SC cams - is that all??

jmiemiec · 03-31-2009, 03:55 AM

Hi, I recently installed new SC cams. Motor is a 1974 2.7s. I cant feel any real 'upgrade' differences aside the fact that the motor revs a tiny bit lower on same speeds. Is that all that one is to get from this upgrade? Is there a way to check aside a dyno?

thanks guys.
JM.

Halm · 03-31-2009, 06:43 AM

First, you may want to move this to the 911 forum.

But I'll venture a guess: You wanted 964 cams on your 2.7 (assuming it still has CIS), not SC cams.

Geronimo '74 · 03-31-2009, 07:48 AM

I'm guessing the same... bummer...

kodioneill · kodioneill's Garage

i put 964 (s for cis) cams in my 74 made a huge difference.

jjrowe · 03-31-2009, 08:24 AM

I noticed a big difference when I put SC cams on my 76, a generally stronger pull at all RPMs. My guess is your CAM timing isn't set correctly. From what I've read you won't see much difference between the late style SC and 964 cams (on that motor anyway), so I think its something else. Do you know what your CAMS are timed at? Who ground them?

Jesse
76 911 S

jmiemiec · 03-31-2009, 08:35 AM

JJrowe, if you had to take a wild guess for torque % increase on your SC cams, what would that be across the range? I currently only see a drop in revs e.g. -200rpm to reach 120km/h.

jjrowe · 03-31-2009, 08:48 AM

Quote:

JJrowe, if you had to take a wild guess for torque % increase on your SC cams, what would that be across the range? I currently only see a drop in revs e.g. -200rpm to reach 120km/h.

Hmm, as a wild guess I would say that I notice almost no difference (0-1500), then it starts to pick up and between 3000-4000 I would say as much as 10% more torque. I also am now running stock exhaust and before the switch I had headers. I am keeping the stock exhaust on now because I don't feel like I need the headers anymore.

Also there were variations of the cams on the SCs, the later style was used after 1984 I think. That is what I have.

You definitely should notice a difference!

-Jesse

stlrj · 03-31-2009, 08:55 AM

Quote:

Originally Posted by jjrowe

Also there were variations of the cams on the SCs, the later style was used after 1984 I think. That is what I have.

-Jesse

All SC cams are identical. Only timing variations were made depending on the model and year.

Cheers,

Joe
74 911 w/ 86 3.2 conversion

ianc · 03-31-2009, 09:06 AM

Quote:

I currently only see a drop in revs e.g. -200rpm to reach 120km/h.

You will not see any drop in RPM's to reach a specific speed. That is related to the transmission's gear and final drive rations, which haven't changed.

ianc

Gunter · Gunter's Garage

Quote:

Originally Posted by jmiemiec

Hi, I recently installed new SC cams. Motor is a 1974 2.7s. I cant feel any real 'upgrade' differences aside the fact that the motor revs a tiny bit lower on same speeds. Is that all that one is to get from this upgrade? Is there a way to check aside a dyno?

thanks guys.
JM.

What cam timing did you use?

Also, the '74-'77 cams for the 2.7 liters have 3 bearings and the SC cams have 4.

How can an SC cam fit into the 2.7 liter cam towers?

Thanks.

afterburn 549 · 03-31-2009, 10:05 AM

Mine was HUGE , B4 it was way too peaky, came on way at the top. Now a much steadier pull.
@ the time I did not know about 964 cams that would be better

dtw · 03-31-2009, 10:26 AM

Cam change won't affect engine speed w/r/t vehicle speed. Only gearing changes (including tire size change) will do that.

afterburn 549 · 10:36 AM

Quote:

Originally Posted by dtw

Cam change won't affect engine speed w/r/t vehicle speed. Only gearing changes (including tire size change) will do that.

?????? Must effect something or people would not do it.
To take your statement to the extreme.. a flat cam, or wrong cam, or wrong timed cam will not improve your eng performance or your car speed.
A "right" cam will

So that's what i think, brought to you from dwn twn Juneau where all the girls frigid and the cars are a pity

The more I think about this.... I am right cause you actually change the CFM the eng works with
that's why head porting valve size and volumes are experimented with all the time..Not just in the P world

Gunter · Gunter's Garage

So, How can a 4-bearing SC cam fit into the 2.7 liter 3-bearing cam towers?

afterburn 549 · 03-31-2009, 11:38 AM

I think just change the towers

Halm · 03-31-2009, 11:42 AM

Quote:

Originally Posted by Gunter

So, How can a 4-bearing SC cam fit into the 2.7 liter 3-bearing cam towers?

A good file and a lot of elbow grease?

jjrowe · 06:03 PM

Quote:

So, How can a 4-bearing SC cam fit into the 2.7 liter 3-bearing cam towers?

The lobes on the 3 bearing cams are welded and reground to match the profile of the 4 bearing SC cams. This is a good option for the 2.7s because Porsche seemed to get the CIS cam profile optimized by the end of the SC era. I really noticed a nice improvement.

- Jesse

afterburn 549 · 03-31-2009, 05:53 PM

Thanks jjrowe,
I remember having a heated discussion with the cam person i was using...at that time they did not think 964 would work....Now I know they would

2.70Racer · 03-31-2009, 06:30 PM

The CIS intake limits the amount of cam duration due to revision and the effect upon the fuel metering.
The stock 2.7 cam runs 224 degrees of intake duration, the SC through carrera cams run 234 degrees of intake timing.
Expecting a big improvement from a simple 10 degree's of additional intake duration without any other improvements is not realistic.
By comparison Solex cams from the early '65 911's run 248 degrees and the "S" cams on the Weber equipped 67/68 911's ran 268 degrees of intake duration.
If you want decent performance from your 2.7, get rid of the CIS, add some 40 Webers, higher compression pistons, open up the exhaust system, and install Solex cams for street use. "S" cams for the track. Dual plug ignition is a great upgrade as well.
Another tact is to dump the 2.7 and go for a larger engine, your choice and budget.
Back dating my transaxle to a 7:31 ring and pinion added substantialy to street performance, at the cost of high end, 125mph plus, speed.

911st · 03-31-2009, 07:07 PM

I am not an expert but is it an S or normal 2.7. The non S has very small ports and lower compression and a bigger cam is not going to help much. What is going on on the exaust side? For the cams to reach there potental you need a 74 style exaust at a mininum. A sport muffler would make it all the better. Also, I think you need to increase the valve spring tension with such a change to keep the rockers on the cam with its more aggressive lift angles.

I would not expect more than about 10-15 hp from the cams. C2 cams with 36mm ports, 9.5 compression ratio pistions, and sport muffler should get you close to 200hp I would guess.