camshaft

[bushyg40]

right people i got a 252 276 11 schrick cam and i know the spec as of wen the inlet and exhaust valve is starting to open and starting closing but i want to know wen the valves are at there fully opened and fully closed any one know

[hardchargin40]

Deseminated from the Schrick Camshaft Catalogue  http://www.avl-schrick.com/dat/MK/Schrick%202009%20E.pdf  Page 1 of it...

Valve Timing degCRA

IO-IC-EO-EC

17-55 71-25

Valve timing is shown as IO (Inlet opens in
°Crankshaft before TDC), IC (Inlet closes in
°Crankshafts after BDC), EO (Exhaust opens in
°Crankshafts before BDC) and EC (Exhaust closes
in °Crankshafts after TDC).

Therefore without drawing a diagram, it's...

Inlet Opens 17deg before TDC.
Inlet Closes 55deg after BDC.
Exhaust Opens 71deg before BDC.
Exhaust Closes 25deg after TDC.

TDC -BDC being a vertical line.  TDC being effectively 0deg, but note the IC and EO valve degrees are taken from BDC.  If ive got that correct.

So a 42deg valve overlap duration during TDC and a 126deg valve overlap duration during BDC.

that make sense?

[hardchargin40]

Fingers crossed thats correct.  The Motorsport degree boys will know the proper equations etc.


Peak timing is shown as °Crankshaft and defines
the angle between the gas exchange TDC
and the lobe center line of the inlet- or exhaust
valves.

therefore I take that that the Exhaust Valve peak timing is 247deg from TDC.

HTH

Paul

[Nick_S]

right people i got a 252 276 11 schrick cam and i know the spec as of wen the inlet and exhaust valve is starting to open and starting closing but i want to know wen the valves are at there fully opened and fully closed any one know

Is this for dialling in with a Vernier? 111 degrees is the other duration you get with this cam info.

[Puncharado]

Been thinking about this myself recently, as I have the same cam to fit (2nd hand, and no data sheet/fitting info). While I understood the durations and also assumed the lobes are symmetrical and max lift being halfway etc. But the 111° peak timing figure has me a bit confused, and what do they mean by 'gas exchange TDC'? I've never done an upgrade cam swap with an adjustable pulley, only ever done timing as standard, and I've been a little worried about getting the timing wrong when I come to fit it.

[Nick_S]

pretty sure the 252/276 Schrick is asymetrical

[hardchargin40]

Assumed 111deg was the lobe separation angle.

(The lobe center angle is the angle in camshaft degrees between full intake cam lift and full exhaust cam lift).

The Lobe Separation Angle (LSA) of the camshaft lobe is where the peak lift occurs in crankshaft degrees either BTDC or ATDC. The LSA is the result of your lobe centerlines added together, then divided by two. Some camshafts are ground with identical lobe centers (e.g. 110° + 110° / 2 = 110°) while others have mismatched lobe centers (e.g. 109.5° + 110.5° = 110°). Although both cams share the same 110° Lobe center, their performance will be much different. The LSA will be a determining factor in what your valve overlap will be in relation to the duration you decide to go with. High-duration camshafts with wide LSAs (e.g. between 106°-110°) are ideal for upper rpm power and produce a lumpy idle. Narrower LSAs (e.g. 111°-115°) accentuate low-end torque and provide a smoother idle.

I would assume that max valve lift would still be the same being symmetrical or asymmetrical?  Just the duration the valve is open is longer or shorter.


Some good info here...

http://www.lunatipower.com/Tech/Cams/CamProfileTerms.aspx

and...

http://www.golfgtiforum.co.uk/index.php?topic=129138.0

[bushyg40]

cheers for the reply guys i had a sit down and worked it out on paper all set up now car will hopefully be running finally by next weekend but never finished theres always more to do