911 Cam & Crank timing 2.7 mfi

[HKZ Bob]

Dear rebuilders.

I would like to avoid bringing my camshaft to a cam doctor. DIY
I have a regrind cam and I am going to buy a Z-block to measure the lift.

The measurement was done as follows.
Adjusted the valve clearance to 0.1 mm

The opening & closing point is defined when the valve clearance is in the transition from 0.1 to 0.0mm.

I would like to know if all my assumtions are OK
Please review my picture.
Thank you

[2.70Racer]

Bob,
European cams are rated in crankshaft degrees from a point when the valve has opened 1.0mm (0.040") until it has almost closed at 1.0mm.
American cam builders rate the duration of their cams at 0.050".
Thus there is some discrepancy between Euuropean specs and American specs for the same cam.
As I understand your description, you noted when the valve first began movement opening until just when the valve was fully closed.
This will add approximately 20 to 25 degrees at opening and an additional 20 to 25 degrees at closing, from cam specs currently used today.
Using your measurements, opening at 76 degrees before TDC and closing at 114 degrees ATDC, we have 370 degrees duration minus 40 to 50 degrees, gives us 320 to 330 degrees intake duration, using today's specs.
This is a likely a racing cam used with turbo's.
By comparison a "S" cam is rated at 268 degrees intake duration.
To accurately measure this cam, I would repeat the test using the 1.0mm criteria. This will eliminate any guessing as to the actual duration.

[HKZ Bob]

Originally Posted by 2.70Racer

Bob,
European cams are rated in crankshaft degrees from a point when the valve has opened 1.0mm (0.040") until it has almost closed at 1.0mm.
American cam builders rate the duration of their cams at 0.050".
Thus there is some discrepancy between Euuropean specs and American specs for the same cam.
As I understand your description, you noted when the valve first began movement opening until just when the valve was fully closed.
This will add approximately 20 to 25 degrees at opening and an additional 20 to 25 degrees at closing, from cam specs currently used today.
Using your measurements, opening at 76 degrees before TDC and closing at 114 degrees ATDC, we have 370 degrees duration minus 40 to 50 degrees, gives us 320 to 330 degrees intake duration, using today's specs.
This is a likely a racing cam used with turbo's.
By comparison a "S" cam is rated at 268 degrees intake duration.
To accurately measure this cam, I would repeat the test using the 1.0mm criteria. This will eliminate any guessing as to the actual duration.

Thank you 2.7 racer.
The 1mm is measured valvelift? I have to measure this with a gauge and z-block. Correct.


BR bob

[tom1394racing]

Bob

I built this DIY cam doctor to map some of the cams in my inventory.

Works pretty well.

DIY Cam Doctor

[HKZ Bob]

Nice post.

I was tapeing the scale to the crank pulley and watching the camshaft.

Thank you.

[2.70Racer]

The 1mm is measured valvelift? I have to measure this with a gauge and z-block. Correct.
Yes, that is what I would do.
Interesting to find out exactly what you have. Any other marks?

[HKZ Bob]

Tom here you see what i got in my engine!



Cam Identification question