squrlathon

For street use, Schrick advises that CAMS should give a small valve opening -- here is what they say:

If the vehicle is intended for normal street use. i.e. with a stable engine idle and the ability to pass an emissions test (idle to lower rpm range), it is important to consider a small valve lift at TDC.

This table gives a guideline for valve lift at TDC.

2 Valve engines with solid lifters 2.3mm

4 Valve engines with solid lifters 1.5mm

2 Valve engines with hydraulic lifters 1.9mm

4 Valve engines with hydraulic lifters 1.1mm

When these values are exceeded, the engine idle will become increasingly unstable and the torque delivery in the lower rpm range be noticeably weaker.

Camshafts with larger valve duration's, and a resulting higher valve lift at TDC, should only be considered for racing applications, or when each cylinder has it's own butterfly valve i.e. 2 twin-choke carburettors on a 4 cylinder engine.

End quote.

So, for my 2.8 12-Valve engine, they recommend valve lift at TDC not to exceed 1.9mm for practical engine performance. If I check CAM specs here(http://www.audiquattroparts.com/schrick/performance_spec.htm)

and here (http://www.eurospecsport.com/camshafts.html#)

I see that the "lift" is posted at 11mm or over for the designated CAMs. Am I looking at the wrong thing or are they're decimals screwed up and/or am I missing something here alltogether?

cuatrokoop

different specs for different times in the cam rotation...11mm = max lift. 1.9mm = lift at some point in the rotation of the cam (which happens to be Top Dead, valve will be mostly closed).

MikTip

Ya need to measure the stock cams, to see exactly where & how much they compare to the Schricks.

Audi V6 2V

Schrick Part numbers: 269.L1.601-00
269.R1.601-00
Lobe lift: 11.1mm

Duration: 260/260/112

Valve Timing: Intake open- 18 (Crankshaft)
Intake Closed- 62
Exhaust Open- 62
Exhaust Closed- 18

Valve lift at TDC- 0.9/1.1

Fill in the above values with the stock cam spec's
then you'll see the improvement offered by the Schricks.

squrlathon

they are indicating that at TDC the opening should be 1.9mm or less (for practical street use) -- but the lift posted is not the TDC measurement...so where can I find the TDC measurement? Basically what I want to know is which degree CAMs will fall into the "practical" street use category, i.e. at which degree is the threshold above which street use will probably be impractical (if you take the Schrick's advise at face value, which I am at this point) --

It seems strange that they say "watch out for openings bigger than "XXXX" at TDC...but then they don't post the figures for their various CAMs??

squrlathon

so that I can keep within the "practical use" limits, as suggested by Schrick.

cuatrokoop

most cams for sale (for the 12v at least) will not dramatically reduce idle quality. a 274 may, but not a whole lot, in my guesstimates...what that type of cam will do, is make your engine like to rev.

squrlathon

okay, so i won't worry about it affecting my idle toooo much then.

thanks guys.

MikTip

Your "practical use" limits have already been decided for you! Because you run the OEM hydraulic lifters.

Now, if you change your lifters, or modify them to gain extra lift, Schrick's numbers are there
because the cams lobes & your modified lifters will start hammering away at each other, if you go beyond the 1.9.

Only Schrick sells different lifters.

If you run "high-lift" lifters, you need to change the valve springs as well. Because the valve springs will squash & lock on you beyond
1.9.

Schrick is stating the "maximum" lift obtainable.

Running the 260's in a "stock" Audi head with "stock" lifters, you'll get 0.9-1.1mm extra lift.

The variation is due to the hydraulic lifters.

squrlathon

Re: "practical use" limits -- are you still running oem lifters/springs?

MikTip

Re: are you still running oem lifters/springs- Yes.