More Engine Tuning Theory Discussion
11-18-2004, 03:50 PM
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More Engine Tuning Theory Discussion
As it seems, there has been a need for another technical discussion on tuning theory. I think more and more questions arise why you run 12:1 afr vs. 13:1 or 14:1 or this certain ignition timing. Anyone can just find threads where such and such ran this ignition timing and this AFR. I think very few people know why you would run this certain AFR or Ignition timing.
Until now, i didnt want to get in depth of the reasons why, but to justify the reasons I recommend certain AFR's and Ignition timing, we will discuss it.
In order to really under stand this discussion, you will need to know a lot of mechanics of the engine. IE. the cycles the motor takes. i really dont want to take the time to go into detail for now, maybe later.
First lets go over a few things. we will talk about ignition first.
The name of the game to making power is making the burn duration when the peak combustion pressure occur around 16 degrees after top dead center. The reason you want this is because it creates the most force on the crankshaft at the optimum angle to produce the most power. Sometimes people refer to this as MBT (maximum brake torque) but i dont really use that term much.
So in order to do that, we need to know a few things. Our boosted application allows the cylinder w/ more dense charges.
Charge density affects the burn rate.
We need to ignite our charge at the right moment that will trigger our peak combustion pressure around 16 degrees after top dead center. We also know that because the air is more dense and more dense the charge is, the less time needed to complete the burn. This all correlates with gas burn rate, however also know that the faster the engine is turning, the shorter the time for the crank angle to reach that 16 degrees ATDC. so we would need to advance the ignition timing accordingly to rpms. Most so called tuners dont know this.
Obviously the afr and charge density are some big factors affecting the burn rate. as mentioned before the higher charge density will burn faster because of the function of gas pressures and gas temps. chamber size, spark plug location and other factors will also affect burn right, but we wont really be concerned with that for now. Slower burn time reduces pumping efficiency, thats why you want to use the lowest octane that will not detonate. The pure fact of higher octane does not make the fuel burn slower, its actually the chemical composition, many people do not know this either.
Lets talk a bit about AFR's. Many people just see people running XX:1 Air Fuel Ratio, and thats what they go by. You have to look deeper into Heat Transfer theory to really understand what is going on here, and why you would run certain AFR's.
About 25 % of the air/fuel mixture energy is converted to work, and the remaining 75% must be transferred from the engine to the environment. .
From what I have read, there are three basic paths for energy flow: coolant, exhaust, and of course work. They are approximately equal, each about 1/3 of the energy of the incoming fuel/air mixture (I think). If you wanted to get extremely technical, there are three heat transfer mechanisms used to derive formulas. I dont really want to get that in depth however. In short, you use a combination of ignition timing, and also importantly AFR's to control heat within the engine.
When you combine all of this theory, it tells you, the more load on the motor, the richer the engine must be. You run richer AFR's on boosted motors to help absorb the heat. Combustion dynamics tells us that when charge density goes up, more heat is generated. If you run too lean, you can guess what happens. There are many arguments on the correct AFR. By theory, you shouldnt ever run over 12.5:1 on high boosted applications. Typically I wouldnt even go over 12:1. Its pushing the envelope.
If you were to compare the power differences between 12.5:1 and even 11.8:1 the gains are very minimal. It provides a much much safer condition running richer and losing, say 5-10 whp on a 500 or 600 whp car. Its just not worth it. many people do not grasp that concept. Also, many people dont realize...especially with systems like hondata, when u can not control the Air Temp
Correction Factor. You go and tune the car to a risk taking 12.5:1 AFR on a high boosted application and lets say your intake temps that day on the dyno are 90 degrees. You take it to the track on a cooler night say 65. I can almost promise you, you're going to be over 13:1. Thats another reason why its important to not only tune on a dyno for high boost, but to put the car in real life conditions, things change a bit from the dyno to the street.
Ok, I got down the reason we want a Rich AFR under boost. But what about out of boost?
well im sure you've all heard of Stoichiometric conditions. This is described as 14.7:1 AFR. This is an important number for manufactures because this AFR allows the catalytic converter to maximize its effect of reducing harmful exhaust gas emissions.
This isnt the best in terms of Fuel efficiency. you can lean the motor out as much as possible when you are at lower load levels (cruising). I typically run 15.0:1 or so.
