this question has been floating around in my head for quite some time now. Never really understood why longer intake and exhaust durations would cause less torque and more hp. How small is too small of a cam so where its pointless? How big is too big? Wheres the sweet spot in an LS1 or are they all sweet spots but just depends on peoples opinions of where they want the power?

 

There is alot to cam theory...and I'm not the one to explain it because there is a lot i don't understand. But keep in mind that larger cams often do not lose torque, it is just moved up in the power band. HP is mearly a measuement of torque. As far as last line, you answered it yourself

 

Cylinder pressure..

Where you make it depends on primarily the IVC..Close it early and cylinder pressure is maximized in the lower rpm's.

Close the IVC late, cylinder pressure is maximized in the higher rpms.

Remember, HP=TQ x RPM/5252.

It took me about a year reading every book I could and playing around with that formula many times to get it.

This is the most simplified explanation I can give. Perhaps a few others can crystallize it even better.

Hope that helps..WeathermanShawn..

 

Longer duration cams also usually have more overlap, which at higher RPMs helps to scavange the cylinder and helps suck in some intake charge while both valves are open. This doesn't really happen untill a higher rpm. At lower rpm, that overlap can cause a loss of cylinder pressure, which is why it has less low end, and idles rough or may need to idle higher.
Hope that helped.

Jason

 

On the small end; I'm using the GM LS6 cam. It offers the least performance advantage but affects the idle nil, passes area e-check and doesn't lope. The car comes off idle with more power. I never stall the thing anymore when easing off the clutch. Gas mileage hasn't fallen and I was able to retain those excellent LS1 exhaust manifolds. As you might detect, I was only looking for 40 to 50 hp with the LS6 heads. The car is exactly what I want with this cam. Others might consider it a waste. You did answer your own question regarding that sweet spot.

 

Check out some of Patrick G's threads on "Torque coming out of my ears". Depending on your intake manifold, he tested over 4 cams. Found that in most cases picking a cam that closes the intake valve any later than 42-44 degrees, produced no appreciable gain in HP and actually lost TQ/HP "under the curve".

Hence the popularity and overall effectiveness of the 224/224 cam. Seem to hit the "sweet spot" for many people..

WeathermanShawn..