:


> Jimmy,
> I used the MSD wire kit with the 8.5 or 9 mm wires and cut them all to length. Using OE wire looms. How do you tell if the spark is jumping? Fire it up in the dark?


You shouldnt have knock, though. 93 octane and 10 degrees is fine... Try 6 degrees and see what happens.


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## geeteeohguy (Feb 2, 2008)

I would run 93 octane or higher, set the base timing at 6 BTDC (where it was when the car was new), and run .035 gap plugs. After that, if it still detonates, look into richening up the mixture or curbing the total spark advance or both. Rule of thumb on octane is to remove the decimal point on the CR and that is your required octane. A 9.5 engine will want 95 octane fuel. My 9.3 400 pings on 91 octane on a hot day because I can't get 93 at the pump. Too much compression. My 11:1 '65 389 runs on race gas only.


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## Tom Tom (11 mo ago)

geeteeohguy said:


> I would run 93 octane or higher, set the base timing at 6 BTDC (where it was when the car was new), and run .035 gap plugs. After that, if it still detonates, look into richening up the mixture or curbing the total spark advance or both. Rule of thumb on octane is to remove the decimal point on the CR and that is your required octane. A 9.5 engine will want 95 octane fuel. My 9.3 400 pings on 91 octane on a hot day because I can't get 93 at the pump. Too much compression. My 11:1 '65 389 runs on race gas only.


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## Tom Tom (11 mo ago)

I had the same issue on my 66 with terrible gas mileage. Come to find out my advance wasn’t working properly. I installed the MSD distributor that Army told me about because I want to go tri power and now mine runs perfect no more chatter under acceleration.


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## Tom Tom (11 mo ago)

Tom Tom said:


> I had the same issue on my 66 with terrible gas mileage. Come to find out my advance wasn’t working properly. I installed the MSD distributor that Army told me about because I want to go tri power and now mine runs perfect no more chatter under acceleration.


Sorry Summit distributor. To many brews last night.


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## BearGFR (Aug 25, 2008)

> I’m running ethanol free regular unleaded


Which is probably the root cause. Run the highest octane pump gas you can find, and see what happens. If your tank isn't already close to empty, it may take several fillups to overcome the dilution effect of the low octane fuel that's already there. I.e. 5 gallons of 87 + 5 gallons of 93 gives you 10 gallons of 90. 

Bear


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## SLSTEVE (Dec 8, 2020)

BearGFR said:


> Which is probably the root cause. Run the highest octane pump gas you can find, and see what happens. If your tank isn't already close to empty, it may take several fillups to overcome the dilution effect of the low octane fuel that's already there. I.e. 5 gallons of 87 + 5 gallons of 93 gives you 10 gallons of 90.
> 
> Bear


Thanks Bear. I’m going to check my timing first. And then give it a try. If it’s still pinging I’ll get to the closest gas station and fill up with premium and see what happens. I’m right at 1/4 tank now. Have been filling it up from a 3 gallon gas can prior to this. What a PITA! Filling it up will be a pain in the wallet though.


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## BearGFR (Aug 25, 2008)

So you have a '65 389, which nearly certainly has closed chamber heads unless you or a previous owner has made changes. For optimum performance those heads tend to "like" at least 36 degrees of total timing (by that I mean mechanical/centrifugal + initial -- vacuum advance disconnected, hose plugged) and can sometimes be as much as 40+. The factory 6 initial assumes a factory distributor that hasn't been 'messed with' in any way and will probably have "about" 25-30 degrees mechanical/centrifugal "in it". 

Addressing a detonation/pinging problem by fiddling with the timing is at best, a bandaid - you may be able to avoid the condition by taking timing "out of it", but you'll also murder performance when you do.

Do whatever you think is best, but if it were me, the FIRST thing I'd do would be to run good fuel (which may be all it needs), then proceed from there to find out exactly how much mechanical timing is "in" the distributor and how much total the engine is actually seeing right now (you'll need a "dial back" timing light and someone to help you while you use it by advancing RPM until all the advance is in - again vacuum line disconnected and plugged). I'd start at 35-36 degrees total (closed chamber heads). Then I'd try 'slowing down' the advance curve by using heavier springs and/or lighter weights, without messing with the total. Taking total advance "out of it" would be my last resort.

