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#4721135 - 04/09/18 04:22 AM How bad is detonation?
NICAT Offline


Registered: 04/05/18
Posts: 15
Loc: Azerbaijan
Hi.
I am able to advance or retard igniton by turning the distributor.
The problem is that, if i adjust distributor position to guarantee that the engine will never detonate, this will result in significant performance loss.
With current ignition timing, car's performance is great, and never detonates during normal or even hard driving at a city. But while the car is full and climbing, there is mild detonation. Which happens rarely. may be once or twice in a month.


I know that the detonation is bad. But how serious is it unless it leads to pre-ignition? Just wonder if anyone experienced mild detonation for a long time, but not serious damage to the engine ?
Higher octane fuel is very expensive here smile






Edited by NICAT (04/09/18 04:23 AM)

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#4721145 - 04/09/18 05:05 AM Re: How bad is detonation? [Re: NICAT]
Lubener Offline


Registered: 01/22/11
Posts: 2503
Loc: N.Ohio
How bad do you think is a piston with a hole in it? Why not investigate the cause? Check your manual for the recommended octane to use. Check for an EGR valve/ system not working, a hotter than normal running engine, carbon buildup on piston tops, lean fuel mix or knock sensor(if equiped)problem. . A check with an analizer to check codes and fuel trims can give some clues.Blocked EGR valve or plumbing can cause preignition. You shouldn't have to deviate from timing specs or run higher than recommended octane gasoline to enjoy a quiet engine.Might help if you gave more information about your car.


Edited by Lubener (04/09/18 05:15 AM)
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#4721174 - 04/09/18 05:55 AM Re: How bad is detonation? [Re: NICAT]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 18863
Loc: Sunny Florida
While I have yet to see any "holy pistons" in a street car I have seen a few at the strip.

I once sold a 78 Trans Am to a younger guy who brought it back running rough. It had every top ring broken! 400 V8. Still ran great off idle, but crazy broken.
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#4721189 - 04/09/18 06:10 AM Re: How bad is detonation? [Re: NICAT]
SubieRubyRoo Offline


Registered: 05/14/12
Posts: 878
Loc: Winchester, Indiana
Check the vacuum advance and other things and try to clean out any carbon buildup. Read this:

Detonation Basics

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#4721223 - 04/09/18 07:21 AM Re: How bad is detonation? [Re: NICAT]
Chris142 Offline


Registered: 06/05/03
Posts: 16528
Loc: Deplorable in apple valley, ca
Breaks pistons,rings and wipes out rod bearings.
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#4721228 - 04/09/18 07:30 AM Re: How bad is detonation? [Re: NICAT]
Silverado12 Offline


Registered: 02/26/13
Posts: 3032
Loc: Central Virginia
A little pinging is supposedly ok as per GM owners manual on a Cavalier (I think) from the 1980s. It's been a long time since I read this but it was before the days of knock sensors. I would say to retard the timing a little just to make sure you're not doing damage to your engine. You can also use colder spark plugs.
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#4721247 - 04/09/18 07:51 AM Re: How bad is detonation? [Re: NICAT]
andyd Offline


Registered: 09/25/04
Posts: 6876
Loc: Marshfield , MA
I used to use a vacuum gauge to tune my old jeep V8s because my timing was difficult to get a good shot at the marks on the crank pulley. Tune it to highest vacuum with a steady reading, After awhile I just tuned it by ear.
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#4721260 - 04/09/18 08:14 AM Re: How bad is detonation? [Re: NICAT]
Ducked Offline


Registered: 10/25/12
Posts: 4074
Loc: Taiwan
Generally not as bad as pre-ignition.

If you're driving a Lada RWD (AKA Zhiguli in the former USSR), which I suppose is quite likely in Azerbaijan, the earlier Mk1 version with the round headlights has a brass vernier wheel on the side of the distributor for easier manual advance or retard of the ignition.

I've read somewhere (either my Haynes manual or my owners handbook) that this was to compensate for variations in fuel octane.

I imagine it might be possible to retro-fit this to other Lada models since parts commonality is generally good across the range.

I THINK my current car (a 1986 Daihatsu) was showing intermittent pre-ignition when I bought it, and probably had been doing so for some time. I used water as a decoke (sucked into one of the vacuum lines) and it stopped doing it for about 7 years.

Recently it started running-on at switch-off, so I arranged a water manometer and additional filter restriction so it would suck in water at high revs. Isn't running-on now but I need to get or make some more distilled water to continue the treatment.

https://www.bobistheoilguy.com/forums/ub...ric#Post4620273

Needs a bit more development but the basic idea seems OK.


Edited by Ducked (04/09/18 08:18 AM)

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#4721268 - 04/09/18 08:21 AM Re: How bad is detonation? [Re: NICAT]
WobblyElvis Offline


Registered: 09/23/14
Posts: 1273
Loc: Toronto Canada
I had a Chevy van with a 5.0 litre V8. It would ping/detonate in warm weather on the highway. Did this for years and never failed. I was surprised it lasted so long.

This engine had a simple vacuum controlled heated air intake that would provide some warm air from the exhaust manifold even in summer. If I disconnected the heated air intake form the air filter housing, it would ping less often. If your engine pings to much and you can cool down the intake air, give it a try.

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#4721282 - 04/09/18 08:35 AM Re: How bad is detonation? [Re: NICAT]
JLawrence08648 Offline


Registered: 01/20/17
Posts: 162
Loc: NJ
I have had a hole in a 2 cycle Yamaha piston from detonation.

