81SC 930/10 cam rec
 

Hello,

I posted earlier about my worn cams. I am waffling back and forth on regrind vs reshape vs new cams. However today I identified my engine as a 930/10 which is a RoW engine. It has 9.8:1 compression stock, and I have no knowledge that the P/C were ever changed. Engine has 97k miles on it. It had good compressions across the board on my PPI (I think it was 145). I have done my search and learned from the posts below.

http://forums.pelicanparts.com/showthread.php?s=&threadid=163860&perpage=10&highl ight=3\\\\\\\.0%20liter%20dyno&pagenumber=1

http://forums.pelicanparts.com/showthread.php?s=&threadid=247448&perpage=20&highl ight=964%20cams&pagenumber=4

I am now no longer leaning towards regrinding to a stock SC profile, but rather a new 964 or 20/21 or preferably camgrinder's version of 20/21. I changed my mind because I think the RoW compression will support the upgraded cam. If possible I would consider reshaping during the regrind to the new recommended profile.

What would you recommend? I figured what the hell, I'm taking out the cams anyways.

Hey Congratulations!! I too have an 81' 911sc RoW. Unfortunately I got mine with 120k miles and after hibernating for 6+ years and am in the beginning of a major rebuild.

Wayne's engine rebuild book has a "Wayne's Top Engine Picks" on pg 112-113. The top of pg 113 lists the combination for an upgraded 3.0L CIS Engine. It runs 9.8:1 Compression, 964 Cams, Stock heads, and the CIS that our engines have. It says with SSI's it will increase the horespower by 30-50 hp over stock config.

I was planning on doing this, but I still need to tear off my heads to inspect the cams. If they need regrinding I am definately goin to 964's. If I am not mistaken it should still have no problem passing smog with the stock exhaust.

Hope this helps. Happy Wrenching!!!

James,
Cam choices sound fine. 145 compression is low for a 10.8:1 motor.
Should be closer to 180 or more.

Who knows how the compression test was done.... Could be a weak battery, maybe the throttle was not opened.... The important thing is that they are even.

I have built a couple of 3.0 with 964 cams from camgrinder, makes a nice strong motor. The 20/21 gets good reviews too and I am sure John has a similar cam. I would use him over WEB, he does all my cams and contributes to this forum as well.

Cheers

Wow, this forum is great. Two new guys and two hardcore Porsche guys. Thanks for the advice.

Emerson: I think I came to the same conclusion you did. Those links I added in the first post really clinched it for me. Did you look at them? I think it is the second one that shows how the 964 torque profile looks so flat after 3500 rpm. the 20/21 profiles all tail off at the high rpm's. Plus, the SC cams we have can be ground down to 964 profiles. That shouldn't cost 250-300$. The Webcam 20/21's are expensive, 875$, and you are supposed to use new rockers with them which would be another 660$. BTW please post an update to your original thread on your "new" old car.

Racer: My cylinders are only 9.8:1. I hope that will be ok. I am not planning on a rebuild or a top end rebuild because I was told I didn't need it my my PPI mechanic.

Jeff: I have seen your car on John Dougherty's website. I am definitely sending my cams to John. Thanks for your advice. John's 20/21 version is called Super Cup, but I think I will stick with his 964's. John aka camgrinder gave me some great advice earlier.

Is it necessary to rebush the rockers? I was just planning on regrinding them and reinstalling in their exact same position. Or is that even necessary if they are reground? There is a nice local camshaft shop next to my work. They were very helpful, and they could grind to original SC specs, but they had no idea how to grind to 964 specs. Then they asked me if I could provide them with the specs. I realized no matter how nice these guys were, I need to have my cams ground properly.

+1 for John aka Camgrinder. Very nice guy. Terrific service.

