Speed density vs ALPHA N

diegom6 · Post by **diegom6** » Fri Sep 08, 2006 10:26 pm

Ok, what is the difference exaclty, i tried to find some info but couldn't find it. Also what is stagged injector?

For what porpouse would be better each option?

Thanks

just learining a bit

newtyres1 · Post by **newtyres1** » Fri Sep 08, 2006 11:34 pm

http://www.megamanual.com/v22manual/mtune.htm#alphan

somehow I think you'll be using speed density. For staged injection check the MSnS-E site:

http://megasquirt.sourceforge.net/extra/

It can be difficult to find info at first, but if you click on the "MegaSquirt EFI Forum Index" under the Megasquirt logo on this page and look at everything on that page you will find enough links to info to keep you going for 6 months.

diegom6 · Post by **diegom6** » Sat Sep 09, 2006 2:34 pm

great! I did miss it somehow. Now that I have used my MS I understand this manual better! Thanks

.

PS: I will come back here to check for other interrogant I have, but when times comes.

-Diego

diegom6 · Post by **diegom6** » Sat Sep 09, 2006 2:37 pm

I forgot to ask, what happens if I have a HOT , very HOT cam in my turbocharged vehicle and use APLHA N, like it is stated in the manual, how do I sopouse to give more fuel under boost? In other words the MS won't know it's a boosted engine? Now that would be difficult to tune

Bernard Fife · Post by **Bernard Fife** » Sat Sep 09, 2006 3:09 pm

use APLHA N, like it is stated in the manual, how do I sopouse to give more fuel under boost?

diegom6,

You can't give more fuel under boost with alpha-N, which is why you can't use alpha-N on boosted engines.

Lance.

diegom6 · Post by **diegom6** » Sat Sep 09, 2006 3:32 pm

Lance wrote:
use APLHA N, like it is stated in the manual, how do I sopouse to give more fuel under boost?
diegom6,

You can't give more fuel under boost with alpha-N, which is why you can't use alpha-N on boosted engines.

Lance.

that means that my idle won't be good or almost none idle for Speed density slection right? So, a solution would be open more the throttle and keep idle higher than 1100 RPm's for example if it was normally idling good at 800 RPM's with stock cams?

IÂ¡m Diego by the way

Matt Cramer · Post by **Matt Cramer** » Sat Sep 09, 2006 4:57 pm

Not too many engine tuners like to combine very hot cams with turbos anyway. I would imagine the solution would be a sort of hybrid tuning that uses alpha-N at a combination of low RPM and off boost, then switches to speed density as soon as the engine got much of anywhere off idle or under boost.

lemons · Post by **lemons** » Sat Sep 09, 2006 11:36 pm

I highly doubt that your cam would be THAT hot.

In the shop i worked at we had a 427ci small block ford that made in excess of 1500hp with boost, and the car idled at at solid 750-800rpm. And this was a speed density system.

On top of that it's a 9 second car that's daily driver in the summer time. You wouldnt even know if it wasnt for the parachute hanging off the back of the car.

So i think it's worth trying the speed density. As long as you get a good map signal, you should be ok, thats the only reason for using alpha-n (as far as i know) is when you cam it so hot that it wont give a good map signal, try relocating.

rs2000 · Post by **rs2000** » Sun Sep 10, 2006 12:40 am

The cam should be a turbo cam. If you use a hot cam like used in NA cars your car will run like a pig. This is because the high duration of hot cams means that back pressure from the turbo will feed back into the cylinder, partially filling it with exhaust. or something like that!

AFAIK aftermarket turbo cams vary more in terms of cam timing and lift, which will behave nearly like a standard cam off boost. It is duration that makes tuning hard.

If you can't get an idle you could use either blended alpha-n as someone suggested or use locked idle VE code.

diegom6 · Post by **diegom6** » Sun Sep 10, 2006 3:55 pm

Thanks guys, I'm just learning and also wanted to know in case it happens, also, because I will install a MS in a N.A:. too and wanted to know. I guess I can use speed density with this N.A. engine to make the tune friendlier.

Thanks

-Diego