Octane Levels
The octane number of a gasoline is NOT a measure of it's hotness or coolness in the burning process, and it is NOT a measure of how 'powerful' it is. The octane number is simply a measure of how good the gasoline resistance of detonation. This is a huge misconception. Higher octane fuels are better at controlling the decomposition into auto-ignition compounds than lower octane fuels. Many people think they can run higher octane fuel at leaner temps. well they are simply wrong.
Until now, i didnt want to get in depth of the reasons why, but to justify the reasons I recommend certain AFR's and Ignition timing, we will discuss it.
In order to really under stand this discussion, you will need to know a lot of mechanics of the engine. IE. the cycles the motor takes. i really dont want to take the time to go into detail for now, maybe later.
First lets go over a few things. we will talk about ignition first.
The name of the game to making power is making the burn duration when the peak combustion pressure occur around 16 degrees after top dead center. The reason you want this is because it creates the most force on the crankshaft at the optimum angle to produce the most power. Sometimes people refer to this as MBT (maximum brake torque) but i dont really use that term much.
So in order to do that, we need to know a few things. Our boosted application allows the cylinder w/ more dense charges.
Charge density affects the burn rate.
We need to ignite our charge at the right moment that will trigger our peak combustion pressure around 16 degrees after top dead center. We also know that because the air is more dense and more dense the charge is, the less time needed to complete the burn. This all correlates with gas burn rate, however also know that the faster the engine is turning, the shorter the time for the crank angle to reach that 16 degrees ATDC. so we would need to advance the ignition timing accordingly to rpms. Most so called tuners dont know this.
Obviously the afr and charge density are some big factors affecting the burn rate. as mentioned before the higher charge density will burn faster because of the function of gas pressures and gas temps. chamber size, spark plug location and other factors will also affect burn right, but we wont really be concerned with that for now. Slower burn time reduces pumping efficiency, thats why you want to use the lowest octane that will not detonate. The pure fact of higher octane does not make the fuel burn slower, its actually the chemical composition, many people do not know this either.
Lets talk a bit about AFR's. Many people just see people running XX:1 Air Fuel Ratio, and thats what they go by. You have to look deeper into Heat Transfer theory to really understand what is going on here, and why you would run certain AFR's.
About 25 % of the air/fuel mixture energy is converted to work, and the remaining 75% must be transferred from the engine to the environment. .
From what I have read, there are three basic paths for energy flow: coolant, exhaust, and of course work. They are approximately equal, each about 1/3 of the energy of the incoming fuel/air mixture (I think). If you wanted to get extremely technical, there are three heat transfer mechanisms used to derive formulas. I dont really want to get that in depth however. In short, you use a combination of ignition timing, and also importantly AFR's to control heat within the engine.
When you combine all of this theory, it tells you, the more load on the motor, the richer the engine must be. You run richer AFR's on boosted motors to help absorb the heat. Combustion dynamics tells us that when charge density goes up, more heat is generated. If you run too lean, you can guess what happens. There are many arguments on the correct AFR. By theory, you shouldnt ever run over 12.5:1 on high boosted applications. Typically I wouldnt even go over 12:1. Its pushing the envelope.
If you were to compare the power differences between 12.5:1 and even 11.8:1 the gains are very minimal. It provides a much much safer condition running richer and losing, say 5-10 whp on a 500 or 600 whp car. Its just not worth it. many people do not grasp that concept. Also, many people dont realize...especially with systems like hondata, when u can not control the Air Temp
Correction Factor. You go and tune the car to a risk taking 12.5:1 AFR on a high boosted application and lets say your intake temps that day on the dyno are 90 degrees. You take it to the track on a cooler night say 65. I can almost promise you, you're going to be over 13:1. Thats another reason why its important to not only tune on a dyno for high boost, but to put the car in real life conditions, things change a bit from the dyno to the street.
Ok, I got down the reason we want a Rich AFR under boost. But what about out of boost?
well im sure you've all heard of Stoichiometric conditions. This is described as 14.7:1 AFR. This is an important number for manufactures because this AFR allows the catalytic converter to maximize its effect of reducing harmful exhaust gas emissions.
