Advantages/Disadvantages of AlphaN/Speed Density?
- Thread starter CSJTA
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The way I understand it, and I could be way off here, is that Alpha-N doesn't read any of the information coming from the sensors. Where Speed Density will look at the TPS, O2, CTS, MAP, etc. and make the adjustments as needed, or read from the specific cells, Alpha-N will jus take whatever is in the VE maps and run it that way.
I think it also has a lot to do with the type of application you're going for. I think Craig Smith said it best when he said, "Alpha-N + boost = Shiny parts on ground."
If you're going for some type of forced induction setup, I think Speed Density is the only way to go. If you're going N/A, then perhaps Alpha-N is a viable option.
I think it also has a lot to do with the type of application you're going for. I think Craig Smith said it best when he said, "Alpha-N + boost = Shiny parts on ground."
If you're going for some type of forced induction setup, I think Speed Density is the only way to go. If you're going N/A, then perhaps Alpha-N is a viable option.
TwinTurboIroc
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- Mar 5, 2002
The MAP is still used but its vented to the atmosphere...i dont remember why
Craig Smith
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- May 25, 2001
Alpha-N is for cars that make little or no manifold vacuum. I run Alpha-N on my bracket engine as it hardly ever drops off the top couple rows in a Speed/Density table. That pretty much makes it impossible to get it to idle or drive around correctly.
It is definitely a simpler process within the ECU while in Alpha-N mode, but to call it "crude" makes no sense to me. Fouling out my spark plugs and belching out black smoke while idling would be crude.
Speed/Density definitely has more to offer in terms of street manners and tuning resolution. And, if you are running a forced induction system, it is a must. As boost levels are a big part of determining fuel requirement, and there is no direct correlation between boost level and throttle position, Alpha-N on a turbo or blower car is an explosion waiting to happen.
The MAP sensor is used for barometric compensation in Alpha-N mode. Just leave it open so that it is sampling atmospheric pressure.
It is definitely a simpler process within the ECU while in Alpha-N mode, but to call it "crude" makes no sense to me. Fouling out my spark plugs and belching out black smoke while idling would be crude.
Speed/Density definitely has more to offer in terms of street manners and tuning resolution. And, if you are running a forced induction system, it is a must. As boost levels are a big part of determining fuel requirement, and there is no direct correlation between boost level and throttle position, Alpha-N on a turbo or blower car is an explosion waiting to happen.
The MAP sensor is used for barometric compensation in Alpha-N mode. Just leave it open so that it is sampling atmospheric pressure.
Looks to me you answered you own statement with another statement.
I'd bet you'd like your setup even more with just a A-N idle and then S/D, for off idle.
To some folks if an engine idles, they're happy, any thing less then complete manners, in my little world is Crude.
And just for grins, I did a MAF/ Alpha-N, and was using the A-N for WOT. No engine parts dangling out of the block.
Baro ain't a requirement of Alpha-N.
If you look closely at some of the GM calibrations, they go Alpha-N in a fashion at WOT.
Craig Smith
That was easy!
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- May 25, 2001
Looks to me you answered you own statement with another statement.
I also think Courtney Cox has more to offer than Jennifer Aniston does, but that hardly implies that Jennifer Aniston is "crude".
I'd bet you'd like your setup even more with just a A-N idle and then S/D, for off idle.
As I stated, my engine makes no vacuum except when I lift at the top end of the track. I have a 15:1 alcohol burner with a camshaft with over 290 degrees of duration at .050" lift. Speed/density is great for engines that create a vacuum signal to work with. On an engine like mine Alpha-N is really the only way to get the car to idle and drive around well without loading up.
To some folks if an engine idles, they're happy, any thing less then complete manners, in my little world is Crude.
I agree completely. Obviously with the nature of my engine I have to sacrifice a couple things (like being able to idle below 1500 RPM) but it purred like a kitty AND roared like a lion. At least until I had some sort of bottom end failure.
And just for grins, I did a MAF/ Alpha-N, and was using the A-N for WOT. No engine parts dangling out of the block.
The trick is at part throttle. At WOT it's going to be fairly repeatable, but at part throttle, you never know where the boost level will be and there isn't a way (at least with the FAST, which is all I am speaking of) to accomodate this in Alpha-N. This could certainly allow for a situation where you would quickly lean out as the turbo started coming up but no additional fuel is coming in.
Baro ain't a requirement of Alpha-N.
