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Old 12-04-2012, 04:48 PM   #719
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Location: AZ
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I forgot to post this in here when I first did the data collection, but here is a comparison of the EJ255/257 cams to the EJ207 cams.

Without much data available on the OEM cams and their specs (or more specifically, a lot of rumors), I decided to gather my own.

So far, I have acquired the following cams:
EJ257/255 (Thanks, Jay!)
EJ207 V8 Spec-C
EJ207 V9 (Thanks, Alex!)

Here are my results:

I made a fixture out of wood. The cam supports were cut to support the shaft on the 38mm and 30mm journal sections and keep the center line of the shaft parallel to the desk top. After repeated loading and unloading of the fixture, the method proved repeatable and stable. I performed each test with the help of a friend (Thanks Mac!), who double checked my data.

EJ257/255 Cams have greater lift on the intake side. The exhaust cam is nearly identical to the two sets of EJ207 cams, with a slight bit more lift. Both sets of EJ207 cams are virtually identical, which is to be expected based on part numbers.

Lift is easily measured with calipers, but what I was really curious about was duration. If you've ever shopped for cams, you know every manufacturer has their own methods and standards for determining duration.

In the domestic world, which has spilled into the import world, it is common for manufacturers to specify duration from 0.01 inches through the lift cycle, back to a lift of 0.01 inches. The reasoning behind this is that any lift below 0.01" is not significant for flow and should not be considered.

In the import world, different values are used. Some measure from the first hint of lift (as I did below) and others measure from 1.0mm or 1.3mm or other combination measurements meant to give a feel for the shape of the lift curve.

This is all very hard to comprehend by reading a spec sheet. Because of this, I decided it would be useful to simply plot the whole lift cycle for various cams and overlay them. The area under the curve is what I think is important and can tell a good amount about the cams.

Please note that my "duration" is simply from first lift to last lift. This value will be much greater than what the manufacturers specify for the reasons listed above. Crankshaft duration is double cam duration due to the ratio for the crank turns to the camshaft (count your pulley teeth if you don't believe (24:48)). Again, my duration value isn't as important as the plotted data.

Feedback is welcomed. I am learning as I go with this and I'm simply trying to add to our knowledge base here.
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kpluiten is offline   Reply With Quote