Can you S/C an active fuel mgt engine?

[Fast1]

When I was considering a new Challenger, I noticed that with the 5.7 (active fuel mgt system) supercharging is out. Now, researching the L99 vs the LS3, I see the L99 has afms. Can this type of engine be s/c?

[SilverTurtle]

yes... since you're going to have to be in the computer system, anyway, to adjust your VE, fuel and spark tables, simply have the tuner turn that option off... this will, however, deactivate the AFM and you will be running on all 8 cylinders all of the time... but if you're adding a blower to a car, are you really worried about fuel economy?

[CamaroSpike23]

Originally Posted by SilverTurtle

yes... since you're going to have to be in the computer system, anyway, to adjust your VE, fuel and spark tables, simply have the tuner turn that option off... this will, however, deactivate the AFM and you will be running on all 8 cylinders all of the time... but if you're adding a blower to a car, are you really worried about fuel economy?

turtle... you just told him yes.... then no.

he wants to know if you can still run a s/c without having to deactivate AFM.

im fairly certain you could, but it would take a donkey butload of tuning, and you'd probably need a BOV so you arent pumping 8 cyl worth of air into 4 cyl

[Mr Twisty]

Originally Posted by CamaroSpike23

turtle... you just told him yes.... then no.

he wants to know if you can still run a s/c without having to deactivate AFM.

im fairly certain you could, but it would take a donkey butload of tuning, and you'd probably need a BOV so you arent pumping 8 cyl worth of air into 4 cyl

What is BOV?

I'm assuming AFM still runs air thru de-activated cylinders, but without fuel/compression/plug fire,...Is this correct? Haven't read up on it since I'll be going with LS3

[Evotion]

Originally Posted by MisterCamaro69

What is BOV?

I'm assuming AFM still runs air thru de-activated cylinders, but without fuel/compression/plug fire,...Is this correct? Haven't read up on it since I'll be going with LS3

BOV = Blow off valve.

[CamaroSpike23]

Originally Posted by MisterCamaro69

What is BOV?

I'm assuming AFM still runs air thru de-activated cylinders, but without fuel/compression/plug fire,...Is this correct? Haven't read up on it since I'll be going with LS3

Blow Off Valve


nope, the cylinders keep pumping, but the intake and exhaust valves are shut down along with the fuel to those cylinders.

keeping the air still in there allows for the compression to help push the pistons back down so it isnt just getting force from one side and free spinning on the other. it just doesnt fire the spark, it just keeps compressing and expanding the air thats in there already

[Mr Twisty]

Originally Posted by CamaroSpike23

Blow Off Valve


nope, the cylinders keep pumping, but the intake and exhaust valves are shut down along with the fuel to those cylinders.

keeping the air still in there allows for the compression to help push the pistons back down so it isnt just getting force from one side and free spinning on the other. it just doesnt fire the spark, it just keeps compressing and expanding the air thats in there already

Gotcha...What signals (conditions) does the computer use to activate AFM mode? Intake vacuum? speed vs. throttle position? etc.

[CamaroSpike23]

Originally Posted by MisterCamaro69

Gotcha...What signals (conditions) does the computer use to activate AFM mode? Intake vacuum? speed vs. throttle position? etc.

that and load on the motor. AFM is only activated during periods of low load on the motor, like cruising

[Mr Twisty]

Originally Posted by CamaroSpike23

that and load on the motor. AFM is only activated during periods of low load on the motor, like cruising

OK I'm with ya. I don't think a BOV would work, when AFM condition is met, 4 cylinders deactivate, blower goes from 3lb to 6, BOV opens, reduces pressure to an unpredictable pressure. Unless there was a way to control the valve to reduce pressure exactly 50% each time AFM kicks in...That make any sense?

[CamaroSpike23]

Originally Posted by MisterCamaro69

OK I'm with ya. I don't think a BOV would work, when AFM condition is met, 4 cylinders deactivate, blower goes from 3lb to 6, BOV opens, reduces pressure to an unpredictable pressure. Unless there was a way to control the valve to reduce pressure exactly 50% each time AFM kicks in...That make any sense?

well, BOVs dont just dump all the pressure, if you set it to say 4lbs, and you surpass that, it will bleed off the pressure till it gets back down to 4lbs then it will close allowing you to stay at 4lbs... or whatever you decide to run.

[Mr Twisty]

Originally Posted by CamaroSpike23

well, BOVs dont just dump all the pressure, if you set it to say 4lbs, and you surpass that, it will bleed off the pressure till it gets back down to 4lbs then it will close allowing you to stay at 4lbs... or whatever you decide to run.

I understand. Problem is I'm seeing a fatal loop in the ecm...AFM kicks in, 4 active cylinders rise to 6 lb boost, exhaust gas goes lean, ecm compensates and richens fuel, car accelerates and kicks off AFM. Am I headed in the right direction?

One thing doesn't make sense here...If the valves are constantly closed during an AFM event, wouldn't that create much more energy loss than allowing valves to open and cycle air thru the cylinders? Closing the valves is like blowing up a balloon, cycling air thru the cylinders is like blowing thru a straw.

Does anyone have a good article on AFM operation?

[CamaroSpike23]

Originally Posted by MisterCamaro69

I understand. Problem is I'm seeing a fatal loop in the ecm...AFM kicks in, 4 active cylinders rise to 6 lb boost, exhaust gas goes lean, ecm compensates and richens fuel, car accelerates and kicks off AFM. Am I headed in the right direction?

but when it goes past 4lbs of boost (since we are using that for our reference) the BOV will drop the boost back down to 4lbs. and if its tuned correctly the extra 2lbs wont do much even during the switchover.

but it will take some work and practice messing with the tune tables to get it working correctly.

[Mr Twisty]

Originally Posted by CamaroSpike23

but when it goes past 4lbs of boost (since we are using that for our reference) the BOV will drop the boost back down to 4lbs. and if its tuned correctly the extra 2lbs wont do much even during the switchover.

but it will take some work and practice messing with the tune tables to get it working correctly.

Thought thru the constantly closed valve situation, it makes sense that downstroke will regain energy lost in compression. I'll think on it later I gotta go to work, can't rub my belly and chew gum at the same time lol. Pass on any good afm articles if ya got em tho.

The more I consider it I'd love to have a blown L99 that would get 30 mpg!

[CamaroSpike23]

Originally Posted by MisterCamaro69

Thought thru the constantly closed valve situation, it makes sense that downstroke will regain energy lost in compression. I'll think on it later I gotta go to work, can't rub my belly and chew gum at the same time lol. Pass on any good afm articles if ya got em tho.

The more I consider it I'd love to have a blown L99 that would get 30 mpg!

there's already a bunch of articles here. just do a search.