cam profiling?

[WP0ZZZ]

Originally Posted by jpnovak

The Thrust curves are calculated from the torque (dyno) curve. Torque (ft-lbs) is converted for each gear ratio into thrust (lbs). The gear ratio gives you the distance traveled per revolution to cancel the (ft) component. The RPM component is also converted to speed using the gear ratio. Its a relatively simple conversion and exceptionally useful.

Unless I'm mistaken, Bill's plots also incorporate the effect of aerodynamic drag which increases quadratically with speed. This explains why the thrust curves for different gears are not scaled versions of each other.

In fifth gear, aero effects become important at high speeds and this explains why net thrust decays more than in first gear. Maximum speed is reached when net thrust becomes zero.

[mikedsilva]

Originally Posted by Trakrat

ok.. I'm looking at changing my cam profile to change the characteristics of my stock engine. I've been told that a different cam profile can move the power curve up or down the RPM scale. I've read that a 911 S cam profile from the earlier years will give my 3.2 a smoother curve (the question is, why would a smoother power curve be beneficial?)

I'm struggling to understand what to choose... in that, I'm struggling to properly communicate what I want because I'm confused as to what exactly I want.

So help me understand how changes to a camshaft can do this.

I know a camshaft just opens and closes the valves... and I understand that the lift and duration are what you are changing, along with the overlap.

But what I don't understand is HOW the different changes actually effect the engine's performance.
The chamber can only hold so much air and fuel, and the piston can compress only so far... so how does the valve change the performance characteristic?

I've been to dozens of websites that show diagrams that look like I'm trying to understand the gravitational mass of a black hole while calculating its impact on tachyon waves through dark matter.
My point is... understanding the diagrams doesn't help me to choose the right profile (or keep from choosing the wrong one).

So when I call Webcams (or whoever), what am I needing to know I want, and how do I communicate that in a way that doesn't make the person on the other end of the conversation think I'm an idiot??

What did you end up choosing?

[Trakrat]

Originally Posted by mikedsilva

What did you end up choosing?

I've narrowed it down to S cams and 964 cams.

I'm leaning to 964 cams because a few shops say that this is a GREAT starting point for me, and once i am used to how the engine responds... I'll have a better understanding what I want changed by communicating that I am starting with 964 but want to change 'this' or 'that' in the engine characteristics.

I've still got a long ways away to get this engine built... just now finally putting in the time and money to get this completed.

[Trackrash]

Originally Posted by Trakrat

I've narrowed it down to S cams and 964 cams.

I'm leaning to 964 cams because a few shops say that this is a GREAT starting point for me, and once i am used to how the engine responds... I'll have a better understanding what I want changed by communicating that I am starting with 964 but want to change 'this' or 'that' in the engine characteristics.

I've still got a long ways away to get this engine built... just now finally putting in the time and money to get this completed.

There is a world of difference between these cams.

When building an engine you have to consider the whole system. I won't bore you with what that means.

But the 964 cam is designed to work with a fuel injection system that needs to meet smog requirements and will work with a single throttle body, meaning mild mannered.

An S cam was designed to work with ITBs and is engineered for power.

What personality do you want from your motor? What intake will you use? What RPM will you want your motor to produce power?

[Trakrat]

Originally Posted by Trackrash

What personality do you want from your motor? What intake will you use? What RPM will you want your motor to produce power?

A torquey motor that pulls hard. are you talking about the intake manifold? or the air intake? Intake manifold will stay the same... no change to fuel system either. But I would like to switch to an aftermarket, performance air intake (haven't been able to find one).

I'd like my motor to produce power at all RPMs.... I guess I don't understand your question. I don't want to have to redline the thing to reach its power peak, that's just putting too much stress on the motor. But at the same time, I don't want to lose power with another 2k rpm left in the gear.

[Trackrash]

Originally Posted by Trakrat

A torquey motor that pulls hard. are you talking about the intake manifold? or the air intake? Intake manifold will stay the same... no change to fuel system either. But I would like to switch to an aftermarket, performance air intake (haven't been able to find one).

I'd like my motor to produce power at all RPMs.... I guess I don't understand your question. I don't want to have to redline the thing to reach its power peak, that's just putting too much stress on the motor. But at the same time, I don't want to lose power with another 2k rpm left in the gear.

OK, so assuming if you are going to stick with the stock Carrera FI and intake manifolds. In that case your only choice for a cam is stock, 964 or Web 20/21 or similar. An S cam will cause your valves to hit your stock pistons and will run foul of your intake (FI) system.

So, how much you can increase your performance beyond a mild 964 cam upgrade, depends on a piston and intake system upgrade.

Look at my Garage for my solution to having power and response throughout the RPM range.

There is a great section in Bruce Anderson's Porsche 911 Performance Handbook on upping the performance of the 3.2s using stock internals and more.

If I missed something on your build, sorry. You have so many responses and questions on different threads, I can't keep up.

[911 tweaks]

I 2nd Bruce’s books..... TONS of info from his asking the pro’s and he raced for a while and worked with the pro’s like Jerry Woods, Tony Calis, etc...

[911 tweaks]

If nothing else, choose a build and go from there...
OR, drive someone’s car and get their build specs
OR, go to your favorite Porsche shop and see what they say...

[Trakrat]

Originally Posted by Trackrash

So, how much you can increase your performance beyond a mild 964 cam upgrade, depends on a piston and intake system upgrade.

There is a great section in Bruce Anderson's Porsche 911 Performance Handbook on upping the performance of the 3.2s using stock internals and more.

Thanks... I have that book and have browsed it many times.
Without getting too custom in my engine build, I am going with 3.4 Moritz style P&C setup. (best for single ignition due to the piston design w/ a lower 9.8 compression)

It sounds like the 964 cams is the best choice to improve performance at a conservative level then?

[stownsen914]

964 cams will probably give you a modest hp bump from the stock earlier cams. If you want to go a little sportier, there are performance grinds intended for use with stock injection. Dougherty, Elgin, and Web should all have some options.

[Trackrash]

Originally Posted by Trakrat

Thanks... I have that book and have browsed it many times.
Without getting too custom in my engine build, I am going with 3.4 Moritz style P&C setup. (best for single ignition due to the piston design w/ a lower 9.8 compression)

It sounds like the 964 cams is the best choice to improve performance at a conservative level then?

Yes, again, assuming you are sticking with your stock Carrera intake system.

BTW, DRACO A5OG did a similar build a year or so ago. If you can find the thread it may be worth reading through. I searched and can't find it.