Retard or advance timing for spool?
#1
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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. )
(I did search, I even searched "Advance Spool" with the username "Corky Bell" you punk. )
#5
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.
#6
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
: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:
Originally Posted by corky bell
Mtex, you are quite correct regarding heat kicking the turbine. Although I've not spent too much time looking for it, there is likely a sweet spot in lower RPMs where the least timing and an abundance of fuel can add significant energy to the turbine.
Perhaps the biggest single affect is had by getting some raw fuel in the exhaust that did not lose most of its energy during the expansion stoke in the cylinder.
While racing 300ZX turbos in the 80's, everytime we busted a spark plug the boost would go up 6 or 8 psi.
Perhaps the biggest single affect is had by getting some raw fuel in the exhaust that did not lose most of its energy during the expansion stoke in the cylinder.
While racing 300ZX turbos in the 80's, everytime we busted a spark plug the boost would go up 6 or 8 psi.
#7
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.
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.
#10
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.
#11
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.
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.
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