at what point do u mess with timing?
at what point do u mess with timing? Like the title says..at what point do I begin to mess with timing? after the idle and pt throttle ve are set? Do I do this along with PE tuning after i get my a/f down?
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
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From: Lake Zurich, IL
Timing has an effect on ve but unless you're making huge changes it shouldn't be very drastic...
I generally dial my VE table in first, then modify part throttle spark if you're getting KR
Then I'll adjust my PE, then I'll adjust my timing... if need be I'll go back and readjust me VE where necessary and then readjust PE as necessary
I generally dial my VE table in first, then modify part throttle spark if you're getting KR
Then I'll adjust my PE, then I'll adjust my timing... if need be I'll go back and readjust me VE where necessary and then readjust PE as necessary
another quick question...say for instance my ve @400rpms@15kpa is 26. what exactly does that mean? more or less air? more or less fuel? and are the lower map numbers going to be for idle and pt throttle and the higher map #'s i.e. 70-105 for WOT??
TECH Enthusiast
Joined: Mar 2003
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From: San Diego
Around idle there is very little air actually filling the cylinder compared to high rpm/high MAP situations. Your VE will be a lot lower because the less air you have in the cylinder the less fuel you need.
If VE was a true representation (it could be in some instances, I'm sure others can tell you how it correlates to true VE) then that 26 means that your cylinder is 26% of its capacity.
Your VE value isn't telling the computer how much fuel to add, rather how much air is in the cylinder. The calculations the computer does uses a few inputs, and air mass is one of them. Depending on the air mass it comes up with, it determines via other tables what AFR its supposed to be at and adds the appropriate amount of fuel to reach that. That a very general explanation, I'm sure a lot of other people will sharpshoot it
If VE was a true representation (it could be in some instances, I'm sure others can tell you how it correlates to true VE) then that 26 means that your cylinder is 26% of its capacity.
Your VE value isn't telling the computer how much fuel to add, rather how much air is in the cylinder. The calculations the computer does uses a few inputs, and air mass is one of them. Depending on the air mass it comes up with, it determines via other tables what AFR its supposed to be at and adds the appropriate amount of fuel to reach that. That a very general explanation, I'm sure a lot of other people will sharpshoot it
TECH Enthusiast
Joined: Mar 2003
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From: San Diego
I think there is a slight difference between the VE numbers in HPTuners and true VE but I could be wrong. You generally only see over 100% VE in forced induction situations, but in very well put together NA engines you can see slightly over 100% VE because the engine pumps air well enough to create a 'ram' effect in the cylinder. If air is moving fast enough into the cylinder when it reaches atmospheric pressure it doesn't just stop moving, since air will compress, so you would have a brief instance of compressed air in the cylinder. Since VE is calculated at atmospheric pressures your air mass would be at a higher pressure and say maybe 105% of normal atmospheric airmass.
Since airmass is a product of density * volume, although your volume would stay the same your density would increase.
Since airmass is a product of density * volume, although your volume would stay the same your density would increase.
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TECH Enthusiast
Joined: Mar 2003
Posts: 618
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From: San Diego
Also, the numbers on your VE table represent how much air you're telling the car is in the cylinder. How accurate that number is relating to the VE of your engine really depends on how well you've tuned it..
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Originally Posted by Bombguy99z28
Also, the numbers on your VE table represent how much air you're telling the car is in the cylinder. How accurate that number is relating to the VE of your engine really depends on how well you've tuned it..
ill try to convince my wife to come with me friday to the Q. Are you gonna be running or just watching? 
Thanks, if I can't grab a set from them I'll let you know.