cam profiling?

[Trakrat]

Originally Posted by KTL

drcamshafts.com or webcamshafts.com are good references just to see what some typical specifications are for various cam profiles.

Dougherty Racing Cams Porsche 911, 930 and 964 camshaft profiles

Web Cam Inc. - Performance and Racing Camshafts

Sort like putting a name to the face so to speak.

Thanks... I had already contacted webcam. They only offer 2 cam profiles for my car... a '2021' and a '964'.

[KTL]

The 993SS grind is also applicable to your engine if you're changing pistons. JeremyD here on Pelican is one who first comes to mind that used this cam in his former 3.4L 9.8:1 compression ratio single-plug build. A number of other guys have used this cam as well.

I believe the key is that the lift & duration specs for this cam appear to warrant pistons with decent size valve reliefs in order to provide ample piston-to-valve clearance. Pretty sure the 993SS cam with original style pistons does not provide enough clearance (typical desired clearance is 2 to 2.5mm exhaust and 1mm intake) and therefore they'd need to have valve pockets machined into them. So if you went with something like Mahle Motorsports, JE or CP Carillo pistons, those already have the reliefs in them you need

[Bill Verburg]

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??

your motor is a system of codependent parts that all have work together/

Change one and you will likely have to change others.

Just sticking to stock grinds say an S grind
yes the cams reshape the torque curve, an S cam moves the torque peak to the right compared to an E grind or T grind, all else being equal

but an S grind in a 2.7 won't behave exactly the same way in a 3.2, the same cam in a bigger motor moves the torque curve back to the left, again all else being equal.

The problem w/ using an S cam in a 3.2 is the reversion pulses in the intake due to the the overlap period when both Intake and exhaust valves are both open, This overlap period is great fro making torque at higher rpm but w/ a single pt throttle body doesn't work well at idle and just off idle. The solution is to also use ITBs w/ the S cams. Of course now you are probably reving the motor higher and need further oiling and bottom end and piston changes to accomodate the high lift and overlap and higher rpm operation, perhaps extra cooling as well,


Here are some stock torque curves, the more sporting ones will have the torque hump to the right, the less sporting more commuterish will have torque humps to the left.

Look particularly at the blue(3.8,993RSvram) and silver(3.6 993nvram) curves, Here both motors have the same RS hydraulic cams, Yet the torque curves are very different, the reason is mostly in the intakes and the extra displacement, The 3.8RS is a wonderful street motor, and serves at track days but the 3.6 would be more satisfying for track even though the motor isn't as strong, the shape of the curve is as important as the magnitude. The most satisfying of course is the GT3


You can also compare the stock 3.2 to the highly modified 3.4, the 3.2 is a stock US the 3.4 has S cams 98mm 9.8 pistons S cams and ITBs, at the lower end it's no stronger than stock but does make more power up high

[Neil Harvey]

Originally Posted by WP0ZZZ

That would be my guess as well. I would advise the OP to talk at length with someone having lots of experience in engine modification who can elicit his requirements.




At the risk of going off-topic, I would like to qualify some of the things in the paragraph above.

First: work and torque are two different things (although one can use the same units for both).

Second: an engine makes both torque and power. Both are equally real or artificial. Forces and torques can be understood intuitively but the are not more "true" than work and power. The two approaches are two sides of the same coin. When studying advanced physics or mechanical engineering, the immense value of the work/power approach becomes apparent. (See Wikipedia article on Analytical Mechanics for more on this...)

You are absolutely correct. My bad. In my haste trying to explain I got both functions connected by leaving out the RPM function.

Engines produce torque. This is the force acting upon the piston and the stroke or distance functions.
Horse power is the calculated factor when the engine speed or RPM is introduced into the equation.
Engines do more "work" when the speed of the engine increases. Its this change in "work" that is measured in HP.

So I believe the OP wanted to know what cam to use to obtain the best engine performance at 5000 RPM. I believe you want the engine to "feel" the strongest around 5000 RPM. This is the peak torque number I think you are after, not the peak HP.

