Compcams CRB XE 268H -10 cam

[polyjohn]

So we tried to fit this cam into our 1969 440 to replace a 509 Mopar performance cam.
We spent out on a Cloyes rollerised 3 bolt chain set and...

On checking the cam timing at 50 thou lift it was nearly 30 degrees out!
So we re-set the chain with maximum advance and still over twenty degrees out.

After about four hours of head scratching we moved the chain one sprocket advanced.
Now with the maximum advance (we calculate) we can get close to the correct setting.

Pictures to follow when I can load them DOH!
How can this set-up be so WRONG???

 

[Don Frelier]

 

[gtxrt]

check it with the old chain and gears. think the cam could be that off I don't ?

 

[6PKRTSE]

Yeah, something doesn't sound correct. I would try the old chain and gears for mock up as well if you still have them.

 

[polyjohn]

OK, this is what is wrong!

Compcams gives instruction example to find Intake centreline @106 in the manual (not cam-card)
That is what we did and it was fine, but not actually written the cam-card.

So we followed the @50 for intake and exhaust and both were a mile out!

Intake BTDC 28 @50
Close ABDC 60 @50

Probably about 20 degrees out showing 8 degrees BTDC @50.

So I have now checked the 268H single bolt cam-card and guess what?
It gives the same numbers, BUT NOT @50....

 

[PRHeads]

Intake BTDC 28 @50
Close ABDC 60 @50

Since Comp has been taken over by Edelbrock, the cam cards are just wrong, in many cases.

28btdc/60abdc = 268*
The XE268 is not “[email protected]”…..so that info is incorrect.

The cam itself is actually [email protected] on the intake side, so for a 106 intake c/l the .050” timing would be:
6btdc/38abdc

The 28/60 numbers are the specs for .006” tappet lift(advertised duration).

I’m sure the cam itself is fine.

 

[6PKRTSE]

Yes, things have been a disaster since the Comp/Edelbrock merger. It seems almost everything is out of stock, especially in all the F.A.S.T. products. Anything special order such as custom grind cams usually takes much longer. If they even have the cores in stock to grind them. Most cases they never have the cores anymore.

 

[PRHeads]

A little tip that some might find helpful if they find themselves in a similar situation as the OP, where the cam timing numbers aren’t making sense.

To see if it’s really as far off as you think it is, try using the old school “centerline” method.
Don’t overthink it.
Line up the dots on the timing set, zero out the timing pointer and the wheel.
Find peak lobe lift, then back the crank up more than .050 worth of lift(like .100-ish).
Slowly rotate the crank in the forward direction until you’re right at .050” before peak lift.
Write down the number the pointer is at on the wheel.
Continue turning the crank, watching the indicator go up and over peak lift, and back down to .050” below peak lift.
Write down the number the pointer is at on the wheel.
Take the two numbers you wrote down, add together, divide by two…….that’s the centerline.
No info from the cam card required.
For cams that are quite asymmetrical, there can be 1-2deg difference in the measured c/l between this method and using the open/close points…..but it will show you if you’re close, or indeed way off.

 

[polyjohn]

That's exactly what we did PRheads, but they don't give a Centreline number on the cam card,
The 106 is in the instruction manual (as an example) which we copied many times.

They give instructions for the centreline method but don't actually print it?
Then only give bogus @50 numbers for every measurement.

Life is supposed to be easier in the 21st Century.
We all know roughly what stuff should be from experience.

Anyone fitting this cam, with this card would have a coronary...
It sure got my mate confused and he builds 3000hp hemi engines...

Its written down and you follow it, without thinking its WRONG!
Why do they do this crap to their loyal customers???

 

[PRHeads]

Well, I don’t build 3000hp Hemis, but I knew what the problem with your cam card was as soon as I saw the numbers you posted.

If you understand what’s going on with cam data, having the cam card is simply a “convenience”.

In any case, the 28/60 numbers, which are @.006, do in fact tell you the suggested c/l is 106.
268/2 = 134
134-28 = 106

Of course, where to actually install it is up to the engine builder.