detonation damage

Suck Squish Bang Blow part 5: Avoidance of Detonation
By Mike Kojima

Detonation is perhaps the deadliest sin you can inflict upon your motor.  It is usually caused by gluttony, another bad sin, gluttony for more power. Detonation is the result of going too far in the quest for power.  Pushing things to the limit when eking the last bit out, too far for your fuel's octane, too far for your fuel system's flow capacity, too much heat for your cooling system to dissipate, the list goes on and on.  All of these can lead to a quick end to your motor. Really bad detonation can destroy any engine very quickly, about the only way quicker would be to dump out your oil while it's running full tilt.  A built engine with tough forged pistons, coatings, racing rods and fortified crank and bearings will still succumb to detonation, it just takes a little longer.

detonation damage
Wow!  We have actually seen worse though.  This was a turbo 1.8 Audi 5 valve motor.  These engines have really small turbos with owners that like to turn the boost up to the moon via "chipping".  Small turbo, lots of boost means a lot of backpressure and a lot of hot exhaust gasses retained in the cylinder.  Not good.

We had better try to define the phenomenon.  Detonation usualy happens as the result of improper modification and tuning.  Detonation simply put is the uncontrolled burning of the air fuel mixture in the engine's cylinders.  Detonation generally happens when the fuel air mixture auto ignites by being compressed too much, kind of like hitting a non-safety match head or toy cap with a hammer.  Compressing the fuel air mixture makes it hot by the ideal gas law (pv=nrt for those of you that care).  Simply put, the molecules of fuel and air when squeezed together closely bump and rub together causing the temperature to rise until the mixture explodes out of control sometimes without the help of the sparkplugs. Fuel quality and things that affect cylinder pressure influence this.

detonation damaged bearings
Engine main bearings hammered by detonation.  We have seen worse, we have seen broken main caps and distorted main bores caused by detonation.

The other main causes are something getting too hot in the cylinder acting like a glow plug in a diesel, making the mixture auto ignite and firing the sparkplug too soon.  Detonation puts a tremendous strain on all the internal engine parts and is the leading cause of death for built, high performance motors.  Detonation blows head gaskets, burns pistons and valves, cracks ring lands, bends rods and pounds bearings.

plug damage
Usually the sparkplugs are the first engine component to be damaged by detonation.  A melted ground electrode is common.  If you are lucky that's the only thing damaged.  When the center electrode is damaged or melted, the cylinder is usually toast.


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Wednesday, October 06, 2010 5:23 AM
Damn, I needed this article a week ago when I was trying to explain why high compression and high boost were a bad mix. Still, now I know where to go. Awesome as always!
Wednesday, October 06, 2010 9:39 AM
How interchangeable are knock detectors?
Wednesday, October 06, 2010 11:34 AM
Knock detectors/sensors are just types of microphones. Microphones hear the noises the engine makes. Knock in a certain engine is in a specific frequency range.

I am not a big fan of water injection as it requires some maintenance to work correctly. I have played with it though the years. Installed various systems on cars. Done incorrectly it can cost horsepower. Done correctly it can help, but its just one more thing, in the list of things that can fail.
Mike Kojima
Mike Kojimalink
Wednesday, October 06, 2010 11:38 AM
The AEM system is pretty failsafe, especially with their new warning monitor. Stand by for news on that.
Wednesday, October 06, 2010 1:18 PM
RE: race fuel

Don't forget CARB's newest insanity restricting leaded, non-compliant fuels to competition vehicles only. Read more here:


I love this state.
Wednesday, October 06, 2010 5:50 PM
Great article! That CARB crap makes me glad my cars are still registered in Wisconsin. I don't have to put up with any crap like that. At least, not for now.

Question: speaking of tuning, are you an advocate of tuning using higher octane fuel than you plan to burn in the car to prevent any horror while in the process of tuning, or tuning to a slightly lower octane than you plan to use so there is an extra buffer zone during driving, or just tuning with the same octane you plan to run for consistency?
Wednesday, October 06, 2010 6:59 PM
besides knock sensors (i've heard some cars don't have any) is there any other device that can be installed as a warning?, like an aftermarket unit or something that can detect it and display information?
Wednesday, October 06, 2010 8:01 PM
Aldayo there are lots of aftermarket offerings.

One of them is the HKS AFK.