I think for the street, this peak torque number should come down some to make the engine more drivable. I would suggest looking at around 3500 - 4000 RPM. This number is more a function of where you set the cam in assembly than anything else. Hopefully you will choose a cam that will have some LSA than will give a torque curve that will not dip to quickly. Your heads and Intake will play a huge part here as well.

When we have to run shorter duration cams to help with the torque and response, we do everything to increase the cam velocities but there are limits to this in these engines. This is where a good design of similar lift and duration can out perform other cams.

Choose well.

[Bill Verburg]

HP is just torque at rpm

1 lb-ft at 1000rpm is 2hp 1 lb ft at 7000rpm is 13hp


You only care about the torque and the rpm where that torque is developed

[Tippy]

Originally Posted by Bill Verburg

HP is just torque at rpm

1 lb-ft at 1000rpm is 2hp 1 lb ft at 7000rpm is 13hp


You only care about the torque and the rpm where that torque is developed

My best analogy is riding a bike. Your legs and cranks are reciprocating, just like an engine.

When you first start pushing on the pedal, that's the torque.

As you approach speeds where you pedal the fastest you can, torque falls off, but you keep accelerating because those smaller and smaller 'torques' are happening more and more frequently in smaller periods of time TOTALLING more work, or in this case, horsepower.

[Bill Verburg]

Originally Posted by Tippy

My best analogy is riding a bike. Your legs and cranks are reciprocating, just like an engine.

When you first start pushing on the pedal, that's the torque.

As you approach speeds where you pedal the fastest you can, torque falls off, but you keep accelerating because those smaller and smaller 'torques' are happening more and more frequently in smaller periods of time TOTALLING more work, or in this case, horsepower.

Human ergonomics are far different from an OTTO cycle engine, Human ergonomics like DC motor torque are more like the curve for #2, you can generate large torque at low rpm and it drops off as rpm increases, you do use this via gearing but it's the reverse of in a car, On a bicycle every gear is an overdrive so instead of torque multiplication you use speed multiplication

I agree w/ you in principle but you are still making a simple thing fuzzier than necessary

here are the torque & hp curves for 2 motors, one has globally rising torque the other globally falling, the magnitudes are the same but reversed, the hp curve for the globally falling torque curve still rises for most of it's range
which is more fun?, ie sporty
which is more of a commuter?

Work is area under the torque curve ie W = ∫T dt
both engines have identical areas under the torque curves ie they both do the same amount of work, it's just that gearing allows the higher rpm torque to be multiplied to a greater extent


The reason torque at high rpm is so valuable is that you use gearing to multiply that torque, the higher the rpm the more opportunity for gearing advantage.

[WP0ZZZ]

Originally Posted by Bill Verburg

The reason torque at high rpm is so valuable is that you use gearing to multiply that torque, the higher the rpm the more opportunity for gearing advantage.

I think this is the key to any power/torque discussion.

When talking about engine torque one needs to take into account gearing because torque at the wheels is what pushes the car forward.

If instead of reasoning about torque one looks at the problem from an energy standpoint, the gearing discussion is bypassed and everything becomes simpler. The rate at which a car gains kinetic energy (which is directly related to speed) is equal to engine power minus power losses (aero, friction, rolling resistance...). No need to look at gearing here!

[Tippy]

Bill, you're being a pedantic engineer.....

But, thanks for the corrections. Even the most nonmechanical of people understand my analogy and a light bulb goes off....

[Bill Verburg]

Originally Posted by WP0ZZZ

I think this is the key to any power/torque discussion.

When talking about engine torque one needs to take into account gearing because torque at the wheels is what pushes the car forward.

If instead of reasoning about torque one looks at the problem from an energy standpoint, the gearing discussion is bypassed and everything becomes simpler. The rate at which a car gains kinetic energy (which is directly related to speed) is equal to engine power minus power losses (aero, friction, rolling resistance...). No need to look at gearing here!

The problem w/ that is that you don't measure energy or power

All you can measure is torque and speed and time, from that all else is derived, why deal w/ the derived results when the measured tell the full story

predictive data is really all that you care about

Predictive comparisons like this are solely a function of measured data

[Trackrash]

Originally Posted by WP0ZZZ

No need to look at gearing here!

