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Stock 930 cam timing advance

My understanding is that the stock 930 cams are timed as follows: 0.65 - 0.80 mm. Just out of curiosity, has anyone experimented with advancing the timing to gain a bit more low/mid response? Or is it a moot point given the lift and duration these cams have as opposed to say SC or 964 cam applications?
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Old 11-23-2009, 11:21 AM
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Since peak HP is about 5500 rpm or less for a stock engine, it seems like the cams are set about as far advanced as you'd want them. JMHO.
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Old 11-23-2009, 04:25 PM
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I believe some have set them for more low end.

I recall one C2 Turbo I read about that was well set up for PCA class racing that did such.

This is probably worth looking at. Probably a solid idea with the stock wide ratio 4 speed transmission.

Especially if living withing any other limitations like small stock intake ports, stock I/C, small turbo, stock rod bolts, and / or trying to live withing the fueling limits of CIS.

Increasing average HP should make a car faster just as well as increasing peak HP can.

The stock cam is not a bad cam in that it keeps the effective compression rate higher than most cams used to increase peak HP.

Would be interesting to see a cam with the timing close to a stock Turbo cam but with the lift of a SC or C2 normal cam combined with larger ports.
Old 11-23-2009, 04:44 PM
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Bottom line, it is easier to make big HP by moving a motors area of efficient operation to higher rpm than trying to increase efficiencies at lower rpm enough to make a significant difference.

For example, a motor making 350 ft lbs that is built to move the HP peak from 5500 to 6200 goes from 378hp to 416hp. Such a change requires no more power per stroke, just doing it at a higher rpm with changes in cam timing and ancillary systems of sufficient size to support doing so (ports, IC size, turbo...).

To get 416hp at 5500rpm it would take 404 ft lbs of TQ. That requires increasing the power per stroke by 15%.


Just for fun, I believe the following is a best of the best example of a low rpm torque cam on a very well built CIS motor.


Old 11-23-2009, 05:16 PM
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A long time ago, I advanced mine to 1mm but as David stated, it did not improve anything. Since I was still using the K27, instead of hitting the wall at +5800 rpm, it hit the wall around 5000 rpm. It was then I ordered SC cams. If I would have paid attention to my motor builder at that time, I would have skipped the SC route and ordered 964 cams.
Old 11-23-2009, 06:15 PM
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Not that it has much to do with CIS, but i have NA 993 3.8RS cams in my 993tt engine, they are set to 1.25mm. Don't know whether the info is useful for comparrison, it's a good choice for over 500bhp in the 993tt, would they work in a 930?
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Old 11-23-2009, 07:03 PM
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1.25mm is the standard setting for intake valve lift at TDC for the beginning of the intake stroke for 964 cams too.
Maybe 993 and 964 cam profiles are same. SC and Carrera cams are milder and also the same profile so it kind of follows a pattern if so.

Anyway, I don't know if 993TT cams will work in a 930 motor.
If they will, just like 964 turbo cams you would have to cut off the power steering drive on the passenger side cam to fit them in a 930 motor.
The end hole on the right side cam tower is capped off with a pressed in steel plug because the 930 engine mounted oil cooler is right there.
Old 11-23-2009, 07:19 PM
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I spent some quality time last night reading Bruce's and Wayne's books on the care and feeding of the 911, relative to cams, and I kinda walked away with the impression from their quotes that high lift cams aren't compatible with CIS for a couple reasons: domed pistons and possible collision with valves, and valve overlap with both intake and exhaust valves being open briefly at the same time, causing oscillations in the CIS fuel delivery (as in a bouncing metering arm, I guess).

I guess the key word here is "high lift", as he (they) were referencing "S" cams. Apparently 964 or SC cams aren't considered high lift, as evidenced by the fact that many people run them in their 930's. I will eventually be running with an SC330 grind, which I understand has the duration of a 964 with the lift of the SC, and was made to run in place of the SC cam for stock lift applications.

Comments?
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Old 11-24-2009, 10:47 AM
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Quote:
Originally Posted by mark houghton View Post
I spent some quality time last night reading Bruce's and Wayne's books on the care and feeding of the 911, relative to cams, and I kinda walked away with the impression from their quotes that high lift cams aren't compatible with CIS for a couple reasons: domed pistons and possible collision with valves, and valve overlap with both intake and exhaust valves being open briefly at the same time, causing oscillations in the CIS fuel delivery (as in a bouncing metering arm, I guess).

I guess the key word here is "high lift", as he (they) were referencing "S" cams. Apparently 964 or SC cams aren't considered high lift, as evidenced by the fact that many people run them in their 930's. I will eventually be running with an SC330 grind, which I understand has the duration of a 964 with the lift of the SC, and was made to run in place of the SC cam for stock lift applications.

Comments?
Your first paragraph would apply to normally aspirated CIS engines which had odd shaped CIS domed pistons. 930 engines are lower compression and the pistons are almost flat topped so there is more valve clearance with 930 pistons than domed CIS - SC pistons.

Long duration valve overlap on a normally aspirated motor like the SC would cause the air flow sensor plate to vibrate with the backflow pulses or oscillations at low to medium rpms because the distance between the air flow meter and intake ports is relatively short and unobstructed with spinning devices.

On a 930 the distance from the intake ports to the airflow meter is alot longer and you have the turbo compressor wheel in the intake air path constantly spinning and making some air pressure even at idle and an intercooler to dampen pulsations in the intake air flow.
With all that stuff, especially the compressor wheel spinning away in the intake track between the intake ports and the airflow meter I think the backflow pulses or oscillations would be removed and dampened so they wouldn't cause any vibration or bouncing of the metering plate with a longer duration cam.

The problem with longer duration cams in a street 930 is effective compression ratio becomes even lower with the intake valve closing later in the beginning of the compression stroke with a long duration cam so with the already low compression of a 930 and slow response of CIS the low speed drivability and turbo lag would be unbearable during normal around town and city driving for most people.

The Elgin CIS 330 is a stock early 930 cam with some of the base circle ground away so the nose of the cam becomes higher in relation to it which increases valve lift some and duration also but not as much, and Elgin SC 330 grinds are SC cams which have had the same thing done.

964 cams have higher a little higher lift than SC cams, different lobe centers, and a little longer duration. They move the powerband a little higher in the rpm range compared to SC or SC330 cams and make a little more horsepower while doing it, but you loose some low speed torque at the same time unfortunately.

Too bad variable valve timing hadn't been invented yet..

I wouldn't say 964 cams are high lift, just a little higher lift than SC cams. The specs are in the Webcam website.
Old 11-24-2009, 11:42 AM
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You da' man, Jim. Great explanation for us neophytes. It's all starting to gel in my mind now.
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Old 11-24-2009, 01:01 PM
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