I always thought I knew the answer, but a recent discussion has me guessing now.

Regarding B or D series motors, or any 4 stroke motor...........

When someone says that ignition timing is at the stock 16 BTDC (Before Top Dead Center) at idle, are they saying that the spark is igniting when the piston is 16 degrees BTDC on the compression upstroke, or 16 degrees BTDC on the power downstroke. I would think the latter is 16 degrees ATDC (After Top Dead Center)

In other words, when does the spark ignite the mixture? On the upstroke BTDC or the downstroke ATDC?

I've always maintained that the spark fires right before the piston is at TDC on the upstroke, and by the time the explosion is complete, the piston has passed TDC. The other guy says that my explanation will cause the motor to be destroyed.

Who is the retard?

 

if it sparks before tdc there is more resistance than if it makes a spark after top dead center. It won't destroy a motor but will rob power.

 

Think about what you are saying. BTDC means before Top Dead Center, so obviously, the spark is ignited 16 degrees before the piston reaches TDC.

The mixture is ignited as it is compressed, so that the timing is perfect between complete combustion and compression. If it ignited too early, it will result in pre-detonation and will kill your motor. If it is ignited too late, you will have an incomplete burn causing wasted fuel and hydrocarbons to be sent out of the combustion chamber. This is why a lot of car fail smog...they need to advance the ignition.

 

Let me explain it another way.

The argument I'm having is the following:

I am trying to explain to the other individual that the spark happens 16 degrees BEFORE the piston arrives at TDC on the compression upstroke. You can advance a little more to the point of detonation for a more complete and efficient burn whereas retarding will lose some power and efficiency.

But the other guy is yelling and screaming profanities at me with big bold text. He says that the spark happens 16 degrees AFTER the piston has been at top dead center to push the piston down for the power stroke. He says that my explanation would counteract the crankshaft rotation and destroy the motor.

Here is his exact explanation:

HOW THE FUCK CAN YOU SPARK BEFORE TDC?!!!!! YOU IDIOT. YOU WILL FORCE THE CRANK IN REVERSE. IF YOU HAVEN'T MADE IT TO TDC YET YOU CANNOT SPARK. YOU WILL TWIST YOUR CRANK INTO SCRAP METAL. THE SPARK HAS TO HAPPEN AFTER TDC SO THAT THE POWER STROKE IS GOING BACK DOWN. YOU CANNOT SPARK WHILE THE PISTON IS STILL COMING UP ON IT'S COMPRESSIONS STROKE YOU FUCKING ARMY RETARD!!!!! IF GEORGE W BUSH SAID YOUR CIVIC WAS GAY WOULD YOU BELIEVE HIM?

Who is correct here??????????

 

You are. 16 degrees is the optimum point for spark for a complete burn. 16 degrees after... basically what shmoo said.

 

Wow, who is this tool?

Maybe you should send him over to www.howstuffworks.com.

 

I think this dude is just messing with you, or he is very ignorant, but let him go about his way of thinking, and let him time his car After top dead center, see how much power he makes, or if it will even run at all which i doubt.

 

Thank you very much for pointing that out.

I posted the following link and he ended up apologizing.

http://auto.howstuffworks.com/ignition-system1.htm

 

Guess that guy expects INSTANTANEOUS spark ignition, LOL...

Doesn't happen that way in the real world as it takes TIME to burn the mixture of fuel... What a fool LOL

 

noooooooooo!!!!!!!! i wanted to argue too!!!!! but u guys beat me to it!!!!!!!!

FTW: Toy Civic!!!!

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