My GT2 vs Peter's 3.8L monster
#91
08-31-2010, 02:31 PM
ooopssss.... you asked me a question as to which one is the better all around setup. Typically, the most advance you can get away with safely is better.... HOWEVER.... there is a big difference between preignition and detonation.... now you tell me... based on bore/stroke and whatever you else you feel you need to include(hint hint), Approximately how much difference in advance is there between the two?
Justin
Justin
#92
08-31-2010, 02:57 PM
Join Date: Jun 2005
Location: Virginia, USA
Posts: 8,510
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No worries, bother. I always enjoy reading your posts, and I'm sure most everyone does else also.
#93
08-31-2010, 03:09 PM
Good one!!
It really depends on the design of the engine at that point, but let's take the 996 TT engine for example(seems relevant in this case). Because of the cam profile, head design and intake manifold; you have various points in the curve that require varying amounts of advance... Theoretically(let's use your 20 degrees advance example) if you were running 20 degrees of advance at 5000 rpm at 18psi on a GT35R setup with moderate hotsides(we'll call this peak torque 
). On the TT, you might actually end up with as much as 30 degrees by 7500rpm at 18psi. Maybe even more; without roasting any metals. So my example was technically a trick question as noone actually asked WHERE in the powerband these advance numbers were.
Porsche actually designed their mapping around this and advanced timing like crazy after 6500rpm or so. This was done to combat the turbos, head design, cam profile, intake manifold designs while still making power. They coupled all of that with a sensitive knock sensing system though. After changing all of those things.... your mapping also has to change to reflect this. Bear in mind that this is all "surface tuning" at this point. We'll assume that the bore and stroke were already taken into account along with the squish(head design) and about 20 other vairiables. Since Porsche uses some form of calculated load, we'll use that as gospel for the determination of what the actual ignition advance is, as opposed to actual load(boost), or just MAF values. So using calculated load, it takes into account injector pulsewidth, MAF, Boost Pressure, RPM, etc to determine the proper advance at that particular moment in time(pretty sleek stuff for something designed in the late nineties). Tony at EPL might have more insight as to the exact algorithm Porsche uses to determine where everything needs to be. The newer cars get a bit more in depth with time based firing as opposed to solely position based firing.
Scott... So sorry to hijack your thread, but you always get stuff stirred up with giving everyone tons of info on your build
Justin
It really depends on the design of the engine at that point, but let's take the 996 TT engine for example(seems relevant in this case
). Because of the cam profile, head design and intake manifold; you have various points in the curve that require varying amounts of advance... Theoretically(let's use your 20 degrees advance example) if you were running 20 degrees of advance at 5000 rpm at 18psi on a GT35R setup with moderate hotsides(we'll call this peak torque ). On the TT, you might actually end up with as much as 30 degrees by 7500rpm at 18psi. Maybe even more; without roasting any metals. So my example was technically a trick question as noone actually asked WHERE in the powerband these advance numbers were. Porsche actually designed their mapping around this and advanced timing like crazy after 6500rpm or so. This was done to combat the turbos, head design, cam profile, intake manifold designs while still making power. They coupled all of that with a sensitive knock sensing system though. After changing all of those things.... your mapping also has to change to reflect this. Bear in mind that this is all "surface tuning" at this point. We'll assume that the bore and stroke were already taken into account along with the squish(head design) and about 20 other vairiables. Since Porsche uses some form of calculated load, we'll use that as gospel for the determination of what the actual ignition advance is, as opposed to actual load(boost), or just MAF values. So using calculated load, it takes into account injector pulsewidth, MAF, Boost Pressure, RPM, etc to determine the proper advance at that particular moment in time(pretty sleek stuff for something designed in the late nineties). Tony at EPL might have more insight as to the exact algorithm Porsche uses to determine where everything needs to be. The newer cars get a bit more in depth with time based firing as opposed to solely position based firing.Scott... So sorry to hijack your thread, but you always get stuff stirred up with giving everyone tons of info on your build
Justin
so say you limit timing with tuning, then where is it being limited at, max point of WOT and RPM? Scott, needs to know
Also since the std ECU is limited to 1.5 bar-ish what happens at levels above that, as well as the stock maf being overflowed. At those levels isn't the system flying blind? I know there are lots of factors but for simples sake assume as many factors as possible to be constant? ooopssss.... you asked me a question as to which one is the better all around setup. Typically, the most advance you can get away with safely is better.... HOWEVER.... there is a big difference between preignition and detonation.... now you tell me... based on bore/stroke and whatever you else you feel you need to include(hint hint), Approximately how much difference in advance is there between the two?