My car does not look like that anymore!!! Once the new motor is running I will be sending John some pics of the engine for his use. The new 3.4 has Johns cams as well. (DC44)

Cheers

so what is the recommendation for the stk 3.0L engine: If you go with john's 20/21 OR use a 964 cam, do you have to redo/replace anything?? i.e. rockers??... I am also going through an 81' 3.0L US spec engine and I am interested in this timely info in case I choose to do this upgrade...what is involved?? need to replace valve springs and/or remove/inspect/pressure test the springs?? Thanks everyone!! Bob

James,
I should have re-read my post. S/B 9.8:1 not 10.8:1.
My 9.5 JE's get 160/165 psi compression at 5000 ft.

Stock valve springs should be fine with either of these cams. I would recommend having John rebush and regrind your existing rockers to go with the cams. I like the 964 cam but have not tried the 20/21. The last 3.0 I built with 964 cams is actually in California and passes emissions no problems.

Cheers

Not to interupt SP@'s thread...however, Jeff: Can you comment on the difference you experienced when you went to the 20/21 cams AND why do the rockers need to be "rebushed and reground to go with the cams??
Thanks alot!! Bob

I have not tried the 20/21 cam.

When the cams are reground they have a new surface on them that needs to be worn in. They wear better when they are used with a rocker that also has a new new surface on it. Some have just polished the rocker face and had good luck with that also. The bushings may or may not be worn, but if you have the rocker reground it makes sense to have the bushings done too.

Cheers

This thread is great and timely. Is there any secret to setting up the timing for the motor you describe here, i.e., the 81 ROW with 964 cams? I've been considering this change but wasn't sure about where to set the timing for maximum benefit. And with the 964 cams installed, would there be any reason to increase airflow out the exhaust? Thanks!

Thanks Noah. As soon as I get the cams out, they are going to John Dougherty.

PS Is it your engine in Wayne's book where he refers to the 3.0 engine upgrade with the 964 cams? I read that in a post earlier. If so, did you really use JE pistons? Would there be much difference if I am using my stock 9.8:1 cylinders. Did you really get an increase in HP? Thanks! :)

Hi Noah, Did you conside the 20/21 cam or others...staying with your stk 3.0L w/SSI's?? Any hp figures you think are accurate from your changing to the 964 cam?? Thanks Bob

SP2/James,
What cam choice did you make?

Did you do anyother updates/changes "while you were in there?"

Hope all is running well!

Bob

Hi Bob,

I had my SC cams reground by John Dougherty to 964 profile. It was about $275 and looked brand new. I also had my rocker faces reground locally at Delta Camshaft for $4/rocker and they polished my rocker shafts for free. They only remove a 2-3 thousandsth from the faces. A few of my rocker faces had pitting. (Probably bad oil by the PO.) Delta is very nice and very knowledgeable. When I rebuild my E engine I will go to them again.

How is it running? I don't know yet. :)

The cams are installed (by me). This isn't a daily driver and I am restoring it, so I am taking my time. I rebuilt the entire 915 transmission myself last month with a help from John Walker. I am now in hypermode to get the car running again so I can take my first DE course. Yesterday the clutch cable came out. It looked terrible. While I was down in there I decided to redo my pedal bushings.

It just goes on and on...:)

What cam did you decide on?

I didn't do any other upgrades except the SSI's and a Monty muffler. Basically it was a long block re-seal. The P/C's are very good (as they usually are on the SC bullet proof engine.)

how do we know what elevation he is at to conclude that?

Actually I was mistaken earlier. Gerber Motorsports measured them at 165-175 all 6. But as Jeff said, it the absolute number doesn't matter because there are too many variables that affect the number. My conclusion was that the P/C's were all in good shape.

mb911,
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Originally posted by 2.7RACER
James,
Cam choices sound fine. 145 compression is low for a 10.8:1 motor.
Should be closer to 180 or more.
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"how do we know what elevation he is at to conclude that? "

Ben, Newcastle, Washington is at 530 ft. elevation. Look it up in your Funk & Wagnells.
A little closer to sea level than Burlington, Wisconsin.