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SC cams in a 930 - valves><pistons?

There's a zillion threads in here about 930s and SC camshafts (and I've waded through most of them during my lunchbreak), but I can't find a clear answer to the question about valves hitting pistons.
In an otherwise standard 3.3 engine, with SC cams at standard timing, should I expect the valves and pistons to clash?
I am rebuilding my engine for more grunt in bottom half of range and planning to have my turbo cams reground to SC spec. (Also using K27 7200 turbo and some head porting.)
If I am likely to have valve/piston clashing, I'd prefer to know about it now so that I can plan to fly-cut pistons before I assemble the engine.
Naturally, I'll do a clearance check during final assembly, but it would be nice to know beforehand if this is usually a problem.
I noticed on one thread that Rarly runs SC cams but no mention of cutting the pistons - Rarly, can you advise?
Old 08-28-2008, 11:00 PM
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Have not heard of this being a problem. I run SC's in mine with flat domed pistons. Do a valve lash test as outlined in Wayne's rebuild book.
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1979 Porsche 930: 3.4L, SC cams, Twin plug, Leask WUR, Custom SSI turbo exhaust, Tial WG, K27HFS, and we can't forget the Zork (short lived depending on my homeowners assoc.)
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Old 08-29-2008, 05:22 AM
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If you have stock pistons, rods, crank, cylinders, heads, and use the recommended cam timing, you'll be just fine. And yes, you always need to check clearances to confirm.
Old 08-29-2008, 06:13 AM
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Not a problem, good that you are thinking that way though. SC cams are still a common addition to the 3.3L engine, I've never heard of any clearance issues.
The best folks to interview on this subject are the smaller mechanic shops. Those guys, such as Johnny Walker, have seen and done it all.
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Old 08-29-2008, 06:23 AM
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What if your adding 78 sc heads and cams to a 3.3? Would I run into any issues with that setup?

DonE, I see you have a P51 mustang in your avitar. Thats not yours is it? I know there is a mustang or two based around atlanta but are you the owner of one of them?

Mike
Old 08-29-2008, 07:46 AM
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Quote:
Originally Posted by billjam View Post
In an otherwise standard 3.3 engine, with SC cams at standard timing, should I expect the valves and pistons to clash?
My heads were fly-skimmed for 8.0:1 static C/R and there's no clearance issues with camgrinder's SC profile on factory 930 cams.

I don't have much off-boost area anymore (a K27/HF will make .5 bar @ 2400 RPM), but off-boost response was good with the 3LDZ - especially with 915 gearing.
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Old 08-29-2008, 08:03 AM
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Quote:
Originally Posted by MikeHall View Post
What if your adding 78 sc heads and cams to a 3.3? Would I run into any issues with that setup?

DonE, I see you have a P51 mustang in your avitar. Thats not yours is it? I know there is a mustang or two based around atlanta but are you the owner of one of them?

Mike
No, I don't own one (I would if I could tho). I'm a member of the CAF (www.dixiewing.org) in Peachtree City and one of the ground crew for the P-51. I get to fly it only occasionally. Here is some trivia: the Merlin engine uses rocker arms for the valves and you adjust the lash exactly like a 911 motor. However, if you have to replace the rockers (worn out bushings), it'll set you back around $15,000 for a set.
Old 08-29-2008, 08:11 AM
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There's no problem running 964 cams in a 3.3 930 engine either, and they have alot more lift and a little more duration than SC or Carrera cams which have the same profile.
If you have stock cams reground to 964 profile all the lobes should be welded up to add metal before grinding, or else the base circle will be ground down too close to the cams centerline.
That would screw up the rocker shaft geometery causing the valve train to be stressed as the engine runs and the cam and rockers will wear out faster.
Old 08-29-2008, 08:19 AM
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Old 08-29-2008, 09:50 AM
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I have SC cams in my 77 930 with no issues, still stock compression. It was done by Squire. Like Rarely L8 said, you can't go wrong with Johnny Walker or Squire.
Old 08-29-2008, 09:53 AM
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Quote:
Originally Posted by DonE View Post
............Here is some trivia: the Merlin engine uses rocker arms for the valves and you adjust the lash exactly like a 911 motor. However, if you have to replace the rockers (worn out bushings), it'll set you back around $15,000 for a set.
I'm sure Motor Meister will rebush those rockers for considerably less. Got a parachute?
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Old 08-29-2008, 10:03 AM
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On a more serious note. Always replace your valve springs, retainers, locks when swapping out cams........and always, always check your valve spring height. These engines are now so-o-o old that it's likely the engine has been opened up once and who knows what's been done. This procedure will insure that your springs don't bind at maximum lift.
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Old 08-29-2008, 10:08 AM
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Thanks for the input guys.
SC cams, here we come!
Old 08-29-2008, 11:48 PM
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Forgive my ignorance, but isn't the concern about SC cams in turbo motor more about getting the spring heights correct to avoid coil bind in the event of an over rev?
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Old 08-30-2008, 02:29 PM
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I thought it was valve to piston clearance with the increased overlap cams
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Old 08-30-2008, 02:37 PM
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Im starting to worry that putting Large port SC heads and cams on my 3.3 is going to be more trouble that I had thought. Anyone have any input on that combo?

Mike
Old 08-30-2008, 02:42 PM
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Uhhm, if the large port '78 SC heads don't have a problem in a motor with domed pistons running 9.3:1 static C/R, why would you think they would in a motor with flat-topped pistons running 7.0:1 static C/R?

SC cams were also used (with small-port heads) in RoW engine type 930/10 (MY 81) which ran 9.8:1 C/R.
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Old 08-30-2008, 11:32 PM
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The SC/Carrera engines have a valve spring height of 34.35mm +/- 0.15 for both intake and exhaust valve springs. The SC cam has a valve lift of .455mm and .402mm, intake and exhaust, respectively.

The turbo engines have a valve spring height of 33.5mm +/- 0.3 for both exhaust and intake valve springs. The turbo cam has a valve lift of .378mm and .343mm, intake and exhaust, respectively.

If you change to a SC cam, you must shim the springs to get the correct spring height. Otherwise, you may experience spring binding due to the higher lift SC cams.
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'85 930 Factory Special Wishes Flachbau
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Old 09-01-2008, 09:01 AM
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SC Cams actually carry a 930 part number, if you hadn't noticed!

Here's a simple demonstration of turbo lag on a 3.3 SC Cammed, K27-7200-S 930 (otherwise the car is completely standard Euro spec - apart from the removed A/C and AirPump systems)

http://www.youtube.com/watch?v=_-0eD0vtb_4

As you can see, boost comes on much sooner than normal, but peak power is at 5,000rpm instead of 5,500rpm..
Old 09-01-2008, 11:18 AM
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Does the SC/3.2 use the same springs as the 930?
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Old 09-01-2008, 12:58 PM
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