Do the degree markings on the cam gears reflect crank or cam degrees?

 

Nope, I'm absolutely correct. Here's why:


Cam degrees are what's printed on the adjustable cam gears, not crank degrees. The reason why cam degrees are printed on the gears is because there isn't enough room to print 720 markings for crank degrees. Look at the photo, then look at your adjustable sprockets. You will find that the numbers are in the same position, which clearly illustrates my point.


ALL the HKS cams for the EVO are on 110 lobe centers, both intake and exhaust, which equates to a 110 deg LSA.

No, you're forgetting that the exhaust lobe comes around before the intake lobe and not the other way around. Therefore, if the exhaust lobe is delayed (retarded), the exhaust lobe becomes closer to the intake lobe, and the LSA becomes smaller.

 

FWIW Teds #s and info are correct (for the most part anyway )

 

Where am I mistaken...?

 

Your right

 

i give up ..we're talking about the same things and understand each other.. since you're such a stickler for #'s.. its 1.75INT CAM / 0.5 EXH CAM satisfied ??

educate me on this.. i'm lost.. i thot with LCA of 110deg your LSA will be 140deg???

beginning to see but gotta digest 1st
so you are saying with 109 LCA its actually adv the exh??

 

But you quoted: "-3.5 /+1E and 0I/-2E", which are clearly cam degree settings, not crank degrees. You don't set your cams using adjustable cam gears, which are indexed in cam degrees, not via a degree wheel on the crank.



LSA = (LC Int + LC Exh)/2. For example, if your intake cam is set on a 110deg lobe center and your exh cam as well, the LSA is also 110deg.



If your exhaust cam has a LC of 110deg, and you bring it to 109deg, you've effectively retarded the exhaust cam 1 crank degree, which = 0.5 deg retard on your adjustable cam sprocket.

 

When you retard cam timing, is it necessary to increase or decrease crank timing to optimize max power production? For instance, (with fuel remaining the same) would a setting of -3/-3 require you to increase crank timing (or decrease) for maximum efficiency?

 

Cam timing does not really have a direct effect on ignition timing. Ignition timing is more sensitive to the position of the crankshaft (pistons) as opposed to the cams. Ignition timing is more so affected by the shape of the torque curve (cylinder pressure) with respect to rpm and boost.

However, if you retard cam timing and/or increase the LSA, you effectively reduce low speed cylinder pressure, which means you can run a little more spark advance at low speeds before the onset of preignition.

Conversely, if you are running a -4/-1 setting and go to something like a +2/-2, you will develop more torque earlier in the rpm range, which will increase cylinder pressure and will cause you to remove some timing there.

 

Increasing LSA boosts the torque curve (cyl. pressure) at very low RPMs and high RPMs at the expense of the mid-range, so you should actually be seeing more cylinder pressure at low RPMs with a wider LSA and therefore you should be running less spark advance at lower RPMs with a wider LSA than with a narrower LSA, right?

 

Widening (increasing) the LSA will typically increase off-idle torque, and therefore low speed cylinder pressure, which necessitates less spark lead.

However, if we narrow the LSA AND advance the lobe centers, then we can increase low speed cylinder pressure.

Here's a nice webpage that sums things rather well. Go to the bottom:

http://hometown.aol.com/ffastcbr/caminfo.htm

 

So when is Ted getting the EvoM Guru title?

I had to re-read these last dozen posts like 3 times for it to sink in...

Terry S

 

Geez u mean i've working off the wrong nunbers all this while??
so when u said -4/-1 u actually set the cam gears 4 marks off n not 2??

 

No, you did it right. Cam gear marks = cam degrees, and -4/-1 is a CAM DEGREE setting!!

 

Ted, I just read this entire thread, I would like to know your opinion on gear settings
for the 272i / 264e combo?