HP, timing vs boost
Dec 30, 2005, 08:20 PM
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HP, timing vs boost
I have been searching the net and evom for months now, but I can not seem to find a definitive answer to this question:
What is more valuable in generating horsepower, timing or boost?
A little background: I started putting together my first modified car ever back in July. I have an AEM ems. I have a 4G64 2.4L stroker kit. I almost bought an Evo which is why I am here ( I wanted to learn about the Evo ). Since I have a DSM, I am guessing that some of you would know the answer to my question. I have never tuned any car, electronic or otherwise, but I have been studying day and night. I am taking my car to a tuner for its initial tuning, but I want to play around with it (otherwise I would not have bought it!).
My theory at this point is to start with a/f ratios so I can conserve gas under closed loops conditions and provide a safety factor during WOT.
After af/ratios, start modifying timing rather than boost since boost creates so much heat. (I have a HUGE intercooler though)
My turbo, unregulated, will spike to 35 PSI, hold 30 PSI for an extended period, and dribble off to about 27 PSI. (it is some sort of mutt turbo that is roughly equivalent to a T3?)
I have been told that each degree of timing is worth about 10HP and that I can expect to max out under ideal conditions at 20 degrees of timing.
How much HP is each PSI of boost worth? Is it worth it to take boost over timing if my turbo pushes 30 PSI? I have been told that each PSI of boost is 10 HP too?
So far, my engine experiences absolutely zero knock at 30 PSI at 0 degrees of timing and the same at 20 degrees of timing at 0 PSI boost. If what I have been told is true, I can make 100 more HP out of 30 PSI boost rather than 20 degrees of timing.
I guess my real question is: which extreme is safer or what balance would you go for considering that safety is the overall concern?
Thanks in advance.
strike (Dave)
(I am 38, not some wild eyed kid looking to street race. I would appreciate real information.)
What is more valuable in generating horsepower, timing or boost?
A little background: I started putting together my first modified car ever back in July. I have an AEM ems. I have a 4G64 2.4L stroker kit. I almost bought an Evo which is why I am here ( I wanted to learn about the Evo ). Since I have a DSM, I am guessing that some of you would know the answer to my question. I have never tuned any car, electronic or otherwise, but I have been studying day and night. I am taking my car to a tuner for its initial tuning, but I want to play around with it (otherwise I would not have bought it!).
My theory at this point is to start with a/f ratios so I can conserve gas under closed loops conditions and provide a safety factor during WOT.
After af/ratios, start modifying timing rather than boost since boost creates so much heat. (I have a HUGE intercooler though)
My turbo, unregulated, will spike to 35 PSI, hold 30 PSI for an extended period, and dribble off to about 27 PSI. (it is some sort of mutt turbo that is roughly equivalent to a T3?)
I have been told that each degree of timing is worth about 10HP and that I can expect to max out under ideal conditions at 20 degrees of timing.
How much HP is each PSI of boost worth? Is it worth it to take boost over timing if my turbo pushes 30 PSI? I have been told that each PSI of boost is 10 HP too?
So far, my engine experiences absolutely zero knock at 30 PSI at 0 degrees of timing and the same at 20 degrees of timing at 0 PSI boost. If what I have been told is true, I can make 100 more HP out of 30 PSI boost rather than 20 degrees of timing.
I guess my real question is: which extreme is safer or what balance would you go for considering that safety is the overall concern?
Thanks in advance.
strike (Dave)
(I am 38, not some wild eyed kid looking to street race. I would appreciate real information.)
Dec 30, 2005, 08:42 PM
#2
hey kid,
you will hear from some who are a lot better informed than I, but here I go anyway.
you do not want to run zero timing., first of all you would have a serious lack of power, not to mention the fire in your exhaust.
you have seen those graphs of horsepower and torque, where the two lines cross, one down and the other up? Same thing with timing / boost. Once timing hits the wall it is all down hill. You keep cutting back on timing , so you can run more boost, but the net is no gain.
If you do want to push the envelope I suggest you run an EGT gauge because you can ruin an engine without enough timing.
good luck, I am sure you will get more informative posts soon.
you will hear from some who are a lot better informed than I, but here I go anyway.
you do not want to run zero timing., first of all you would have a serious lack of power, not to mention the fire in your exhaust.
you have seen those graphs of horsepower and torque, where the two lines cross, one down and the other up? Same thing with timing / boost. Once timing hits the wall it is all down hill. You keep cutting back on timing , so you can run more boost, but the net is no gain.
