4 replies to this topic

[Alex Kay]

Hi everyone

I was hoping someone might have the phasing numbers (opening and closing numbers), lift, and LSA's for these cams? Interested in buying one, but they have NO technical info on them on their site.

Thanks

[Pigeonto]

Hi everyone

I was hoping someone might have the phasing numbers (opening and closing numbers), lift, and LSA's for these cams? Interested in buying one, but they have NO technical info on them on their site.

Thanks

Checking height: 0.016" @ lobe

Timing: (Intake): 16/48 (Exhaust): 52/12

Nominal lobe lift: (Intake): 0.281" (Exhaust): 0.281"

Duration (Intake): 244 (Exhaust): 244

Lobe centre angle (Intake): 106 (Exhaust): 110

Lobe separation angle: 108

Lift on overlap: 0.036"

[carts60]

*Sorry to hijack*, BUT
I was thinking of getting one of these too, and with different cams, you get all the numbers seen above, but what on earth do they all mean??? Whats good and whats bad?

[Alex Kay]

Hi everyone

I was hoping someone might have the phasing numbers (opening and closing numbers), lift, and LSA's for these cams? Interested in buying one, but they have NO technical info on them on their site.

Thanks

Checking height: 0.016" @ lobe

Timing: (Intake): 16/48 (Exhaust): 52/12

Nominal lobe lift: (Intake): 0.281" (Exhaust): 0.281"

Duration (Intake): 244 (Exhaust): 244

Lobe centre angle (Intake): 106 (Exhaust): 110

Lobe separation angle: 108

Lift on overlap: 0.036"

PIGEONTO, you're a champion thanks very much thats exactly what I wanted to know Many thanks.


carts60, please, feel free to hijack you're more than welcome to

There's no real short answer to your question but I'll have a crack at it.

Camshaft time is measured in degress of crankshaft rotation. TDC means "top dead center" (when talking about cam timing Top dead centre reffers to piston number one.... so piston number 1 is at the top of its stroke), ATDC means "After top dead center", BDC means "Bottom dead centre, BTDC means "Before top dead centre".

The timing, or phasing numbers (eg in the case of the cam I was asking about 16/48-52/12) relate to the opening and closing events. In this case the intake valve opens at 16 degress BTDC, and closes at 48 degress After bottom dead center (ABDC).... so you add the degress BTDC (16) plus the 180 degress between TDC and BDC to the time After Bottom Dead Center (48).... So its 16+180+48= 244 degress duration. But its more important to know when the events take place than it is to know the duration alone. You could have intake timing of 18/46 and its still 244 degress duration but will behave totally differently.

Checking hight is where you start measuring th cam timing from. So in this case, you would Zero your dial gauge on the point of lowest lift (the very back of the cam or "base circle), then, turn the crank over till the needle rises to 0.016" (0.4mm) then "re" zero it and start conducting all your measurments from there.

Lift at the lobe is just that... the amount that the nose of the cam lobe lifts from zero... lift is measured at the lobe or at the valve... To save confussion I personally reckon its easier to get lobe lift. Then you can work out what the valve lift will be with YOUR rocker set up. So to work out your valve lift with your set up, you multiply the ratio of your rockers by the lobe lift, then deduct the valve clearance. So if you were running this cam with 1.5:1 rockers, you would go 0.281 X 1.5 = 0.4215".... then you'd minus your clearance (usually.. not always "about" 0.018-0.019" with 1.5 rockers... it depends on the opening rate or ramp up.... basically how fast the lobe opens the valve and the stress it places on the valve train...)


Lobe Center Angle (LCA) is where you "time" the cam from. So in this case, you would "time" the cam, so that the intake valve for cylinder #1 is at full lift (open as far as it will go) at 106 degress ATDC. Some cams might recommend 110, 108... but it really depends on the characteristics of YOUR engine... as an example I have a 1310 withh 11.2:1 comp with a MD276... I found that for what I wanted out of the motor, timing it at 104 worked best. By advancing yout cam (timing it in so that the intake opens sooner) you'll find it comes on the cam a little sooner and has a bit more torque at low rpm.... but it runs out of breath at high rpm and doesn't produce as much power. At the same time, by winding it back and retarding it (so that it opens later) it will come on the cam later but produce more power up higher..... So its kind of a trade off depending on what your after. Usually, starting with what the Cam grinder recommends is fine... and you only need to shift it 1 or 2 degrees to notice a big diffence. But the LCA quoted by the manufacturer is important because without it your phasing numbers are near useless.

LSA (lobe seperation angle) is the pitch or degrees of seperatin between the intake and exhaust. The impact of of different LSAs is a long complicated thing to explain on its own (as are all these seperate terms) but on an A series... it seems "popluar" to go for 108-110..... thats all I'll say




Now that is the EXTREMELY brief version of what they mean....

As far as whats "good" it really depends on the the displacement of the engine, the comp ratio, head spec (for a start) and what it is that you want out of it. For instance a cam with 0.500" lift and 310 degrees duration is going to be a total pig in your 998 with 8:1 comp and std 12G202 if you want to drive it to work every day in traffic. At the same time you wouldn't put at 260 degree cam with 0.290" lift in a 1412 that your going to take to the track.

For road use, as a rule of thumb (and only a rough one at that) in a road going 998, the most duration you'd want would be about 270ish degrees.... and in a 1275+ the hottest you might go for would be something like mid 280's.... But it really depends on the motor and what you want.


Pwar... I think its time for a coffee.... and time to find my flame proof suit

<edit> Just tried to fix some of my spelling... brain works faster than fingers... sorry lol

Edited by Alex Kay, 30 August 2010 - 12:22 PM.

[carts60]

Any chance i can PM you about cams and get you're opinion some time sooner to when il actually be getting one? You definitely seem to know your stuff!! I tried my hardest to understand, and i do partially, but im only just starting to understand the workings of an engine.