Timing
Timing
Post Fiend
Joined: Feb 2000
Posts: 5,130
Likes: 8
From: Brea CA
Timing is the relationship of when the spark fires compared to where the piston is. TDC means top dead center of the compression stroke. Early engines used to fire the spark plug(s) right at TDC. Then they got wise and started firing the spark plug a little earlier than TDC. This is where you get BTDC or before top dead center. So timing is a general term to describe when the spark is firing compared to TDC. Specifications are given for how much timing an engine has at certain speeds or rpms.
Initial timing is what the initial relationship is preset to. It's like your starting point of your timing before other variables like centrifugal and vacuum advance come in. This is done by rotating the distributor CW or CCW in relation to the crankshaft. You'll see specs. for initial timing range from right on TDC to 12 degrees BTDC and more. Initial timing never changes after you set it. Well, it can change if your timing chain stretches or your points wear down.
Initial timing is what the initial relationship is preset to. It's like your starting point of your timing before other variables like centrifugal and vacuum advance come in. This is done by rotating the distributor CW or CCW in relation to the crankshaft. You'll see specs. for initial timing range from right on TDC to 12 degrees BTDC and more. Initial timing never changes after you set it. Well, it can change if your timing chain stretches or your points wear down.
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
To kinda expand on BB's thought. Initial timing is what you set the dizzy "at idle". Most engines run 6-10 degrees(there about). TOTAL timing is "initial" plus what is available IN the dizzy. For instance....the dizzy has the ability to "add" 20 degrees of timing thru cent. or vacuum advance. Take your initial setting of 6 (for instance) and add 20 to it. You have 26 degrees of TOTAL timing. For most performance applications most people only talk about TOTAL timing. The initial timing is there just to start the motor easily. Not many starters will turn over a motor with 30 degrees of timing in it. This in the fact that it's trying to fire the cylinders 30 deg. BEFORE TDC. That has a tendency to really KICK at a starter. So, as you start the motor, it does it easily at 6 degrees, then as you rev the motor into the powerband the dizzy adds in timing that creates the power.
Hope this gives you some insight.
Hope this gives you some insight.
Senior User
Joined: Feb 2004
Posts: 185
Likes: 0
From: Crownsville, MD
Great answers. Almost like you translated them into English from some overly technical text book 
. Thanks. I learned a few things here without even having to ask. You gotta love these forums.
. Thanks. I learned a few things here without even having to ask. You gotta love these forums.
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