More on the 20/21 cam and some questions
 

Just curious if anyone has the data on what the following will do for a '79 SC? Be nice if we had some real world data of before and after dyno results.

back dated pre '74 SSIs

2 in and 2 out sport muffler (model and manufacture?)

20/21 web Cam

964 Cam

lightened flywheel

Anyone dynoed their car with all/any of the above mods?

I do not have a lightened flywheel, I have never used 964 cams and I have never dyno'ed my car or engine. But I do have the pre-'74 heat eschangers and a competition final exhaust on an '83. And 20/21 cams. I am hopelessly in love with my cams. I believe they yield a modest improvement in peak horsepower, perhaps something in the 10 hp range. But the big improvement is in the width of the power band. The car pulls strong from 3200 to 7000 rpm. There is still a 30-40 hp improvement when the tach hits 4000 rpm, and another smaller increase at about 5000, but the power band is much smoother now.

Super,

If I recall correctly you're using stock re-ringed pistons with alusil cylinders, right?

Yes. My engine got new main and rod bearings, new valves, guides and seals. So, it's fresher than it would be without those new parts, but they're still stock parts. Engine is therefore bone stock except for the cams. And yes, the later SCs had 9.3:1 compression pistons whereas the earlier ones had 8.6:1 pistons. But then the early SCs had larger intake ports, intake runners, fuel distributor and possibly sensor plate. Maybe even throttle body. Not sure how all these differences might translate to performance with the above-listed performance goodies, but I can just offer my opinion that, in my engine, the cams have made the car very much more driveable.

Most folks say right at 20 hp with back dated SSIs.....

Superman and I started at 180 in our USA SCs. I agree on the 20/21 cams performance but keep hearing cams (along with flywheels, throttle bodies and air cleaners don't improve or performance or hp on an SC).

The 20/21 cam certainly improves the drivability on my SC. Just wondered if anyone had any numbers they might share. Web Cam isn't saying past the actual cam numbers in comaprison to the SC and that the engine will rev higher.

Noah's 3.0 CIS car dynoed 203 at the rear wheels, ~230 at the crank with 964 cams...
Ryan

Ok, Noah says, "964 camshafts are compatible with CIS injection, but produce about 10 more horsepower and a more peaky power curve.... Where stock CIS engines are out of breath by 5,000 RPMs, with 964 cams they pull strongly straight up to redline.

All the U.S.-market 911SC’s ran 8.5:1 compression until 1980, when they were permanently upgraded to 9.3:1 compression, and the Carrera 3.0’s had 8.5:1 compression. You can get a respectable power increase (especially in torque) by bumping compression up to 9.5:1, or even 9.8:1.........roughly speaking, you get about a 10 percent power increase per compression point increase. "

That should be 20 hp for the SSI and muffler, 10 on the cam and another 20 for the compression increase from 8.5 to 9.5. That makes an additional 50hp on a 180 start. Gives you 230 at the crank.

Not sure I buy-in to your numbers at all. From what I've read it is 10 hp for SSI's, 10 hp for the pistons and 0 for the cams. They just move the power band upward. So that is 200 at the crank, maybe 210 with a fudge factor.

In any case, that why I too would love to see certified dyno numbers to put all these rumors to rest. :)

we need to develop a "super fund" to pay for the testing of all the possible combinations for extracting power out of a CIS 911.

once we've tested all the combinations we'll have a model to work off of.

we can use my car for the test vehicle.

contributions can be made at any Bank of America. make all deposits to the "CIS Superfund"

You've got to remember that there is a synergy when all of those componets are installed together that doesn't exist when only 1 or 2 individual components are used.

In particular the cams and tuned exhaust complement each other, of the 3 a lighter fly wheel is the least relevant because the stock one isn't all that heavy.

I would want the cams, p/c, valve/valve train, headers in an engine that I was dgoing to use. Those are the areas where the smog motors are weakest.

Not sure I buy into the figures either, just quoting them as posted else where.

