Why combinations need different amounts of timing
Why combinations need different amounts of timing Originally posted in a thread by Patrick G where he tuned a cam only C6 to amazing levels of power with stock heads https://ls1tech.com/forums/dynamomet...s-503rwhp.html
I am interested in finding out what components in particular have the greatest impact on the amount of timing needed. Port velocity? Swirl/Tumble? Combustion chamber design? Cam timing?
I'm assuming everything has some impact. If you look at the question I asked above in the quoted area I assumed the AFR combustion chamber was the difference. Was I onto something or off base?
Can anyone point me to books,articles,websites,etc. or have some information on hand that they would like to share?
Thanks
I should have been more specific with my question. I tuned a C5 with a TR224 cam,LG longtubes,etc. This engine made best power around 29* of ignition advance.Why it made best power there I am not really sure..
An AFR 205 equipped car with a TR224 cam and similar bolt ons to the C5 that I mentioned used less ignition advance,around 26* if I recall, for max power than the stock headed vette.
I automatically assumed the AFR combustion chamber was the reason for this.I assumed the L92 style heads required more ignition timing than the cathedral port style because they lacked swirl and tumble or velocity.
Seeing the low timing required on the car you worked on and the fact that it has stock heads makes me wonder what has the greatest impact on the timing required for max power.
Maybe I should ask this in the advanced engineering section instead of cluttering this thread?
An AFR 205 equipped car with a TR224 cam and similar bolt ons to the C5 that I mentioned used less ignition advance,around 26* if I recall, for max power than the stock headed vette.
I automatically assumed the AFR combustion chamber was the reason for this.I assumed the L92 style heads required more ignition timing than the cathedral port style because they lacked swirl and tumble or velocity.
Seeing the low timing required on the car you worked on and the fact that it has stock heads makes me wonder what has the greatest impact on the timing required for max power.
Maybe I should ask this in the advanced engineering section instead of cluttering this thread?
I'm assuming everything has some impact. If you look at the question I asked above in the quoted area I assumed the AFR combustion chamber was the difference. Was I onto something or off base?
Can anyone point me to books,articles,websites,etc. or have some information on hand that they would like to share?
Thanks
TECH Resident
Joined: Dec 2004
Posts: 845
Likes: 0
From: K-W, Ontario
I think there are too many variables to determine why there is a difference in timing.
Everything down to the piston speed, fuel type (not octane), spark plug projection,
air/fuel ratio, compression needs to be considered.
If absouletly nothing else changed but the camshaft (IE: no AFR tuning,
no change in spark plug type, engine temps, etc.), then you are still left
with a change in dynamic compression which changes the cylinder pressure
at every step in RPM.
A reduction in cylinder pressure alone can allow you to increase timing.
When you begin introducing cylinder heads changes along with camshaft
changes, then you can include chamber design, quench area, static and
dynamic compression into the list.
Given the same fuel and best fuel ratio for power I would estimate that
cylinder pressure and piston speed are the two most important factors
effecting timing.
The best book that I have read on this topic is, "Automotive Mechanics and Technology"
by Tillmann Steckner (third edition).
Everything down to the piston speed, fuel type (not octane), spark plug projection,
air/fuel ratio, compression needs to be considered.
If absouletly nothing else changed but the camshaft (IE: no AFR tuning,
no change in spark plug type, engine temps, etc.), then you are still left
with a change in dynamic compression which changes the cylinder pressure
at every step in RPM.
A reduction in cylinder pressure alone can allow you to increase timing.
When you begin introducing cylinder heads changes along with camshaft
changes, then you can include chamber design, quench area, static and
dynamic compression into the list.
Given the same fuel and best fuel ratio for power I would estimate that
cylinder pressure and piston speed are the two most important factors
effecting timing.
The best book that I have read on this topic is, "Automotive Mechanics and Technology"
by Tillmann Steckner (third edition).
Well, I've been trying to do alot of research on my own and from what I've been reading it seems to be heavily dependent on head design.I gather that swirl,tumble,quench area and air velocity seem to play a large part in this. I have determined that PART of the reason forced induction engines require less timing is due to the increased homogenousness (this is a real word,lol) of the mixture while increased pressure and velocity is present. The other part is the cooling effect of additional fuel.
What I have read is open to interpretation. The source material I have looked at doesn't come right out and say it.I could be totally wrong here. It'd be nice if some of the good head porters,cam designers,engine builders,etc. would chime in and correct me/provide additional insight.
Adrenaline Z: Thanks, I looked for that book on Amazon and came up with nothing.
What I have read is open to interpretation. The source material I have looked at doesn't come right out and say it.I could be totally wrong here. It'd be nice if some of the good head porters,cam designers,engine builders,etc. would chime in and correct me/provide additional insight.
Adrenaline Z: Thanks, I looked for that book on Amazon and came up with nothing.
TECH Resident
Joined: Dec 2004
Posts: 845
Likes: 0
From: K-W, Ontario
No longer in circulation? I've had mine since highschool 1990.
Here's a lead to some used versions:
http://www.amazon.ca/gp/offer-listin...condition=used
Here's a lead to some used versions:
http://www.amazon.ca/gp/offer-listin...condition=used
I have determined that PART of the reason forced induction engines require less timing is due to the increased homogenousness (this is a real word,lol) of the mixture while increased pressure and velocity is present. The other part is the cooling effect of additional fuel.
Regarding air/fuel mixture an important thing to remember, and this has nothing to do with forced induction that I'm aware of, is a richer mixture will burn faster and result in higher cylinder pressures sooner thus requiring less timing. A lean mixture would require more timing to get full combustion because it takes longer for the mixture to combust and yield the highest cylinder pressure when piston is at TDC. You can observe this when carb tuning, if you lean out the mixture then advancing the timing will result in a better idle, or if you have a rich mixture then retard the timing will result in better idle, all within reason of course.
Last edited by 1 FMF; Aug 22, 2010 at 08:27 PM.
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Well, I've been trying to do alot of research on my own and from what I've been reading it seems to be heavily dependent on head design.I gather that swirl,tumble,quench area and air velocity seem to play a large part in this. I have determined that PART of the reason forced induction engines require less timing is due to the increased homogenousness (this is a real word,lol) of the mixture while increased pressure and velocity is present. The other part is the cooling effect of additional fuel.
What I have read is open to interpretation. The source material I have looked at doesn't come right out and say it.I could be totally wrong here. It'd be nice if some of the good head porters,cam designers,engine builders,etc. would chime in and correct me/provide additional insight.
Adrenaline Z: Thanks, I looked for that book on Amazon and came up with nothing.
What I have read is open to interpretation. The source material I have looked at doesn't come right out and say it.I could be totally wrong here. It'd be nice if some of the good head porters,cam designers,engine builders,etc. would chime in and correct me/provide additional insight.
Adrenaline Z: Thanks, I looked for that book on Amazon and came up with nothing.
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