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#4721283 - 04/09/18 08:35 AM Re: How bad is detonation? [Re: NICAT]
SubieRubyRoo Offline


Registered: 05/14/12
Posts: 878
Loc: Winchester, Indiana
Detonation/pinging on an engine with sub-9.0:1 compression is mechanically a whole lot different than one that is over 10.5. It's one of the reasons people usually overkill octane on race engines- a low compression engine may last a very, very long time with some detonation, whereas a 14:1 engine may only last a couple seconds before a catastrophic failure.

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#4721333 - 04/09/18 09:20 AM Re: How bad is detonation? [Re: NICAT]
NICAT Offline


Registered: 04/05/18
Posts: 15
Loc: Azerbaijan
Wow. Great answers here. Thanks
Originally Posted By: Silverado12
A little pinging is supposedly ok as per GM owners manual on a Cavalier (I think) from the 1980s. It's been a long time since I read this but it was before the days of knock sensors. I would say to retard the timing a little just to make sure you're not doing damage to your engine. You can also use colder spark plugs.


That is good news. Mine is also GM engine, G15MF.
About spark cold plugs, i think they should only help preignition but not detonation. Since detonation happens after the spark plug firing, but preignition is before. So Too hot spark plug can cause preignition, but would it also cause detonation ?



Originally Posted By: Ducked


If you're driving a Lada RWD (AKA Zhiguli in the former USSR), which I suppose is quite likely in Azerbaijan, the earlier Mk1 version with the round headlights has a brass vernier wheel on the side of the distributor for easier manual advance or retard of the ignition.

I THINK my current car (a 1986 Daihatsu) was showing intermittent pre-ignition when I bought it, and probably had been doing so for some time. I used water as a decoke (sucked into one of the vacuum lines) and it stopped doing it for about 7 years.

Recently it started running-on at switch-off, so I arranged a water manometer and additional filter restriction so it would suck in water at high revs. Isn't running-on now but I need to get or make some more distilled water to continue the treatment.

https://www.bobistheoilguy.com/forums/ub...ric#Post4620273

Needs a bit more development but the basic idea seems OK.


Yes. Lada is very common in my country smile
In my car, retarding and advancing the ignition is also very easy.
Water decoke seems to be something very interesting. However i couldn't understand the logic behind it. i will investigate it and install in my car. smile


Originally Posted By: WobblyElvis
If your engine pings to much and you can cool down the intake air, give it a try.


How to cool down the intake air if the ambient temperature is not that cool ?


Originally Posted By: SubieRubyRoo
Detonation/pinging on an engine with sub-9.0:1 compression is mechanically a whole lot different than one that is over 10.5. It's one of the reasons people usually overkill octane on race engines- a low compression engine may last a very, very long time with some detonation, whereas a 14:1 engine may only last a couple seconds before a catastrophic failure.


Compression ratio in my engine is 8,6:1. So does it mean that it would tolerate mild detonation better ?

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#4721349 - 04/09/18 09:35 AM Re: How bad is detonation? [Re: NICAT]
WobblyElvis Offline


Registered: 09/23/14
Posts: 1273
Loc: Toronto Canada
The GM van I had used a thermostatically controlled air intake set around 130 degrees F. This meant that in summer with an outside temp of 95 F, the intake system would continue to add some hot air from around the exhaust manifold. Sounds odd but his is how it worked. I disconnected the power to the thermostat control so it would intake only outside air. This would help lower the frequency of detonation. Perhaps this can be done with your car perhaps not.

Doing this may cause a hesitation when the engine is cold.

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#4721366 - 04/09/18 09:49 AM Re: How bad is detonation? [Re: NICAT]
JeffKeryk Offline


Registered: 01/09/10
Posts: 115
Loc: Los Gatos, CA
Is this an older car? I thought today's computers would pull back the timing when detonation occurs.
By the way, any pinging you can hear means there is more you cannot hear.
I would try and figure it out.
If it is something like a 60's V8, you may need to alter your timing curve as well as vacuum advance.
Gas was different back then.
Good luck.

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#4721432 - 04/09/18 10:42 AM Re: How bad is detonation? [Re: NICAT]
Ducked Offline


Registered: 10/25/12
Posts: 4074
Loc: Taiwan
Originally Posted By: NICAT



About spark cold plugs, i think they should only help preignition but not detonation. Since detonation happens after the spark plug firing, but preignition is before. So Too hot spark plug can cause preignition, but would it also cause detonation ?



I thought, like you, that hot plugs would mostly promote pre-ignition, but I am not certain of this.

You mention above that detonation can lead to pre-ignition. The reverse is also true, and at least some Low Speed Pre-Ignition events seem to consist of detonations initiated by pre-ignition and therefore starting before the timed spark.

Although detonation and pre-ignition are still distinct and different, they now don't seem to be as separate as they classically used to be.

Originally Posted By: NICAT

Water decoke seems to be something very interesting. However i couldn't understand the logic behind it. i will investigate it and install in my car. smile



Its more chemistry than logic. At the high temperatures in an operating engine, in the presence of hot (incandescent) carbon, water breaks down to hydrogen and oxygen radicals which react with the carbon.

C + H2O -> CO + H2

If there is excess oxygen the carbon monoxide and hydrogen will burn, otherwise it is exhausted.

The same reaction was used to make town gas from coal (well, coke, which is coal with the hydrocarbons cooked off)

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