Preferred Cam Timing adjustment
 

Hello, it's been a few months, but my cylinder heads are back from the machine shop. They were fly cut so I wanted to partial assemble to check intake valve to piston clearance.

Engine is a 1980 3.0 SC ROW stock. Cam timing adjustment spec is 1.4 to 1.7mm. Splitting the difference at 1.55mm I have an additional .058" valve to piston clearance. If I set the cam at 1.7 mm, valve to piston clearance lessens as expected to .052" Sorry for going back and forth between mm and inches.

I have a question. Is it preferred to time the cam with more advance at 1.7mm or is it better to split the difference and shoot for 1.55mm average or the least advanced at 1.4mm gaining more valve to piston clearance? I'm inclined to split it evenly unless consensus it to retard or advance within the spec. During tear down, #1 intake measured at 1.85mm and #4 intake measured at 1.71mm

I did try searching but felt I could reask this even if its been asked before, I didn't notice. thank you for your patience. Mark

I thought, off the top of my head, not being near the garage, the settings you’re using is for the 9.3 US cars
The ROW cams set about 0.9mm giving better power at high RPMs
Bruce

Thank you. I’ll do a little more reading to verify the ROW values. I did read it in a specialty book, but could be mistaken. .9mm would yield quite a bit more piston to valve clearance, which is nice to have.

Edit: After more research, I’m no closer. The car is new to me. Came with broken head studs. Engine case and chassis are ROW. 930/09 case. So, I’ve decided to slow down a bit. Plan is too verify compression ratio while it’s apart. Unfortunately one of the cam lobes was pitted. Both cams were repaired by WebCams to stock SC specs. They provided a cam spec card, so I’ll use their specs and see where the intake opening measurement ends up. Then decide how to proceed from there.

Bruce, thank you for the reply. Mark

When I ran my stock class SC in PCA I dynoed my car with the cams at multiple settings. There is a wide range for setting based on the year for 911SC and Carrera's. I Dynoed the most retarded spec, middle and most advanced. The most advanced cam timing was the best for my setup. All other settings were big traded off in torque. The HP gains with the other settings were 2-3HP around 6300rpm. Torque difference from full retard to full advance was about 18FT/lbs. This was on a 78 big port motor, CIS, Headers and later 9.3 to 1 pistons. Dyno comparison below shows full advance and full retard cam settings. There is also some tuning that was done as well that helped overall power.


johnhttp://forums.pelicanparts.com/uploa...1646598259.jpg

john

John, thank you for your experience and the chart. Your graph shows .003 and .020 measurements. How does that translate to the actual intake cam setting and I assume those are inches not mm.

Using Bruces value of .9mm = roughly .035” using 1.55mm = roughly .061” so I’m a bit more confused by the values on your graph. I do understand the general basics of advancing and retarding cam timing.

Thanks again. Mark

is that a 24 hp difference at 4000 rpm ?

Spent today determining what engine configuration I have. It’s definitely an 8.6 :1 ROW 3.0 Was then reviewing the cam card from Web Camshafts. If these were unique Euro cams, that uniqueness has been machined away.

Upon closer examination of the cam spec card. They recommended 1.4 to 1.7 mm timing with .004” lash. I attempted to attach the cam card to this post. I’m going to consider this case closed. Thank you. Mark
http://forums.pelicanparts.com/uploa...1646688286.jpg

Hi Mark,
Those are the dyno runs. The 3rd and 20th.

JOhn

John, thanks for clearing that up for me. So 1.7mm worked best or is the actual number a secret?
;-)

hi Mark
just an opinion here.. but I think the preference comes down to you and where you plan to drive the car.
For me, who doesn't see the track, but does a lot of street and mountain driving, I prefer an engine with more torque produced early in the rpm range. So I try to advance the cam timing as much as possible and still having adequate valve clearance. I find that the intake valve is usually the one that gets close when advancing the cam.

That is what I have decided to do to. It was a barn find and the goal is to use it as my daily driver. Possibly a track day from time to time. Thank you

Hi Mark

I just wrote a thread about the same.
I also have a 1980 SC and it has its own setup when it comes to set the cam timing as you also figured.
My question to you, when you set your timing, do you use your BTDC mark on the pulley? I was planning to set my to 1.55mm but on what mark? Z1 or BTDC?

Many Thanks
Patrick

Hey Patrick, you are likely asking the wrong person. but I did start setting my cam timing today. I’m using the same TDC mark to set #1 intake and 360 degrees to set intake #4. The important thing is when you begin, cam must be in the ignition stroke of TDC. Intake valve adjusted to .004” install your dial indicator and turn crank one complete revolution and read your dial indicator and adjust as necessary. Before turning the engine again, set intake valve #4 at .004”. Install dial indicator after adjusting l/s intake and zero it. Now turn crankshaft 1 complete revolution to the TDC mark and read your dial indicator. Adjust as necessary. Probably best to recheck both cams.

