Spark knocking, pinging, detonating

[gwandro]

I’m still fighting spark knocking as before on my k10 that’s got a built sbc 350.
I think it’s been the cause of it blowing head gaskets so I need to figure it out.
When I had the heads off I realized the spark plugs were not long enough so I changed them to thread down more. This fixed all my spark knock and hesitation at top end all while running on 87. Not too much longer later a keeper failed so I had to pull heads again.
I put different head gaskets on it that are .002 thicker so if anything that should better it.
After putting it back together it now wants to spark knock again. Tried all sorts of different timing and wont take it out. The carb was never messed with. I just don’t know why the spark plugs fixed it before and now back the same as it was with still the same spark plugs

 

[jcperformance]

Man, that’s a frustrating cycle with the K10. Since the longer plugs fixed it once but aren't working now, you might have developed a hot spot or heavy carbon buildup on the pistons from the previous knocking and head gasket issues. Even with those 0.002 thicker gaskets, a "built" 350 is usually asking for a lot on 87 octane, so you might just be hitting the limit of what that fuel can handle regardless of the plug reach.


Since you didn't touch the carb, double-check for a vacuum leak around the intake manifold from the recent teardown, as a lean condition will make that spark knock way worse. If your timing is already dialed back and it still pings, try a tank of 91 or 93 just to see if it goes away instantly. If it does, your compression ratio is simply too high for the cheap stuff.

 

[PrairieDrifter]

I run afr gauges on all my carb stuff now.

All of my out of the box carbs have ran pretty lean even on a stock wore out 350. The Holley was the best but still a little lean.

What do the plugs look like? White? I'm betting this is a lean carb issue.

What plugs are you running? I run ac delco r45's

 

[Rickf]

How "built" is it? Were the heads cc'd? Domed pistons? Cam specs? A little more info is needed.
Try 93 octane and see what happens.

 

[fast 99]

Check compression

lots of causes and solutions

as Rickf said a little more info would help

 

[gwandro]

I run afr gauges on all my carb stuff now.

All of my out of the box carbs have ran pretty lean even on a stock wore out 350. The Holley was the best but still a little lean.

What do the plugs look like? White? I'm betting this is a lean carb issue.

What plugs are you running? I run ac delco r45's

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[gwandro]

I run afr gauges on all my carb stuff now.

All of my out of the box carbs have ran pretty lean even on a stock wore out 350. The Holley was the best but still a little lean.

What do the plugs look like? White? I'm betting this is a lean carb issue.

What plugs are you running? I run ac delco r45's

They don’t seem too bad I’m going to try 93 maybe turn fuel up a little

 

[gwandro]

I run afr gauges on all my carb stuff now.

All of my out of the box carbs have ran pretty lean even on a stock wore out 350. The Holley was the best but still a little lean.

What do the plugs look like? White? I'm betting this is a lean carb issue.

What plugs are you running? I run ac delco r45's

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[PrairieDrifter]

They don’t seem too bad I’m going to try 93 maybe turn fuel up a little

That's definitely on the lean side.

What carb?

 

[Ricko1966]

Are you running 3/4 reach plugs? What heads are you running? If they are vortecs what heat range are you running,and do you have a bypass on the manifold or have you drilled a thermostat for bypass. Temps at the head will be too high without a bypass.

 

[gwandro]

That's definitely on the lean side.

What carb?

Edelbrock 650

 

[jh86]

Front 2 bolts on my qjet used to loosen up every 3000 miles and cause enough vacuum leak to detonate badly. Fixing vacuum leak stopped it every time.

 

[gwandro]

Are you running 3/4 reach plugs? What heads are you running? If they are vortecs what heat range are you running,and do you have a bypass on the manifold or have you a thermostat for bypass. Temps at the head will be too high without a bypass.

I have NGK bkr7e they are 3/4 reach and heat range is 7. They are pro comp aluminum heads. What do you mean by a bypass?

 

[xm20k]

Probably too lean at the carb. Are the idle air screws set around 1.25-1.75 turns out? What hole in the arm is the accelerator pump shot set on?

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[Ricko1966]

I have NGK bkr7e they are 3/4 reach and heat range is 7. They are pro comp aluminum heads. What do you mean by a bypass?

A bypass allows water to flow through the heads and intake while the thermostat is closed. Most,not all, SBC have a passage between the water pump and block to allow water to keep moving,even with the thermostat closed. Vortec blocks do not have the bypass. Some water pumps don't have the bypass,truck blocks used to have the bypass blocked and ran a bypass from the water pump to intake. Some hot rodders and racers used to block the factory bypass because they got better cooling and more consistent temps running a different bypass. Also not using the correct head gaskets can end up blocking the bypass. No bypass and the temps get goofy at the heads. Try running with no thermostat or a thermostat with 3 x 3/16ths hole drilled in it. If that cures the problem we'll dive deeper as to why. Also are you sure the intake is sealed good,too lean causes detonation. Plug the valve covers and pcv. Put a vacuum gauge on the dipstick tube. If you are pulling vacuum there,the manifold is sucking air on the bottom ,which will cause lean.