what cam should i use

[slakjaw]

hi

ok the cams are going in to get reground this week and I am wondering if anyone has any expirence with diffrent grinds,
its a 2.2 T and it will have 9.9:1 compression.

someone recomended the E cams but because I have high Compression id like to go a litter hotter than E. so i was looking at the specs for all the cams and the L seems to be half way between the E and the S

i guess i am looking for a cam grind that wont leave me with nothing in the low end

spec for the L is intake dur 244 intake lift .439 ex dur 234 ex lift .406 lobe center 97 drg

please tell me your thoughts

Thanks
Kyle

[kstar]

Seems like the Solex ('66) grind may be what you are looking for - makes power early and is great for a street car.

I had this grind in my 2.7 and the power band was on demand at lower RPMs and strong to redline, but without the high RPM rush of an S grind.

I must admit I have a lack of greater understanding of cam profiles as engine displacement changes - from what I think I know, the more radical cams get "softer" or less radical as displacement grows.

Hopefully a 'pro' will chime in with more help!

Best,

Kurt

[tobluforu]

Does your moteo have mfi? Now sure if L cams have the sprocket if your motor is mfi. But, what the heck do I know..

[jluetjen]

Kyle;
I'm assuming that your engine has not been ported and has the stock 32 mm ports.

The "later model E" cams which seemed to start with the 2.2's will create its peak torque at 4500 RPM and peak HP at 4200 RPM.

The '69E that I have has the same cam as the 911L. So the "911L" cam should be available with the MFI drive. This cam is a little peakier and creates it's peak HP at 6500 RPM with the same 4500 RPM engine speed for peak torque. My car has 2.0S pistons with 9.8:1 CR and I can idle around town at 2000 RPM and then turn around and spin it up to 7000 RPM without a complaint. I recently drove another 911 for the first time (a 3.2) and my car doesn't feel any slower in around town driving. I was surprised.

Finally, a GE40 appears to be just a little milder then an "S" cam. I've never seen any data from anyone running it, but I 've estimating that it will make it's peak torque at about 5100 RPM and peak HP at 6700 RPM. I doubt if anyone has an MFI spacecam to match off the shelf.

Finally, Porsche once used their "S" cam in a little known 914/6 2.0 rally engine with 9.9:1 CR, 32mm intake ports and 40 IDS carbs. (Sound familiar?) The smaller ports might have taken some of the "peakyness" off of the cam by limiting the top end, while the increased gas speed may have helped a little down low. The numbers that I see quoted in BA's book are 180 HP at 6800 RPM and 132 lb/ft at 5200 RPM. Compare this to a regular 2.0S (MFI) which made 170 HP at 6800 RPM and 134 lb/ft at 5500 RPM (BA's table is wrong)(PS:I wonder how they got the extra 10HP???). A 2.2 version of this might lose a little bit at the top end (peaking at 6600 RPM rather then 6800 RPM) becuase the intake gas speed will be higher still, but you should still get a 2.2S's 147 lb/ft of torque at around 5200 RPM rather then the E's 141 lb/ft at 4500 RPM. I'm guessing that you'll get about 172 HP at 6600 RPM rather then a normal S's 180 HP.

[Early_S_Man]

The 901/30 'Rallye' engine only made 150 hp DIN ... from multiple sources (Frere & Aichele) other than BA, but nobody gives rpms or torque to go with the hp value ... so it would seem the 'T' ports cost 10 hp off the carbed 'S' engine ... reasonable trade-off given better torque in the low and mid range!

I vote for GE-60 or 'S' cams ...

[jluetjen]

Actually Warren, I was looking at the 901/26 engine (1 line up). It had the later 42/38 valve size which may have helped a little. I checked Boschen and Barth's "The Porsche Book" and the /26 engine isn't listed in the couple of pages dedicated to the 914/6 racing varients.

But we agree, the smaller ports will cost you about 10HP and a couple of hundred rev's at the top end.

[slakjaw]

i should have stated in the first post that the heads have been ported to "S" type ports and it has the webber 40s on it

thanks for all the responce to my post
your help is appreciated

i am confused about the lobe seperation thing.

will a cam with 97 deg of lobe seperation give a lopey idle compared to one with 113 deg

Thanks Again
Kyle

[Wayne 962]

Unfortunately, the 2.2 T motor is a bit of a dog to start modifying. Best bet is to get another engine to start with:

- Weak mag case (4R)
- Cast pistons
- T Cams
- non-counter weighted crankshaft
- T-cast iron pistons
- Zenith carbs (replaced in your case)

You can't run an 'S' cam, and I doubt that you would be able to run a Solex cam with your T pistons. They will most likely impact. E pistons would probably give you a lot of problems as well.

You mention that your engine has high compression? How did you achieve this with T pistons? Seems to me like this would be a disaster engine, but then again, I don't know the whole story...

-Wayne

[slakjaw]

it also has "S" pistons now

[slakjaw]

sorry i guess I need to be more specific

its got S pistons, heads ported to S spec, webers. its going to be rebuilt in a 7r case the only thing that is not getting changed is the crank and rods

[Wayne 962]

Ahh, that clears it up just a bit - not really a T-motor any more.

I would search for the counter-weighted crank - they really aren't that much money.

Now that we have all the information, I would recommend the 'S' cams. Some people think they're a bit peaky, but I personally think that they feel great when they kick in. Kindof like a NA turbo lag!

-Wayne

[jluetjen]

If you have the 36mm S ports, then that changes things significantly. Don't worry about having the top end choked off. It won't happen until you get to the far side of 225 HP. Instead you have to make sure that your cam isn't too mild and as a result never achieve the desired gas speeds at the bottom end! In this scenario you might find the motor lacks the desired torque down low. For example a T cam in this engine will only be pulling 50 m/s of air at its maximum torque speed of 4200 RPM which is slower then any other factory Porsche. An E cam looks like it would be OK since it would be pulling 54 m/s of air at its peak torque speed of 4500 RPM. An S cam pulls 62 m/s at 5200 RPM. The slowest gas speed that I've found in a factory car was the '71 ST which was pulling 55 m/s at 5300 RPM.

Lobe separation is meaningful only in so much as it affects overlap. The other important variable is duration. A short duration cam can have a narrow lobe separation angle, but still have a nicer idle then a long duration cam with a wider lobe angle. For example, both the early E/Solex cam and the S cam have 97 degree lobe separation angles. But as I mentioned earlier, the S cam is noticably wilder then the Early E cam. Why? Because the S has an additional 20 degrees of intake duration it has an additional ~10 degrees of overlap.

You can take a look at the attached where I've summarized a lot of the cams. Note the different overlaps compared to the lobe angles.

Of the 4 cams, Solex, S, GE40 and GE60 I've estimated the following peak torque/HP speeds in your engine.

Solex: 4500+/6500+ Est.
GE40: 5100/6700 Est.
GE60:5500/6800 Est. (More lift and less overlap then S)
S: 5500/6800

[jluetjen]

BTW; Was the 7R case a recent addition from EBay????

[dbltrbl]

Can "T" cam be made to "S" specs,
or to some other performance profile?

Is welding needed to get enough lift+duration?

kristian

[Wayne 962]

Yes and Yes...

-Wayne