camshaft advice

gamin · 12-10-2020, 05:14 AM

My 70T currently runs a 79 euro large port 3.0 with PMO and SSI. Still has CIS pistons and cams. A little down on compression so plan on replacing the pistons and cams. Probably going with 9.5 CR pistons. The question is which cams. Lots to choose from and I am far from knowledgeable concerning cam selection. So I need some advice.
This is a street only car that will never see a track. So I need torque down low. Max HP is not a consideration. Driveability in traffic is. So which cam would fit that description?
And yes I have done the searching. Most want top end HP. Advice please.

trond · trond's Garage

but 9.5CR pistons are normally not compatible with single plug. Twin plugs are expensive and difficult and is better avoided. Look at 9.3 CIS pistons and Melissa (M1) cam ? I have no experience with that cam but tend to believe everything I read.

motogman · 12-10-2020, 08:28 AM

Quote:

Originally Posted by gamin

...
This is a street only car that will never see a track. So I need torque down low. Max HP is not a consideration. Driveability in traffic is. ...

If this is your requirements why change from the factory SC CAM or the 964 cam?

However, from my searches you can get a bit more torque and HP without having to do much other updates with a few options. These include the 20/21 and the M1 (which I just ordered for my 3L) mentioned above.

kent olsen · kent olsen's Garage

Gary
I also have a 3.0L in my 72T, although mine is an 80 with smaller valves. I did go the twin plug route but only 9.5 pistons. I have a Dougherty GT2-102 cam. Peak torque 227 @ 4800 and peak horsepower 245@ 6200-6800. Very pleased with the low torque. It pulls 217 ft/lbs at 3800 so lots of low end torque.

kent olsen · kent olsen's Garage

Oh and Webers

gamin · 12-10-2020, 11:41 AM

As I stated, I am far from knowledgeable concerning cams. So, what are a Melissa (M1) cams?
Who makes them and where is info available? I never heard of them. Never mentioned in any of
the searches that I did.

Bill Douglas · 12-10-2020, 11:59 AM

Quote:

Originally Posted by trond

but 9.5CR pistons are normally not compatible with single plug. Twin plugs are expensive and difficult and is better avoided. Look at 9.3 CIS pistons and Melissa (M1) cam ? I have no experience with that cam but tend to believe everything I read.

I'm no expert. All I know is what you guys tell me. But my SC is a 930/10 and has 9.8:1 CR pistons, single plug, and runs fine on ordinary gas station fuel.

targa72e · 12-10-2020, 04:05 PM

The cams mentioned so far are all targeted for use with CIS or Motronic. These induction systems can not tolerate pulses in the intake track. Since you have PMO carbs you can go with a more aggressive cam that will give you more power. In general if you pick a cam that has the same or more lift than the SC cams you have now and then add some more duration you will add more power overall.

john

Jonny042 · Jonny042's Garage

Quote:

Originally Posted by kent olsen

Oh and Webers

40's? Just curious.

Jonny042 · Jonny042's Garage

The 9.5 JE pistons tend to be on the low side of 9.5, and they are fine with decent pump gas (91 octane).

I would contact John Dougherty and get his advice and assistance in picking a grind best suited to your combination and use. Suspect a Mod-S or the GT2-102 will be the hot setup. One consideration will be if the chosen grind will be compatible with your (presumably stock) valve springs.

'78 SC · '78 SC's Garage

Quote:

Originally Posted by Jonny042

... I would contact John Dougherty and get his advice and assistance in picking a grind best suited to your combination and use...

+1 on this advice. John is great resource and is very helpful. Make sure you know the particulars of your build (pistons, heads, valve train, induction system, exhaust design, intended use, RPM targets, etc.) since he will take all these into account when selecting the cam.

Jonny042 · Jonny042's Garage

PS - I know you say you want torque and driveability, and aren't concerned about top-end, but with the PMO's and SSI's you've got the basis for a great setup that will have a fantastic meaty toque curve AND pull hard to redline.

kent olsen · kent olsen's Garage

My weber's were 40's until Paul Abbott and i played with the jetting and he opened mine up to 42mm.

MichaelSJackson · 12-11-2020, 09:43 AM

Since you already have replaced the CIS you can upgrade the cam without going top end crazy. I'd second the advice of talking to John Dougherty (964 or 993s) or other cam specialist (M1).

And if you think you're going to upgrade your pistons, why not bump up the displacement with a set that will take it to a 3.2SS? Wedge tops that will still run a single plug and run on pump gas.

From Wayne's "Quick FAQ 3.0/3.2 upgrades to 3.2/3.4"...

To upgrade a stock 3.0 Engine to a 3.2, you need a special "Big Bore" kit.
This kit turns your 3.0 into what is known as a short-stroke 3.2. The stroke remains the same at 70.4mm because you're not swapping out the crankshaft. Instead, you are installing what are known as "Big Bore" pistons and cylinders which are 98mm wide (as opposed to the normal 95mm for the 3.0). These are special pistons and cylinders that were never a factory kit available from Porsche (as far as I know). There is no Porsche part number for these - they are an aftermarket kit available from Mahle. These are also sometimes known as the Max-Moritz kit. They are available in various compression ratios - I have a set that is 10.5 and resembles the original RSR setup in design. These sets are "plug-n-play" and do not require modifications to your case or heads. The piston pin offset in these kits is specifically made to work with the 3.0 crankshaft, and these will not work with the 3.2.

...Both upgrades would be inline with your path of a torquey street machine.

I think you'd need to settle on the pistons decision before you choose your cams.

Charles Freeborn · Charles Freeborn's Garage

https://supertecperformance.com/pages/how-to-select-a-porsche-camshaft

Trackrash · Trackrash's Garage

I chose to go with GT2-102 cams by John Daugherty. Talk about midrange power, it drives like a V-8. Pulls to 7K.

Honestly, in order to really wake up these motors you need to change the pistons and use a cam that is designed to work with carbs.

JE 9.5 pistons can drop right in, IF your cylinders are in spec, with a de-glaze.

I found that the JEs were spot on as far as compression ratio goes. In-fact I am running 9.8-1 CR, according to my burette. Single plug, with that cam is no problem on 91 octane. Of course I am possibly a little conservative with my timing.

Seriously, in the big picture with carbs and an exhaust backdate, changing the pistons should be a no brainer, IMO.