3.0 CIS cam grinds, 964 vs. web 20/21

[emcon5]

I am rebuilding my 82 911SC, and would like to get my cams reground. I have heard good things about both the 964 grind (from Noah and Wayne), and Web's 20/21 grind (From Super-Jim and others).

Wayne, why do you prefer the 964 profile?

Will I have any problems passing California smog with either of these cams?

Thanks,

Tom

[Doug Zielke]

Tom,
As I think I told you in a PM, I bought some 20/21's for the 'Bomber. The motor goes back in the car next weekend, but I never did install them. As a matter of fact, I sold them, brand new in the box to a fellow in WA.

Why?
Our local smog nazis increased the standards just days after I ordered the cams. We are now very near California standards. I'm sooo proud I could almost $hit myself with excitement!

A pro-wrench I trust, told me the car would likely fail with the 20/21's. He knew of a couple of 3.0's with 964 cams that did.
As much as I enjoyed driving a 20/21 equipped car (Superman's), it just isn't worth the hassle to me.

[911nut]

Tom,
I've been corresponding with both Superman, who has the 21/20 cams and GT911, who has just had his SC cams reground to the 964 profile.

The spec sheet shows that the 21/20 cam has more lift than the 964 cam so we could expect the 21/20 to make more power. Accord to Superman he has good power throughout the rev range.

GT911 says that with his 964 cams set to factory spec the power kicks in at 3500 rpm ( as opposed to the 21/20 which makes it's power starting at 2200 rpm, per Superman). GT911 had his cams reground by Elgin, who recommended that he retard the cam timing for better low-end grunt. He hasn't done that yet but it will be interesting to know how that timing affects high-rpm power.

Cost could be a deciding factor, though. Web cam charges $670 for a regrind to 21/20. Elgin charges $250 for the 964 regrind.

Hope this helps.

[emcon5]

Doug, I remember you telling me you put the stock cams back in. Did your wrench say it wouldn't pass at all, or could he tweak it to pass?

I am plannin on using Elgin, as they are local. Elgin has a few 911 cam grinds of their own, I need to call them and find out what is the best I can do and still pass the tailpipe test.

Reading the specs on Web's page. Elgin's page and Bruce Anderson's book has me a little confused though. From BA's book, the 964 is a little higher lift and longer duration, and from Web's catalog, the 20/21 has more still:

911sc--I=229° .455" E= 220° .402"
964----I=240° .464" E= 230° .425"
20/21--I=258° .485" E= 246° .452"

The elgin listings really don't make sense when compared to these numbers, I don't think Elgin is using the same scale, and without really understanding I am comparing apples to oranges.

I just want to make sure the more agressive profiles will pass smog. If I have to lean it out for the test, I am OK with that, as I plan on using John Walker's 3% open loop mode and will need to do that anyway.

Any Californians running 964 or 20/21 cams in a SC?

Tom

[jluetjen]

Tom;
I've done a lot of comparisons of the different cam profiles and here's a few conclusions which I've drawn...

ID= Intake Duration
IL = Intake Lift
ED = Exhaust Duration
EL = Exhaust Lift
LC = Lobe Center (If stated)
OL = Overlap
PeakHP = Predicted Peak HP speed
PeakTor = Predicted Peak Torque Speed

The following have been sorted by actual/predicted torque speed based on a regression analysis that I ran.



In general, the peak HP speed (assuming other things like intake design and valve size (not an issue on 911's) are not limiting it) seems to be the engine speed when the intake valve is open 0.00011 seconds. I noticed when using a different analysis. This is as follows for the 3 cams that you listed:

SC: 6000 RPM
964: 6000 RPM
20/21: 6500 RPM

The other two major variables are lift and lobe-center/overlap.

Lift: Since a valve is at full lift for only a portion of the time that it's open (~25%?), this has less of an impact then duration. It is also dependant on how well the ports flow at full lift. If you have an early SC with the 39 mm ports, this may not be an issue, if you have a later SC with the 34 mm ports, it may limit the benefit of the 20/21's extra lift. I have seen very little data on 911 head flows, but BK911 on the 911 Technical BBS did flow a couple of early 911S heads. The same thread has the flow data for a 930 head.

Lobe Center/Overlap: As far as I can tell, these are two ways of discribing overlap. As detailed in a lot of places, overlap is great because at higher rev's it allows better filling of the combustion chambers. I suspect that this is why the E camshafts make more torque then the T's (abiet at higher rev's), and the S's more then the E's and the 906's more then all of them -- but at 6200 RPM.

CIS systems don't like overlap because of the pulses that it causes in the intake. These mess up the air metering system so that the flow of fuel does not match the flow of air. The result is poor running and a lot of pollution. Pollution sniffers don't like overlap because at low rev's unburned fuel can be sucked into the exhaust. If my memory is correct,

Webcam allows you specifiy the lob centers for your cams from 3 choices. If you are concerned about emissions, I'd select the widest lobe angle/least amount of overlap option for your cam.

As far as which is best...

