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Old 06-29-2007, 02:16 AM   #1
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Default spark knock in a 350

hey guys, i have a really big problem with my 350 in my truck. Its a 350 bored 60 over, stock rods, and crank. It has a mild cam, intake and HEI ignition ( usually run 12-14 degrees advance)
So one day i fill it up with gas at the local stop and shop with 93 octane like usual and i went out for a drive. about 20 miles down the road i get a real bad case of spark knock. i retarded the timing 14 degrees and still got bad knock. I drained all but like 2 gallons of the tank and drove it home. I let it sit for 3 weeks and the MSD ( Multi Spark Discharge) box is shot. So i hook up the old HEI wires and run it straight HEI with no box and it starts. I put on new AC DELCO wires, with R44T plugs, new fuel filter, check out the cap and rotor and put it all back together. I have it to the point of were it does not knock anymore but i have no where near the power i used to have. Anybody have any ideas???/
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Old 06-29-2007, 02:38 AM   #2
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Did you adjust the timing back to where it should be?
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Old 06-29-2007, 08:03 AM   #3
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If he brings the timing back to 12-14 he gets plenty of pinging. With the timing low..he obviously has little power and no knock.
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Old 06-29-2007, 06:43 PM   #4
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An MSD box usually allows you to open up the gap some. Have you regapped the plugs if there not at spec anymore? Heck, I'd pull them and check them anyways.

I would also trash ALL that gas and buy fresh then check for a vacuum leak if the plugs/gap wasn't the problem..
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Old 06-29-2007, 06:50 PM   #5
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Being that this engine is bored out .060 over... That would mean to me that you have taken a totall.120 from the walls in the middle cylinders...

What is the effective Cubic Inches of the motor now being that each cylinder is .060 Over?

Did you use the original 350 heads?

And is this a Carb? Or throttle body injection?

Is this an older chevy with conventional lifters or a little newer with roller lifters and FI heads?

Flat top or dish pistons... and what is the lift of the mild cam?

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Old 06-30-2007, 03:05 AM   #6
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With it bored out it makes it a 360ci. i have on 202/160 heads off a 67 corvette. they have been all done out with stainless race polished valves and 63cc chambers. the cam is a 427/454 lift with a 308/310 duration. 110 lobe separation. it has flat tappet hydrallic lifters with roller rockers on top. in the lower end is stock valve relief pistons.
also i changed the gap of the plugs back to stock with a .45 gap. i am using R44T acdelco
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