Retard or advance timing for spool?
 

Which, and why? Stephanie just said that they advance for spool on M.net, but I've always thought you should retard to move heat into the exhaust stream.

(I did search, I even searched "Advance Spool" with the username "Corky Bell" you punk. :fawk: )

I've always heard pull timing down low for spool.

Its a zero sum game when you try to increase spool by retarding timing at any point other then not moving on the start line.

To get the most spool you advance timing and have the mixture leaner than full boost. Try 13:1. Just by leaning out my mixture on my last ms car it brought the boost on 200-300rpms earlier.

Based on what I've read- retarding ignition causes the power event to complete during the opening of the exhaust valve, so even though the power stroke is weakened, that "energy" from the combustion actually accelerates the turbine wheel - improving spool. So the trade off is worth the return in spool.

Last I read Corky had suggested advancing timing coupled with raw fuel in the turbine.

:P I know there's a thread he suggested it, maybe in the last 4-5 months. i actually couldn't find it...i was going to edit my post and link it.


think about how spark cut limits spool up the turbo like crazy during launch control, yet even retarding back to 5° and cutting fuel spools it slow and only partially.


this is the best i could go back and find:
this suggest ignition RETARD coupled with raw fuel

Here's my take on it. Retarding timing doesn't work. You should run optimal advance as to maintain peak cylinder pressures around 14*ATDC. Retarding the timing does a lot of bad things too.

I will agree that running it lean (13's) at low boost does help spool. I ran mine at 10:1 (no joke, pig rich) at low boost and it would climb to 11:1 by full boost at 4500. And it felt like it fell on its face when going into boost. Because it was. Now I'v got it leaned to around 13:1 in low boost tapering to 11.5:1 by 11 PSI. Much better spool up and much better power.

You have to remember that "spool up" isn't what's so important and power to the wheels a given RPM. If retarding 10 degrees knocks out 30 HP, but you gain a pound of boost, and get another 18, then the net is a loss of 12 HP and higher EGTs.

If you added in a true air bypass, that is how an antilag system works. Well, adding in a misfire rotational idle, but more or less its firing super retarded and letting still burning fuel out the exhaust.

My thought is, sure you may make more boost, faster, but you won't be making more power.

I know i'm new on this site but i've tuned a dozen or so megasquirts. DD 3 of them. You get the best spoolup with advanced ignition and 13:1 afr. I did 14:1 and didn't notice a difference. 12:1 and it started to take longer. Adding fuel delays the ignition so it is like you retarded the timing. So you don't want to do that.

I also experimented with this a couple of yrs ago, and found that even though the spool may speed up, the whp was down, so now I run more timing from 1-10psi with mixtures as lean as 13.5:1 and the power is up in the low rpm range..

Could you elaborate on what AFR's you run a bit? Like 13.5:1 going into boost but then what? Are you still around 13:1 by say 10 pounds? I know FM likes to run theirs pretty lean up to 12 pounds or so.