Justin
Justin
How much of a difference in timing? phew!! How do you determine where preignition even starts? 5-10 degrees before TDC? detonation happens after so maybe 5 degrees?
you can't make comments like the above and leave us hanging
I'm just pulling answers out of the exhaust pipeand Scott is right, I definitely enjoy reading your posts, whatever I can understand of them.
#95
08-31-2010, 08:58 PM
Good one!!
It really depends on the design of the engine at that point, but let's take the 996 TT engine for example(seems relevant in this case). Because of the cam profile, head design and intake manifold; you have various points in the curve that require varying amounts of advance... Theoretically(let's use your 20 degrees advance example) if you were running 20 degrees of advance at 5000 rpm at 18psi on a GT35R setup with moderate hotsides(we'll call this peak torque ). On the TT, you might actually end up with as much as 30 degrees by 7500rpm at 18psi. Maybe even more; without roasting any metals. So my example was technically a trick question as noone actually asked WHERE in the powerband these advance numbers were. Porsche actually designed their mapping around this and advanced timing like crazy after 6500rpm or so. This was done to combat the turbos, head design, cam profile, intake manifold designs while still making power. They coupled all of that with a sensitive knock sensing system though. After changing all of those things.... your mapping also has to change to reflect this. Bear in mind that this is all "surface tuning" at this point. We'll assume that the bore and stroke were already taken into account along with the squish(head design) and about 20 other vairiables. Since Porsche uses some form of calculated load, we'll use that as gospel for the determination of what the actual ignition advance is, as opposed to actual load(boost), or just MAF values. So using calculated load, it takes into account injector pulsewidth, MAF, Boost Pressure, RPM, etc to determine the proper advance at that particular moment in time(pretty sleek stuff for something designed in the late nineties). Tony at EPL might have more insight as to the exact algorithm Porsche uses to determine where everything needs to be. The newer cars get a bit more in depth with time based firing as opposed to solely position based firing.
Scott... So sorry to hijack your thread, but you always get stuff stirred up with giving everyone tons of info on your build
Justin
It really depends on the design of the engine at that point, but let's take the 996 TT engine for example(seems relevant in this case
). Because of the cam profile, head design and intake manifold; you have various points in the curve that require varying amounts of advance... Theoretically(let's use your 20 degrees advance example) if you were running 20 degrees of advance at 5000 rpm at 18psi on a GT35R setup with moderate hotsides(we'll call this peak torque ). On the TT, you might actually end up with as much as 30 degrees by 7500rpm at 18psi. Maybe even more; without roasting any metals. So my example was technically a trick question as noone actually asked WHERE in the powerband these advance numbers were. Porsche actually designed their mapping around this and advanced timing like crazy after 6500rpm or so. This was done to combat the turbos, head design, cam profile, intake manifold designs while still making power. They coupled all of that with a sensitive knock sensing system though. After changing all of those things.... your mapping also has to change to reflect this. Bear in mind that this is all "surface tuning" at this point. We'll assume that the bore and stroke were already taken into account along with the squish(head design) and about 20 other vairiables. Since Porsche uses some form of calculated load, we'll use that as gospel for the determination of what the actual ignition advance is, as opposed to actual load(boost), or just MAF values. So using calculated load, it takes into account injector pulsewidth, MAF, Boost Pressure, RPM, etc to determine the proper advance at that particular moment in time(pretty sleek stuff for something designed in the late nineties). Tony at EPL might have more insight as to the exact algorithm Porsche uses to determine where everything needs to be. The newer cars get a bit more in depth with time based firing as opposed to solely position based firing.Scott... So sorry to hijack your thread, but you always get stuff stirred up with giving everyone tons of info on your build
Justin
I have enjoyed your posts and I'm always looking to learn something new. I have a question regarding the item above in bold. My question actually is directed to the part in bold red.
