What cams for a 3.0 w/CIS?

pbs911 · pbs911's Garage

I will be pulling the motor to get the engine compartment repainted (and other things do to a rear ending). So I will have some time to do some motor work.

I want to change the cams to get more HP/torque out of my 78SC. A complete rebuild was done on my motor about 50K ago. But I want to change the cams. What would be a good cam? Everything else will remain the same - pistons, valves, springs and CIS. I will retain the 3.0 pistons, valves, CIS and pre-74 header system.

Also what are the things that are a MUST to replace when the motor is out?

Thanks.

emcon5 · emcon5's Garage

The common thinking seems to be that Webcam 20/21 grind is as far as you can go with CIS. 964 profile is supposed to be nearly as good. Super-Jim has Webcams, Noah has 964's if'n I remember correctly.

Tom

Rich L · 07-17-2002, 02:12 PM

Agreed. The 20/21 is probably the limit for CIS. Here's a link:
Web Cam

Superman · 07-17-2002, 02:42 PM

I was skeptical whether cams could make that much difference. Not any more. I'm a BIG believer. the 20/21 cams are a HUGE improvement over the stock torque profile. This engine may or may not have higher peak power. I suspect it does. But it certainly has TWICE the torque at 300 rpm compared to before. Also, power does not poop out at 5500 rpm. They make this car MUCH more driveable.

Be sure to replace the oil thermostat o-ring while the engine is out, and probably the oil pressure switch whether it is leaking or not. Intake runner boots, too.

Wayne 962 · Wayne 962's Garage

Nothing is absolute without before and after dyno tests. However, the 964 cams are good replacements for the CIS cars (both NA and SC for the Turbos). The 964 grind is what I recommend...

-Wayne

dd74 · 07-17-2002, 06:22 PM

Did you do any other mods to the motor when you put the cams in: i.e. valvetrain work, pistons, etc...?

Thanks.

hilandscott · hilandscott's Garage

I'll add as well that the 964 (C2) cams are a *very* nice change to the engine: torque is stronger sooner (3 grand) and the car pulls well past 6K w/o hesitation. If you have time to look there are usually used cams for sale. I picked up the set and all followers and nuts/washers for $450. Webcam is at least $600 I think. I increased the CR to 9.7:1 from stock as well during the rebuild.

I posted comparisons of cam spec differences a while back (do a search), and the Webcam 20/21 is closer to the limit of CIS than 964-- though I don't know the differences in torque and idle characteristics between them as I've never seen them compared side by side.

No complaints from folks with either cam swap-- only praise, noting that the SSI or early exhaust should be considered as well.

BlueSkyJaunte · 07-17-2002, 06:47 PM

Maybe this is a silly question, but would 964 cams screw up my emissions?

I'm pretty much borderline with my dead stock configuration.

SSI's are in the cards (eventually), but they'll have to be removed and replaced with the old exhaust every two years so I can pass my e-test. Bleh.

Doug Zielke · 08:04 PM

Quote:

Originally posted by BlueSkyJaunte
Maybe this is a silly question, but would 964 cams screw up my emissions?
I'm pretty much borderline with my dead stock configuration.

Now that's a good question, Blue.
I was looking at doing a cam change this winter as well, but I'm concerned about the smog angle. My SC's 3.0 passes smog easily even without the cat, but I'm wondering if a cam would take it into smog-failure city. There are many factors affecting this, but a cam with a lot of overlap will be pretty "dirty". The 20/21 has a fairly mild overlap, as that is all the CIS will tolerate.