I posted a couple of pictures of what happens after cheap gas is put into a high compression engine. Go to the assorted page.

http://wrx-now.tripod.com

When the owner dropped the car off at the dealer where I was working, ( Now closed due to the economy - bankrupt), he was complaining about a bad miss. Well I guess so!
Found out that he had bought gas at a no name place. Must not of been to spec because we had to get new pistons and rebore the block to fit. Saved money on the gas spent money with us to fix the engine. It would of been cheaper to buy good gas obviously.

What I am saying is watch what you put in the tank!

 

Ya definently worth paying for 93. I usually dont go to off name gas stations down in hicksville where they have water in the gas.

Ya definently worth it to me paying for 93. I usually dont go to off name gas stations down in hicksville where they have water in the gas.

 

so the bottom of the piston failed due to bad gas??? please explain.

 

It is called Detonation.

Hi comp ratio engine require a higher octane rating to prevent Ping/Knock/Detonation. If you have a SC or TC engine it becomes even more critical. 93 – 94 Premium is called for not 87 Regular. Some cars have knock sensors to retard the spark advance as ping or knock is encountered. Some cars such as the 2.4 in my Cobalt will allow the use of lower octane gasoline but it is stated that the engine is derated to compensate for the lower octane fuel.
The Knock sensor is there to help reduce the ping/knock/detonation but if the sensor fails or the fuel is not correct and the ECM does not compensate quickly enough as the transicents of detonation can be very short but powerful you will get piston damage.

You probably noticed that many guys install an alcohol injection system. This does 2 things
1. Cool the intake charge depending on the intake system design.
2. Increase the octane number of the fuel. This also helps to compensate for times when you can not get the octane number that you need.

Your highest loading on the engine does not tend to be at its highest rpm but usually somewhere closer to the peak torque rpm. That is usually where the peak cylinder pressures are encountered as all the factors governing efficiencies for cylinder filling occur. I.e. valve timing and overlap, resonance of the intake manifold and exhaust manifold, temperature and multitude of other things. Every engine has a unique rpm and load that will encourage detonation.

In the case of this engine he had fuelled with cheap fuel and had his foot in it. The car was accelerating and began to rattle, which is more than a ping and the miss began.

Detonation can set in very quick and can at times cause instanteneous damage to pistons etc. Usually we see the top compression ring and land let go. In this case it was the second compression ring instead.


The following is from Hastings. A ring manufacture that I have used in the past with great success in 350 SB Chevy engines etc.

Detonation can be caused by:
1. Lean fuel mixture.
2. Fuel octane too low.
3. Improper ignition timing.
4. Lugging the engine.
5. Excessive milling of heads or block which will increase compression ratio.
Detonation is a form of abnormal combustion in the combustion chamber. During normal operation of the engine, the burning of the fuel-air charge produces a steady, smooth push on the pistons of each cylinder. At the instant of ignition by the spark plug, the flame of combustion moves rapidly outward from the plug very much like the waves when a stone is dropped into a pool of water.
Abnormal operation may allow combustion pressures to develop so fast that the heat and pressure will "explode" the remaining unburned fuel. This produces the knock, often called ping, carbon knock, etc. Actually this is detonation. The knock results from the violent explosion when the normal flame front runs into the secondary flame front. Detonation will cause piston and ring damage, top ring groove wear, scoring, sticking rings, loose head gaskets and possible complete engine failure.

I hope this helps explain what happened.

 

^^ we all know what detonation is. i think he was asking how detonation caused the supposed destruction of the bottom of the piston, instead of the piston surface.

 

Like I said usually its the top ring not the second. Maybe the piston had a top ring that was a little marginal and blew down to the second one, or maybe the piston had a defect that only showed now. All I can say is that that is what came out of the engine.

 

ive seen a lot of damaged pistons, to me that looks like what happens on a blown alcohol motor when you plug a nozzle up. basicly it goes very lean, coupled with high cylender pressure and a very hot ignition, it cuts the side of the piston like a tourch.

to me that looks like a very lean condition, not bad fuel.