Correct. Again, just speaking about FAST. You can disconnect the MAP sensor completely in Alpha-N and no correction will be applied. If you connect the MAP sensor to the ECU and leave it vented to atmosphere it will apply correction based on barometric pressure. Not a requirement; just an option.
I also think Courtney Cox has more to offer than Jennifer Aniston does, but that hardly implies that Jennifer Aniston is "crude".
I'd bet you'd like your setup even more with just a A-N idle and then S/D, for off idle.
As I stated, my engine makes no vacuum except when I lift at the top end of the track. I have a 15:1 alcohol burner with a camshaft with over 290 degrees of duration at .050" lift. Speed/density is great for engines that create a vacuum signal to work with. On an engine like mine Alpha-N is really the only way to get the car to idle and drive around well without loading up.
To some folks if an engine idles, they're happy, any thing less then complete manners, in my little world is Crude.
I agree completely. Obviously with the nature of my engine I have to sacrifice a couple things (like being able to idle below 1500 RPM) but it purred like a kitty AND roared like a lion. At least until I had some sort of bottom end failure.
And just for grins, I did a MAF/ Alpha-N, and was using the A-N for WOT. No engine parts dangling out of the block.
The trick is at part throttle. At WOT it's going to be fairly repeatable, but at part throttle, you never know where the boost level will be and there isn't a way (at least with the FAST, which is all I am speaking of) to accomodate this in Alpha-N. This could certainly allow for a situation where you would quickly lean out as the turbo started coming up but no additional fuel is coming in.
Baro ain't a requirement of Alpha-N.
Correct. Again, just speaking about FAST. You can disconnect the MAP sensor completely in Alpha-N and no correction will be applied. If you connect the MAP sensor to the ECU and leave it vented to atmosphere it will apply correction based on barometric pressure. Not a requirement; just an option.
No vacuum?.
Can't happen, unless your actually running a diesel.
Not to split hairs to fine, but as long is there is ANY vacuum signal, with enough code you can get it to run S/D.
Fairly repeatable?. That again is like well it idles with my foot off the gas.
The stuff's been out there long enough the Bar should be raised some for what folks expect, and can get. I'm not shooting at FAST or anyone in particular. Just as I see things.
Some info
IMO, if it's tuned and it works...then it's right. Personally, I would never run a blown motor with Alpha-N but, that just me. For those with giant camshafts and a blower...
The Race version Cmdr950 from Holley allows Alpha-N to be switched to S/D at any given RPM. So I guess...You can have your cake and eat it too.
IMO, if it's tuned and it works...then it's right. Personally, I would never run a blown motor with Alpha-N but, that just me. For those with giant camshafts and a blower...
The Race version Cmdr950 from Holley allows Alpha-N to be switched to S/D at any given RPM. So I guess...You can have your cake and eat it too.
Craig Smith
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- Joined
- May 25, 2001
Yes, you can.
Craig,
I thought I'd have the same problem with no vaccum .. but I was able to use a canister and build great vaccum even with my 305 duration cams and 17:1 compression idling at 1400rpm ... I'm pretty sure you may have tried this already on your alky car, but curious why it didnt work for you and you have twice the number of cylinders as I do.
Greg
I thought I'd have the same problem with no vaccum .. but I was able to use a canister and build great vaccum even with my 305 duration cams and 17:1 compression idling at 1400rpm ... I'm pretty sure you may have tried this already on your alky car, but curious why it didnt work for you and you have twice the number of cylinders as I do.
Greg
Craig Smith
That was easy!
- Joined
- May 25, 2001
Something I have found in bracket racing applications (which is what I do) is that keeping fuel delivery rather than a/f ratio consistent produces less of an ET variation as the weather changes. Even in open loop, speed/density will adjust fuel delivery as barometric pressure and outside temperature changes. Alpha-N mode in open loop will not do this. All my experience thus far indicates that maintaining the same a/f ratio as the air changes makes a bracket car less consistent than a variation in the a/f ratio will.
Then it sounds like the corrrection factors need tweaked, assuming the fault is in the ecm, assuming there are no other outside influences coming into play.
Given the right fueling, and timing you should be able to maintain a consistant average. But, when you twist it to get 100% out of it then you'll always be fighting it. Running at 95% of 95% is what seem to me would win Brackets.
An explanation can be found here, about 1/2 way down:
http://www.turbojim.com:231/jim/ccom/config.htm
http://www.turbojim.com:231/jim/ccom/config.htm
