a brief on SD...
a brief on SD... ive spent some time reading about SD and MAF and everything and just need someone to elaborate on one point for me; speed density is tuned and set up considering current conditions of atmosphere during the tune ( much like a carb...) And once those conditions change, the tune would more likely become less than ideal. So how far off can this get? Are we talking about losing a tenth of a second or absolutely destroying a motor? Im not worried about doing a SD tune in death valley and then driving to alaska, but i live near sea level, close to seattle, and I wanted to drive up through the mountains through eastern washington? Is it more severely out of whack than a carb would be, or about the same making a few thousand feet of elevation change? Can you tune it on a day with mild weather ( 60 degrees? ) and then drive it through summer up to 100 degrees and all winter at 35? any way someone can break it down would be greatly appreciated 
This is in relation to a mild turbo build on a stock L92 motor...
This is in relation to a mild turbo build on a stock L92 motor... 
TECH Enthusiast
Joined: Nov 2006
Posts: 620
Likes: 0
From: Katherine N.T Australia
Pressure is not as big a problem as alot of people make it out to be. Without getting into huge detail the crust of it is. The PCM calculates Barometric pressure. That accounts for altitude for the most part. Temperature has the biggest influence on the density of the air charge. The PCM accounts for that too. There are inherent errors in the end application of how the PCM calculates this but there is hope. If you use EFI LIVE COS 5 you have available a nice little table that allows the tuner to apply a factor to the VE table that is IAT driven and in addition to the normal dynamic airflow calculation. With that one table you remove 95% of the error. For most people that is fine. For the rest there is always closed loop.
I've been running SD for several years now in all kinds of weather and temps.
I have not seen any issues with it.
You still have the baro, coolant temp, intake air temp, engine vacuum, etc. sending signals to the ecm and the ecm making adjustments accordingly.
I have not seen any issues with it.
You still have the baro, coolant temp, intake air temp, engine vacuum, etc. sending signals to the ecm and the ecm making adjustments accordingly.
Pressure is not as big a problem as alot of people make it out to be. Without getting into huge detail the crust of it is. The PCM calculates Barometric pressure. That accounts for altitude for the most part. Temperature has the biggest influence on the density of the air charge. The PCM accounts for that too. There are inherent errors in the end application of how the PCM calculates this but there is hope. If you use EFI LIVE COS 5 you have available a nice little table that allows the tuner to apply a factor to the VE table that is IAT driven and in addition to the normal dynamic airflow calculation. With that one table you remove 95% of the error. For most people that is fine. For the rest there is always closed loop.
I also have been running SD using EFILive COS 5 for a few years. That IAT table does keep the tune really close. I still check mine every few months just to keep tabs on my tune.
Bill
Bill
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