Unless you are autocrossing. I would hate to have to downshift to first gear at every slow corner.

[Trackrash]

The analogy, I like to use is this. Imagine three people pushing a car down a drag strip. Can they do it, yes, but it will take a while.

If the car was running on its own the POWER of the motor would get it down the drag strip much more quickly than the three people did.

Same amount of work done, but with more power, it is done more quickly. Power is measured by the speed you do work.

Sorry, back to cam choices.....

[WP0ZZZ]

Originally Posted by Bill Verburg

The problem w/ that is that you don't measure energy or power

All you can measure is torque and speed and time, from that all else is derived, why deal w/ the derived results when the measured tell the full story

predictive data is really all that you care about

I totally love the plots you often share of thrust vs speed. That's the ultimate tool to maximise performance!

Do all inertia dynos have load cells or do they infer power/torque by how fast a rotating mass is accelerating?

[Bill Verburg]

Originally Posted by WP0ZZZ

I totally love the plots you often share of thrust vs speed. That's the ultimate tool to maximise performance!

Do all inertia dynos have load cells or do they infer power/torque by how fast a rotating mass is accelerating?

There just 2 basic types of chassis dyno
inertial - where rollers of a known mass are accelerated by the cars wheels, these can only measure WOT and coastdown parameters
load - either hydraulic(usually water) or electric. hydraulic and electric dynos with sophisticated control software can do step-tests, constant-speed pulls, and even part-throttle testing to the point that full vehicle road-load simulations can be conducted right on the dyno. These are the only kind I'll personally use

[WP0ZZZ]

Originally Posted by Bill Verburg

There just 2 basic types of chassis dyno
inertial - where rollers of a known mass are accelerated by the cars wheels, these can only measure WOT and coastdown parameters
load - either hydraulic(usually water) or electric. hydraulic and electric dynos with sophisticated control software can do step-tests, constant-speed pulls, and even part-throttle testing to the point that full vehicle road-load simulations can be conducted right on the dyno. These are the only kind I'll personally use

What I was trying to highlight is that if an inertial dyno bases its measurement in how fast the car is able to accelerate a given rotational inertia, it is not actually measuring torque. For a given measurement of rotational acceleration one can back-calculate both torque and power. All this is an attempt to present power as a first class citizen and not torque's ugly little brother. But I realise that I'm trying too hard and I'm deviating too far from the topic of this thread...

[Bill Verburg]

Originally Posted by WP0ZZZ

What I was trying to highlight is that if an inertial dyno bases its measurement in how fast the car is able to accelerate a given rotational inertia, it is not actually measuring torque. For a given measurement of rotational acceleration one can back-calculate both torque and power. All this is an attempt to present power as a first class citizen and not torque's ugly little brother. But I realise that I'm trying too hard and I'm deviating too far from the topic of this thread...

correct the inertial dyno actually measures power

But to do any predictive evaluation you need to back out and have the torque
Throwing hp #s around can be great fun but if you want actually evaluate something you need torque, rpm, gearing, aero etc.

Just looking at the GT3 torque curve gives me goosebumps, It's no wonder that these cars are so desirable

[Trackrash]

Bill, so the thrust in this graph was measured by an accelerameter in the car? How does that translate to #s thrust?

Originally Posted by Bill Verburg

The problem w/ that is that you don't measure energy or power

All you can measure is torque and speed and time, from that all else is derived, why deal w/ the derived results when the measured tell the full story

predictive data is really all that you care about

Predictive comparisons like this are solely a function of measured data

[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.

Yes, they can be measured using an accelerator. The reverse calculation is used for phone based "dyno' programs.

[Trackrash]

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.

Yes, they can be measured using an accelerator. The reverse calculation is used for phone based "dyno' programs.

Makes sense, explained that way. A good way to compare torque and gear ratio combinations, if I am understanding it correctly.

[Bill Verburg]

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.

Yes, they can be measured using an accelerator. The reverse calculation is used for phone based "dyno' programs.

correct

For my cars I also have data acquisition to compare fit, that was why after the initial efforts I went to full data integration w/ aero, weight ets all included to come up w/ acceleration predictions, A is easy to gather data for