Knocking at 2000+
 

Got my exhaust done on my 66 with a 352. Sounds awesome. But now sadly I can hear everything else lol. This noise has been around for awhile. Anything below 2000, no matter what, no load, heavy load, light acceleration, hard acceleration, or just cruising around town, I have no engine noise and it sounds great. Above 2000 I get this odd knocking. It’s hard to explain how it exactly sounds. If i am reving the engine at 2000, speed up to 2500 and back to 2000 I can hear it good. (Although it’s not terribly loud). And when I leave it at or around 2000 it’s barely if at all noticeable. My best guess what spark knock. When I retard the engine, the sound goes down, but the engine becomes a massive turd and it struggles to get going from a stop. Things I have put in is a new cam and lifters (broken in per instructions and when I took I take off again to replace intake gasket I checked them and were perfect). Also have an Edlebrock intake and a Holley 600. I’m running 87 octane and no ethanol. Talked to a buddy and told me where I can get 93 so I will try that. Anyone have thoughts? I should mention that the noise isn’t as bad cold but quickly starts making noise (no a big difference though). I also replaced the distributor with a crappy Chinese hei and I’m eventually gonna get a pertronix. But don’t have the money right now. Also thought maybe harmonic balancer, but I verified that it hasn’t slipped and I thought they made noise all the time. Thanks for any help.

If you can make it happen in the driveway, have someone rev it for you while you use an automotive stethoscope to isolate the sound.

I should also mention, when I rev it by hand, I can feel the knock through the carb

What are your base timing, mechanical advance timing (in the distributor), and do you know how much vacuum advance the can allows?

With the vacuum adv. disconnected and plugged how much timing is there all in and at what RPM?

Where is your vacuum advance plugged into on the carb?

And you can confirm this noise was there before the exhaust work?

I know for sure that it was there before exhaust work. I wasn’t even running vac advance but now I am. Plugged into port vac. I have it adjusted almost all the way out so it won’t advance as much. Initial timing is at ten or 11 now, can’t remember. Was at 8 but was a dog then. But didn’t really knock or not as bad. Not sure what full advance is. It said mech is 24. So 34 without vac advance. Not sure when it’s all in. Got the stiffest springs I could get and not as heavy weights.

If all that's correct it doesnt sound like excessive advance even at 10/11 initial. Doesnt sound to me like rod knock either. Could be a lean detonation, I'd check the carb main jetting, accelerator pump, and secondary systems to make sure they are operating correctly. Also make sure you have correct spark plugs (not too hot).

Curious what is your typical engine operating temperatures.

I also keep going back to your chinese distributor....do you have another to swap in even if its not electronic?

Lastly what Trans, tire size, and rear end ratio?

Temps have been cool around where I’m at so engine has only been around 170, 160 if I’m cruising. Today it got up to 175-180. Trans is a 3 speed manual, rear is a 3.25, and about a 30 inch tall tire.

I put 66 jets in primary. Had 65. Plugs are tan Slightly on the whiter side. Secondaries is a metering plate. It’s stock so whatever would come in a 4060 with vac secondaries.

Also should mention I doubt it’s a rod knock. Had the engine up to 5000 more than once. I’m sure I’d be on the side of the road if it was a rod.

Any accelerating bogs? May want to increase the jetting - "white" plug has me thinking its a bit lean. Should be properly tan/beige.


https://cimg4.ibsrv.net/gimg/www.for...b125c6b16e.jpg

I agree. And a rod knock would be heard at all RPMs and get louder the higher the RPM.

So my guess is it is spark knock, now just to figure out why.

No acceleration bogs what so ever. Doesn’t bog at all. I’ll get a pic of plugs. Color may have changed since I last looked at them since I changed to a 66. It was definitely not as dark as the “perfect” one in the pic.

https://cimg0.ibsrv.net/gimg/www.for...341e12504.jpeg
Looks to have darkened up better now. Looks good.

Ya my knock doesn’t get louder. Just gets faster with rpm. The new distributor I got does have some play that makes a noise, wonder if somehow it could make that noise?

Ok - also typically when changing jets (at least holley does) they suggest you jump 2 sizes at a time.

Check out this vid for main jet tuning

https://www.holley.com/blog/post/how...a_holley_carb/

Hm yeah plug looks alright. Both engine banks the same?

Well i'd try to nail in your timing numbers with a timing light and make sure the numbers you said are accurate, and see when your mechanical advance is all in.

Then assuming your timing marks are accurate you know what you're dealing with.

Trying some higher octane gas can't hurt - do you know what compression ratio you're running?

And again i'd be wary of that cheap distributor...