Bear


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## SLSTEVE (Dec 8, 2020)

BearGFR said:


> So you have a '65 389, which nearly certainly has closed chamber heads unless you or a previous owner has made changes. For optimum performance those heads tend to "like" at least 36 degrees of total timing (by that I mean mechanical/centrifugal + initial -- vacuum advance disconnected, hose plugged) and can sometimes be as much as 40+. The factory 6 initial assumes a factory distributor that hasn't been 'messed with' in any way and will probably have "about" 25-30 degrees mechanical/centrifugal "in it".
> 
> Addressing a detonation/pinging problem by fiddling with the timing is at best, a bandaid - you may be able to avoid the condition by taking timing "out of it", but you'll also murder performance when you do.
> 
> ...


Thanks Bear, as always, great advice.


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## tallrandyb (Jun 12, 2021)

BearGFR said:


> So you have a '65 389, which nearly certainly has closed chamber heads unless you or a previous owner has made changes. For optimum performance those heads tend to "like" at least 36 degrees of total timing (by that I mean mechanical/centrifugal + initial -- vacuum advance disconnected, hose plugged) and can sometimes be as much as 40+. The factory 6 initial assumes a factory distributor that hasn't been 'messed with' in any way and will probably have "about" 25-30 degrees mechanical/centrifugal "in it".
> 
> Addressing a detonation/pinging problem by fiddling with the timing is at best, a bandaid - you may be able to avoid the condition by taking timing "out of it", but you'll also murder performance when you do.
> 
> ...


Agreed! I’m running 15 degrees base with full mechanical and vacuum advance on 110 octane leaded on my 65 with a 66 389 block. No pinging at all, and performance drops way off reducing to 10 degrees base. I’m looking around for the highest ethanol free around here, then I’ll drop base timing accordingly. Good cooling keeps it around 180-185 in the heat with no A/C and around 200-205 with A/C cranking.


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## geeteeohguy (Feb 2, 2008)

It's amazing how strong the old high compression 389's run with real fuel that has enough octane. Almost like they were designed for it! LOL...


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## tallrandyb (Jun 12, 2021)

No doubt, no comparison adding timing back in. I need to get it on a dyno to see the A/F and be more precise on the base advance.


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## armyadarkness (Dec 7, 2020)

Last night I finally got out to work on my car... It's been running so good that all I want to do is drive!!! 

After the new cam went in on Thanksgiving... I through the dizzy in and just turned it until it sounded nice. I drove it around a week and then gave it a little more, and it liked it.

I have the original 400 with 670 heads and I run 93 octane. I use an MSD Pro Billet, with a vac can that's all in at 6hg, and a Lars timing corrector, to limit it to 10 degrees of advance. 

I had spent several months making the perfect timing curve for the old cam and jetting, so Ive known since Thanksgiving that I needed to make a new one... but with the car running so perfectly, there was no rush.

Anywho... last night I hooked up a timing light to record my settings, for future reference. The base timing was at close to 20 degrees, and the can was adding another 10 degrees! Total was at least 38 degrees!

Would I ever tell anyone to set their car this way? No, but it goes to show that as many of the guys around here say, you need the seat-of-the-pants in order to conclude business. I have heard that 670's liked more timing, but also that they didnt like lower octane... 

One thing is clear, on the South Jersey Coast, in June of 2022, a 1967 Pontiac 400 with 670 heads, headers, free flowing exhaust, MSD wires, an Edelbrock 800 carb, a Mallory Hyfire, and a full roller ram air cam, loves almost 20 degrees of base timing!

And it's in the 90's here, and it'll idle at 140 degrees, indefinitely. It cruises at 160 all day, and lord knows that it's not due to my conservative driving.


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## geeteeohguy (Feb 2, 2008)

The cool engine temps are a huge help, as long as the more humid coastal environment. Out here in arid dry and hot CA, I could never get my '67 to run without detonation after they got rid of the 94 octane pure gas decades ago. Even with water injection and retarded timing, it was a no-go out here. That's why I installed lower compression heads. A good friend has a '67 with the original engine and 670's and he runs 100 octane leaded and a stock timing curve. Car will not run on our 91 octane pump gas with 10% ethanol.


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