Mopar "Purple Shaft" Mystery Cam

General engine tech -- Drag Racing to Circle Track

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DaveMcLain
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Mopar "Purple Shaft" Mystery Cam

Postby DaveMcLain » Tue Sep 12, 2017 10:14 am

Yesterday a customer brought in some 340 Chrysler stuff including the cam that had been in the engine. The cam is a purple painted core and most likely a Mopar Performance grind. He said that it seemed to run pretty good but it was getting a flat intake lobe so I plotted it for him so that he would know the specs of the cam which was unknown to him since it came in the car/engine.

Plotting it I found that it has specs that are very close to the P4120231AE cam except for the lobe separation. In this case that happens to be 106 vs what is listed, 108. Was this sort of thing common on these cams?

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Re: Mopar "Purple Shaft" Mystery Cam

Postby F-BIRD'88 » Tue Sep 12, 2017 11:10 am

You determined the lsa based on what measurement?

.050" lifter rise open close?
seat to seat events? (at some lift point eg: .015 or.020 or at lash point...) or
point of max lobe lifts of in ex?

Different than Chrysler's method?
I believe Chrysler used max lobe lift points....
Non symetrical shape cam lobes create a offset of this
depending on where measured.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby DaveMcLain » Tue Sep 12, 2017 1:21 pm

I use Performance Trends' Cam Analyzer software for this sort of thing. I use their "new" method of finding the centerlines:

Once we were using electronics to measure the cam lobes, we found that the method we were using to determine centerline was not as accurate or repeatable as it could be. We were using several points at near peak lift to determine centerline. Now we go much farther down the opening and closing profile to determine the lobe centerline. This has proven to be much more repeatable, within .1 degrees or better. The old method was repeatable within .5 degrees or so, which was sufficient for the hand measurements we used to do. We recommend setting this to Yes. No should only be used if you want to repeat results from an older version of Cam Analyzer.

In the past other Mopar Performance cams have agreed very closely with their advertised specs including lobe sep which was within about 1/10 of a degrees so this grind is definitely different.

Another interesting thing is that this cam is just like another Purple Shaft hydraulic cam that I plotted in that it doesn't use anywhere close to the .904 lifter diameter which is often talked about in Mopar circles. In fact they both use about .765 of the lifter diameter so in other words they would easily run on a .842 diameter "CHEVY" lifter.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby F-BIRD'88 » Tue Sep 12, 2017 1:30 pm

So what is this "new Method"?

What is the LSA when measured using the .050" lifter rise open close events?

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Re: Mopar "Purple Shaft" Mystery Cam

Postby DaveMcLain » Tue Sep 12, 2017 1:57 pm

If I use the .050 events for the cam the intake lobe is opened 9.2 BTDC and closed 49.8 ABDC for a duration of 239 degrees on a centerline of 110.3 degrees. The exhaust events are: Open 42 BBDC and Close 18 ATDC for a duration of 239.9 and a centerline of 102 degrees. This gives a lobe separation of 106.1 degrees.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby F-BIRD'88 » Tue Sep 12, 2017 2:36 pm

The average of the .050" error of each lobe added together equals the LSA error real close.

I'd bet a physical measurement accuracy problem Mechanical and or electrical.
Wrong follower. Deflection, Wear.

A real Mopar Purple shaft cam should have a part number ID stamped on it.
What is the measured lobe lifts? Other lobes?

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Re: Mopar "Purple Shaft" Mystery Cam

Postby F-BIRD'88 » Tue Sep 12, 2017 2:40 pm

Measure at .100" down from peak lift both sides. What is the timing numbers at this spec?
What is the timing numbers at .006" lifter rise? (hydraulic)

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Re: Mopar "Purple Shaft" Mystery Cam

Postby F-BIRD'88 » Tue Sep 12, 2017 2:59 pm

here are Comp cams "Purple Plus" cam lobes
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Re: Mopar "Purple Shaft" Mystery Cam

Postby statsystems » Tue Sep 12, 2017 3:00 pm

F-BIRD'88 wrote:The average of the .050" error of each lobe added together equals the LSA error real close.

I'd bet a physical measurement accuracy problem Mechanical and or electrical.
Wrong follower. Deflection, Wear.

A real Mopar Purple shaft cam should have a part number ID stamped on it.
What is the measured lobe lifts? Other lobes?


They have never put any numbers on any mopar camshaft like that.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby sjre » Tue Sep 12, 2017 3:23 pm

mopar made some purple shaft cams for circle track with l/s 106 to 108.I remember seeing these in an old direct connection cat.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby PRH » Tue Sep 12, 2017 4:27 pm

P4529958 is the 484/284 hyd cam on a 106.

Just curious what you got for .006 and .200 duration numbers.
Somewhat handy with a die grinder.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby DaveMcLain » Tue Sep 12, 2017 5:12 pm

PRH wrote:P4529958 is the 484/284 hyd cam on a 106.

Just curious what you got for .006 and .200 duration numbers.


For .006 I've got 294 and for .200 I've got 145

There are no numbers on this camshaft but the Engine Power core is painted purple. Another thing is this cam is Parkerized and I know I've seen the Mopar Performance flat tappet cams that are not.

Thank you for that part number. I'll put that in my notes. You say it was offered as a circle track grind for the 340?

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Re: Mopar "Purple Shaft" Mystery Cam

Postby Jeff Lee » Tue Sep 12, 2017 11:27 pm

If that is the .484" Purple Shaft, it was the first cam above the .474” street hemi grind cam which was relatively mild. The .484" cam was a pretty good cam in the day. That’s just my opinion, no dyno #’s but I used it in 340’s and even one 440-6. My fellow Mopar buddies at the time agreed that for a hydraulic cam, it ran just about as good as the .509” PS cam which could have PV clearance issues that the .484 PS cam did not have.
.484” was good for 7,000 RPM all day long with Isky adjustable rockers with slight pre-load. Loved my 340’s!
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Re: Mopar "Purple Shaft" Mystery Cam

Postby Geoff2 » Wed Sep 13, 2017 4:37 am

The 58 cam is also in my Mopar Perf catalog, 284/284/106. Pretty old catalog, 1996.

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Re: Mopar "Purple Shaft" Mystery Cam

Postby DaveMcLain » Wed Sep 13, 2017 10:03 am

PRH wrote:P4529958 is the 484/284 hyd cam on a 106.

Just curious what you got for .006 and .200 duration numbers.


Thanks for that info. I was just using on line resources and I didn't find the one on a 106. At least now I'll have some good info for the customer.


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