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p930t's Avatar
 
Join Date: May 2007
Location: Norway
Posts: 55
I am facing a cam change due to pitted lobe on no.3 intake. and are looking for street driveability so the SC cams are probably the ones for me.
What abbout the turbo scavenger pump drive from the LHS cam. Are the SC cams prepared for mounting of the parts to drive the pump or will thecam need some work?
Also there is the difference in mounting the cam chain sprocket to the cam that changed in ..... 1980 or so?
Anyone know the bolt on part number for SC cams that can replace my 1978 3.3l cams.
Old 12-10-2007, 09:26 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #41 (permalink)
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The turbo cams are different from SC cams in that they have a boss on the rear of the left cam to drive the scavenge pump. There are no factory SC cams that have this boss, only Turbo cams have it. My car came with SC cams out of a pre-80 SC that had been converted by adding the boss to the left cam. The car had the older 46mm cam nuts rather than the correct cam bolts for an '86.

It is better to get the SC grind on the Turbo cam blanks (in my opinion) than to convert an SC cam to drive the scavenge pump.

It's also a good thing to order the correct cams (46mm nuts pre '80 1/2 vs 19mm bolts post 80 1/2). I needed both cam tools to replace mine as I ordered the correct cams from Webcam and then discovered that a previous owner backdated my cams. Order the correct grind on a Turbo blank for your year and you can keep the changes to a minimum.

Webcam had the SC grind in the correct cams for my car in stock.
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Andy Glass
'86 930 Kokeln IC, K27-7200, SC cams, GHL headers, Fabspeed muffler, Short R&P , misc other mistakes made...
Old 12-11-2007, 12:59 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #42 (permalink)
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I had to have the powersteering pump drive milled of of my right Gt-2 cam so it could clear my oil cooler.
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Kris @ Tech9
86' 930/GT-40R Sold
94' Rustang GT daily (long gone)
2008 C6/Z51 Corvette
Old 12-11-2007, 06:20 AM
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I believe that John Dougherty, "camgrinder" on this board, does not favor regrinding 930 cams to other specs. That's certainly true for the 930 to 964 change (I'm not sure about 930 to SC). Though some grinders will still do it (Elgin, for one), and I had it done long ago on one of my engine iterations, it has at least one disadvantage. In order to obtain the correct lift/duration numbers (say, for the 964 cam), the base circle must be ground smaller than stock, which means that the adjusting foot on the rockers must be screwed in quite a bit further than stock. Though it works okay, it's a little disconcerting to see those adjusting screws cantilevered out so far. There may be other problems as well; I'm sure John should address this for the final word.

But when you buy a new cam from John (and likely, from other grinders as well), all the new blanks are of the later style (sprockets held on with bolts rather than nuts), and both the left and right cams come with provisions for driving the scavenge pump (on the left side) and the power steering pump (on the right side). Depending upon your configuration, the grinder simply cuts off the unnecessary drive bosses. That way, there's only one universal blank for all 911 based engines.

Rob
Old 12-12-2007, 08:15 AM
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I have got same advice from several experienced grinders so i have searched a set of good original 83 SC cams that already are converted.
Old 12-12-2007, 08:53 AM
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Quote:
Originally Posted by WydRyd View Post
FWIW, I run 993 GT2-EVO CAMs in my blown Carrera and I love them. They "come on" at around 3.5-4K RPM, when the turbo has reached max boost of ~1.25bar and they pull like nothing. They truely are an awesome CAM for an EFI setup.

I have no experience with the CIS stuff, so I can't really comment to be honest, but with EFI it's a no brainer.

I'm soon going with a TT configuration, so it'll be interesting to see how they perform in such a configuration
Merv,

I'll be doing a turbo conversion on my EFI '87 Carrera soon. Would SC cams be beneficial for my setup? I see that you noted the GT2 evo cams as being a "no brainer", but I'm not interested in dropping another grand at this point. There is a set of SC cams for sale on the board at a relatively inexpensive price. Just wondering if it would make a difference.
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Old 02-25-2008, 08:41 PM
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Quote:
Originally Posted by 125shifter View Post
In addition to not being a fan of knife edge crank or boat tail pistons in the 930, I'm also not a fan of boat tailing the case. A little radiusing is fine, but I'd want as much meat in the case as I can get.
Yeah. Boat tailing and knife edging are worth like 10-15 hp total IF you do it right.

If you do it wrong, they will cause issues.

Build your engine correct, and adding an extra tenth of a bar of boost will add more horsepower than all the messing around with your bottom end.
Old 02-26-2008, 06:14 AM
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Sent my 930cams off to DRcamshaft for regrind under $300.
Old 03-01-2008, 07:49 AM
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craigerz
 
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Knife-edging a crank on a dry sump motor like the Porsche is not going to do much in terms of horsepower... Boat-tailing the pistons may help a little, but not much, my guess is only 2-3 hp at the 5500 -6000 rpm level. But remember, theres as much movement of air on the inside of a motor as there is thru it on a normally asparated motor. If you were racing Nascar where they work all year just to find 5 hp, then knife-edgeing and boat-tailing may make sence...
Old 03-01-2008, 01:48 PM
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Craigerz, I agree with you on the knife edging on these motors- I believe that it removes need material from the crank and sacrifices durability for little gain. But the boat tailing if done correctly; Ive heard of people picking up 20-30 horse on a 6-800 horse motor across the rpm range- maybe it dont help peak horse power, but it does reduce pumping losses
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86' 930/GT-40R Sold
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2008 C6/Z51 Corvette
Old 03-02-2008, 05:46 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #50 (permalink)
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