Cam Timing and Performance??
 

After searching past posts on cam timing I still don't understand the issue of cam timing. Posts have stated advanced timing improves the low end power and some say advanced improves the top end power. Can someone explain which is correct and how advancing or retarding actually works? Also, several posts stress that it is more important to get both sides of the engine timing the same. How close does one need to be?

Tuning of camshaft timing will allow to target a preferred powerband for the vehicles driving/racing type. By advancing camshaft timing, the intake event will begin opening the intake valve sooner and will build more low end torque (power). While retarding camshaft timing will delay the intake closing event, keeping the intake valve open later. This will build more high-rpm power.

On a DOHC engine where the intake and exhaust profiles are separate, camshaft tuning becomes even further beneficial. Now overlap tuning comes into play and will greatly impact powerband.

The watercooled vw world has been running adjustable can gears for decades to take advantage of the flexibility of access. I ran one myself for awhile ; 15° is noticeable in the seat of the pants. Too advanced and it falls flat up top. Too retarded and boggy throttle response but gets cooking up top.

There used to be devices that went on the cam gear with a spring loaded assembly...to advance the timing of the cam at low speeds and let it retard as the RPMs went higher.
Haven't seen them in years.
Bob

Although large changes will make a difference, small changes go unnoticed.
I've set cam timing on race engines at the track (by eye / no measuring tools) with no noticeable performance change.
Of course I get closer than 15 degrees by eye.

Interesting...
I have a friend with a 993 RS that we can't get to run properly. It lacks power above 5000 rpm, dynoed to ~250 hp so its about 50 ponies missing.... On low rpms it pulls like a train.

Someone suggested that the cams wasn't set properly (slightly hotter aftermarket cams).

Is it possible to loose 50 hp, 20%, on cam timing??

When I did my timing after the rebuild last year I set the timing at about .015 retarded from where I had set it 15 years ago. I felt a big difference in performance. The low end was much smoother and did not have the kick that I was use to. I interpreted this as improved low end performance but from what is being said I would have had a better top end. I set this time half way in between the old setting of .062 and and the original setting of .078. Will see if it makes a notable difference. Thanks for all the input.

In my experience yes, 20% loss for a cam out of time is quite achievable. Even far more pronounced on forced induction engines....

Safe,

Dyno tuning for a few years a variety of motors, biggest gain / loss catagory #1 error ignition (timing or other), #2 cam (duration, timing or both), #3 intake (too small or too big) #4 exhaust (too big or too small in that order). And yes you could lose 50 on a cam change and or big timing error. HP is TQ X RPM / 5252 if it will not RPM it will not make the HP it did before.

On a high compression race motor, cam timing may be critical for valve to piston clearance. Not such a big deal on an SC.

The only way to see what a change does is to have before and after dyno runs. Or to find people with the exact same motors who kept track of their timing and did dyno runs and compare torque curves. Porsche eventually put the SC/3.2 motors about the middle of the settings they tried. Don't know how 964 cams affect that, though.

I'm building a 3.0 liter with Ross pistons ( 10.5:1 ) and Elgin modified S cams. Specs on the cams call for 4.5mm at overlap. Would I benefit from the std S timing for an engine that is going to see more street than track use?

No. The Elgin mod S cams are not Porsche S cams. Use the number spec from Elgin. These cams are better than S cams because they have more torque at low RPM. They also should be used with stiffer valve springs (IMO).

-Andy

The sheet that Elgin sent me showed 4.5 to 5.0mm for the modified S, so seeing the normal S Cam timing at 5.0 to 5.4, we got it set at 4.93 on #1 and 4.97 on #4...

I hope I don't have to redo the timing...

Neil