998 cams what does it all mean.
Turbo Mini Forums

hello all,

I have been doing some searches on CAM's as I'm thinking of having my spare engine rebuilt and want to spend my money as wise as possible.

Its going to be a road engine 998 or over-bore. MG metro cam come up a lot, and I found a load of info from AC dodd on timing figures but I'm not sure what they all mean. People mention the 266 but it doesn't seem widely used.

So what do all the figures mean:

MG cam
Checking height: 0.017" @ lobe

Timing: (Intake): 16/56 (Exhaust): 59/29

Nominal lobe lift: (Intake): 0.263" (Exhaust): 0.263"

Duration (Intake): 252 (Exhaust): 268

Lobe centre angle (Intake): 110 (Exhaust): 105

Lobe separation angle: 107.5

Lift on overlap: 0.054"

266 Cam
Next is the Kent 266 a nice all round road cam, these figures are based on kents own specs, plus with my own additions.

Checking height: 0.016" @ lobe

Timing: (Intake): 24/56 (Exhaust): 61/29

Nominal lobe lift: (Intake): 0.263" (Exhaust): 0.268"

Duration (Intake): 260 (Exhaust): 270

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

Lobe separation angle: 106

Lift on overlap: 0.054"


Thanks all

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

is this for a 998 turbo lump?

Have a look at this:

http://auto.howstuffworks.com/camshaft.htm

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

supercharged 988

Thanks Paul will have a look

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

1. Timing: (Intake): 16/56 (Exhaust): 59/29
• 16/56: The inlet valve opens 16 degrees before TDC and closes 56 degrees after BDC

• 59/29: The exhaust valve opens 59 degrees before BDC and closes 29 degrees after TDC

2. Nominal lobe lift: (Intake): 0.263" (Exhaust): 0.263" This is the distance between the valve and valve seat when the valve is fully open.

3. Duration (Intake): 252 (Exhaust): 268
• This is a little more complicated to explain so bare with me. The cam shaft rotates at half the speed of the crank shaft. The duration is number of degrees of crank shaft rotation that the valve is off of the valve seat. So although the crank shaft has rotated 252 degrees the cam shaft has only rotated 126 degrees and in this 126 degree arc it has opened and closed the inlet valve. And as you can se from the above the exhaust is open for longer.

4. Lobe centre angle (Intake): 110 (Exhaust): 105
• This is the angle created by the flat sides of the cam lobe

5. Lobe separation angle: 107.5
• This is the angle between the centre line of the inlet lobe and the centre line of the exhaust lobe.

6. Lift on overlap: 0.054"
• This when the inlet and exhaust valves are open at the same time, and is the measurement of how far off of the valve seat the valves are.
• Note that head modifiers say noticeable flow does not really happen below 0.050” of lift

7. Checking height is the gap you set between the tip of the rocker and the top of the valve stem.

If any of the above is seen to be incorrect correct away.

Own the day

thats a good description, thanks :)

Yes i moved to the darkside

Instagram @jdm_brett

Thanks for the great description

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

you might find the needs of a supercharged engine (camwise) is quite different to a turbo engine

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

thats what I was thinking.. VMAX do a SC cam might be worth a go

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!