The actuator on both the 996tt and the GT3 has a physical limitation. If you use GT3 actuator, it’s 45 degrees. If you use a 996tt actuator, you can move it 30 degrees.
Is there a way to get more than 30 degrees on a 99ttt other than to place a GT3 program on the 996tt ECU and run a cam with GT3 syncs and use a GT3 actuator?
Last edited by cjv; 08-31-2010 at 09:27 PM.
#96
08-31-2010, 09:54 PM
Basic Sponsor
Speaking of Engine loads... I took a screen shot of a stock ignition map... as you can see its load vs RPMs... same as one of the fuel maps... those are target in Lamda... again, Load vs. RPMs...
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2001 996TT 3.6L and stock ECU
9.66 seconds @ 147.76 mph 1/4 mile click to view
160 mph @ 9.77 seconds in 1/4 mile click to view
50% OFF ON PORSCHE ECU TUNING BLACK FRIDAY SPECIAL
#97
08-31-2010, 11:13 PM
ooopssss.... you asked me a question as to which one is the better all around setup. Typically, the most advance you can get away with safely is better.... HOWEVER.... there is a big difference between preignition and detonation.... now you tell me... based on bore/stroke and whatever you else you feel you need to include(hint hint), Approximately how much difference in advance is there between the two?
Justin
Justin
#98
08-31-2010, 11:39 PM
Justin,
I have enjoyed your posts and I'm always looking to learn something new. I have a question regarding the item above in bold. My question actually is directed to the part in bold red.
The actuator on both the 996tt and the GT3 has a physical limitation. If you use GT3 actuator, it’s 45 degrees. If you use a 996tt actuator, you can move it 30 degrees.
Is there a way to get more than 30 degrees on a 99ttt other than to place a GT3 program on the 996tt ECU and run a cam with GT3 syncs and use a GT3 actuator?
I have enjoyed your posts and I'm always looking to learn something new. I have a question regarding the item above in bold. My question actually is directed to the part in bold red.
The actuator on both the 996tt and the GT3 has a physical limitation. If you use GT3 actuator, it’s 45 degrees. If you use a 996tt actuator, you can move it 30 degrees.
Is there a way to get more than 30 degrees on a 99ttt other than to place a GT3 program on the 996tt ECU and run a cam with GT3 syncs and use a GT3 actuator?
I think you are speaking of cam advance which although relevent, doesn't play into our scenario here
The cam home signal might be different between the two forcing you to use a GT3 trigger pattern(hence a reprogram). If there are multiple cam/home triggers because of the variable timing, I can see the need for a change in tuning. This part I am not 100% sure on as I have not set up a TT with GT3 cams yet. I can research it though. Due to the design of the 996TT cams, I would think that there is a physical limitation limiting you to the 30 degrees maximum. With enough time, you can reprogram the DME to do whatever you want(even activate your brake lights over 100mph ) It just involves adding some additional code. With that known, it must be a physical limitation of the cams or actuator.Justin
#99
09-01-2010, 05:40 AM
are you speaking of ignition advance? or cam advance?
