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Old 02-09-2001, 02:52 PM   #1
Primm Motorsports
Vendor
 
Member#: 2098
Join Date: Aug 2000
Location: Mission Viejo, CA, USA
Cool Q. What is Detonation?Q? Answer!!!

Another tid-bit.

Dante
Primm Motorsports

Detonation

What is detonation?
Other words for it are "pinking", pinging" or "detting". It is when the flame front meets the piston crown too soon.

What?
The explosion caused when fuel and air meet a spark plug with a lightning bolt going across it is combustion. The leading edge of that explosion is called the flame front. If this flame front hits the piston crown when the piston is still travelling upwards there is a sound shock wave which sounds like pinging, hence the name. (Don't ask where "pinking" comes from.) This shock wave is so powerful it can crack a piston. It usually breaks the piston between rings 1 and 2 causing vertical cracks on the ring lands. This is called "ignition det". There are other reasons for detonation such as incorrect spark plugs, too high boost pressure, weak mixture and some others, but it gets a bit involved.

OK, clear on that one. But why is everyone worried about detting on the Impreza?
A number of reasons.

For an engine to make the most efficient power, it has to run very close to detting all the time. Any changes made to increase power will increase the chances of detting. The other reason is that the STi cars are made only for the Japanese market and are set up for 100 RON fuel. Running 95 RON (UK 'Premium Unleaded') or even 97 RON (UK 'Super Unleaded') is not what they were designed for.

Any modifications to increase power need to be done carefully and very properly, and include full
ignition and fuel re-mapping but retain the closed loop boost control and knock sensor.

Should I run 97 RON fuel in my car?
Difficult that one. It depends on the car. STi, yes. UK, 95 RON is OK if Subaru says. For everything else use 97 RON for safety if not sure. With our modified ECU we can map a car for whatever fuel the owner wishes to use, so this is the only way to be 100% sure that a modified or Japanese car will run perfectly on 95 RON fuel.

What is the ECU reset all about?
You want to know all the difficult stuff don't you! Some of this information is confidential, you won't tell our competitors will you?

Who me?!
If the car senses detonation then inside the software it retards the timing. It does this in four stages. When the car stops detting then it remembers that it used to det and waits for ages until it starts to advance the timing again. If you remove the ECU or disconnect the battery for sometime it wipes the horrid memory of engine-destroying detting and advances the timing. The lesson here is that if your car runs better after an ECU reset then it is detting and you should not do another one.

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Old 02-09-2001, 04:00 PM   #2
nsotak
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Member#: 3048
Join Date: Nov 2000
Chapter/Region: NWIC
Location: WA/MA
Vehicle:
2008 OBS
Silver/Silver

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I have a question for you. I had some fog lights installed, they disconnected the battery, and I wasn't sure if they had let the ECU reset properly, so I reset it. The car ran WAY better! After about a day it was hesitating. The only mods I have done are a hi-flow intake, and I have a cat-back. The intake probably should be cleaned, and there might be too little back-pressure from the cat-back. Other than that I can not think of why this hesitation happens, unless my car is knocking and the ECU retarding the ignition, like you stated above.

-nick
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Old 02-09-2001, 04:12 PM   #3
nsotak
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Member#: 3048
Join Date: Nov 2000
Chapter/Region: NWIC
Location: WA/MA
Vehicle:
2008 OBS
Silver/Silver

Post

I have a question for you. I had some fog lights installed, they disconnected the battery, and I wasn't sure if they had let the ECU reset properly, so I reset it. The car ran WAY better! After about a day it was hesitating. The only mods I have done are a hi-flow intake, and I have a cat-back. The intake probably should be cleaned, and there might be too little back-pressure from the cat-back. Other than that I can not think of why this hesitation happens, unless my car is knocking and the ECU retarding the ignition, like you stated above.

-nick
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