This isnt the best in terms of Fuel efficiency. you can lean the motor out as much as possible when you are at lower load levels (cruising). I typically run 15.0:1 or so.
Octane Levels
The octane number of a gasoline is NOT a measure of it's hotness or coolness in the burning process, and it is NOT a measure of how 'powerful' it is. The octane number is simply a measure of how good the gasoline resistance of detonation. This is a huge misconception. Higher octane fuels are better at controlling the decomposition into auto-ignition compounds than lower octane fuels. Many people think they can run higher octane fuel at leaner temps. well they are simply wrong.
11-18-2004, 05:00 PM
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Re: (System-7)
Very good mase very correct information
Put very well for the ppl that may not understand
If you wanna put a more in depth one i would love to read
Put very well for the ppl that may not understand
If you wanna put a more in depth one i would love to read
11-18-2004, 05:42 PM
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Re: (96GSRkId)
good stuff mase...
one thing not too many people realize is that different brands of gas can have very different propreties.. when you are pushing the limit its something you have to be aware of. even in the world of leaded race gas there are differences you much account for. ex.. our local shell gas station is usually good for about 5-8hp on a 300hp honda, the texaco results in detonation if used with the same tune as the shell gas.
in general use timing to make the power, use the fuel for thermal management. put the timing where it makes power, use the fuel to keep the egt's in check. leaded gas in my experience will run cooler than unleaded gas.
and READ the plugs.... i cant tell you how many people i see that try to tune a car w/o reading the plugs, you can have knock sensors and egt's and o2's and everything else, but nothing will replace reading the plugs.
one thing not too many people realize is that different brands of gas can have very different propreties.. when you are pushing the limit its something you have to be aware of. even in the world of leaded race gas there are differences you much account for. ex.. our local shell gas station is usually good for about 5-8hp on a 300hp honda, the texaco results in detonation if used with the same tune as the shell gas.
in general use timing to make the power, use the fuel for thermal management. put the timing where it makes power, use the fuel to keep the egt's in check. leaded gas in my experience will run cooler than unleaded gas.
and READ the plugs.... i cant tell you how many people i see that try to tune a car w/o reading the plugs, you can have knock sensors and egt's and o2's and everything else, but nothing will replace reading the plugs.
11-18-2004, 06:00 PM
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Re: More Engine Tuning Theory Discussion (Mase)
I agree 100% with everything you said. I am one that already knew that stuff, but thanks for sharing your vast knowledge on the subject. One more minor thing you kindof said with spark timing is the plugs. The heat range and gap make a big difference on power output of a motor too. Playing with the gap kindof messes with the timing alittle, though making it to big can cause it to be blown out at higher rpms. I know you already knew that, just stating another point. 
I am one that already knew that stuff, but thanks for sharing your vast knowledge on the subject. One more minor thing you kindof said with spark timing is the plugs. The heat range and gap make a big difference on power output of a motor too. Playing with the gap kindof messes with the timing alittle, though making it to big can cause it to be blown out at higher rpms. I know you already knew that, just stating another point.
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11-18-2004, 07:43 PM
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Re: More Engine Tuning Theory Discussion (sporkcrx)
great thread . Mase, so as far as mbt goes basically it occurs at 16 degree's at idle im assumig and you tune for mbt? So as engine speed increase's and the air density changes your mbt will change right? That is why your timing increase's or decrease's for boost correct?
Modified by NAPIER at 4:53 AM 11/19/2004
. Mase, so as far as mbt goes basically it occurs at 16 degree's at idle im assumig and you tune for mbt? So as engine speed increase's and the air density changes your mbt will change right? That is why your timing increase's or decrease's for boost correct?Modified by NAPIER at 4:53 AM 11/19/2004
11-18-2004, 08:01 PM
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Re: More Engine Tuning Theory Discussion (Mase)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase »</TD></TR><TR><TD CLASS="quote">In order to really under stand this discussion, you will need to know a lot of mechanics of the engine. IE. the cycles the motor takes. i really dont want to take the time to go into detail for now, maybe later.</TD></TR></TABLE>
Give us the stuff you think we cannot understand. I'm sure everyone that doesn't understand it will start searching, and teach themselves to undestand it. I know i will. Great write up, thanks
Give us the stuff you think we cannot understand. I'm sure everyone that doesn't understand it will start searching, and teach themselves to undestand it. I know i will. Great write up, thanks
11-18-2004, 08:15 PM
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Re: More Engine Tuning Theory Discussion (Si Shane)
good stuff, so many times someone asks me to tune thier car, i say it will be tuned to 11.8:1, they then balk and act like i'm robbing them of power, i remind them that they are welcome to go elsewhere, but if you are in my garage, you are goign to be running at 11.8:1.
