Rover owners: VVC and Piper exhaust cam conparison (picture heavy)

In order to complete my ongoing mission to build accurate cylinder head CAE models and satisfy my general curiosity I measured my exhaust camshafts.

I have a Piper BP270H exhaust cam and 4 standard VVC exhaust cams (they come with heads usually) and their time had come to be measured.

Normally the main reference of cam timing is the crankshaft angle, but the data here is presented for the cam itself, so is referenced to the angle wheel.

The pictures should make this clear.

To set a useable reference the cam is placed on it's sprocket and laid in with the inlets to get the reference.

Note: This photo is on the cam ladder and not the head.

Note 2: This would actually be 90 degrees on the crankshaft - the safe position for all cylinders.

I deliberately flipped this photo so that the pulleys appear to be on the head, so you can imagine the pulleys on the car.

You can see the timing lines aligned. This will be used to reference 0 degrees on the cam.

Now get your angle wheel.

Probably 99% who glance at this thread will not have an angle wheel, so go here and get one: http://ift.tt/1A3yyjJ

Print it out as large as you can and mount it on stiff card, plastic, whatever and you have a never ending source of angle wheels

Mark the back for 90degrees:

put a hole in it for the camshaft bolt and use two camshaft washers to grip the wheel

Match the 90 degree mark with the camshaft sprocket timing mark

and bolt up using just friction. The clamping of the washers will allow you to trim the wheel to the mark

Either use v-block and a clamp, or place the cam in an old head

Now you need a reference for the angle wheel.

I got some sheet material and made up one like this:

making sure you have a easy to see point.

You don't need a drawing or anything sophisticated- it will be referenced to your 0 degree mark, which is tied to your sprockets timing marks.

and fold it close to the wheel to prevent parallax error

Now mount a dial gauge on a stand, making sure it cant deflect and hampering your accuracy and place it on a cam lobe of no.1 piston, aligining it vertically on the centreline of the cam's rotation.

*This photo is mocked up - you need to put a magnetic gauge on a heavy steel base to make sure it dosn't rock*

Now set your angle wheel by aligning the sprocket and set your wheel reference arrow to 0 degrees.

Set your dial gauge to 0 (or accept the offset in your readings and correct as you go along)

You can now generate these:

Each cam was measured 3 times at 5 degree increments, with a few wildcards thrown in either where there was huge changes over 5 degrees or just for checking and hysteresis purposes.

The shown values are averages of the three attempts.

Remember:

The cam rotates clockwise in the engine along with the crank, so the actual information is gleaned from turning the wheel clockwise, which means 0, 355, 350, 345 etc.

I've corrected it here for you, so it reads with crank direction.

The online quotes of the exhaust cams I could find were-

Standard; 252 degrees duration with lift of 9.2mm

Piper; 264 degrees duration with lift of 9.86mm

What I found was-

Standard; 286 degrees duration with lift of 9.274mm

Piper; 284 degrees duration with lift of 9.618mm

Standard; Opens 83 degrees, Closes 226 degrees (cam angle not crank)

Piper; Opens 89 degrees, Closes 231 degrees (cam angle not crank)

If you are unfamiliar with cam selection then one item to realise is that manufacturers quote duration on different conditions. It's not uncommon to find, as is here, the open-to-close duration to be longer than the quoted because the manufacturer quotes at 0.05inch of lift (0.000197mm) rather than actual 0, as i've measured here. This was traditionally due to the difficulty in measuring tiny ramps on the cam.

The Piper website did not furnish that information, and I can't find Rover info either.

Because of this, the apparent difference does not mean the Piper cam is being mis-sold - there will be a lift specification for each cam that makes sense to the quoted values.

I want the actual open/close points for what I do with them, so i'm using what i've found, and do not care about the quoting method.

The expanded chart shows the difference in the cams.

You can see the Piper is more 'beefy' on the flanks and has the all important higher lift. The nose of the Piper has more duration as well, meaning more dwell around full lift.

Assuming, and I have no reason to doubt it due to repeated measurements, that the Piper actually has less duration open-to-close than the standard then the magic is in the initial ramping to the flanks and nose.

The other thing to notice is that the cams appear to have a different phase.

As the wheel, pulley, head, dial gauge and preparation method were identical (and repeated) the culprits are potentially;

1. The cam itself, as cast and ground.

2. The drilling for the pulley dowel.

I can't say one of the cams is better than the other in that respect, only fitting it all up to an engine and timing the whole assembly would give us an answer.

This goes to show that the final timing of the cam is critical to getting the best out of the part.

I note that Mr. Reaper in his VVC inlet cams thread (http://ift.tt/1tW3FkT) has found a 5 degree discrepancy in his assembly, so a very practical example there of what this can mean.

As a bonus here is the valve velocity at 6000RPM (crank):