Thursday, October 07, 2010 6:35 AM
Paul a smart builder and a good tuner will be good enough to tune using the desired fuel from the start. The tuner should be able to start with a conservative set of parameters and work towards a more ideal tune.

Like Mike said in the article, higher octane fuel burns slower and can handle more compression before detonation. So why tune with a higher octane fuel just to switch to a lower grade? If you use lower octane fuel while tuning, you 1). won't be maximizing your build and 2). may still be running your engine in unsafe parameters. It's shooting yourself in the foot either way.

Thursday, October 07, 2010 6:01 PM
Thanks for the info. That makes sense, I remember reading about the whole switching up fuel octane thing somewhere as being a flamewar starter, but it never made sense to me to tune with different fuel.
Thursday, October 07, 2010 8:08 PM
# Evo2nr Thanks for the reply, however at $900 usd the HKS unit is a little off for me right now, i read a little and found the apexi safc-ii had knock monitor functions, how ever i wonder if anybody knows how accurate this is, or if there is another "low budget" option for know monitoring.

Tuesday, October 12, 2010 5:37 AM
You know, for years I always thought higher octane fuels also burned slower. And it was partially for that reason that putting higher octane fuel in an otherwise normal, stock engine would reduce power output.

But then it was pounded into my head by countless (credible?) sources that fuel burns about the same speed no matter the octane. While it didn't make complete intuitive sense to me, I accepted it as truth.
(And putting higher octane in a stock engine would neither gain nor lose power. Put still advancing base timing might provide a power gain, hopefully coupled with higher octane to combat the increased likelihood of detonation.)

Now I'm again being told that higher octane fuels burn slower than lower octane fuels. Again, this makes intuitive sense (if you know any chemistry at all). It would be nice to have an exhaustive test to read (I'm sure done by countless race engine builders and all OEM engine manufacturers) or an exhaustive chemistry explanation to read and point to when trying to hash out the facts on the Internets.

Mike Kojima
Mike Kojimalink
Tuesday, October 12, 2010 6:46 AM
Hi octane fuels have less BTU and burn slower than low octane fuel. However the slow burning allows the engine to be tuned to be more efficient.
Tuesday, October 12, 2010 8:58 AM
I believe you Mike. I'm just surprised that this nugget of information seems to have lingered so long in limbo for me. I'm usually pretty good at finding The Truth pretty quickly when it comes to details like this. *sigh*
Tuesday, October 12, 2010 8:59 AM
The reason I care, is that when dealing with tuning ignition timing for engines (which I do quite often) I like to know all the factors at play, and how major one is compared to another.
Tuesday, September 27, 2011 4:43 AM
Octane rating (anti-knock index) has absolutely Nothing to do with a fuel's flame speed characteristics..
as they have no correlation it is misleading to generalize this..

E10 pump gasoline(any grade 91,92,89,87 octane) = so/so flame speed

VP C16 (116leaded)has bad response characteristics & slow flame speed
(fullthrottle NHRA passes don't need transient response characteristics)

VP MotorSport103(103unleaded) has a quicker flame speed & better response characteristics.. tho it revs UP quick its also feels kinda empty(low BTU's)
(race jetski's & dirtbikes are constantly wacking the throttle at various rpm's)

MeOH gasohol(unleaded) has a MUCH faster flame speed than any of those and only a mid field octane rating.. go figure?

please explain how a slow burning fuel "Allows" an engine to be tuned to be more "Efficient"??
increasing engine RPMs = decreasing available "time" for pressure to be applied to the piston before said pressure is released by the exhaust valve..
so how does a air/fuel mixture which has burned less due to a slower flame speed generate MORE power? or use less fuel? to do the same work?

you know all over motoIQ and there are articles about man's latest & greatest metallurgy/mechanical techniques & the electronics gadgets & doooohickeys...
And all any of this stuff ever does is attempt to capture a CHEMICAL reaction better.. (Rule#10572794 Start with better chemicals = get a Better reaction)
why is there no Article giving a basic historical overview of the internal combustion engine & associated fuels throughout history?
after all we we have been to WorldWars over this stuff!!
a nice motoIQ article could clear up MUCH of the silly cut&paste googleSearch misconceptions that permeates most inquisitive enthusiasts' minds..
Mike Kojima
Mike Kojimalink
Tuesday, September 27, 2011 7:54 AM
Higher octane fuels with a higher volatility rating do have lower flame speeds. Their is almost a direct correlation except for some specialty fuels like C12 and other highly oxygenated fuels designed for NA engines.