now i can point them to this thread versus everywhere else they say, but so and so runs 12.5:1.....
now i can point them to this thread versus everywhere else they say, but so and so runs 12.5:1.....
11-18-2004, 08:16 PM
#16
Re: More Engine Tuning Theory Discussion (Mase)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase »</TD></TR><TR><TD CLASS="quote">Slower burn time reduces pumping efficiency, thats why you want to use the lowest octane that will not detonate. The pure fact of higher octane does not make the fuel burn slower, its actually the chemical composition, many people do not know this either.</TD></TR></TABLE>
Could you expand on this a little more?
Could you expand on this a little more?
11-18-2004, 08:26 PM
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Re: More Engine Tuning Theory Discussion (NAPIER)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NAPIER »</TD></TR><TR><TD CLASS="quote">great thread . Mase, so as far as mbt goes basically it occurs at 16 degree's at idle im assumig and you tune for mbt? So as engine speed increase's and the air density changes your mbt will change right? That is why your timing increase's or decrease's for boost correct?
</TD></TR></TABLE>
you're confusing with 16 degrees before top dead center. you dont really tune idle for best torque, you tune it for smoothness and consistancy. as the engine rpms change, you will need to ignite the charge at different times to achieve your max brake torque.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman »</TD></TR><TR><TD CLASS="quote">
Could you expand on this a little more? </TD></TR></TABLE>
Basically, you will make more power w/ lower octane that will not detonate vs higher octane ....
. Mase, so as far as mbt goes basically it occurs at 16 degree's at idle im assumig and you tune for mbt? So as engine speed increase's and the air density changes your mbt will change right? That is why your timing increase's or decrease's for boost correct?</TD></TR></TABLE>
you're confusing with 16 degrees before top dead center. you dont really tune idle for best torque, you tune it for smoothness and consistancy. as the engine rpms change, you will need to ignite the charge at different times to achieve your max brake torque.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman »</TD></TR><TR><TD CLASS="quote">
Could you expand on this a little more? </TD></TR></TABLE>
Basically, you will make more power w/ lower octane that will not detonate vs higher octane ....
11-18-2004, 09:13 PM
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Re: More Engine Tuning Theory Discussion (Mase)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase »</TD></TR><TR><TD CLASS="quote">ive done enough, i should publish something, u can buy it off me....hah</TD></TR></TABLE>
Lol...kinda like the Ben Strader book huh?? We'll call it:
"Mased: An Official Look Into Mase's Tuning Theories"
Lol...kinda like the Ben Strader book huh?? We'll call it:
"Mased: An Official Look Into Mase's Tuning Theories"
11-18-2004, 09:15 PM
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Re: More Engine Tuning Theory Discussion (Bulldogg83)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bulldogg83 »</TD></TR><TR><TD CLASS="quote">
Lol...kinda like the Ben Strader book huh?? We'll call it:
"Mased: An Official Look Into Mase's Tuning Theories"</TD></TR></TABLE>
as a bonus: "Mased: An Official Look Into Mase's Tuning Theories and how to pull hot chicks"
Lol...kinda like the Ben Strader book huh?? We'll call it:
"Mased: An Official Look Into Mase's Tuning Theories"</TD></TR></TABLE>
as a bonus: "Mased: An Official Look Into Mase's Tuning Theories and how to pull hot chicks"
11-18-2004, 09:21 PM
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Re: More Engine Tuning Theory Discussion (Mase)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mase »</TD></TR><TR><TD CLASS="quote">ive done enough, i should publish something, u can buy it off me....hah</TD></TR></TABLE>
Sweet, then I can photocopy it and put it on the internet and claim it as mine
Sweet, then I can photocopy it and put it on the internet and claim it as mine
