20V Cam Timing

[Just1n_mc]

Can anyone tell me the stock cam timing for a silvertop? As in when inlet and exhaust valves open and close ATBC, BTDC, etc.

I've tried to search but come up with nothing.

Thanks.

[davew7]

1st generation 20V spec
Static timing that you could use when installing a cam: Exhaust timing opens 54 degrees BBDC and closes at 16 degrees ADT.
The intake opens 0 degrees TDC and closes at 70 degrees ABDC. The Intake will advance 30 degrees when the VVT is activated.
Davew7

[Just1n_mc]

Cheers for that.

[Just1n_mc]

I was looking at different aftermarket cams this afternoon and was using a camshaft calculator to work out lobe seperation angles and overlap and noticed that when I entered the inlet and exhaust cam valve timing specs it always gave me the duration the manufacturers listed at 1mm of lift.


For instance Kelford 194-D. When I entered the inlet cam specs; Intake cam opens 23 BTDC and closes 47 ABDC. The calculator gave me the intake duration of 248 with a centreline of 120. Kelford list advertised duration at 290 degrees and 248 at 1mm of lift. Every cam I tried all gave me the duration at 1mm of lift.


So I entered the information for the stock cam listed above and it gave me the duration as 250 degrees and a centreline of 125. Now since every cam I entered and had specs sheets for cam back with duration at 1mm of lift I'm assuming this is true for the stock cam.


Now either I've got myself all confused or does this mean that comparing the factory cam to the Kelford cam it must have similar if not more "advertised duration" then the Kelford since the lift at 1mm is actually higher? Surely there must be a mistake somewhere in the measurements of the factory cam??

[davew7]

You are headed down a dumpy road !!! The 1mm lift is not used by all mfr's.
Trying to work out cams spec, is very frustrating!!! There is not any standard way for measuring cams.
Some Mfgr's include open and closing ramps, some use no clearance, some use lash clearance, some use .5mm, 1.0mm, 1.25mm lift.
There is no way an average Joe can actually work out lift rate and profile to get a real comparison between different cam manufactures when just look at catalogs or brochures. Dave W

[Just1n_mc]

Ok so I worked out where I went wrong. Still doesn't get me any closer to sorting out which cams to get though...

[davew7]

If you look at the timing when advanced a 30* before TDC, the 46* overlap is excellent for top end, the closing is on the mild end of a cam profile. I'm sure that they design the best possible compromise. Dave W