For those with the 272 cams
Oct 11, 2003 | 07:36 PM
#32
Evolving Member
Joined: Sep 2003
Posts: 298
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From: nj
Originally posted by QuantumEVO
You can, but the 264 set is sufficient for stock turbo. For big turbo, 272's will yield more gains and still remain driveable which is a problem on DSM's.
A few things to correct; if you have mods to make more power at the same boost level, the ECU already knows that because you had to suck more air past the MAF to do it even though it's the same boost pressure. The first level of understanding as to why this happens is your basic pV=nRT equation. The second level requires understanding of fluid dynamics and whatnot. Essentially, the boost pressure is nowhere near constant ANYTIME despite how smooth the boost gauge may say. (I hope that doesn't confuse anyone). Your basic understanding, however, is simply that colder air at the same pressure yields more power. The extra atoms of air had to be drawn past the MAF sensor (which is still ingesting air of the same density) so the ECU knows it is flowing more air despite the same manifold relative pressure level. The problem with using a tool that fools the MAF sensor is because the ECU will use additional timing when it sees less MAF at the same rpm and relative pressure level, etc. Thus, using an SAFC can be dangerous in extreme cases because you cannot retard the timing on the top end to reduce some of the unwanted advance associated with -12% fuel, etc.
Also, you cannot "clamp" the voltage of the MAF sensor because it is a Karman based sensor. It reads in cycles per second; not voltage unless I am missing something.
The method of using larger injectors and then reducing the fueling with a piggyback will yield zero change in fueling (if setup properly) and result in the ECU not hitting MAF cut. The byproduct of this is that the ECU is now using a lower part of the timing table (with MAF as a lookup) and yielding more advance (as said before). That is why you should only try big injectors (when simply fixing a MAF overrun problem) with an eManage or something that can control timing or at least offset it somewhat.
The eManage has a great tool to plug in an injector size change which automatically yields a reduction in MAF across the board. Just note that while most ppl say the stock injectors are 550, they are really 560's. Also, because different injectors take different amounts of time to actually open (based on battery voltage) this will come into play when changing injectors. The common piggybacks don't have any way to make a pulsewidth offset (since they are only changing MAF) and therefore your fueling may be a tad off when simply plugging in a change from, say, 560's to 660's. Larger and/or aftermarket injectors usually take longer to open (stock injectors are usually pretty nice design and quick to open) so the same amount of fuel; corrected for injector size) will give you a bit less actual fuel based on the delayed opening of the injectors. Normally this is in tenths of a millisecond but it can make a difference. There are different types of injectors designs as well and that will have as big or bigger effect on the "minimum injector on time" or minimum injector time; MIT. So, just so you know, not all injectors are the same. Some open faster; some spray a better pattern, etc. The stock injectors have four separate openings and I suspect they spray a rather larger pattern for better atomization and lower air flow levels.
Whew, hope that helps someone.... anyone...
Mark
www.Quantum-Racing.com
You can, but the 264 set is sufficient for stock turbo. For big turbo, 272's will yield more gains and still remain driveable which is a problem on DSM's.
A few things to correct; if you have mods to make more power at the same boost level, the ECU already knows that because you had to suck more air past the MAF to do it even though it's the same boost pressure. The first level of understanding as to why this happens is your basic pV=nRT equation. The second level requires understanding of fluid dynamics and whatnot. Essentially, the boost pressure is nowhere near constant ANYTIME despite how smooth the boost gauge may say. (I hope that doesn't confuse anyone). Your basic understanding, however, is simply that colder air at the same pressure yields more power. The extra atoms of air had to be drawn past the MAF sensor (which is still ingesting air of the same density) so the ECU knows it is flowing more air despite the same manifold relative pressure level. The problem with using a tool that fools the MAF sensor is because the ECU will use additional timing when it sees less MAF at the same rpm and relative pressure level, etc. Thus, using an SAFC can be dangerous in extreme cases because you cannot retard the timing on the top end to reduce some of the unwanted advance associated with -12% fuel, etc.
Also, you cannot "clamp" the voltage of the MAF sensor because it is a Karman based sensor. It reads in cycles per second; not voltage unless I am missing something.
