What does detonation sound like?

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dartfreak75

dartfreak75

Restore it, Dont part it!
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I got my trans pan back on today (another thread coming on that) and was driving the car around to check it out and under a light load going up hill accelerating barely had any throttle in it just enough to accelerate up the hill running appropriately 2k rpm around 30 mph I heard a pretty load popping sounded to me like it was back firing out the exhaust it did it maybe 3 or 4 times and I immediately let out and it stopped? I know im pushing the limits on pump gas with my compression. Do you think this is just a carb issue and it was backfiring ? I have never heard detonation to know what it sounds like. Thanks
 
dartfreak75 said:
I got my trans pan back on today (another thread coming on that) and was driving the car around to check it out and under a light load going up hill accelerating barely had any throttle in it just enough to accelerate up the hill running appropriately 2k rpm around 30 mph I heard a pretty load popping sounded to me like it was back firing out the exhaust it did it maybe 3 or 4 times and I immediately let out and it stopped? I know im pushing the limits on pump gas with my compression. Do you think this is just a carb issue and it was backfiring ? I have never heard detonation to know what it sounds like. Thanks
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From my experience, it sounds like pea gravel rattling around in a can.
 
To me it sounds like a low tone tick or light rattle, usually shows up at low RPMs under load.
 
Pinging sound. If it is pinging then timing is slightly too far advanced. Try retarding the timing and see if the detonation sound/pinging sound goes away.
 
I'd be wary of it if it does it under acceleration and stops when you let off. That sure sounds like what it's doing. It doesn't always sound the same on every engine, so be careful.
 
Enjoying it again said:
Pinging sound. If it is pinging then timing is slightly too far advanced. Try retarding the timing and see if the detonation sound/pinging sound goes away.
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At idle, I run my automatic 440 at 5 degrees BTDC. The 1969 service manual states 7.5 degrees BTDC, but the engine starts to knock going up a hill with modern gas. I used to use 91 octane, but now I mix 91 and 100 to get 93 octane.
 
Ironracer said:
Kinda sounds like timing, or tune. But what do I know? There is Way more experience than mine here
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It very well could be timing related i had been tuning on my timing before I changed the trans gasket. It was running like crap too. Usually when I punch it at a roll it will smoke the tires today it just bogged down and loaded up. After I got up in the rpm range it ran great but its a dud down low. Timing is set at 16 intial 36 total
 
RustyRatRod said:
I'd be wary of it if it does it under acceleration and stops when you let off. That sure sounds like what it's doing. It doesn't always sound the same on every engine, so be careful.
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Thanks Rob I was hoping to get your opinion. It got dark on me so I had to quit im gonna work on it some more. Looking like I'm gonna end up dropping the trans pan again its still leaking like a slave :BangHead:
 
dartfreak75 said:
Retard? I thought for detonation you advanced the timing?
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No sir. Retard. Or run a higher octane. You can try a step or two or three colder plug. Anything you can do to cool the incoming air charge will also help. Thermoquads are known for being notoriously lean unless they've been modified. Fattening it up may help some. I would be trying a THICK insulator gasket WITH heat shield under the carburetor. Blocking off the exhaust cross over in the intake. Install a high flow 160 degree thermostat. What distributor do you have? What's the initial timing? What's total and when does it STOP advancing? You may need to limit the total mechanical advance. Might be coming in too soon. Lots of things to try.
 
RustyRatRod said:
No sir. Retard. Or run a higher octane. You can try a step or two or three colder plug. Anything you can do to cool the incoming air charge will also help. Thermoquads are known for being notoriously lean unless they've been modified. Fattening it up may help some. I would be trying a THICK insulator gasket WITH heat shield under the carburetor. Blocking off the exhaust cross over in the intake. Install a high flow 160 degree thermostat. What distributor do you have? What's the initial timing? What's total and when does it STOP advancing? You may need to limit the total mechanical advance. Might be coming in too soon. Lots of things to try.
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Right now im running 16 intial 36 total the all in around 2200 iirc maybe it was 2500 I got it wrote down somewhere. I am running plug that is one step colder than stock right now
 
dartfreak75 said:
Right now im running 16 intial 36 total the all in around 2200 iirc maybe it was 2500 I got it wrote down somewhere. I am running plug that is one step colder than stock right now
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But WHERE does it STOP advancing? It's all IN by 2200-2500.....whatever but is that as FAR as it goes? If you've done nothing to limit it, it probably advances more.

