Over the weekend, those of us that gathered in Ohiuo to watch Mark race, one of the topics was Camshafts.

I looked up some of the data available for our cars covering the 85/86 model, the S4, and the GT. It was mentioned that the 85/86 Cam may be a pretty good selection for more ummpphhff.

So...

A noticeable difference is when the Intake valves begin to open...

And close....

The valve settings are also a bit different...

Drawing the profiles out on a radius chart is pretty interesting.

The only info that I don't have is the 'lift' values for each cam.

As you can see from the above data - the 85/86 cams have a higher value of duration - which might provide for more 'charge' into the cylinder during the cycle. However, the lower value of valve depression in the settings seems to indicate that the lift may be less in height than the S4 or GT cams. Hmmmm....

So - anyone out there have the missing piece of the puzzle? (i.e. Lift heights?)

TIA and hth-

Jay
87 S4 Auto

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The exhaust cam data...

Duration -

The opening and closing positions for the 85/86 and the GT cams are the same (opens at 30 degrees BBDC - closes at 5 degrees BTDC)

The S4 exhaust valves open at 17 degrees BBDC and close at 2 degrees BTDC.

So...the exhaust valves open earlier and close just slightly earlier for the 85/86/GT cams and are open a bit longer - which would indicate that they would be better for scavenging purposes I would think.

Jay

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We have gotten questions about the Factory Workshop Manual method of setting the cam timing - it is a very confusing procedure. This seems like a good time to add a few comments.
TDC-firing for #1 and TDC-firing for #6 are one full turn apart.


When #1 is at TDC-firing, the rotor buttons point left (toward the driver's fender on a USA car), the marks on the cams point left, and the cam sprocket marks align. Both valves are closed in #1. The intake valve will start opening in one crank turn.


When #6 is at TDC-firing, the rotor buttons point right (toward the passenger fender on a USA car), the marks on the cams point right, and the cam sprocket marks are at the bottom. Both valves are closed in #6. The intake valve will start opening in one crank turn.


To set the passenger-side (USA) cams - #1 cylinder:
Put the crank at TDC-firing for #1.
Set a dial indicator on zero with some preload on the #1 intake lifter, parallel to the valve stem. You are at TDC-firing on #1, so the intake is closed.
Turn the crank one full turn, then start watching the dial indicator. Stop turning when the dial indicator reaches the specified lift. Look at the crank damper - the 20 deg mark should be aligned with the pointer. If it is not, you loosen the cam sprocket and turn the crank while holding the cam at the specified lift until the 20 deg mark is aligned. Tighten the cam sprocket.


To set the driver-side cams (USA) - #6 cylinder
Put the crank on TDC-firing for #6.
Set a dial indicator on zero with some preload on the #6 intake lifter, parallel to the valve stem. You are at TDC-firing on #6, so the intake is closed.
Turn the crank one full turn, then start watching the dial indicator. Stop turning when the dial indicator reaches the specified lift. Look at the crank damper - the 20 deg mark should be aligned with the pointer. If it is not, you loosen the cam sprocket and turn the crank while holding the cam at the specified lift until the 20 deg mark is aligned. Tighten the cam sprocket.


Use the extra bolts and the manual procedure to control the cam movement when you loosen the sprocket.
__________________
Wally Plumley
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========

"32-Valve Cam Timing"

We have gotten questions about the Factory Workshop Manual method of setting the cam timing - it is a very confusing procedure. This seems like a good time to add a few comments.
TDC-firing for #1 and TDC-firing for #6 are one full turn apart.


When #1 is at TDC-firing, the rotor buttons point left (toward the driver's fender on a USA car), the marks on the cams point left, and the cam sprocket marks align. Both valves are closed in #1. The intake valve will start opening in one crank turn.


When #6 is at TDC-firing, the rotor buttons point right (toward the passenger fender on a USA car), the marks on the cams point right, and the cam sprocket marks are at the bottom. Both valves are closed in #6. The intake valve will start opening in one crank turn.


To set the passenger-side (USA) cams - #1 cylinder:
Put the crank at TDC-firing for #1.
Set a dial indicator on zero with some preload on the #1 intake lifter, parallel to the valve stem. You are at TDC-firing on #1, so the intake is closed.
Turn the crank one full turn, then start watching the dial indicator. Stop turning when the dial indicator reaches the specified lift. Look at the crank damper - the 20 deg mark should be aligned with the pointer. If it is not, you loosen the cam sprocket and turn the crank while holding the cam at the specified lift until the 20 deg mark is aligned. Tighten the cam sprocket.


To set the driver-side cams (USA) - #6 cylinder
Put the crank on TDC-firing for #6.
Set a dial indicator on zero with some preload on the #6 intake lifter, parallel to the valve stem. You are at TDC-firing on #6, so the intake is closed.
Turn the crank one full turn, then start watching the dial indicator. Stop turning when the dial indicator reaches the specified lift. Look at the crank damper - the 20 deg mark should be aligned with the pointer. If it is not, you loosen the cam sprocket and turn the crank while holding the cam at the specified lift until the 20 deg mark is aligned. Tighten the cam sprocket.


Use the extra bolts and the manual procedure to control the cam movement when you loosen the sprocket.
__________________
Wally Plumley
928 SPECIALISTS ONLINE STORE
30,000+ Parts Online!
Search for 928 Parts by Your Model Type!
928 OC Charter Member