Confused on sc cams???

ertech · 10-29-2009, 10:45 PM

Hi all
I am looking for cams for my 930 for a future rebuilt . I found late Bolt on Type sc cams will they work on a 930. I will not put back the smog stuff will I still need to
modify them to work? If so how?
Thanks again and again

billjam · billjam's Garage

SC cams will fit straight in without any major mods if you delete the air pump and its drive.
I took lots of photos of how I did it so I'll post them below.
There are no problems with piston to valve clearance and, depending upon other mods, off-boost power is much better and power curve is much broader.

One thing to keep in mind is that the camshaft still needs to drive the turbo scavenge pump. The SC cams usually have two 5mm holes in the end so you will need to fit two roll pins to drive the pump. In a standard car, the heads of the two air pump pulley bolts normally drive the pump.
There are also some minor mods required to sheetmetal and piping. The inlet pipe to the pump needs to be shortened about 30mm and the sheetmetal needs to be notched to clear the outlet pipe. See pics.

ertech · 10-30-2009, 12:01 AM

Thanks for the great reply . Before I purchase them is there a difference between the late bolt on type sc cams and the early one?the seller told me he has the late bolt on type ?
Thanks

billjam · billjam's Garage

By "bolt on", I presume the seller is referring to the two methods of securing the camshaft drive sprocket.
Later models have a bolt which screws into the end of the camshaft.
I think the early cams used a large nut which screwed onto the end of the camshaft. Don't know when this change occurred but I guess it must have been just before or during the SC models.
The cams you need should look like this at the sprocket end.

proffighter · proffighter's Garage

Mine looks a bit different:

ertech · 10-30-2009, 01:42 AM

So I need the bolt type? For the 930

billjam · billjam's Garage

Quote:

Originally Posted by ertech

So I need the bolt type? For the 930

Yes.

proffighter · proffighter's Garage

Quote:

Originally Posted by billjam

This one the right side is the right one. You have to make a spacer, because the shaft of pump is a bit too long. Just take measurements from surface at cam housing to camshaft vs. pumpshaft to pump surface, add 1mm for clearance, there you got thickness of spacer. I made mine as big that it closes whole in sheet metal too.

billjam · billjam's Garage

Quote:

Originally Posted by proffighter

Mine looks a bit different:

Roland,
It looks like the standard housing for the air pump drive pulley has been replaced by a plain machined spacer on your engine. You would need to do this if you deleted the air pump drive but are still using turbo camshafts (which still have the drive boss for the air pump pulley).
See first picture above for difference between 930 and SC cams.

proffighter · proffighter's Garage

Bill

You're right, with 930 cams you need a spacer, as thick as housing before.

I have 964 cams, they have the same layout as SC cams. So I needed a thin spacer, maybe 3mm (can't remember exactly). I think with SC cams you'll need a spacer too, in cause of the length of the pump shaft as I wrote above

billjam · billjam's Garage

Quote:

Originally Posted by proffighter

Bill

You're right, with 930 cams you need a spacer, as thick as housing before.

I have 964 cams, they have the same layout as SC cams. So I needed a thin spacer, maybe 3mm (can't remember exactly). I think with SC cams you'll need a spacer too, in cause of the length of the pump shaft as I wrote above

Correct.
When I fitted my cams, I found the pump shaft was only about 1mm too long so I ground 2mm off the end of the shaft to give me 1mm clearance.
The potential interference between end of pump shaft and end of camshaft is an important point to watch for when bolting up the scavenge pump.

proffighter · proffighter's Garage

1+

Mine was like this (measurements are only ca.)

911st · 10-30-2009, 07:46 AM

Dose anyone know if the air pump drive is the same size as a MFI pump drive?

mark houghton · 10-30-2009, 07:47 AM

Excellent detail and pictures! I'll be printing this out for my "how to" scrapbook. Just saved me asking a lot of questions for when I do the same this winter. My SC cams are currently wrapped up and waiting on the shelf.

Final question: Where did you end up with cam timing and is it any different than the stock 930 cams?

JFairman · 10-30-2009, 10:32 AM

Quote:

Originally Posted by ertech

So I need the bolt type? For the 930

You don't have to use the bolt type cams on a 930 or any other 911 motor, just get the 46mm nut and fat wavy washer that goes under it and use those instead of the 19mm bolt and washer that goes under it on the '81 and later cams.

Most 911 shops will have some used 46mm nuts and the wavey washer hanging around.

I've heard 1.7mm for an SC cam timing spec but you can vary that so just call a camgrinder and ask them for recommendations.

Advance the cam timing to lower the powerband and retard the cam timing to raise the powerband. A higher number is advancing the cam timing and a lower number is retarding it.

jacksd3 · 10-30-2009, 10:35 AM

As for cam timing I went with 1.6mm to enhance the low end response.

mark houghton · 10-30-2009, 10:43 AM

Thanks, 1.7mm is what I was thinking...just wanted to hear it from another source.

Thierry25 · 10-30-2009, 12:44 PM

Quote:

Originally Posted by mark houghton

Thanks, 1.7mm is what I was thinking...just wanted to hear it from another source.

Hi mark

I timed mine at 1 mm ....this timing value works perfectly with 1 bar of boost and if the AFR is correct in the mid range. ( RPM switch or whatever )

JFairman · 10-30-2009, 12:57 PM

Wouldn't timing them at 1mm be more optomized for top end track use?

And what cam timing is optimal for reground high lift SC cams like the Elgin SC330 cams.

I know some people time 964 or C2 cams at 1mm for a powerband from 4500- 7200 or so but that takes away low end power for street driving so 1.25-1.33mm is a good range for street driven 964 cams, but I don't know the whole range for SC or high lift SC330 cams.

camgrinder · 10-30-2009, 03:02 PM

FWIW .23mm is close to 1 degree of cam timing. So going from 1.26 mm to 1.00 mm (1 degree retard) on the 964 isn't much. The SC330 cams are usually timed at 1.8mm.
1.7mm is a good setting for the SC in a turbo application. With higher boost levels going back to 1.2 or 1.4 makes sense.

I like your solution to the pump drive issue Bill. I wonder if drilling the holes a little bigger for a larger diameter pin is worthwhile?