Someone told me that just because you dont hear it, doesnt mean detonation isnt happening and that I shouldnt just tune it by ear like that. Any truth to this? If so, how can we know for sure if it is detonatin or not? so we can get the max advance without damage.
With a stock exhaust through the mufflers, you will always be able to hear it. With a loud exhaust, maybe not. If you can't hear it, it isn't heavy detonation, the kind that does damage. In the Buick chassis manual, they state that a certain amount of light ping is normal when operating a manual transmission, or automatic in high gear at low speeds. I don't like to hear any if I can help it. Whenever I race my car, I always add some Race Gas to my tank just as insurance against detonation I may not hear at wide open throttle.
NO,,,,,I have read more than a couple times. Detonation, what you can hear is only 10% of the problem, there is 90% more going on, and killing your engine, that you do not hear. Take this from someone who learned the hard way. I burned the top out of two pistons in the new 454 crate engine that was in a crew cab 1 ton truck I used to tow with. The engine was in the truck when I bought it, was a big reason I did, hey new engine, good. But they had just grabbed a distributor from a car (likely) and stuck it in there. It had too much advance, I couldn't hear the detonation, I burned it up. Had to rebuild it. A costley way to learn about detonation. You need to "total" time your car and forget about initial setting, and forget about regular gas. I never, never use anything but the highest octane in any old car that I own, no matter what I "might be able to get away with" or what my car was designed to run on. Old cars need all the help we can give them, and high octane is just cheap help. I even use the highest octane I can buy in all my power lawn/maintainence tools, a l l of them a l l the time, and sta-bill all the time, every time. I didn't dream that up, when I bought some nice expensive new equipment I got that from the owner of the shop who sold them to me. I am not a racer, and a lot of people here know a lot of stuff I don't and never will. But you don't own a race car. You need to figure out how to make it live so you can enjoy it. Trying to squeeze every ounce of power from it, and on regular fuel, is not a recipe for longevity.
I can hear it in my engine. If I can't hear it, I don't worry about it. If you don't hear it, how can you ever be sure it isn't there. It takes heavy detonation to cause real damage to pistons. Of course that is relative to what type of pistons you have. Cast pistons are more likely to be damaged than forged pistons, and Hyperuetectic have been known to shatter. Heavy detonation at wide open throttle will definitely hurt the engine especially in a drag racing scenario when you are wide open for a relatively long time relative to street operation. Even if your timing is correct, detonation can be caused by other things, lean mixture, wrong heat range plugs, local hot spots, carbon deposits, ect. Again, if you can't hear it, how do you ever know it isn't there? The only other way to be sure is to install a knock sensor like in more modern engines. I could never get my GS to run on pump gas when it had iron heads. I always had to mix in some race gas. That was with 9.4:1 SCR. Now I have 10.4:1 and aluminum heads. It never detonates on the street. Like I said before, I add race gas at the track for the extra insurance.
I've run my 12.5-1 455 on the street with premium pump gas when I run out of straight 100LL. I drive it like a regular car and its fine. Ive detonated that engine on occasion. When I hear it, I just back off. On the last tear down, there was no evidence of any detonation damage. The pistons are probably 15-20 years old at this point
And Jason has a 3" exhaust which is fairly loud, and he can hear it when it detonates. My 70 with iron heads would detonate on pump gas at anything over 3/4 throttle. 2 gallons of 110 race gas per tank full was enough to take care of it.
Larry, we have to be very careful here. For a relatively stock engine those guidelines may be ok. We have to make sure that anyone else reading this will know that detonation happens and may not be audible, even with a quiet, closed exhaust. Trust me, I've been there. If you're thinking you may have problems with pre-ignition or detonation (they are not necessarily the same thing), you have to look at the spark plugs, and that's not something the average Joe does on a regular basis. Devon
Devon, I've always been able to hear it, and I always listen for it when I'm on it. I'm convinced there are a lot of guys who wouldn't know it even if they heard it. Those are the guys that are going to damage things. For sure, there can be abnormal combustion that you won't hear, but heavy detonation is unmistakeable, at least for me.
