Chevy 350 knocking under mild-hard acceleration

[Johanes ivan]

So I’ve got this 1970 Monte Carlo and just had the engine rebuilt, nothing crazy just stock rebuilt bored .30 over. After the break in period I noticed during medium-hard acceleration a knocking sound. Had the timing adjusted, new mad HEI distributor, plug wires, new Holley 650 cfm, but still couldn’t figure out why it knocks. My next move is putting an exhaust system on since right now it has a pair of glasspacks bolted right after the long tube headers. Please check out the video attached and all inputs will be highly appreciated. https://youtu.be/Cc0ZM4tzUyY Sorry I don’t have a computer so I could only paste the link here

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[Billy]

How confident are you in that rebuild? That sounds to me like inherent rod bearing noise more than spark knock. Mufflers might make it easier to narrow down.

To make sure you’re not getting detonation due to a too-lean mixture, you could tune the carb slightly richer at open throttle. Maybe change your PVCRs, I’ve never tuned a Holley. This website will help with that, as well as providing info on an AFR monitor you can install to help get your mixtures just right.
http://www.bob2000.com/carb.htm

[Mike]

I’ve watched and listened a few times, and I don’t hear what you describe. Sorry.

What puzzles me is the peculiar movement of your tach needle. You punch the gas and, instead of climbing in a smooth manner, the tach needle instantly jumps up 1000 rpm, without a corresponding increase in road speed. Seems weird to me, like the needle is being flicked around by an electric on-off switch.

[Johanes ivan]

Well I pulled the engine and took it to a machine shop, they rebuilt it to stock specs as an original 1970 Monte Carlo, with the receipt and everything. My friends also said it’s not detonation because it would sound different. And wouldn’t rod bearings knock even on idle? The knocking sound only occurs in gear and not in neutral or idle. I do appreciate your inputs and soon I should have saved enough money for an exhaust system haha

[Johanes ivan]

It’s a somewhat faint knocking sound in the background. Sounds pretty soft on the video, but I can definitely head it while driving. But if I’m not mistaken it’s the 2200 stall converter that lets the engine rev a little before it actually moves the car. Something along the line haha, but the tachometer is perfectly fine

[James P Grosso]

I could not hear much in the video? Almost sounds like a header gasket leak to me?

[Billy]

[quote=”451Mopar” post=186594]I could not hear much in the video? Almost sounds like a header gasket leak to me?[/quote]
I too was leaning toward an exhaust leak, but the OP said it happens under load.
To verify, does it happen when revving in neutral/park?

[Author]

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