If you do want to push the envelope I suggest you run an EGT gauge because you can ruin an engine without enough timing.
good luck, I am sure you will get more informative posts soon.
Dec 30, 2005, 08:46 PM
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Originally Posted by nothere
hey kid,
you will hear from some who are a lot better informed than I, but here I go anyway.
you do not want to run zero timing., first of all you would have a serious lack of power, not to mention the fire in your exhaust.
you have seen those graphs of horsepower and torque, where the two lines cross, one down and the other up? Same thing with timing / boost. Once timing hits the wall it is all down hill. You keep cutting back on timing , so you can run more boost, but the net is no gain.
If you do want to push the envelope I suggest you run an EGT gauge because you can ruin an engine without enough timing.
good luck, I am sure you will get more informative posts soon.
you will hear from some who are a lot better informed than I, but here I go anyway.
you do not want to run zero timing., first of all you would have a serious lack of power, not to mention the fire in your exhaust.
you have seen those graphs of horsepower and torque, where the two lines cross, one down and the other up? Same thing with timing / boost. Once timing hits the wall it is all down hill. You keep cutting back on timing , so you can run more boost, but the net is no gain.
If you do want to push the envelope I suggest you run an EGT gauge because you can ruin an engine without enough timing.
good luck, I am sure you will get more informative posts soon.
i have almost every guage imaginable (IAT, EGT, Oil Temp, Coolant Temp, etc etc).
the car is not tuned yet, which is why it is at 0 timing. i won't be able to tune it myself for a couple more months since i am in iraq. thank you for your insight.
strike (Dave)
Dec 30, 2005, 09:31 PM
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Each psi of boost worths about 10HP, but it will take a few degree of timing for a gain of about 10LBof torque. Timing has less effect on HP than torque too.
As always, YMMV. It depends on what size your turbo is and its most efficient boost range. The quality of the fuel has a lot to do with the ideal AFR, ignition timing and boost. FWIW, I gained about 50LB of torque and 50+ horsepower from straight 91 octane to 91octane + methanol injection. It takes 4 additonal psi of boost and 5 additional degrees of ignition timing to make that kind of difference, which was impossible to achieve with stright 91 octane without major knock.
As always, YMMV. It depends on what size your turbo is and its most efficient boost range. The quality of the fuel has a lot to do with the ideal AFR, ignition timing and boost. FWIW, I gained about 50LB of torque and 50+ horsepower from straight 91 octane to 91octane + methanol injection. It takes 4 additonal psi of boost and 5 additional degrees of ignition timing to make that kind of difference, which was impossible to achieve with stright 91 octane without major knock.
Dec 31, 2005, 06:59 AM
#6
Originally Posted by strikethree
After af/ratios, start modifying timing rather than boost since boost creates so much heat.
Assuming your IC is 100% efficient (and it isn't), increasing boost pressure with no intake air temp change increases the air mass going into the engine. This is what creates the potential for more power. Because the volume of the engine and compression ratio are constants, increasing the incoming air mass increases static cylinder pressure. Of course, the pressure goes WAY up when that compressed mix is ignited.
The standard rule of thumb is for best power, ignition timing is adjusted such that max cylinder pressure (from the ignited, expanding air/fuel mixture) always occurs at 10-15 deg ATDC. If this point occurs earlier, you get preignition. If later, you lose power. As you turn up the boost, the higher static pressure causes the mix to burn faster, so less ignition advance is required to achieve max pressure in that same 10-15 deg ATDC range. So, as you increase the boost, you retard the timing to compensate.
Increasing the boost will increase power until you reach the practical limits of your fuel. At that point, you will not be able to run enough ignition advance to accomodate higher cylinder pressures, and this will negate any increased power potential afforded by applying more boost. So when tuning, boost pressure vs. ignition advance is a balancing act.
So how much boost can you run until you cannot give enough ignition advance to produce more power? That depends on your fuel quality, turbo efficiency, engine design, etc. And of course, ICs aren't 100% efficient.
