optimising fueling vs timing
Thread Starter
TECH Fanatic
Joined: Aug 2005
Posts: 1,691
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From: Sunny London, UK
optimising fueling vs timing Ok, after noticing how changing timing changes afr if VE is kept the same.
I asume that max power would be attained by obtaining the maximum ve at any point while meeting the commanded afr. This can be done by varying timing and watching afr changes.
So you would move timing around so afr was at its leanest, (optimal combustion) then add fuel (increase ve table in SD mode) to get back to commanded afr. Seeing you are burning more fuel and combusion is optimised (Stoich, or whatever you command), cylinder pressure is optimised!?
How valid is this, or have I missed something?
If its semi valid perhaps this is a good way to tune timing without dyno?
Comments, corrections and points of note appreciated.
I asume that max power would be attained by obtaining the maximum ve at any point while meeting the commanded afr. This can be done by varying timing and watching afr changes.
So you would move timing around so afr was at its leanest, (optimal combustion) then add fuel (increase ve table in SD mode) to get back to commanded afr. Seeing you are burning more fuel and combusion is optimised (Stoich, or whatever you command), cylinder pressure is optimised!?
How valid is this, or have I missed something?
If its semi valid perhaps this is a good way to tune timing without dyno?
Comments, corrections and points of note appreciated.
Thread Starter
TECH Fanatic
Joined: Aug 2005
Posts: 1,691
Likes: 1
From: Sunny London, UK
Yeah, I have done. My comment isn't correct to a point. Timing also depends on the combustion rate and pressure wave. Advanced timing will generally always be leaner than retarded, the key is to place the right point of the combustion pressure curve at the right point (14* atdc or so). So while more fuel is good, too much pressure before tdc is bad.
So I guess this method might be a useful tool, but not a rule.
So I guess this method might be a useful tool, but not a rule.
Originally Posted by ringram
Yeah, I have done. My comment isn't correct to a point. Timing also depends on the combustion rate and pressure wave. Advanced timing will generally always be leaner than retarded, the key is to place the right point of the combustion pressure curve at the right point (14* atdc or so). So while more fuel is good, too much pressure before tdc is bad.
So I guess this method might be a useful tool, but not a rule.
So I guess this method might be a useful tool, but not a rule.
Real-world doesn't always match up to the ideal world.
In a way the engine makes it easy for you to maximize the timing. When you have gone too far you will notice a power loss.
This is easy to see for WOT tuning with a g-meter or accelerometer.
For part throttle you need to log throttle-angle vs speed.
If you can hold a steady speed on flat ground with less throttle, then you're making more power.
There will be 2 or 3 degrees of advance where power levels off before it drops. If you ride the edge of maximum timing, then other little things like air temp, engine temp, or fuel quality can push you over the edge into power loss or spark knock. That's why most people stay a bit on the conservative side.
You were right in that you want to increase advance to get the most power, but some people look at it or state it another way. They say you want to run as little advance as nessessary for best running.
That just means don't go overboard and then use extra fuel to cover it when it's not making you any more power.
That's why I say to watch your throttle angle.
Originally Posted by white2001s10
No you were pretty much correct in your assessment.
Real-world doesn't always match up to the ideal world.
In a way the engine makes it easy for you to maximize the timing. When you have gone too far you will notice a power loss.
This is easy to see for WOT tuning with a g-meter or accelerometer.
For part throttle you need to log throttle-angle vs speed.
If you can hold a steady speed on flat ground with less throttle, then you're making more power.
There will be 2 or 3 degrees of advance where power levels off before it drops. If you ride the edge of maximum timing, then other little things like air temp, engine temp, or fuel quality can push you over the edge into power loss or spark knock. That's why most people stay a bit on the conservative side.
You were right in that you want to increase advance to get the most power, but some people look at it or state it another way. They say you want to run as little advance as nessessary for best running.
That just means don't go overboard and then use extra fuel to cover it when it's not making you any more power.
That's why I say to watch your throttle angle.
Real-world doesn't always match up to the ideal world.
In a way the engine makes it easy for you to maximize the timing. When you have gone too far you will notice a power loss.
This is easy to see for WOT tuning with a g-meter or accelerometer.
For part throttle you need to log throttle-angle vs speed.
If you can hold a steady speed on flat ground with less throttle, then you're making more power.
There will be 2 or 3 degrees of advance where power levels off before it drops. If you ride the edge of maximum timing, then other little things like air temp, engine temp, or fuel quality can push you over the edge into power loss or spark knock. That's why most people stay a bit on the conservative side.
You were right in that you want to increase advance to get the most power, but some people look at it or state it another way. They say you want to run as little advance as nessessary for best running.
That just means don't go overboard and then use extra fuel to cover it when it's not making you any more power.
That's why I say to watch your throttle angle.
