DoctorLGT Posted May 31, 2012 Share Posted May 31, 2012 Hey guys I have a quick tuning question for all the tuners I have a 2005 Legacy GT which has a custom tune map for a Cobb Accessport V1. I am also running an AVO intake. (took the pics from Edmundu) http://legacygt.com/forums/attachment.php?attachmentid=31813&d=1171122587 http://legacygt.com/forums/attachment.php?attachmentid=31815&d=1171122587 I was curious. When you guys are tuning for an intake are you tuning it because of the new intake pipes diameter or because it is a different filter or what is the sole reason? The reason I ask is I think I may need to cut the pipe that comes off from the intake pipe to about 3 or 4 inches shorter, so I was wondering if by shortening the entire length of the AVO intake if I will need a retune? Link to comment Share on other sites More sharing options...
Mega Users seabass07 Posted May 31, 2012 Mega Users Share Posted May 31, 2012 There is no "sole" reason. Filter resistance, pipe diameter, pipe shape, position of maf, all affect scaling. Link to comment Share on other sites More sharing options...
legspecb08 Posted June 16, 2012 Share Posted June 16, 2012 AVO doesn't say it on there description but its a large 3in maf. I found out the hard way Link to comment Share on other sites More sharing options...
DoctorLGT Posted June 16, 2012 Author Share Posted June 16, 2012 Why is that bad? Link to comment Share on other sites More sharing options...
dr_sharp Posted June 16, 2012 Share Posted June 16, 2012 Why is that bad? MAF sensor actually measures velocity. If you change intake diamter where the sensor is located, you're changing that velocity without actually changing the airflow. lol Link to comment Share on other sites More sharing options...
bnguyenbb6 Posted June 18, 2012 Share Posted June 18, 2012 MAF sensor actually measures velocity. If you change intake diamter where the sensor is located, you're changing that velocity without actually changing the airflow. Yes but just to extend on this.MAF measure the mass of the air. The weight at a given velocity(grams per second). Let say your MAF is calibrated to read 300g/s at 4.5 volts with a 65mm intake. Lets say you bump it to a 76mm intake. Now your car hits 300g/s at 4 volts(because it can flow more air per second at a slower rate which heats up the wire less) but your car thinks that 4.5v is 300g/s. At 4.5v is now like 360g/s...you're running WAY more airflow for that given voltage. So without a tune, your car is flowing WAY more air(leaner) at every given voltage than it thinks. It might be easier to think of bigger/smaller water hoses and water flow. Link to comment Share on other sites More sharing options...
fahr_side Posted June 18, 2012 Share Posted June 18, 2012 If you've gone to the trouble of installing an intake and getting tuned for it, it should be because you're into the range of turbos that move enough air to need one. That range usually demands larger injectors and a pump to support it. It's pretty much impossible to set up these sort of fuel system mods without a wideband O2. Once you have a WBO2 you have all the tools you need to scale the MAF and it'd be negligent not to do so. Given you have a WBO2, at the very least you could plot your AFR curve before you chop the intake tube down and then check afterwards to be sure you still have the AFR you wanted. Obligatory '[URL="http://legacygt.com/forums/showthread.php/2008-gh8-238668.html?t=238668"]build thread[/URL]' Increased capacity to 2.7 liters, still turbo, but no longer need spark plugs. Link to comment Share on other sites More sharing options...
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