Here's an article that has a handy table: http://www.motion-dynamics.net/Compression-Boost.html. The commentary is somewhat flawed (be advised), but the table at the bottom more or less puts into perspective that a typical EVO with 16G and 93 oct will withstand ~22:1 effective compression until the point is reached whereby greater boost pressure requires too much ignition retard to make more power.
Of course, this is just a thumbnail sketch and omits numerous influencing factors, so accept that FWIW.
Last edited by Ted B; Dec 31, 2005 at 07:08 AM.
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Dec 31, 2005, 10:13 AM
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Originally Posted by SlowCar
hope you got wideband too?
thank you for making sure i did not miss something so important. i have sensors to monitor every aspect of my engine.the only thing i do not have is a g-force meter... and i may pick one of those up too.
strike
Dec 31, 2005, 12:11 PM
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Originally Posted by Ted B
In a nutshell, it doesn't work that way, simply because boost pressure affects cylinder pressure, which dictates ignition timing. Obviously, the limits of the fuel play a role in this as well.
Assuming your IC is 100% efficient (and it isn't), increasing boost pressure with no intake air temp change increases the air mass going into the engine. This is what creates the potential for more power. Because the volume of the engine and compression ratio are constants, increasing the incoming air mass increases static cylinder pressure. Of course, the pressure goes WAY up when that compressed mix is ignited.
The standard rule of thumb is for best power, ignition timing is adjusted such that max cylinder pressure (from the ignited, expanding air/fuel mixture) always occurs at 10-15 deg ATDC. If this point occurs earlier, you get preignition. If later, you lose power. As you turn up the boost, the higher static pressure causes the mix to burn faster, so less ignition advance is required to achieve max pressure in that same 10-15 deg ATDC range. So, as you increase the boost, you retard the timing to compensate.
Increasing the boost will increase power until you reach the practical limits of your fuel. At that point, you will not be able to run enough ignition advance to accomodate higher cylinder pressures, and this will negate any increased power potential afforded by applying more boost. So when tuning, boost pressure vs. ignition advance is a balancing act.
So how much boost can you run until you cannot give enough ignition advance to produce more power? That depends on your fuel quality, turbo efficiency, engine design, etc. And of course, ICs aren't 100% efficient.
Here's an article that has a handy table: http://www.motion-dynamics.net/Compression-Boost.html. The commentary is somewhat flawed (be advised), but the table at the bottom more or less puts into perspective that a typical EVO with 16G and 93 oct will withstand ~22:1 effective compression until the point is reached whereby greater boost pressure requires too much ignition retard to make more power.
Of course, this is just a thumbnail sketch and omits numerous influencing factors, so accept that FWIW.
Assuming your IC is 100% efficient (and it isn't), increasing boost pressure with no intake air temp change increases the air mass going into the engine. This is what creates the potential for more power. Because the volume of the engine and compression ratio are constants, increasing the incoming air mass increases static cylinder pressure. Of course, the pressure goes WAY up when that compressed mix is ignited.
The standard rule of thumb is for best power, ignition timing is adjusted such that max cylinder pressure (from the ignited, expanding air/fuel mixture) always occurs at 10-15 deg ATDC. If this point occurs earlier, you get preignition. If later, you lose power. As you turn up the boost, the higher static pressure causes the mix to burn faster, so less ignition advance is required to achieve max pressure in that same 10-15 deg ATDC range. So, as you increase the boost, you retard the timing to compensate.
Increasing the boost will increase power until you reach the practical limits of your fuel. At that point, you will not be able to run enough ignition advance to accomodate higher cylinder pressures, and this will negate any increased power potential afforded by applying more boost. So when tuning, boost pressure vs. ignition advance is a balancing act.
So how much boost can you run until you cannot give enough ignition advance to produce more power? That depends on your fuel quality, turbo efficiency, engine design, etc. And of course, ICs aren't 100% efficient.
Here's an article that has a handy table: http://www.motion-dynamics.net/Compression-Boost.html. The commentary is somewhat flawed (be advised), but the table at the bottom more or less puts into perspective that a typical EVO with 16G and 93 oct will withstand ~22:1 effective compression until the point is reached whereby greater boost pressure requires too much ignition retard to make more power.
Of course, this is just a thumbnail sketch and omits numerous influencing factors, so accept that FWIW.
