Cam timing cuestion

[cheitane2003]

Hello Guy:
I would like to know the timing of these cams I don‚´t if they are 40-80-80-40 or 26-66-66-26.I just can calculate the lift.
Is there an easy method to know this numbers?
Thank you very much.
Yours faithfully,

[Guy Croft]

Sure that's easy.

Full lift (if cam timing is known) is determined by adding together with 180 deg, divide by two and subtracting the smaller cam timing number, ie:

[(26 + 66 + 180)/2] - 26 = 110
[(40 + 80+ 180)/2] - 40 = 110


In other words full lift at 110 crank degrees. This is true for both those cam types. You can't go far wrong setting of 110, even if you don't know the exact cam charateristics. Certainly most normally aspirated TC engines will run with that setting on inlet and exhaust, although it may not be absolute perfection.

Full lift 100 means inlet full lift 110 crank deg after TDC on inlet stroke, ex full lift 110 deg before TDC on ex stroke.

Set the cams up on the head and off the block:

Inlet no1 lobe at 55 cam degrees (half crank) before cam full lift at TDC
Ex 55 cam deg after full lift at tdc.

There's more on in this in GC V/W somewhere, TC dry build and cam timing or something like that, don't have time to look just yet; perhaps another kind member will find it and post the link.

GC

[cheitane2003]

Hello Guy:
Thank you very much again, that was my question: how can i Know the cam timing???Not only the full lift...

[Guy Croft]

You need to know the duration, or at least measure it with dial guage and protractor. The choose a full lift setting and use simultaneous equations to work out the timing:


say the final timing is 40/80, nice easy example, but we don't know those fitures yet, let A represent the 40 and B represent the 80, and suppose the duration measured with 16 thou" running clearance is 300 cam degrees:

Equation (1)
[(A + B + 180)/2] - A = 110 (we have to choose the full lift figure, as I said, 110 works with many cams)

Equation (2)
and A + B + 180 = 300
or A = (120 - B)

Using eqn (2) you can write A in terms of B and solve eqn (1). If you try it with this example you'll find B comes out at 80 deg, so A is 40.

Hope I go my maths right all you clever readers! I'm number blind!

GC

[NOSferatu]

My cam manufacturer has given timing instructions by open@TDC figure.
IN 3,2mm and EX 2,7mm.
The cams are both identical, so how could I know the timing? Which cam is advanced and which retarded and so on, and what that timing does compared to timing when both valves are open as much at TDC?
Cams duration is 304 degrees.
These cams are old, and I don't have anymore the paper which came with them, but I remember still that timing instruction.

[Guy Croft]

Well, you certainly need to print off what I have written and get to work measuring and doing the arithmetic to find out.

Try putting 304 deg instead of 300 duration in my equations, and start with a guess at 110 deg cam full lift.

Bolt the cams to the head and shim the cams at 0.4mm inlet, 0.45 exhaust (if billet) or 0.30mm if regrind and measure the lift at TDC on each cam using the method in the GC V/W and see if the fugures you get for those cams match the lift at TDC figures he has given you.

If not, tell me here what lift you do get.

GC