Even with the correct pin there is some slop. So that’s why you need to hold the cam when you tighten it. Also, the case center line and the pulley mark are hard to get precise. Don’t expect to get it right first try. But your technique will improve. Also some very good you tube videos how to do this. Search cam timing Porsche 911. Good luck.

Mark , the web cams need to have zero lash while setting the cam timing .
See your cam card , 10* BEFORE TDC WITH .050" LIFT ON THE VALVE
This is different than the factory spec for z1
the cam card is correct
Ian
lots of other info on cam timing and why it can be different

I realize the webcam specifies zero lash, but I’m fairly sure the cam card lists the 911 mm measurement with .004” clearance or using a degree wheel and their provided lift specs at zero lash.

I was not able to easily mount my degree wheel without some effort including a longer pulley bolt. So I decided to do the factory way. I’m on my phone, so I can’t see the cam sheet above from web cam while replying.

Justin,
This link should give you an idea of how fantastic the cams are , read the whole link
Ian

http://forums.pelicanparts.com/porsche-911-technical-forum/1073886-3-0-rebuild-performance-advice-2.html

yes it does spec the 1.4-1.7mm at z1 @ .004"
but the spec @ .050 for 350* is more exact .
Compare that to the range and you will see a big difference

Icarp. Looking at the card I posted from web cams. Duration is measured at .050” But you lost me. At zero lash, intake opens at 4 degrees before TDC. It closes 48 degrees after bdc. That’s the duration off the intake lobe. Either 250 degrees or 232 at 050”.

The Porsche method if I could attach my degree wheel is probably very close to the web cam method. In other words 4 degrees with zero lash before TDC is very close to 1.4 to 1.7mm intake open at TDC I imagine.

I may have to get my degree wheel attached. The crank pulley bolt is 12mm x 1.5 pitch which is an odd ball for my stock hardware. May have to buy some from McMaster carr and see for myself. But I’ve enjoyed thinking about this. Thank you.

The "zero lash @ 0.050" is the cam timing (NOT the spec to set the cams).

From the cam card:
Intake, 4 deg BTDC (+ 180 deg) + 48 deg ABDC= 232 degrees @ 0.050" valve lift.
Exhaust, 44 deg BBDC (+ 180 deg) + -2 deg ATDC = 222 degrees @ 0.050" valve lift.

The 250 deg and 240 deg specs are the "advertised duration" at 0.004" valve lift (or something close to that).

If you set the lash at zero and rotated the crank to 4 BTDC, the valve lift should read 0.050", just like it says on the cam card.

Any of the modern digital "degree wheels" are far more accurate than even the big old wheels.

Those SC cams were used in quite a few engines, with Porsche varying only the cam timing to get the intended effect. 1980SC is nothing special, and uses the same cam timing method as the others. The "preferred" setting is 1.55mm, or 0.061" with 0.10mm (0.004") valve lash.

Dannobee, this morning I mounted my old fashioned degree wheel that I have used for ever. Its not precise, but here is what I measured. My intake valve is opening at 39 degrees btdc after setting it yesterday using the Porsche method. That is way off from 4 degrees btdc.

So, I rotated the engine clockwise till the intake valve was open .050" and my degree wheel is reading 4 degrees BTDC. I then switched the dial indicator to mm and rotated the engine the last 4 degrees of crank rotation to TDC and sure enough, I'm measuring 1.69 mm of lift at the intake valve.

The enclosed card above specifies, "Valve Timing is checked with zero valve lash @ .050 inches of valve lift." That would imply that "the 4 degree intake opens value" includes .050" of lift, which is very close to my rough checking this am. Which is what you are saying.

I'm going to put in a call to WebCam today to ask for clarification. Also, I'm not trying to be disagreeable with those offering to make suggestions and help. Just attempting to understand what I am doing. Thank you. Mark

Edit, talked with WebCam and yes, when it states "Intake Opens 4 degrees before TDC". Intake opens includes .050" already open. Briefly the point of this thread was to get a consensus of where to set the cams. 1.4 mm to 1.7 mm is a big range and as I understand the range could be .9mm to 1.7mm depending. 4 degrees before TDC is a specific setting not a range. I figured if WebCam took the time to specify overlap there was an ideal adjustment for the camshafts. Looking at page 151-11 in my Bentley manual, they show two stock cam profiles. They discuss valve overlap for 930/04 and 930/07 and 930/16 engines. They don't specify .004" valve lash or zero valve lash. Using the 930/07 specs in the manual "Intake Valve Opens" 7 degrees before TDC, which is not happening without some "?" valve open amount.

Cams will always have a certain attractive mystique about them interesting to note that the actual running timing will be at roughly .010 given the expansion at temp. Basically the important things for the designers of translating follower camshafts are the initial acceleration at the ramp when the rocker starts moving and the portion just after the nose dwell time where it starts acceleration again these don't seem to be altered much it at all in the cam on rocker arrangement as the constraint is the bearing housing which won't allow a larger lobe which limits lift to control the adverse effect of hammering the valve open and slowing it down to return it to the seat.
So duration and L/C are out parameters and we are probably lucky because fourth order polynomials really suck.

regards