All that said, 16 initial doesn't sound like too much.......unless maybe you're running 87 octane.
 
RustyRatRod said:
But WHERE does it STOP advancing? It's all IN by 2200-2500.....whatever but is that as FAR as it goes? If you've done nothing to limit it, it probably advances more.

All that said, 16 initial doesn't sound like too much.......unless maybe you're running 87 octane.
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The distributor is locked at 36 mechanical it has 20 degrees mechanical and its done. Im running 91 non ethanol atm
 
dartfreak75 said:
The distributor is locked at 36 mechanical it has 20 degrees mechanical and its done. Im running 91 non ethanol atm
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About what RPM are you hearing "whatever" it is?
 
dartfreak75 said:
I only heard it the one time it was around 2k
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I would verify it is detonation first. In other words, if you can make it duplicate under the same conditions every time, I would say it is.
 
RustyRatRod said:
I would verify it is detonation first. In other words, if you can make it duplicate under the same conditions every time, I would say it is.
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Ok thanks im hoping it's not and just carb related. I have played with the carb and timing since the last time I drove it. I never heard it before. So let's assume its not detonation and it's backfiring. Then what do I need to lean it more? Backfiring is a sign its too rich correct? Like I said before its a dog off idle. If I punch it from a dead stop or idle it just bogs and backfires once I get the rpms up it runs pretty good. It will pin me to the seat over 2500
 
RustyRatRod said:
But WHERE does it STOP advancing? It's all IN by 2200-2500.....whatever but is that as FAR as it goes? If you've done nothing to limit it, it probably advances more.

All that said, 16 initial doesn't sound like too much.......unless maybe you're running 87 octane.
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Rob is dead on point right there Sir! He saved my engine.... still hoping no damage was done
 
dartfreak75 said:
Ok thanks im hoping it's not and just carb related. I have played with the carb and timing since the last time I drove it. I never heard it before. So let's assume its not detonation and it's backfiring. Then what do I need to lean it more? Backfiring is a sign its too rich correct? Like I said before its a dog off idle. If I punch it from a dead stop or idle it just bogs and backfires once I get the rpms up it runs pretty good. It will pin me to the seat over 2500
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No. Backfiring through the pipes is always a lean condition "somehow", whether it's because of crossed wires, lean carburetor, or "whatever" it's a lean condition.
 
To me, detonation sounds like a bunch of rattle can paint cans being shaken incredibly fast. It usually happens when you lug the vehicle, like going uphill and just barely giving it some gas. When you let off it stops. A friend of mine's Dad was an old timey mechanic, and he would set timing by ear that way. Run it up till it rattles a little, then ease it back down a little at a time till it quit rattling. He used to roll his eyes at us "Boys" and our timing light....lol.
 
Again....... tuff to diagnose by reading a post. However, backfire doesn't sound like detonation. I'm starting the bombcycle at 16/36. My 360 in my Duster is about the same. I doubt your timing setting is the problem.
 
JDMopar said:
To me, detonation sounds like a bunch of rattle can paint cans being shaken incredibly fast. It usually happens when you lug the vehicle, like going uphill and just barely giving it some gas. When you let off it stops. A friend of mine's Dad was an old timey mechanic, and he would set timing by ear that way. Run it up till it rattles a little, then ease it back down a little at a time till it quit rattling. He used to roll his eyes at us "Boys" and our timing light....lol.
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That's the best description I've ever heard.
 
JDMopar said:
To me, detonation sounds like a bunch of rattle can paint cans being shaken incredibly fast. It usually happens when you lug the vehicle, like going uphill and just barely giving it some gas. When you let off it stops. A friend of mine's Dad was an old timey mechanic, and he would set timing by ear that way. Run it up till it rattles a little, then ease it back down a little at a time till it quit rattling. He used to roll his eyes at us "Boys" and our timing light....lol.
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Our auto shop instructor was the same way. He used to tell us an engine will run best when it has ALL the timing it can stand without rattling and 99 times outta 100 that wasn't what the factory recommended.
 
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