First, I would like to thank you for your response and for the link that you provided. I apologize for the semi-coherence of my initial question, I posted it after 30 hours without sleep.
My understanding about TDC and timing and such is that for max power, the burn should start precisely when TDC (max compression) is achieved and the piston starts moving back down. My understanding of why timing is "advanced" is because it takes X amount of time for the spark to actually be generated so that there is a lag between when TDC is achieved and when the spark actually occurs; therefore, the spark is initiated 20 degrees or whatever before TDC so that the spark actually occurs at TDC. Is this correct? I am assuming that the post 10-15 degree timing that you mention above is for safety margin and when the burn is actually completed. Is this correct too?
It appears as if you are telling me that timing should give way for max boost (to a certain extent), rather than maintaining max timing with boost being limited to pre-knock levels. Is this correct?
Thank you again for your time.
strike
Dec 31, 2005, 12:15 PM
#10
almost,
no, you want Peak Pressure to hit at approx. 15 degrees AFTER TDC.. But yes you start ignition early because it takes time for the fire to spread to the maximum power.
sort of like swinging a bat, if you wait for the ball to be at the sweet spot you will be sitting on the bench.
no, you want Peak Pressure to hit at approx. 15 degrees AFTER TDC.. But yes you start ignition early because it takes time for the fire to spread to the maximum power.
sort of like swinging a bat, if you wait for the ball to be at the sweet spot you will be sitting on the bench.
Dec 31, 2005, 12:24 PM
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Originally Posted by BJai02
Each psi of boost worths about 10HP, but it will take a few degree of timing for a gain of about 10LBof torque. Timing has less effect on HP than torque too.
As always, YMMV. It depends on what size your turbo is and its most efficient boost range. The quality of the fuel has a lot to do with the ideal AFR, ignition timing and boost. FWIW, I gained about 50LB of torque and 50+ horsepower from straight 91 octane to 91octane + methanol injection. It takes 4 additonal psi of boost and 5 additional degrees of ignition timing to make that kind of difference, which was impossible to achieve with stright 91 octane without major knock.
As always, YMMV. It depends on what size your turbo is and its most efficient boost range. The quality of the fuel has a lot to do with the ideal AFR, ignition timing and boost. FWIW, I gained about 50LB of torque and 50+ horsepower from straight 91 octane to 91octane + methanol injection. It takes 4 additonal psi of boost and 5 additional degrees of ignition timing to make that kind of difference, which was impossible to achieve with stright 91 octane without major knock.
so you are saying that timing is more important for torque than boost?
also, since i have your attention and you have an alcohol kit: do you run straight meth or do you run a mix of meth and water? did you do dyno measurements with and without meth or are those butt-dyno numbers? what are you tuning with: standalone or piggy back?
i am dying for max torque. when i push the accelerator, i want to be squished deeply into my seat. i care nothing for top speed, it is all about the acceleration.
strike
Dec 31, 2005, 12:26 PM
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Originally Posted by nothere
almost,
no, you want Peak Pressure to hit at approx. 15 degrees AFTER TDC.. But yes you start ignition early because it takes time for the fire to spread to the maximum power.
sort of like swinging a bat, if you wait for the ball to be at the sweet spot you will be sitting on the bench.
no, you want Peak Pressure to hit at approx. 15 degrees AFTER TDC.. But yes you start ignition early because it takes time for the fire to spread to the maximum power.
sort of like swinging a bat, if you wait for the ball to be at the sweet spot you will be sitting on the bench.
strike
Dec 31, 2005, 12:38 PM
#13
Originally Posted by strikethree
First, I would like to thank you for your response and for the link that you provided. I apologize for the semi-coherence of my initial question, I posted it after 30 hours without sleep.
My understanding about TDC and timing and such is that for max power, the burn should start precisely when TDC (max compression) is achieved and the piston starts moving back down.
My understanding about TDC and timing and such is that for max power, the burn should start precisely when TDC (max compression) is achieved and the piston starts moving back down.
Originally Posted by strikethree
My understanding of why timing is "advanced" is because it takes X amount of time for the spark to actually be generated so that there is a lag between when TDC is achieved and when the spark actually occurs; therefore, the spark is initiated 20 degrees or whatever before TDC so that the spark actually occurs at TDC. Is this correct? I am assuming that the post 10-15 degree timing that you mention above is for safety margin and when the burn is actually completed. Is this correct too?
