Please Educate Me on Cam Application....

[boyt911sc]

Subject: Stock 3.0 liter SC engine with 964 cam.

I heard people talk about power band, low torque, it has not come on cam yet, etc. Could somebody give me some basic explanation about the advantage/disadvantage of a 964 cam over stock cam? Would a 964 cam make the engine/car more responsive, quicker, faster, etc. than stock motor? TIA.

TD

[asphaltgambler]

Probably should direct this 'camgrinder' (member here) This is his business. He has many grinds and can do custom apps. Depending on your requirements.

I obtained my set from him. Good value/ prices as well.

[davidppp]

Hello there.

If the motor is truly stock, why change the cam?

presumably, you are looking for more power.

This will come through using more revs with more BMEP..cylinder pressure...at those revs than stock.

And cam is a central factor in setting the usable rev band.

So the cam is only part of the matter: first you need to tell us what you want to achieve..or put another way what you can afford.

The SC motor is well up to quite high outputs with not too much cost..it does mean junking the induction and exhaust though..

Kind regards
David

[chancecasey]

Yeah, second the recommendation for camgrinder if that's john dougherty - he will be happy to tell you what you need to know, and does a bang-up job for a very reasonable price as well.

Generally speaking, though this isn't always the case, when "beefing up" the cams, you are increasing lift and/or duration and overlap.

Lift and duration means the flow "ability" at the valve is increased - which by itself doesn't necessarily increase flow a "lot", but usually does at the higher RPMS. Usually re-working the heads is required to complement the increased lift/duration if you want "significantly" higher flow.

Overlap will help get more exhaust gas out and more intake charge in at the beginning of the intake stroke - to a point - at the cost of course of eating more fuel and, forgot the year of your car, but can cause emissions violations if pushed to far (unburnt intake charge going out the exhaust valve).

The only real mod I did to my engine was cams - increase all 3 of the mentioned factors just a bit - and a primary muffler bypass. I think I can tell a difference in the butt dyno but never really dyno'd the engine beforehand so I'll never know for sure. Other 964 owners who've driven it say it's "very powerful" compared to stock 964s. I'm probably lucky if I got 10% increase with the cam and bypass combo, but for the money it was worth it. And it has more "personality" now for sure. Definitely sounds/runs different - the word "chunky" or "twitchy" comes to mind - a little slower throttle response on the very low end (below 2000 RPMs) and a little irregular idle, but ridiculously powerful above 5000 RPM. It goes from 5500 to 6750 so ****** quickly even in 3rd gear I have trouble not hitting the rev limiter. I'm thinking about upping the limiter to 7000 or 7250 just to see what may be up there now - engine life be d&mned!!! Fun fun fun - I highly recommend this mod if you've already got the shafts out and need a little work on them anyway.

You'll want slightly heavier valve springs if you track or drive "hairy knuckle" style at all - miss a shift and float those valves at over-rev and you might hit a valve with the piston - very very bad. I got springs from John as well, and he re-bushed and polished my rockers. Great guy.

[camgrinder]

The 964 cam works best in 9.3-1 or higher compression engines. If you have an 8.5-1 engine the sport Sc (DC15) cam works best.
If you use the 964 in the 8.5-1 engine the power band will have that "comes on the cam" feel. You lose power below 3000 rpms, but have a nice increase above.
Typically adding duration moves the powerband up. Without an increase in static compression, low speed power can be lost.
Adding valve lift increases cylinder filling thru out the rpm band.

Asphalt and Chance, thanks for the kind words!

[jluetjen]

I had the same question a while ago and with the help of Camgrinder and others on the BBS we condensed the subject down to this thread.