My point was, and is, that it may not be audible. If you can hear it, some damage may have already been done. I have hurt spark plugs and have had to tame my ignition timing many, many times because I pushed the limit on 93 octane with 10:8:1 compresion with my 430 cylinder heads. I've had many fun runs at full throttle and never heard a thing, but looking at the plugs later told me a story. Devon
That would mean that you have to look at your plugs everytime you run the car. Is that realistic? My experience with my car says you really can't expect our cars with stock 1970 compression and iron heads to run on the cat piss they call gasoline today:laugh: I've detonated my cars many times over the years, but never damaged any plugs or seen evidence of it on the plugs. I back off immediately when I hear it. Who knows? I'm sure having suffered engine damage from detonation, you are very apprehensive about it now. I think you will like your aluminum heads. They make a definite difference in detonation resistance.
Larry, you must've missed my first comment regarding the "guidelines" being ok. I want others to know that detonation happens and that is is not necessarily audible. No, we don't have to pull spark plugs every two miles, but we should inform anyone here that looking at the plugs is a good way to know what's up. There is no Detonation resistance between aluminum or iron heads, all else being equal. Perhaps you are confused about thermal conductivity. Devon
I went from 9.4 to 10.4:1 compression with my aluminum heads. I understand that aluminum conducts heat much faster than iron. I had to mix race gas in with the iron heads. Detonation was a constant problem for me. Not so with the aluminums. I understand why. You had even higher compression, and iron heads and a cam with a lot more overlap. I'm not surprised you had detonation if you tried to run on pump gas. I haven't heard a peep on the street since switching to the aluminum heads. I heard it all the time with the irons until I started using the race gas. While I'm sure that detonation can be inaudible, there is no way it is as damaging as detonation you can hear. You can disagree if you want, and that is fine. All I see this doing is scaring guys and preventing them from enjoying their cars. Just my opinion.
Maybe the factory knew about the 90% thing when they developed that electronic hearing device, knock sensor, because our hearing can't be trusted to detect it that well. I say it must have been a highly important problem to get those car manufacturers to spend a dime developing and using them on the engines. They are not known for spending money on things unless it helps,,,,a lot. Maybe has something to do with the quality of the stuff we are forced to buy at the pump they call gasoline, but I don't really know.o No:
What is the best way you guys would describe the sound of this? Ive heard people describe it as "marbles in a can" and "hail on a tin roof "etc,,, Maybe with a little more description some of us Nubees could be a little more accurate with an attempted diaognosis. I myself run all org. 401 w/66,XXX tuned, rebuilt carb, and a slpash of race gas every now and then with premium. I do get in it occasionally while street driving and is alot less noisey if not present audibly with the race mix than without. I can tell you Ive heard it,(having had my mechanic in the car with me and tell me thats what it was) just not sure how to explain what it sounds like. Thanks -William
You people with good hearing!! I can hear ringing from my ears right now as I sit here. Been that way since I was a little guy, as long as I can remember. If I can hear the ping, it's big problems!
Good point, but I think the knock detectors also meant increased economy from a smart ignition system. A computer can maximize ignition timing right up to the edge while listening for knock and make timing changes 60 times a second. I totally agree that some abnormal combustion can be inaudible. Do we need to worry about it being catastrophic to a motor? I'm not sold on that. I agree with Devon that plugs should always be examined for the telltale signs of detonation. Actual damage like fractured insulators and bent or melted electrodes are the result of heavy detonation. You have to be able to hear that unless you are at WOT with open headers. The lesser detonation will show up as little aluminum balls on the white porcelain of the plug. A good magnifying glass helps to see this. When you are trying to get as much power out of a motor, the tendency to go right up to the edge with timing is there. Is there some ping present when you are on a dyno even when you think you have the best timing. When you do make your best pull, is there any detonation present? How do you know for sure? With my engine, there was about 3 MPH trap speed difference between 34* and 39* of timing. I can't explain why my engine wanted that much timing, but it did. Did I go too far? Maybe I did. JW told me that the engine might have wanted that much timing, but it wouldn't like it at over 5000 RPM. I then programmed the MSD to pull 4-5* of timing at 5000 RPM and over. Trap speed was almost the same, a bit less. I was running about 3-4 gallons of 112 mixed in with a half tank of 93. I always do this at the track.
To answer the original question, no, it is not always audible. Ping/detonation/piston rattle can occur and not be noticed. Is it damaging? Well, any piston rattle is not good. When an engine pre-ignites, which is what causes the pinging noise, the piston is trying to find a way out of the cylinder. Hence the usually audible noise, the piston is rattling back and forth in the bore. How long an engine can take it depends on build, every one is a little different. Even if you don't hear any pinging, it doesn't hurt to check the plugs periodically for the presence of the little aluminum balls Larry mentioned.