I think you are speaking of cam advance which although relevent, doesn't play into our scenario here The cam home signal might be different between the two forcing you to use a GT3 trigger pattern(hence a reprogram). If there are multiple cam/home triggers because of the variable timing, I can see the need for a change in tuning. This part I am not 100% sure on as I have not set up a TT with GT3 cams yet. I can research it though. Due to the design of the 996TT cams, I would think that there is a physical limitation limiting you to the 30 degrees maximum. With enough time, you can reprogram the DME to do whatever you want(even activate your brake lights over 100mph ) It just involves adding some additional code. With that known, it must be a physical limitation of the cams or actuator.
Justin
I think you are speaking of cam advance which although relevent, doesn't play into our scenario here
The cam home signal might be different between the two forcing you to use a GT3 trigger pattern(hence a reprogram). If there are multiple cam/home triggers because of the variable timing, I can see the need for a change in tuning. This part I am not 100% sure on as I have not set up a TT with GT3 cams yet. I can research it though. Due to the design of the 996TT cams, I would think that there is a physical limitation limiting you to the 30 degrees maximum. With enough time, you can reprogram the DME to do whatever you want(even activate your brake lights over 100mph ) It just involves adding some additional code. With that known, it must be a physical limitation of the cams or actuator.Justin
#100
09-01-2010, 08:07 AM
Preignition is result of a hot spot (carbon, etc.) in the combustion chamber that leads to the fuel/air mixture lighting off some time other than when the spark plug fires...not good. Detonation is when the fuel/air mixture explodes and this is where cylinder pressures go through the roof and cause havic and eventual damage to your engine....double no good. If I'm understanding your question Justin (doubtful) I'd say it's a trick question because these, preignition and detonation, are both unintentionally consequances meaning they could happen at varying times semi-independent of the timing map and are more closely related to improper AFRs (fueling).
preignition is a result of an anomoly in the combustion chamber, yes; however, this usually occurs before any form of detonation as typically detonation occurs AFTER you command the spark event. Pre ignition is just that.... occurring on the compression stroke before a commanded firing... so we know that PI falls before detonation, but it is a variable amount...
oh... and let's not forget about detonation INDUCED preignition
sounds kinda backwards, right?Jsutin
Last edited by justinn; 09-01-2010 at 08:14 AM.
#101
09-01-2010, 09:14 AM
This folks is why I have to have Justin explain stuff over and over to me all the time. If you all ever get a chance to meet him you will understand even more why he is called a walking wealth of information LOL! I'm not saying to suck up, but after the first time I met him when he was tuning some Supra's at my friends shop I had already made my decision that if I ever went with a standalone on any car that he would be tuning it.
Luckly he also has the skills even make my father (who knows hardly anything about late model cars) understand stuff. My dad asked why I was spending money on a another computer to control the car. Justin broke it down even for him to understand. With my father that is hard thing to do considering he was in sales for almost 30 years and is the man with a thousand questions LOL!
Also will mention Tony also. He has put up with me for 2 years now with thousands of questions. Even before I was a customer he had an answer for everything and didn't think twice about not answering it. Between him and Justin when I was on the stock DME I was not afraid at all of what they were doing. Great minds put together always put out good results.
Luckly he also has the skills even make my father (who knows hardly anything about late model cars) understand stuff. My dad asked why I was spending money on a another computer to control the car. Justin broke it down even for him to understand. With my father that is hard thing to do considering he was in sales for almost 30 years and is the man with a thousand questions LOL!
Also will mention Tony also. He has put up with me for 2 years now with thousands of questions. Even before I was a customer he had an answer for everything and didn't think twice about not answering it. Between him and Justin when I was on the stock DME I was not afraid at all of what they were doing. Great minds put together always put out good results.
Last edited by Powell; 09-01-2010 at 09:17 AM.
#102
09-01-2010, 09:33 AM
Registered User
#104
09-01-2010, 09:38 AM
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Join Date: Aug 2009
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hes usging a hybrid type of gt3 cam ground to turbo specs(but much higher lift in duration) ina gt3 head on his car for much more lift and duration then a 996tt cam could ever make or be made to have.