They also but not always tend to have lower BTU so the way to get more power is more compression, boost or timing or maybe some combination of the three.
Mike Kojima
Mike Kojimalink
Tuesday, September 27, 2011 8:23 AM
Methanol is used as an oxygenating agent in California pump fuel. The OH bond is tough so it probably has decent burn speed so thats why it is also a good motorsports fuel.
Tuesday, September 27, 2011 3:09 PM
sorry Mr kojima
to me it feel like such absolute statements/definitions are more so limited to "Gasoline" based fuel component blends..
unfortunately with hybrid fuels these generalizations are not quite accurate..
and neither are these fuels Specialty nor Designed For engines with NA or mechanical supercharge in mind..

lets take a M25 Gasohol for example..
it has a R.V.P. much higher than Any gasoline based fuel
& flamespeed closer to Methanol(fast) than Gasoline(slow)
tho a fuel's Distillation Curve can give you an idea about a fuel's transient response characteristics, unfortunately (just like Octane rating) it does not tell us the Entire Story we'd like to hear.

Gasoline is Not the future, Gasohol IS
and prolly the reason why the EPA is pushing us towards it..
in California, Ethanol is used in E10 pump gasoline as an stretcher/clean burning component of the fuel
i don't think Methanol is used as a blending agent unless it's a M85 @ pump??
(which was a pilot program if i'm not mistaken? maybe i'm wrong?)

Tho both are Alcohols..
Methanol has Fast flame speed, Ethanol does Not(slow like gasoline)
Methanol has a stronger Latent heat of vaporization effect over Ethanol's
And when blended with gasoline, MeOH has much More effect
sooo ask yourself..
would you trade that extra "Wasted" BTU's released by the exhaust valve
for Quicker flamespeed + more complete combustion ?
Power is a byproduct of efficiency..
not trade efficiency for a small byproduct of power..

do a MotoIQ article about "Fuels"
cause i'm still trying to learn too!!!
Mike Kojima
Mike Kojimalink
Tuesday, September 27, 2011 3:15 PM
Haha, I have been trying to find a real expert on fuels and oils to do something for awhile now. The one guy who used to post here a lot that was a chemist didn't want to do it.

In our fuel methanol has been used more since MTBE was outlawed.
Mike Kojima
Mike Kojimalink
Tuesday, September 27, 2011 3:15 PM
Haha, I have been trying to find a real expert on fuels and oils to do something for awhile now. The one guy who used to post here a lot that was a chemist didn't want to do it.

In our fuel methanol has been used more since MTBE was outlawed.
Wednesday, September 28, 2011 12:37 PM
Me tooo!!!
can't find anybody who wants to give up their secrets?!?!?!
guess that's why its "secret"??

Everywhere i read it says Ethanol (not Methanol) is used to replace MTBE in Cali gas..
and according to (C)A.R.B. under the CaRFG 3 (california pump gasoline)
"ALL oxygenates other than Ethanol is Prohibited"
on a good note: CaRFG3 allows aromatic volume to go from 30% to 35%!!

fun reads !!

currently i only have 2 blend charts so far
One for Neat(pure) gasoline / TM38 mix
& another for E10/TM38 mix

of course the EPA does allow Methanol to be blended in with pump gasoline in other parts of our country @ 2.75% with equal % parts of co-solvents..
unfortunately just not California..
Btw: tho allowed, it has almost no support from manufacturers/sellers of "pump gasoline as it would require logistics unprofitable..

i tried to upload pic's of my blend charts on my MotoIQ album
unfortunately idk the photo album feature is not working..
or acting funky or something?? easier to just tag you guyz on Facebook..

in my opinion..
many enthusiasts can barely afford an internal combustion engine
Modding it costs plenty [$money$] !!
fuel is paid for & used up Anyways..
dollar per dollar hard to beat fuel as a mod!!
then again with the gas/money saved from increased MPG
you can buy more parts?? ha ha
Mike Kojima
Mike Kojimalink
Wednesday, September 28, 2011 1:59 PM
Check out the photo file size limit, we want to see the charts!

Thursday, September 29, 2011 12:36 PM
Blend Charts are posted!!
remember they are only approx guidelines
please notify me of any mistakes??

really wish we could arrange the picture order somehow??
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