I can't give a before and after dyno but I can get my car as is dynoed next week. Be interesting to see the results FWTW.

Anyone in the SeaTac area want to join me with a bone stock, '78 or '79 SC Monday morning in Tacoma for a side by side comparison?

I've been able to wind my stock SC motor to 6,500 RPMs without any noticeable fall off in power. I'm sure I can touch 7,000, but don't want to break something in the process of getting there. Nevertheless, if 5,500 and beyond is the "Dead Zone" for stock SC motors, I'm not at all sure why mine keeps pulling, as it is also supposed to be stock. :confused:

I figure it could have something to do with the r/p or maybe the Triad muffler. But that's iffy at best. Maybe I'm irrationally exhuberant as far as the revs and power of my engine, but at 6,500, it still has pull that isn't any less than at 5,500.

Tyson has stated with 20/21 cams, the engine will streak beyond redline in third and fourth gear. It certainly feels like my engine wants to do this now, so I wonder, as I've stated before on another thread, might I by chance already have 20/21s?

Hmmm...

My engine definitely used to poop out around 5500. "Poop out" is a technical term, probably explained in technical journals somewhere.

Like a loss of power? Or just slowly-building revs?

"with 20/21 cams, the engine will streak beyond redline in third and fourth gear. It certainly feels like my engine wants to do this now"

My stock SC engine would pull to redline no problem with the normal SC cam. Easy enough to hit the rev limiter in third or fourth with the older set up. Certainly no lapse of performance for a 3.0. But somewhere around 5500+ the car didn't pull like it did at 4500. The "streak" to redline is there with 20/21s and is noticable past the original cam performance. 20/21 engine seems to breath easier at higher revs and "streak" the revs to 7K with little strain but hard to compare on a "butt test" without driving both imo.

If someone did a top end rebuild recently your engine it could indeed have 964 or 20/21 cams in place. Check your old invoices if the car is new to you. The 20/21 cams are fairly expensive parts wise compared to the 964 cams.

Hmm I have a stock SC motor (As far as I know) 78' with SSIs and sport Muff. I dont notice falloff after 5k either. Could it be the exhaust will cure that part?

I ran an SSI and a sport muffler for a year before I added the 20/21 cams. Those two mods did make a difference in performance. The fall off in power is marginal but the difference is noticable as Superman says. But then anything with a 180 hp motor is fairly easy to notice :)

rdane - did you perform the 20/21 cam modification yourself? In other words, how difficult was the install?

And if not, in your estimation, is $3K a reasonable price to do the install, in your estimation?

Thanks

DD I had my local shop do the work this spring, 670 for the cams, 360 for the rockers and $100 for shipping. $500 for the engine drop. Another 1000. for the reseal and replace the chain tensioners, resurface the chain housings ect..for a total of $2630. Easy to spend $3k opening up an engine is my take. But I would think it would mention somewhere adding a different cam. I have reciepts on my car back 20 years and some of them are lacking some detail so you never know.

Should be able to get some idea on the age of your cams during a valve adjustment by the pitting visable. Not sure what that tells you but my car has 180K miles and the cams were fairly pitted which is why I changed them out.

If you car wines past 7K is a split second and the car doesn't sound like it is going to blow up doing so, there is a good chance you have a 964 (or 20/21) cam. Although if it was not noted in reciepts I suspect the 964 would be more easily believed simply because of the price difference.

My car was basically stock when i bought it. No invoice for the Weltmaster short shift or the alarm system either so who knows when you get into a 20+ year old car. The 964 cam change didn't happen though until the fall of 1989 whren they were first available I would guess. I suspect the web cam 20/21 came even later.

Anyone care to quess when they first stared doing the 964 cam switch?

I am having a 3.0 SC engine built with webcams. '74 style SSIs, factory '74 muffler (2 in 1 out), slightly bigger ports and JE Pistons (9.3 to 1). Both top and bottom end are being redone with mostly new parts. Should be installed by the end of the month. I will let you know how it performs.