Engine knock issue

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Matt98

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Hi,
I have a 1992 that I've swapped the engine with a 305 out of an 84 camaro. I don't know everything that was done to the engine, as I got the car because it was abandoned. I do however know it has 0.030 over pistons as well as a mild cam. Also running an edelbrock 600

The issue I'm having is that if I set the ignition timing to 8 degrees the truck runs great and has loads of power. However at about 2000RPM it sounds like a bag of marbles under the hood. Running 91 octane fuel, have tried from different places. If I retard the timing to where it doesn't knock, it runs like crap, has no power/backfires etc.

I put lighter springs in the advance so it would advance at a lower RPM so I could maybe retard the total timing, which definately helped but not well enough.

I'm wondering if anyone has any input, maybe a colder spark plug? I should also add there is no EGR. At times, while it hasn't done it in a while (though I havent driven the truck all winter) it would run on sometimes after you shut it off.

Thanks.
 

Supercharged111

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I'm guessing HEI? How much timing does it idle with and how much when you rev it up? Chances are you need to restrict the total advance. This will let you run more base timing without it advancing to the moon once it seems some RPM.
 

Matt98

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I'm guessing HEI? How much timing does it idle with and how much when you rev it up? Chances are you need to restrict the total advance. This will let you run more base timing without it advancing to the moon once it seems some RPM.
Yes HEI. I'm running a moroso advance kit.

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I started with the heavy springs, though if memory recalls it still did it, maybe i'll try again. It's been a while since I played with it and I don't remember why i switched them out. Currently running the light ones and reduced my total timing. I'll get the actual numbers for it shortly @ idle, though it's set to 4 degrees right now with the vacuum advance unhooked.
 

Supercharged111

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23 degrees of mechanical advance is a bit much IMO. Really depends on how much it wants at WOT. If it only wants 30 total and you idle at 15 then 15 is all the advance you're gonna want.
 

Hipster

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A hotter cam is going to want more initial advance and about the same total around 34 degrees. Changing the springs does nothing to limit total. Oem distributors have no adjustment to limit the travel of the weights so some resort to tack welding the slots shorter, set screws roll pins etc to limit it where as some aftermarket distributors have a means to adjust the travel of the weights built in.

I usually set the initial where it runs and starts best without kicking back against a starter, check, adjust, set the total, then play with the springs.

Unless you're setting it up on a distributor machine it can take some trial and error to get it dialed in. Continuing to drive as is and pushing it through the detonation can cause damage so get it sorted
 
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cookseyb

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Did the builder advance the cam timing with a adjustable or multi key timing set. You have to allow for that in your total timing set-up if so....
 

Supercharged111

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Did the builder advance the cam timing with a adjustable or multi key timing set. You have to allow for that in your total timing set-up if so....

Not if you measure timing from the crankshaft. . .
 

Matt98

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I've done some playing around with it. I got it to run really well with the light springs and the vacuum advance disconnected. Running 31 degrees of total advance.

However it seems like it likes more timing at idle, so I need to hook that back up. I'm wondering how I should go about this, if I should just simply make a block off plate to limit the travel of the vac advance, install an adjustable vac advance or change the whole distributor to like an MSD street fire or something. This truck is a daily driver and the distributor has fairly low miles on it so I'm leaning more towards one of the first two just for price reasons.
 

Supercharged111

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I've always liked the idea of an adjustable can myself. You will want less vacuum advance that stock I imagine since base timing is elevated. What is your base and when is it all in?
 

Matt98

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I've always liked the idea of an adjustable can myself. You will want less vacuum advance that stock I imagine since base timing is elevated. What is your base and when is it all in?
Base is set to 8 degrees, total is 31 degrees ATM with the vac advance disconnected. I'm not sure exactly how much advance the vacuum advance adds but its a stock distributor. Like I said the engine sounds happy right now but If I'm sitting at about 14" of vacuum right now, if I advance the distributor I can get it close to 20".
 
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