964 v 20/21 cams

[jpkelly3]

Can anyone explain (or direct me to a thread) the difference between the 20/21 and 964 cam grinds. I have an SC w/ 3.0.

Thanks in advance.
Cheers,
John

[jpkelly3]

TTT

Thanks

[88-diamondblue]

I have no direct experience with the 20/21 can but is more aggressive than the 964. It would move the power band up higher in the rpm range. Emailing or calling John at Dougherty Racing Cams would be able to tell you what cams he has that would be close to the 20/21 and the characteristics of the cam. I went with a DC-22 regrind from John and am very happy with it. Power comes on strong around 3900 rpm through 7000 rpm. Check out the specs at Web Cam Inc. - Performance and Racing Camshafts and the 964 cams and what John offers here. Dougherty Racing Cams

[jpkelly3]

Thanks

[Superman]

Originally Posted by 88-diamondblue

I have no direct experience with the 20/21 can but is more aggressive than the 964. It would move the power band up higher in the rpm range. Emailing or calling John at Dougherty Racing Cams would be able to tell you what cams he has that would be close to the 20/21 and the characteristics of the cam. I went with a DC-22 regrind from John and am very happy with it. Power comes on strong around 3900 rpm through 7000 rpm. Check out the specs at Web Cam Inc. - Performance and Racing Camshafts and the 964 cams and what John offers here. Dougherty Racing Cams

At least some of this is not true. I have no experience with the 964 cams, but I know how your '82 will react to the 20/21 cam. Your '82 has the higher compression pistons (compared to early SC's) and the narrower intake runners. The 20/21 cam (and perhaps the 964-?) will do a nice job of packing your combustion chamber due to the higher velocity in the runners. The dyno guy just kept staring at my dyno printout, saying it has a power band like a V8. Really fat bottom end (compared to stock SC cams). Good power at 2000 rpm. Seriously. And a power band that looks like a table top. The dyno sheet was imaged and posted here a few years ago. Search using the username "RDane," and you will find it. Max power at something like 4000 rpm, with a flat power curve between there and 5500. It's an interesting shape. Power does fall off after 5500 or so, but the power band is so wide it will make your car easier, and more fun, to drive. Stock SC cams are "peakier" than the 20/21.

[jpkelly3]

I use mine strictly for the track, so I'd like to have my power band higher in the RPMs. My car is a Euro with the larger 78-79 intake/exhaust heads. I think the 964 is what I'm looking for. Thanks for the input. I'll search out the thread.

John

[Superman]

I've heard the differences between the 964 and 20/21 cams are subtle. They are similar cams. The 20/21 is sometimes referred to as "964+" cams.

And as you probably know, CIS systems won't work with radical cams. Specifically, they won't work well with cams that allow much overlap. The cams we are talking about here (964 and 20/21) have a modest amount of overlap, and plenty of lift and duration. In order to move the power band much higher, overlap is necessary.

[KTL]

The Web-cam site sucks for comparative purposes (which is probably intentional) to see what compares to what Dougherty makes. The 964 is a good choice for a basic bump up in performance. Anything above that will see better results by improving your pistons to something more aggressive than the stock smoggy smushed dome pistons.

Plus the more aggressive you get with your cams, the more cognizant you need to be of the piston-to-valve clearance. Those cams with higher lift @ overlap spec want to have relieved piston pockets. With that comes higher compression ratios and more power and then more
risk of pre-ignition if you don't have twin plug or run high octance racing gas.

And as Supermain alluded to, the 964 and 20/21 cams retain basically the stock lobe separation/overlap spec. Which limits the power you can gain with them. A cam NOT based off the stock SC/Carrera lobe separation is where you need to go (up to a point, to allow the fuel injection to still operate well) to find more benefit from your cams. It all boils down to a matched system from the injection, be it carbs or individual EFI throttle bodies, to the cams and pistons. Just changing cams on a stock 3.0L isn't going to do earthshattering things for you.

[jpkelly3]

I'm planning a 3.2SS with 9.5, maybe 10.5 JE pistons. The 20/21 cams came with the car with engine ready to assemble.

I have ghl headers n muffler, CIS, single plug. I'll use 94 octane for the track.

Thanks for the input.