BTW -- For some reason I can never seem to find Webcam's web site when I'm looking for it. Does anyone know what it is?

[emcon5]

Thanks for the info John. Looking at your chart, it looks like the 20/21 has less overlap than the 964, which is suprising considering it has 18° and 16° longer duration. Must be because the lobe center is different. Your numbers make me lean towards the 964, peak power above redline does nothing for me.

Web's home page is http://www.webcamshafts.com/

Still hoping to hear from someone who has passed CA smog with 964 cams....

Tom

[dd74]

I'm not sure if that weird 24-year smog rule will apply to your car, or even if it's actually 24 years before an '82 SC becomes smog exempt, but for CA you might want to check. Because if so, your car won't be free from smog rules until 2006.

I would call TRE and ask them if a 20/21-equipped (EDIT: and/or 964) 3.0 will pass smog, but my thoughts are it won't.

In the meantime (before 2006?), my suggestion is install a 7.31 R/P in your transmission. I can't be entirely certain, but the ring and pinion swap could be comprable in price to the cams, and secondly (more importantly), you won't have smog to worry about.

I'd go that route if smog's an issue. There are other things, too:

1) lower profile tires can speed up a car some.
2) lighten the car
3) lower restriction muffler (not the SSI/HEs and muffler setup - they aren't smog legal - just a muffler), might help a bit.

Good luck

[makaio]

Tom, Mikey Z was running 964 cams in his SC before he upgraded to a 3.6.

[Yoyo]

Hey guys,
I am new to all this. Just bought my first 911 a couple of weeks ago. It is a 78 911 SC 3.0. As all of you, I am interested in boosting up my HP from the 180 stock. I would like to get to 220 - 230 if possible. What are some things I can do and roughly how much would each one be? Does switching to 964 cams do a lot?
I appreciate all the help thanks,
Miro

[emcon5]

Originally posted by Yoyo
Hey guys,
I am interested in boosting up my HP from the 180 stock. I would like to get to 220 - 230 if possible. What are some things I can do and roughly how much would each one be? Does switching to 964 cams do a lot?

It really depends on what the main use of the car is, if it is subject to smog rules, and how much you want to spend.

There is some good info here and here.

964 cams should make the power come on a little lower in the RPM range.

Tom

Edit: to fix link to rennlist

[Wayne 962]

CIS systems are horrible for power, but the 964 cams seem to be a bit more aggressive, and also allow the car to pass smog. If you're doing a rebuild, then everything should be new, and the car should pass smog no problem. If you are simply swapping cams on a tired engine, you may have smog problems.

I'm not too familiar with the 20/21 cams, but keep in mind that power increases are minimal due to the limitations of the CIS system.

-Wayne

[Yoyo]

Thanks for the replies,
I am not worried about smog since I am in Florida.
So what are some of the most basic upgrades (what should be done first)?
And also I have no idea of how much the P&Cs or anything else is?
I am getting the transmission rebuilt this week and while it is out, do you recommend changing to 7:31 gear ratio? I read in one of the forums that it speeds the car up. Wayne I am waiting on your book to come out in March. I guess I'll get most of my questions answered there.
Thanks again guys,
Miro

[Wayne 962]

The 7:31 is a personal preference - you need to do some calculations on your driving preferences, and also your torque curves before you decide...

-Wayne

[emcon5]

If I was in your shoes, I would go for the exhaust backdate. Most people agree it is the most bang:buck, and it is external to the engine.

Everything else is internal to the engine, and is probably best if done in conjunction with a rebuild, which is why I am doing it.

If your engine is in good shape, sell it and swap in a 3.6.

Tom

[Ken Louie]

well i just got my 79 930 3.3 w/ 964 cam smogged and it passed with eases. the allowable emission are 0180 hc ppm mines were 0062. CO % is 1.70 mines were 00.50. Also my car did not have the thermo reactors on.

[Chas911]

Tom, which cams did you end up using and why? And if you went with 20/21s, did they pass smog?

[emcon5]

Originally posted by Chas911
Tom, which cams did you end up using and why?

I sent my cams to Elgin and had them reground to 964 profile.

The reason was a combination of things, economic (Elgin was about half the price of Web) and that for the smog thing I would rather err on the side of caution. A couple people told me they passed, and Dema at Elgin said it should pass with no problem.

I haven't tried yet, as the engine is still not back together.

Tom

[Chas911]

Thats exactly what I am intending to do unless someone can convince me the Web cams are that much better. I have to believe Porsche has put some thought and testing into their own cam profiles.

[dd74]

I think the 20/21 cams have a bit more lift and duration than the 964s, but I'm not sure.

Pelicanite Jluetjen once circulated a graph showing a slew of Porsche cam specs, including the 964 and 20/21 cams.

Do a "20/21" search or "WebCams," and maybe that graph will come up.

[emcon5]

Originally posted by dd74
Pelicanite Jluetjen once circulated a graph showing a slew of Porsche cam specs, including the 964 and 20/21 cams.

That would be this thread, 5th post from the top (2 above your first reply).


Tom