cam question

[Bill Verburg]

for the above cam, how do they get 3° of overlap?

when I do the #s the, duration's work out fine, but If the intake opens 6° after TDC and the exhaust opens 2° Before TDC I get zero overlap, if there is no overlap how do they get the .5mm lift?

I guess if the cam is installed 7.5° advanced the intake would be 1.5° into it's lift

[911pcars]

Bill,
What does a "– 6º setting at a BTDC reference point mean?

Typically, all valve events that occur before TDC are categorized as BTDC and events after TDC are ATDC. Does a minus number merely reinforce a BTDC event or indicate something else? The chart also uses a minus number ATDC. I don't know.

If aftermarket, perhaps contact the manufacturer for clarification.

Sherwood

[Bill Verburg]

Originally Posted by 911pcars

Bill,
What does a "– 6º setting at a BTDC reference point mean?

Typically, all valve events that occur before TDC are categorized as BTDC and events after TDC are ATDC. Does a minus number merely reinforce a BTDC event or indicate something else? The chart also uses a minus number ATDC. I don't know.

If aftermarket, perhaps contact the manufacturer for clarification.

Sherwood

The question came up elsewhere and I got to thinking about it, I checked my dB of cam specs and that cam was listed, I forget the source though

Because it was in a table format the valve events were as per the column headings and most of the I openings are BTDC, for this particular cam -6º means 6º ATDC and -2º for the exhaust means that it closes 2º BTDC unlike most which close sometime ATDC.

When the exhaust and intake are open at the same time you have an overlap here I don't see how there can be 3º of overlap per the spec and the only way I can see that there will be .5mm of I lift at TDC is to install the cam advanced from it's usual

I figure I have to be missing something here but just can't see it

[Bill Verburg]

this one makes sense but is still off by a few degrees in the overlap, when I do the #s overlap comes out as 48º instead of the 53º in the spec

I guess I am not fully grasping the Advance or retard spec

[roblav]

I get 48 degrees too Bill. I plotted them in a 720 degree circle. Maybe the overlap is measured with zero lash clearance and valve open/close is measured with a specified clearance?

That's the Solex cam right?