Originally Posted by strikethree
It appears as if you are telling me that timing should give way for max boost (to a certain extent), rather than maintaining max timing with boost being limited to pre-knock levels. Is this correct?
Thank you again for your time.
strike
Keith
Last edited by Fourdoor; Dec 31, 2005 at 12:44 PM.
Dec 31, 2005, 12:41 PM
#14
peak pressure occurs at the end of the burn?
strike
I wouldn't say that, but the burn is more complicated than one would think. The quality of the flame determines power vrs. knocking. To fast a burn can be harmful.
I have read descriptions of fuel burns where the author used the example of a dry grass field burn, where when all works correctly, it starts at one end and flows across the field almost instantly.
A number of things determine burn rate, extra fuel slows the rate, increased pressure speeds it up.
strike
I wouldn't say that, but the burn is more complicated than one would think. The quality of the flame determines power vrs. knocking. To fast a burn can be harmful.
I have read descriptions of fuel burns where the author used the example of a dry grass field burn, where when all works correctly, it starts at one end and flows across the field almost instantly.
A number of things determine burn rate, extra fuel slows the rate, increased pressure speeds it up.
Dec 31, 2005, 01:02 PM
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Originally Posted by Fourdoor
Nope, as Ted B stated the important event is having maximum cylinder pressure at 10 to 15 deg past TDC. This is because the piston is acting as a pushing force on the rod connected to the crank shaft. If max pressure was at TDC the piston would not move down the cylinder because it would be directly lined up with the crank journal.... it would not have anywhere to go. It has to be at an angle in order for that downward force to be converted into a rotational force. I have trouble explaining this clearly without diagrams so it probably sounds like gibberish to you
It is not the spark that takes time, it is the actual time it takes for the flame front to propogate through the air fuel mixture. It may seem like it takes no time at all, but it does. The higher the RPM the motor is spinning at, the more you have to advace the timing for max pressure to happen at 10 to 15 deg after TDC. This is because if boost pressure remains constant the fuel burns at the same speed no matter what, but the amount of time the piston is at the top of its stroke goes down the higher the RPM you are running, so at high RPM you have to start the burn sooner for it to reach max combustion chamber pressure at 10 to 15 deg after TDC. Now, as boost pressure rises, your flam front travels faster through the air fuel mixture... this is why when your run more boost you need to run less timing advance. Once again, math equations and diagrams are needed to explain this fully....
The ideal situation would be to set up the system to run at the highest boost your turbo can make while remaining in it's max efficiancy island on the compressor map as long as your fuel octane can support that boost level, and then adjust your timing map for max power production. This would be best done on a load bearing dyno that has real time power output so you can hold at a specific boost and RPM point and then adjust timing for max power at that point. Many people tune for the ragged edge of knock, but that is not usually where you make the most power.
Keith
It is not the spark that takes time, it is the actual time it takes for the flame front to propogate through the air fuel mixture. It may seem like it takes no time at all, but it does. The higher the RPM the motor is spinning at, the more you have to advace the timing for max pressure to happen at 10 to 15 deg after TDC. This is because if boost pressure remains constant the fuel burns at the same speed no matter what, but the amount of time the piston is at the top of its stroke goes down the higher the RPM you are running, so at high RPM you have to start the burn sooner for it to reach max combustion chamber pressure at 10 to 15 deg after TDC. Now, as boost pressure rises, your flam front travels faster through the air fuel mixture... this is why when your run more boost you need to run less timing advance. Once again, math equations and diagrams are needed to explain this fully....
The ideal situation would be to set up the system to run at the highest boost your turbo can make while remaining in it's max efficiancy island on the compressor map as long as your fuel octane can support that boost level, and then adjust your timing map for max power production. This would be best done on a load bearing dyno that has real time power output so you can hold at a specific boost and RPM point and then adjust timing for max power at that point. Many people tune for the ragged edge of knock, but that is not usually where you make the most power.
Keith
I believe I understand completely. You have clarified many things for me. Thank you very much for your coherent explanation.
no, i will not be tuning on the ragged edge of knock. i am hoping to get 200,000 miles out of this engine.
strike (Dave)