Question about what detonation sounds like. At idle I hear a lot of pinging noise but when I put my ear up close to the noise it's he headers making that noise. I read that detonation will sound like a pinging noise or bacon frying in a pan. It sort of sounds like that. Is this detonation or is it just the manifolds/headers making the noise? It's been doing this since I've started the freshly built engine up and I have over 3,000 miles on it now. I'm thinking it's just the headers making the noise. Thanks!

Most detonation is heard when the engine is in a load whether it be part throttle or full throttle.  Detonation typically sounds like loose nuts being rattled around within the engine.

Lorena, Texas (South of Waco)

Okay, would it affect performance any? Would it be a noticeable difference?

And would it be a constant rattle noise? Or just here and there?

It is typically just here and there, rather than a constant noise.  However, if the engine is under load for a long period of time, like when climbing a big hill, it could seem constant.
Detonation will affect performance.  At the very best, power is reduced because ignition takes place sooner than it should.  However, in gasoline engines, it typically leads to engine failure if it is not addressed.



Lawrenceville, GA

Okay I think it's just my headers making the noise. Cause if I put my ear up close to the header I can hear the pinging noise and it does it on both sides. This also while it's idling. I'm also not having any performance issues at all. So the engine would shut off if it were to detonate?

The only reason I was curious about it detonating is cause yesterday when I shut it off the engine dieseled. And I read that detonating would make a pinging noise. I have to run an octane booster in this engine otherwise it'll diesel. The engine dieseled yesterday after I shut it off and I had just filled it up and put the booster in. That's why I was confused about why it dieseled, I'm guessing it just had a little bit of a bad mix maybe? Cause I've driven twice since then and it hadn't done it. This might be a dumb question but if an engine diesels that doesn't mean it's detonating right?

Thanks for all the advice!

The engine does not shut off when detonation occurs.  It will detonate until it destroys itself, at which point it does shut off, for good.

Dieseling is detonation.  You need to fix that.  It could be as simple as a tuning issue.  It can also be a mechanical issue like too much compression, which is a more involved and expensive fix.  In your oil pressure drop thread, you stated that you have 11:1 compression.  This is usually far too much for pump gas and can very likely be the reason.

The only way you will achieve 11:1 with a 314ci Y Block and iron heads is with domed pistons, which is sort of good news, as you will only have to mill the domes to reduce compression and then have everything balanced again.  It should only be machining required, rather than new parts.

If you have not spent much time tuning, then you also need to do that.  Spark plugs which are too hot can also cause detonation.  Sharp edges can cause it; if cylinders or combustion chambers are not chamfered or beveled  after milling, it can be a source of hot spots.


Lawrenceville, GA

Well let me get your opinion about this, when I first got the engine running it started dieseling. So I started using a Lucas Oil Octane Booster, the diesling stopped, I've put over 3,000 miles on the car. The only time it's ever dieseled on me is when the fuel mixture is off or sometimes if I'm really low on gas but hardly ever. The carburetors (3X2 Fenton Intake, 2110's Holleys) are professionally built, specifically to my set up. Timing is correct, havent checked it in awhile but probably will again. If it was detonating since day one it probably would've already done the damage and hurt the car by now right? Do you think continueing to use the octane booster is the solution? It's been running fine and doesn't deisel when I run the booster

Re octane booster, there are a couple things I would call problems about using it.  First, read the bottle.  The front always has something flashy like "Increases octane 10 points!"  Read the back, and what you will see is that each of their "points" is a fraction of a point you see at the pump.  For this hypothetical, lets say 10 of the octane booster points is equal to 1 point of the number you see at the pump.  So assuming that 93 octane is premium in your area, the octane booster makes it 94, rather than the 103 you thought it was if you did not read the bottle.
Now the problems.  If that 1 point in octane is the difference between detonating and not, then you are on the ragged edge of what street gas can support.  If you ever need gas at a station that has 92 octane, then you will be in trouble.  A second problem is a reliance on octane booster.  What if for some reason none is available, or all that is available is not as good?  How about the increased cost of enjoying the vehicle?

RE the  carburetors, have you checked that they are jetted correctly?  A pro builder who knows what he is doing and has all pertinent information about the engine absolutely should be able to get them in the ball park.  But only once they are on the engine can it be determined if they are right or still need fine tuning.

RE timing, what is the initial timing, how much mechanical advance does it have and at which rpm does it get full mechanical advance?


Lawrenceville, GA

I'll never claim to be an expert, but contrary to popular belief most high performance parts are not ready to go out of the box. Domed Pistons are the worst. Guys and shops just don't seem to want to touch them. All sharp corners, edges, etc must be smoothed out. The edge around your cylinder head chamber also especially after a slight milling. I'll always knock it down with a die grinder and follow up with emory. The top of the bore too.
You don't say if your using an automatic trans and if you are shut off the engine in gear. DON'T let it diesel at all. Back in the day if I had an engine that did it I immediately turned it back on. You can always kill it with the clutch with a standard trans but that's no good either. Right now it sound like you have some hot spots making like "glow-plugs".
I would also look to the center carb as lean at idle. Jetting usually won't have much to do with that. 11-1 is tough on the street without aluminum heads or a computor controlled ignition system. As a thought some racing gas around doesn't hurt. I can buy Sonoco from our local circle track supplier in 5gallon cans and 1/2 gallon of leaded 112 octane can work wonders. Sure makes my old Harley come alive. . . . Good luck.

56 Vic, B'Ville 200 MPH Club Member, So Cal.