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jimberg · 06-14-2001, 01:26 PM

I have thoughts on timing

, and yes, tuning the timing on a dyno is the best thing to do. Too much timing will do more harm than good.

Advancing the timing will net you more power throughout the powerband since you are able to utilize more of the energy being released by the explosion of the air/fuel mixture.

Bear with me since this is probably something that most people know, but it's a good idea to keep in mind and not all people know it.

When we get our basic lesson on how four stroke engines work, we know that there is an intake stroke where air is sucked into the cylinder and fuel is injected. This is then compressed and ignited. Before I ever understood what timing was, I always assumed that the fuel was ignited at the top of the compression stroke and then the piston was just pushed down buy exploding gases.

What they really do is start the explosion before the piston gets to TDC to get the mixture expanding during the compression stroke. It's kind of like compressing a super duty spring that then releases its full amount of potential energy after passing TDC. This is where it becomes relevant to the thread. The danger, though, is that if you start the expansion too early along with high combustion chamber temps, the fuel will spontaneously ignite (Detonation). My guess is that if you could take a movie of the explosion in super slomo, you'd see the explosion start up by the sparkplug and grow downward toward the piston. During detonation, all the fuel explodes at once before it reaches TDC.

There's a lot of important information that can be derived from knowing this.

When you advance timing, you increase the amount of potential energy that can be released after the piston reaches TDC.

Cooler combustion chamber temps as a result of aluminum heads will allow you to advance your timing farther.

Cooler combustion chamber temps as a result of running richer will also allow you to advance your timing farther.

Octane is the lab measured amount of compression that fuel can take before it detonates. This is why you use a higher octane with high compression engines, or with engines that have advanced timing. High octane fuel also burns slower so using it with stock timing will give you less power since the amount of potential energy released at TDC will be less.

This is why timing advance is important as engine RPMs go up. Since the piston is moving faster, it is important to start the expansion of gases earler so that you maintain your maximum amount of potential energy throughout the rpm range.

There's probably a lot more, but I think you guys should have a good idea of what's going on.

Before anyone harps on me about going into such detail on what we consider basic, there are a lot of people on this site and other sites who have no clue about this stuff. It's obvious in a lot of questions that are asked.

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351W 89 Mustang GT Convertible

[This message has been edited by jimberg (edited 06-14-2001).]

06-14-2001, 01:26 PM	#20
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I have thoughts on timing , and yes, tuning the timing on a dyno is the best thing to do. Too much timing will do more harm than good. Advancing the timing will net you more power throughout the powerband since you are able to utilize more of the energy being released by the explosion of the air/fuel mixture. Bear with me since this is probably something that most people know, but it's a good idea to keep in mind and not all people know it. When we get our basic lesson on how four stroke engines work, we know that there is an intake stroke where air is sucked into the cylinder and fuel is injected. This is then compressed and ignited. Before I ever understood what timing was, I always assumed that the fuel was ignited at the top of the compression stroke and then the piston was just pushed down buy exploding gases. What they really do is start the explosion before the piston gets to TDC to get the mixture expanding during the compression stroke. It's kind of like compressing a super duty spring that then releases its full amount of potential energy after passing TDC. This is where it becomes relevant to the thread. The danger, though, is that if you start the expansion too early along with high combustion chamber temps, the fuel will spontaneously ignite (Detonation). My guess is that if you could take a movie of the explosion in super slomo, you'd see the explosion start up by the sparkplug and grow downward toward the piston. During detonation, all the fuel explodes at once before it reaches TDC. There's a lot of important information that can be derived from knowing this. When you advance timing, you increase the amount of potential energy that can be released after the piston reaches TDC. Cooler combustion chamber temps as a result of aluminum heads will allow you to advance your timing farther. Cooler combustion chamber temps as a result of running richer will also allow you to advance your timing farther. Octane is the lab measured amount of compression that fuel can take before it detonates. This is why you use a higher octane with high compression engines, or with engines that have advanced timing. High octane fuel also burns slower so using it with stock timing will give you less power since the amount of potential energy released at TDC will be less. This is why timing advance is important as engine RPMs go up. Since the piston is moving faster, it is important to start the expansion of gases earler so that you maintain your maximum amount of potential energy throughout the rpm range. There's probably a lot more, but I think you guys should have a good idea of what's going on. Before anyone harps on me about going into such detail on what we consider basic, there are a lot of people on this site and other sites who have no clue about this stuff. It's obvious in a lot of questions that are asked. ------------------ 351W 89 Mustang GT Convertible [This message has been edited by jimberg (edited 06-14-2001).]