Cheatin' Chad

iTrader: (3)

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

Cheatin' Chad

iTrader: (3)

L92 heads seem to NEED more timing that the cathedral port heads.. No one knows why or is interested in figuring it out?

Adrenaline_Z

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).

Cheatin' Chad

iTrader: (3)

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.

Adrenaline_Z

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

1 FMF

iTrader: (1)

regarding forced induction I don't think the homogenousness has much to do with it. I know you said part of the reason and that is probably true, but I think the vast majority of the reason is less timing is required simply because there is more pressure in the cylinder to begin with and igniting the mixture at the traditional amount of degrees BTDC would cause such a rise in pressure before actual top dead center that too much negative work would be done on the piston. That's how I see it, there are other factors like you mentioned that affect combustion but I see those as the last 10% or 5% for achieving optimal combustion. Also with forced induction, I don't think there is any cooling affect. When you pressurize anything basically, it heats up. Maybe you are referring to a richer A/F mixture? That would have additional fuel, and depending on fuel type can have a huge cooling affect. Strictly speaking forced induction however, A/F ratio in independent or another variable to juggle.
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.

Hector

"Homogeneity" is probably the word that eluded you, lol.

gametech

iTrader: (1)

In order for someone to give you the level of detailed answer you are looking for, they would have to violate their "non-compete" agreement with whatever Nascar or F1 team they work for. Seriously, most of us are content to know that there are differences, but we don't know all of the why's. If you ever get a satisfactory answer to your question, everyone here will LOVE to read it.