930 cam timing w/SC cams
 

When replacing the stock cams w/ SC cams, in a do you need to make any adjustment in the cam timing or do you use the stock setting?
Pat

I just did SC cams in my '87 930. The cam timing range on the packaging that the cams came in was 1.4mm to 1.7mm. I set mine at 1.65mm.

I beleive my SC cams are set at 1.60mm.

Set mine at 1.42mm. WebCams recommends the lower value(more advanced) to shift the torque sweet spot into the lower RPM ranges which the low compression 930's are notoriously famous for.

When Neil Harvey of Peforrmance Developments had my engine parts to perform all the machine work, I had him perform a mock-up to check the valve to piston clearance as well as the actual CR measurements. In his build sheet which was sent back to me with the engine parts, 1.7mm is what he used during the mock-up.

The lower the number, the more lag you will experience, but you will be able to acheive peak HP at higher RPMs. The higher the number, the quicker off the line it will be, but your peak HP will be at a lower RPM. Also, the higher the number, the less vacuum you will have, so idle might be a bit rough.

For example, my super C2 cams have a timing range of 2.2 - 2.4mm. I first tried 2.4, but the engine ran out of HP at 6200 rpm. I reduced it to 1.9mm to see if I could really tell a difference. There was a pretty good difference - laggy. I then adjusted to 2.2 and found the best of both worlds - good low end and peak HP at red line of 6500rpm.

"Set mine at 1.42mm. WebCams recommends the lower value(more advanced) to shift the torque sweet spot into the lower RPM ranges which the low compression 930's are notoriously famous for."

Dave,

This is backwards. The higher the number the more advanced the cam.

-Andy

DonE and Andy,
Thanks for setting the record straight. When I asked Tech Support at WebCams about increasing low end torque, they suggested setting at the low end of the spec. Shame on them! :rolleyes:
Oh well, I was going to drop the engine this coming winter to change cams anyway.

Mine was set at 1.7mm and, according to the dyno sheet, torque begins to drop off at 5200rpm.
Pat

One other comment about timing is that I found it to be more critical (to performance) that you get both cams timed exactly alike, rather than worry about 1.7mm vs 1.75mm total timing.

TRUE...TRUE!

Also, an SC cam in a 930 is really a low-end power grind. In most cases the SC is done by about 5,600 to 5,800 RPMs regardless of the timing.

I need some understanding of valve timing regarding this thread. I always thought that valve timing was much the same as ignition timing. The more advance you run in ignition timing( up to knock), to more efficient the combustion at higher RPM's. Doesn't valve timing work in the same manner? The more advance added to valve timing, the more efficient the cylinder filling at higher RPM's?

Is there a cam that will offer a more broad and sustained torque curve than the stock cam or an SC mated w/ a K27? Of course, staying out of the higher revs should help w/ longevity.
Pat

Dave, check this link for a quicky on cam timing.

http://www.deltacam.com/tech.php?p=3

Thanks Mike!! Good info!

What about naturally aspirated motors? Does anyone have experience with advancing cam timing in Carrera 3.2 motors? I have read that SC's in 78 to 80 were advanced 6 degrees relative to 81 to 83 SC's, and that the Carrera's timing split the difference, being advanced 3 degrees relative to 81-83's, with all the motors in these series having the same camshafts. I would guess that the 6 degree advance would give the best performance in all cases. True or False? Yes, the factory spec is better for the 83 than the 78, but there are changes in the intake tract for the later SC motors, and an admission by the factory that earlier numbers may have been conservative. So, I feel the cam timing question is a good one.

I'm trying to get the timing on the left and right at 1.7mm but the right cam the best I can do is 1.63mm and the left is at 1.69mm
The engine is a 3.3 with stock turbo and a 7.5cr with a fabspped exhaust and intake system.
the camshaft gring is of the SC cams on turbo cam cores.
Any ideas on getting the cams at the same distance. i don't care too much if it is at 1.7mm or 1.6mm but i like the idea of having all the cylinders working at the same timing.
Thanks.
Juan

JuanJose,
Some of the more esoteric intricacy's of cam timing were dicussed in a post I participated in from 2-1-2007, titled "Cam timing different on 1-3 & 4-6"
You should be able to use the search function using "Cam timing" to find this post.
The Porsche 911 cam can be timed into any one of over 7,000 positions.
It is not necessary to accept the error you have referred to from the left and right sides.
In your case simply loosen the cam timing chain and jump the chain over the cam sprocket 5 teeth.
Now tighten the cam chain and retime.
If this isn't as close as desired, jump the chain as before one or two teeth forward or backwards until you get the exact number you are looking for.
It's all covered in the above referenced post.
Thanks again to Mike at MBE Engineering for bringing this to my attention.