Chevy Corvette Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
9,745 Posts
Discussion Starter #1 (Edited)
Most people have the mistaken belief it's the rapidly expanding gasses caused by combustion that force the pistons down when in fact all of the combustion takes place before the pistons reach TDC. The combustion "chamber" is the volume where the combustion takes place and it's the high pressure exhaust gasses that force the pistons down. That's why a retarded ignition results in flames and un-burned fuel blowing past the exhaust valves.

It's also why a "tight quench" doesn't accomplish anything because the combustion is about 99% complete before any "quenching" takes place. The benefit of a "tight quench" is just one of the many "performance adding" myths that refuse to die.

Larger engines need more timing advance than smaller engines because the larger engines have a greater volume of air/fuel to be burned so they required more timing advance to get the job done before TDC. That's why the 265's and 283's had 4 degrees of initial advance, the 327's and 350's had 6 degrees, and the 454's had 8 degrees.
 

·
Registered
Joined
·
6 Posts
You are correct. Nice explanation.
There is also a few degrees BTDC and ATDC where the crankshaft moves without the pistons going up or down. I think it was called swing over?? The inertia from the flywheel keeps it going in the correct direction. Keep in mind that the timing is set so the end of the burn (duration of burn based on plugs, heat range coil saturation etc....) is optimal at about 12 degrees ATDC for most stock engines, This allows for the most combustable force to be applied in the downward power stroke.
 

·
Registered
Joined
·
9,745 Posts
Discussion Starter #3 (Edited)
Yeah, there are many C3 myths that refuse to die because they are constantly repeated. Like the need to drill thermostats, soak hydraulic lifters, do figure eights, and shim distributors.
 
1 - 3 of 3 Posts
Top