The method of using larger injectors and then reducing the fueling with a piggyback will yield zero change in fueling (if setup properly) and result in the ECU not hitting MAF cut. The byproduct of this is that the ECU is now using a lower part of the timing table (with MAF as a lookup) and yielding more advance (as said before). That is why you should only try big injectors (when simply fixing a MAF overrun problem) with an eManage or something that can control timing or at least offset it somewhat.
The eManage has a great tool to plug in an injector size change which automatically yields a reduction in MAF across the board. Just note that while most ppl say the stock injectors are 550, they are really 560's. Also, because different injectors take different amounts of time to actually open (based on battery voltage) this will come into play when changing injectors. The common piggybacks don't have any way to make a pulsewidth offset (since they are only changing MAF) and therefore your fueling may be a tad off when simply plugging in a change from, say, 560's to 660's. Larger and/or aftermarket injectors usually take longer to open (stock injectors are usually pretty nice design and quick to open) so the same amount of fuel; corrected for injector size) will give you a bit less actual fuel based on the delayed opening of the injectors. Normally this is in tenths of a millisecond but it can make a difference. There are different types of injectors designs as well and that will have as big or bigger effect on the "minimum injector on time" or minimum injector time; MIT. So, just so you know, not all injectors are the same. Some open faster; some spray a better pattern, etc. The stock injectors have four separate openings and I suspect they spray a rather larger pattern for better atomization and lower air flow levels.
Whew, hope that helps someone.... anyone...
Mark
www.Quantum-Racing.com
If it is possible to do so then a nice dyno tune with a flash could help the car run without any real drivabilty issues at all. The latency associated with some piggybacks can then be eliminated all together.
Thanks in advance for your comments.
Oct 11, 2003 | 09:42 PM
#33
Well I don't know if there is truly a latency. It isn't like your ECU now has a delay in fuel delivery; it perhaps has a slight latency for fuel correction but that is pretty smooth anyways.
The flash might be able to bump the MAF cut but it won't eliminate the problem. My understanding is that the MAF cut is there to avoid running the car off the fuel map; which uses MAF for load input. I am sure, however, that there is a large margin of safety given what past EVO's have seen on MAF numbers. Again, though, I also don't know if perhaps the MAF sensor gets unstable that high. You could reduce the fueling to compensate for larger injectors but the ECU is still referencing the maps at the high MAF values. I can't say for sure since most of my customers use a piggyback only long enough until they are ready for the big turbo and standalone route. Eliminating the MAF altogether is the best approach, IMHO, for big power. Piggybacks are decent and reflashes have been proven to work as well. The choice between the two is really preference to a great extent. I personally wouldn't like reflash as a customer since I don't have any way to control my maps, etc. You also have to schedule dyno time if they won't simply put a map in without testing and even if they will, it requires pulling your computer.
From what I have heard by European EVO guys, the 8 is harder to deal with and more resistant to tuning with piggybacks and whatnot. Thanks, no doubt, to tighter controls for emissions and whatnot. I suppose it also makes the car more reliable and less prone to failure.
Mark
www.Quantum-Racing.com
The flash might be able to bump the MAF cut but it won't eliminate the problem. My understanding is that the MAF cut is there to avoid running the car off the fuel map; which uses MAF for load input. I am sure, however, that there is a large margin of safety given what past EVO's have seen on MAF numbers. Again, though, I also don't know if perhaps the MAF sensor gets unstable that high. You could reduce the fueling to compensate for larger injectors but the ECU is still referencing the maps at the high MAF values. I can't say for sure since most of my customers use a piggyback only long enough until they are ready for the big turbo and standalone route. Eliminating the MAF altogether is the best approach, IMHO, for big power. Piggybacks are decent and reflashes have been proven to work as well. The choice between the two is really preference to a great extent. I personally wouldn't like reflash as a customer since I don't have any way to control my maps, etc. You also have to schedule dyno time if they won't simply put a map in without testing and even if they will, it requires pulling your computer.
From what I have heard by European EVO guys, the 8 is harder to deal with and more resistant to tuning with piggybacks and whatnot. Thanks, no doubt, to tighter controls for emissions and whatnot. I suppose it also makes the car more reliable and less prone to failure.
Mark
www.Quantum-Racing.com
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