Last night while I was out making my rounds, my 20 year old nephew called to ask me some questions about his 1976 Camaro I gave him when he graduated High school. (Yeah, uncle Squid is cool.)
Anyway, it seemed that as he put it some POS Honda ricer smoked him? I asked him how the Honda could be a POS if he had lost? He ignored me as expected. (Sometimes Uncle Squid shows his age.)
What he was looking for was some information on how to make the venerable Chevy 350 a little more potent. As we were talking I noted some misconceptions he had concerning some very basic aspects of internal combustion engines that I thought I?d share with all of you.

Octane
Plain and simple, octane is simply a measure of fuel-detonation resistance.The higher the number, the less prone the fuel is to detonation.
Detonation is the un-uniform ignition of the air/fuel mixture in the combustion chamber. Normally, the combustion flame front originates from the spark center. When detonation occurs, the charge is lit at not only the spark center, but also from hot spots caused by build up from carbon deposits within the combustion chamber. This causes an uneven flame front, resulting in a sudden rise in combustion pressures, which can damage a piston on the power stroke.

What?s even worse than detonation is what's called pre-ignition, which occurs when the air/fuel mixture (Charge) unintentionally lights off without a spark. This usually means the event occurs toward the end of the compression stroke when charge temperatures and pressures are still rising. With pre-ignition, the sudden change in charge pressure from premature ignition as the piston is still moving up is equivalent to taking a hammer and beating it on top of your pistons. The sound is very similar, just like a ping.

Higher octane fuels are especially helpful to boosted or high-compression performance engines, along with older engines. With boost or a high-compression ratio, the air-fuel charge is compressed to higher pressures, which makes it more susceptible to detonation. Older engines with carbon deposits built up in the combustion chamber also benefit from high-octane fuels as the added space occupied by the deposits also effectively increases the compression ratio.

Now this is where it gets fun.
Today?s engines, like the VK56DE in our Titan and the Infinity QX56 control detonation with knock sensors that retard the spark timing at the onset of knock. Retarding spark timing or richening the air/fuel mixture to reduce knock ultimately robs power. This is why an increase in octane increases horsepower. Since the engine's knock threshold is effectively raised with higher octane fuels, spark timing is not retarded. This allows combustion and charge expansion to occur so that more force is put into the power stroke. Bottom line: Higher octane fuel only helps you make more power if your engine is at the verge of detonation (whether you know it or not).

In the case of my nephews Camaro with the H.E.I 350 (No ECU or Knock Sensors) a higher octane fuel won?t help. But with the Titan you can gain the extra 10 HP that the QX56 gains by using Premium fuel.


Comments and additions are expected and appreciated.

The other thing my nephew asked about was.