What rocker arm ratios do people see? Options

[stugray]

I am adjusting the valve geometry while putting in a Raby 9700 cam and I am seeing .38 on the exhaust cam lift and .496 at the valve (an exh rocker ratio of 1.3) and I have a .39 on the intake with a .546 at the valve ( an int rocker ratio of 1.4) is this what everyone else gets for rocker ratios:

Intake rocker ratio = 1.4
Exhaust rocker ratio = 1.3

These are the 1.7 (1.8?) rockers that accept the 911 swivel feet.
I am using the swivel feet, have modified the rocker faces, adjustable push rod, and zero lash to do the meaurements.

Do those rocker ratios look like stock?

I want to take 50 thousandths off the Combustion chambers to increase the CR, but my measurements say I wont have enough clearance on the Intake valve once I shave off 50 thousandths.

I only have ~0.075 clearance now from the piston to the Int valve as it is with a deck of 0.030 and everything else (crank & rods) stock - flat top 96mm pistons.

That Intake valve travel of ~0.55 looks huge to me. Anyone else care to comment?

Stu

[stugray]

Ok, so I decided to go with a webcam 86b instead of the other.

I measured it prior to installation.
The wecam 86b has an advertised "Valve Lift" of .500/.500 Int/Exh.
http://www.webcamshafts.com/pages/automobi...691_001095.html

So I measure the cam and get: .365/.365 lift at the cam.

.365 * 1.37 = .500 valve lift.

So apparently Webcam knows that these rockers are closer to 1.4 than 1.3, but I must just be a "mentally ill idiot" just like webcam.....

So based on the advice above (Type-IV rockers are always 1.3), I need to adjust these rockers until I get a valve lift of .365*1.3 = .474 instead of the advertised valve lift of .500.

So which is it? Both webcam and I must be "off our rockers"

I now have just what I needed. Valve lift of less than .510 on both int & exh. and I can dial my deck height to get a close as possible valve clearance whie maximizing CR.

Thank you webcam.
Stu

[worn]

Ok, so I decided to go with a webcam 86b instead of the other.

I measured it prior to installation.
The wecam 86b has an advertised "Valve Lift" of .500/.500 Int/Exh.
http://www.webcamshafts.com/pages/automobi...691_001095.html

So I measure the cam and get: .365/.365 lift at the cam.

.365 * 1.37 = .500 valve lift.

So apparently Webcam knows that these rockers are closer to 1.4 than 1.3, but I must just be a "mentally ill idiot" just like webcam.....

So based on the advice above (Type-IV rockers are always 1.3), I need to adjust these rockers until I get a valve lift of .365*1.3 = .474 instead of the advertised valve lift of .500.

So which is it? Both webcam and I must be "off our rockers"

I now have just what I needed. Valve lift of less than .510 on both int & exh. and I can dial my deck height to get a close as possible valve clearance whie maximizing CR.

Thank you webcam.
Stu

Hi Stu,
When I got the head on for a trial run I got the exact valve lift that web cam advertises. I added shims under the pedestals so that the end of the elephant foot screw (inside the foot) was lined up at the mid point of the rocker shaft at mid lift. That is the starting point. After that, the screws do not alter valve geometry very much. Then I cut the push rods so that they also contacted the rockers at centerline height at mid valve lift. In both cases you draw the line at right angle to the valve stem or pushrod through the rocker shaft center line.

OK, I miss cut the chromemoly pushrods, so now I have to shorten them by 1.5 mm. They will be in my case 2 mm shorter than stock. I strongly endorse this link to help solve things:
http://www.crankshaftcoalition.com/wiki/im...ER_GEOMETRY.pdf
This has a lot of info about SBCs, but at the bottom it discusses our type of rockers. It is a fantastic article. Good luck with the build. Ice may melt eventually here.