"S" cams in a 3.0

[surfdwn]

I just acquired a 1980 SC with the stock CIS system. It does not have anywhere close to the performance I want and I am looking to replace the CIS with webers. I have a set of '73 2.4 "S" cams from a previous project and a '73 2.4 S distributor. I actually have the whole engine, but that is another very long story....

Do these cams fit in the 3.0? If not does anyone have suggestions to get early S grinds for a 3.0?

[jluetjen]

Surfdwn,
This just came up recently and you might want to do a quick search of this BBS. If my memory is correct, the number of cam bearings is 4 on the SC motors and 3 on the earlier bearings - so the cams won't just fit in. The trick might be to use the S's cam towers and cams with the SC's heads. Remember that's from memory, I'd do the search.

[surfdwn]

Thanks. I've got the cam towers from the 2.4. That one is totally apart.

[Bill Verburg]

You will need different pistons also. There will be a lot of ugly noise when it's first turned over with S cams and CIS pistons

[john walker's workshop]

the larger the displacement, the less nasty the S cams become. still better than SC though. you also need higher compression, (as well as deep valve reliefs in the new pistons) to fully appreciate them.

[surfdwn]

Are the 964 cams the most readical ones that can be used with the stock pistons? I really didn't want to go to the expense and hassle of replacing the pistons, although I have a wonderful set of Mahle 2.2S pistons that I could trade!

[cstreit]

No way an "S" cam will work with CIS pistons.... If you want to up your cam and retain the pistons, WebCam makes a "20/21" cam that increases lift somewhat and a little more duration, but the valve to piston clearance is not condusive to do much. Plus, to much duration and overlap will disrupt the induction system (air flow sensor plate)

[surfdwn]

My question is more aimed at a weber converted car. I want a higher lift cam to go with the webers, but don't want to replace the pistons. Can the stock pistons be "pocketed" or is the profile not conducive or not enough "meat " in the piston to allow for this?

[A Quiet Boom]

Originally posted by surfdwn
My question is more aimed at a weber converted car. I want a higher lift cam to go with the webers, but don't want to replace the pistons. Can the stock pistons be "pocketed" or is the profile not conducive or not enough "meat " in the piston to allow for this?

I've wondered about pocketing the pistons myself since I've done it many time with 5.0 Ford engines. I think I still have a set of 3.0 SC pistons lying around I could look at and give you an answer. As for webers, consider modified Zeniths!, I've got a set in which I installed 36mm venturis and opened up the main and idle jets, they run like a scalded dog with VERY crisp throttle response. The downside to carbs of course is that once you dial them in perfect, they'll run terrible for the first few minutes you start it on a cold day, but that's a small price to pay for the HP, throttle response and weight reduction you'll gain. PM or email me if you'd like info on setting up Zenith's for a 3.0.

[A Quiet Boom]

Here's a pic,

[Porschephanatic]

Quiet Boom, did you retain the stock pistons and cams in your 3.0? I was told w/ SSI's and carbs on my stock 3.0 I would have good bottom end torque that I would lose w/ "S" or 20/21 cams and higher compression. My car will be used on the street only. I am having a 7:31 ring/pinion installed currently, so would torque be less of an issue?

[surfdwn]

Good looking setup! As far as losing bottom end torque, it's a small price to pay for that rush of power when the car "comes on the cam". I had a '68 911S for 5 years, and the surge of power and the marvelous engine noises are just too wonderful. The stock SC is a tractable, reliable car, but no near enough fun! Let me know about the pocketing of the stock pistons. I have a decision to make about gettting rid of my 2.4S engine or using pieces of it for this project.

[A Quiet Boom]

Bottom end torque is relevant, for example my car was originally converted to 2.0 six power, I doubt I could cam the 3.0 enough to reduce the bottom end to the point where the 2.0 was, at 2200 or so pounds I can pull 1500rpm in gear no problem whereas the 2.0 would have shaked and bucked if I tried that with it. Higher compression does not lower bottom end torque at all. And yes for now I have the stock pistons and cams in my car but like surfdwn, I'd love bigger cams they are indeed fun!

[si2t3m]

Seems like someone ''pocketed'' CIS pistons:

http://kotisivu.mtv3.fi/914-6/ENGINE/04/ENG46.jpg

Marc-Andre

[cstreit]

Wouldja look at that!

I wonder what the thickness is under those pockets though? Can't be much I expect...

[914timo]

cstreit,
I am sorry I don´t remember the numbers now, but I measured the thickness of the pistons first. Then I read somewhere how much it should be at least. There were 2mm extra material. I think the source for the information of the minimum thicness was BA´s Performance handbook.

Those valve pocekets are exactly 2mm deep. I have measured with modelling paste there is now enough room between valves and pistons with old Solex cams.

If I remember right, the S-cams would need deeper valve pockets. Then you should go under the recommended minimum thickness in the pistons. So, my opinion is that you can´t use CIS pistons and S-cams together in SC engine. But, as allways, I may be wrong.....

[82SC]

well I hate to give any type of misinformation but...

from my knowledge and from many of the people who know tons more then me I think the 964 cams are the hottest cams that can be run on the SC+CIS combination...

but in a conversation I had with the well renowned Andial I was told a SC + S-cam is a viable combination. I think he said the clearance would be tight...but possible
But with this combo the CIS system would not be possible because the CIS is intolerant to high lift cams...

I know wayne is doubtful about this statement and I am too, but I'd be intrested if Andial has actually built such a motor...

So I don't know if the information that S-cam can't work on and SC are due only to the CIS system, valve clearance, or a combination of both.

If you are really interested in trying this combo, I'd call andial and maybe ask more indepth question then I did...I'd be interested if this can actually be pulled off...

plus if you have all the parts all you have to do is do a partial assembly and use the molding clay method to check clearance

[Wayne 962]

No way would 'S' cams fit in a stock engine - the lift is too high. They will barely work with 'E' pistons. Again, you got bad info.

If you pocket the pistons, then you might have a chance, but I would then just go with new JE pistons for the amount of cost and trouble that you will have pocketing the pistons.

-Wayne

[speeder]

Actually, webcam 20/21s, (or equivelent GE, etc.), are the biggest cams that work with CIS, 964 cams are sort of "in between" stock SC cams and these. As for "wildest", none of these are very wild, they all produce a nice, even power/torque curve with good idle and drivability.

I am currently debating which ones to use in my SC motor that is getting rebuilt, I have a set of 964s that need repair so it would be easy to have them made into whichever grind I want. It is pretty common knowledge that CIS will not tolerate much overlap, as for the carbureted/CIS pistons/'S' cam set up, I think that the CIS piston dome shape will effectively limit the performance gain from those cams, but confirm this with some good engine builders. Good luck.

[cstreit]

Well to refer back... Surfdwn mentioned that he wanted to convert to Webers... so the CIS issue is really off the table at that point. The real question becomes how much CAM you can run with the CIS piston that's been pocketed.

Wayne, He most likely has ALusil cylinders and I've heard mixed reviews about mixing Alusil with J&E pistons, so in fact he may be better off modifying his existing pistons. (New ring seating capabilities left to someone leses debate.)

Bottom line is THe 20/21 is the largest you can run with an un-modified piston. A larger CAM can only be used in concert with modified pistons. I would not attempt this haphazardly but rather go to someone who's done it successfully before. It's somewhat of a custom job.