So, during medium to hard acceleration, or passing someone on the freeway, I hear this rattling sound coming from the engine bay. When I'm on the freeway about to pass someone it happens around 3k rpms. It sounds exactly like they way a spray paint sounds when you shake it....that little rattle, but 10x faster

Anywho, I googled the problem and people tend to say it's detonation.

My question, how do I fix it?
*retard timing?
*advance timing?
*better gas?
*any other ideas??

THANK YOU!

 

Answers in bold above, you may only need one or the other. If you have the timing where it's supposed to be, then your engine requires a higher octane for best performance. Does the engine have a higher compression ratio from factory?
If you have your timing set too far advanced, then retard it.
What you're getting is octane "knock" (pinging), which sounds like marbles in the cylinders. Modern engines have a knock sensor that automatically retards the timing to take care of that.
Your fuel might be burning too fast from being a low octane (low octane burns faster), or from the timing being too advanced. What's happening is the explosion inside the cylinder is occurring too soon and it's trying to push the pistons back down before they reach TDC. The condition that is causing that knocking isn't good for the engine.

 

That's a great explanation, thank you! The engine should be stock compression...the only mods to it are: edelbrock intake and carb. I just got the car back from smog so it should be at 8* BTDC. I always get the 89 octane too. So you're saying get better gas huh? Crap. I think 92 octane is $3.50 or so per gallon.

Well, I'll check timing this weekend and put some 92 in and see if there's a difference. Thanks for the help!

 

Check the spark timing, just because it passed smog inspection does not mean the spark timing is correct. If you are using the timing mark on the front damper, and the damper is still the original, there is a good chance that the outside ring has slipped, thus making the timing mark useless. Also make sure you have the proper spark plugs, if heat range is too hot, it will also cause pinging. You can also try a long high speed trip (100+ miles) to burn out carbon deposits on exhaust valves and combustion chamber

 

Sorry it took me a while to say thanks...so, Thanks! I busted my hamstring while running this past weekend so I've been in bed icing. Anyways, I'll definitely check the timing ASAP. The original damper is still there so that's what I use to check timing. How would I know if it 'slipped'?

A long high speed trip, huh? lol. I'm not to sure about that. Cali highway patrol wouldn't like that too much

 

If you think the harmonic damper might be off whack, you'll need to check the relationship between the crank key notch and timing mark. There are different configurations, I'd have to look up (or you could too) which one you should have. You can sometimes tell if the damper is bad just by looking at it. If the inner and outer hub look like a misfit, or if the rubber between them is pushing out, it might be spun.
Since you have a carbureted engine (and no oxy sensors), look up water injection and the things it can help your engine do. If you like to play with different things on the car, that may interest you.

 

Well, I don't think its off..Pete thought it might. I just checked the timing and it's at 8* and the balancer in not wobbling. I can try to get a better look at the balancer next week and report back. I did, however, put some 91 in so I hope it will run better

 

I am surprised nobody mentioned trying to Seafoam the motor, you can buy some Seafoam at your local auto parts store, sometimes a motor will collect a lot of carbon on the top of the pistons and or on the cylinder head, this actually raises the Compression ratio, which in turn requires less timing, better fuel or both.

By doing the Seafom into the vacuum line it will break loose the carbon deposits and send them out your tailpipe, however be prepared for a LOT fo smoke, you neighbors will be calling the fire dept due to giant plumes of white smoke coming from your car. Maybe just let them know in advance to avoid this scenario.

My motorhome did the same thing as your car and in my case it was tons of carbon deposits, after the seafoam it does not detonate anymore at all.

Make sure your timing is spot on ad then try seafoam to clean the engine to be sure carbon is not the gremlin causing your problem..

 

Sorry to bring up my old topic again. But here's an update!!
I just put on a Procomp distributor (Don't hate, I know it isn't the best!) But I didn't hear any detonation past 3k rpms However... I just replaced my stock air cleaner with a K&N 14" filter with a XStream top. And now it sounds like it's backfiring through the carb during acceleration!!!! PLUS, my car bogs my I step on it....almost like the carb floods...I just don't get it!! I thought more air would be better??? Any explanation on why my stock air filter has better performance than a K&N?

 

I actually heard of that and will be planing to buy some soon. Thanks Speedie