Valve overlap, 930 with SC profile cam ?
 

I have installed 930 cams with SC profile and are wondering what overlap I should use.
I read different overlap for SC, typical (0.9-1.1) 1.0 and (1.4-1.7) 1.55

Am I going to use 1.55 as reference, or 1.0?

The SC cams I installed could be timed from 1.4mm to 1.7mm. The lower number gives very good top end performance where the higher number is good for early power for the street. With an SC cam, there is not that great of a difference though, so I tend to advance the setting (1.7mm) for all around driving. If its a track car, you could go as low as 1.0mm for constant wide open throttle.

CHECK VALVE TO PISTON CLEARANCE !!

Just a note, you have some control over where you are going to make power. Most time there SC cams to make peak HP at about 5500rpm on a turbo.

You can if desired time them to make peak HP at about 6000rpm (use euro 3.0 76/7 timing specs).

Porsche 911 Performance Handbook - Google Books

Ya, what Don said.

From Appendix A in Waynes book, there is 2 different settings for SC.

For 78-79 SC the timing is: 0.9 - 1.1
for 80- timing is 1.4 - 1.7

How do I know which timing is correct for me?

BTW my intake port has been ported to 35mm

Is this really overlap? Overlap is the degrees that both valves are open at 0.1mm lift. I think you are talking about IVO, aren"t you?

Yes you are correct about the valve overlap, sorry my mistake.

I am going to adjust the timing with the dial gauge, and here I read different settings for the SC cam.
That's why I am confused about the value I am going to use when setting correct timing

If you look at the cam specs in the appendix, you will also see that there are two different SC cam profiles that correspond with the two different timing settings you are seeing. I would think that the correct timing will depend on which SC profile you have. I know we always read about using the SC cam in our turbos, but no one ever really specifies which SC profile.

I had my 930 cams reground by DRC, and he sent me the timing range...it is 1.4-1.7, which tells me these are the later SC profile.

Right.
Problem is that I bought the cams regrinded here at the forum.
Will see if I can figure out what cam profile I have

.....AND CHECK AND SET VALVE SPRING HEIGHT to avoid binding. 930 versus SC grinds have different lifts, obviously, and valve spring heights must be set accordingly. Check with your cam grinder for specs.

If you already have this covered, .............never mind. :cool:

I did mine at 1.6mm. Haven't driven the car yet, but the engine sure does sound smooth (I did other work too).

The 930 engine is bone stock otherwise.

The cams for all the SC's and 3.2 Carrera's are the same, they are just timed differently. The 3.0's were at first timed for higher RPM power, later SC's for low RPM power, than the Carrera split the difference.

As Don said, the larger the number seems to make more low end HP, the smaller the number the more power will be made at a higher rpm.

Thus, if you are building a track car, running a larger K29 style turbo, and have proper fueling mods to support it, you could go to .1 and pull power to red line. If this is the case there are better cams for this including the C2.

Most are going to be happiest closer to 1.7 as this helps get you to power faster.

Also, the spring height is supposed to be changed to increase seat pressure to handle the more aggressive ramps and or upgraded springs should be used. It is also good to have your rocker arms resurfaced when going to a renewed cam.

Disclaimer -- I am not an expert and know just enough to be dangerous.

ps, I did a search of Cam Timing for the 930 section and found the following thread that seems pretty good.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/455840-cam-timing-x33-option-sc-cam.html

IIRC, in the appendix in Wayne's book, I noted two different part numbers for the SC cams with different specs...such as duration, which would not be impacted by timing. Don't have the book with me today to verify my memory though.

Like you...not an expert, but I know enough to be dangerous.

I am pretty confident in my info in that the grinds are the same but they get timed differnetly. Part numbers might be different, I do not know.

Check out the Bruce Anderson Book/ Google link I posted in post #3 above and all said cams are listed as the same grids with his suggestion as to what they should be timed at for install in a 930.

Still, I have been wrong before.

All "SC" cams, be they on the Carrera 3.0l (76-77) the various SCs and the 3.2 use the same "grind". Porsche has changed the timing several times. Sometimes in the early 80's (I believe in 1980), Porsche changed the mounting system of the cam - which may explain the different part numbers (or not!).

Have been trying to set the timing today.
I was aiming for timing somewhere around 1.6.

It seems like I was only able to go with 1.4 or 1.7. Could not set timing between.

Am I doing something wrong or is this the case?
The setting in the wheel was only 1 hole to the side to get either 1.4 or 1.7.

Should I go with the 1.4 setting?

My goal is mostly street with some trackdays

I would go with the larger value for a fat mid range. This is as useful on the street as it is coming out of a corner on the track.

I found with SC profile cams (and I didn't know there were two profiles), you won't feel the difference between 1.6 and 1.7 mm. However, a good dyno will tell you if the sides aren't timed perfectly at the same value (assuming you've done a baseline run before the re-timing) - make sure each side is dead-on.

The second chapter to this story is to take your time and do a great job on setting the valve lash.

Do a couple of cam timing jobs and you'll swear by adjustable cam timing gears. I can now set timing accurately and QUICKLY, even to odd numbers like 2.52mm on high lift cams

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