How does changing the VE relate to A/F?
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TECH Fanatic
Joined: Mar 2003
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From: La Porte, TX
How does changing the VE relate to A/F? How does changing the VE relate to A/F? For example if I scale the VE up, am I adding more air or taking it away. What is the relation with VE and Fueling.
Using NoGo's "getting a heads, cam car to idle", I multiplied the VE table by 90% @ 1200. In doing that did it make the car richer or leaner. Same question for IFR...If I want to fatten the car up, would I make the #'s bigger or smaller?
I would like to scale the IFR to make it a little richer all over, and then adjust the VE accordingly.
Thanks,
Matt
Using NoGo's "getting a heads, cam car to idle", I multiplied the VE table by 90% @ 1200. In doing that did it make the car richer or leaner. Same question for IFR...If I want to fatten the car up, would I make the #'s bigger or smaller?
I would like to scale the IFR to make it a little richer all over, and then adjust the VE accordingly.
Thanks,
Matt
In the ve table making the numbers bigger will richen up the mixture. If you are tuning in the ve table you prolly dont want to go to the IFR table to make the mixture richer as this can be acheived from the ve table. If you still want to go to the IFR table making the numbers smaller will in turn richen the car up....... Multiplying the ve table @ 1200 by 90% is leaning the car out over those map points.
check this article out for what happens when a cam is installed in a fuel injected car
http://www.kalmaker.com.au/page37.html
This should help you in understanding the changes being made and how they will affect the car
check this article out for what happens when a cam is installed in a fuel injected car
http://www.kalmaker.com.au/page37.html
This should help you in understanding the changes being made and how they will affect the car
The proper use of VE is to represent the pumping
efficiency of the engine (intake manifold to exhaust)
so the speed-density fuel calcs are righteous.
A "big" cam will reduce efficiency at the low end
if it has high overlap - you will see some exhaust
draw-back (reversion) into the intake stroke. But
the VE at the high end will increase as the valves'
limiting effect on post-plenum airflow is lessened.
Headers, head work also increase the top end VE
and headers' tuned scavenging effects can extend
down into the midband (better cylinder emptying
makes for a higher amount of in-taken air next
stroke).
The stock PCM programming is presuming the stock
cam/exhaust meaning a very low overlap, relatively
high VE at idle & low end and a valve-lift-limited top
end with early VE fade. So with a cam the idle will
be over-fueled and the top end fuel-starved when
the SD scheme is in play. Fortunately at the top end
the MAF is pretty much in charge except for things
fast throttle / airflow changes - here you fall back
on SD, and maybe not so coincidentally this is where
I pick up my only KR and transient lean-outs.
At the low end the SD calc seems to have almost full
authority and it can get your LTFTs anywhere you
want in cells 0-3, 4-5; maybe others. Do not yet
know where, or how abrupt, the SD-MAF "handover"
is.
Given that the SD tune has this level of authority
in the low end, you want to work your way into it
slowly. If *0.90 is good, *0.80 may not be better;
there is a "sweet spot of truth" with misfit mixture
to the left (lean) and the right (rich).
efficiency of the engine (intake manifold to exhaust)
so the speed-density fuel calcs are righteous.
A "big" cam will reduce efficiency at the low end
if it has high overlap - you will see some exhaust
draw-back (reversion) into the intake stroke. But
the VE at the high end will increase as the valves'
limiting effect on post-plenum airflow is lessened.
Headers, head work also increase the top end VE
and headers' tuned scavenging effects can extend
down into the midband (better cylinder emptying
makes for a higher amount of in-taken air next
stroke).
The stock PCM programming is presuming the stock
cam/exhaust meaning a very low overlap, relatively
high VE at idle & low end and a valve-lift-limited top
end with early VE fade. So with a cam the idle will
be over-fueled and the top end fuel-starved when
the SD scheme is in play. Fortunately at the top end
the MAF is pretty much in charge except for things
fast throttle / airflow changes - here you fall back
on SD, and maybe not so coincidentally this is where
I pick up my only KR and transient lean-outs.
At the low end the SD calc seems to have almost full
authority and it can get your LTFTs anywhere you
want in cells 0-3, 4-5; maybe others. Do not yet
know where, or how abrupt, the SD-MAF "handover"
is.
Given that the SD tune has this level of authority
in the low end, you want to work your way into it
slowly. If *0.90 is good, *0.80 may not be better;
there is a "sweet spot of truth" with misfit mixture
to the left (lean) and the right (rich).
TECH Addict
Joined: Feb 2004
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Originally Posted by HumpinSS
In the ve table making the numbers bigger will richen up the mixture. If you are tuning in the ve table you prolly dont want to go to the IFR table to make the mixture richer as this can be acheived from the ve table. If you still want to go to the IFR table making the numbers smaller will in turn richen the car up....... Multiplying the ve table @ 1200 by 90% is leaning the car out over those map points.
check this article out for what happens when a cam is installed in a fuel injected car
http://www.kalmaker.com.au/page37.html
This should help you in understanding the changes being made and how they will affect the car
check this article out for what happens when a cam is installed in a fuel injected car
http://www.kalmaker.com.au/page37.html
This should help you in understanding the changes being made and how they will affect the car
TECH Addict
Joined: Jul 2002
Posts: 2,261
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Originally Posted by jimmyblue
Right; that's because the MAF calc is in charge in
some areas, SD/VE in others, but IFR is across-the-
board.
some areas, SD/VE in others, but IFR is across-the-
board.
FWIW.
joel 
