451RB, SR heads, steel valves, HS 1.5 rockers(measured closer to 1.55), Isky 9375/85 springs @ 250 closed, Comp RT .435 lobe, 302/272/193, 3/8” x.080” pushrods......... peak power at 7200, no indication of issues thru 7500.

The cam was specially ordered via Crane here in Australia.
The original spring pressure recommendations were 180-220 seat and 550-580 open. At the time I spoke them about the spring I had on PACs advertised figures and they gave me the green light. They said the pressures were a little higher than they would recommend, but that’s fine.

I contacted Crane direct at the their office in Olive Branch MS after this happened and the advice was to shim the spring more and after some more calculations I could yielding 280 seat and 640 open and 0.050” to coil bind measured with the retainer.

Im waiting here back from Crane about another issue I found with the cam but will have sit tight.

Their spring recommendation was 180-220 seat and 550-580 open on this cam. And I’m running in excess of that.
I kind of agree with what you are saying about the pushrods. Makes sense.
Should have listened to you and went the Comp .420 lobe.........too hard at the time and this was a comparable gentler lobe similar to that of the Comp.

This cam was not meant to be. First grind they sent me was on 1.100 base circle after I ordered a 1.050. And they ground 264/268@0.050 instead of 266/270@0.050 I ordered.
Apparently this was intentional as I was using a 0.815 roller wheel and this was done to compensate for that?? Might have to explain that one, I’m not sure.
But now I have found another manufacturing defect they are now looking at.
Never ends my friend!

If you wanted to do a test to see if it were more of “float” type of situation, or a spring “surge” situation, you could set up the current springs so they were pretty close to coil bind......... like .020-ish.
This changes to point of resonance, so if it’s a surge condition, it should make a noticeable difference.

I don’t think it would be enough of a pressure difference to add more than a couple hundred rpm to the usable range if the issue is really a spring load issue.

Of course....... the issue could be a little of both....... spring load, and surge.

The short answer is....... the bigger wheel adds some duration if the profile was designed around a smaller wheel.
The lobe design for a 1.050bc is probably done with a SBC in mind........ .750” wheel.
Using an .815 wheel on a .750 designed lobe generally adds 1-2deg@.050.

So I theory, those 264/268 lobes, if designed for a .750 wheel, would measure closer to 266/270 when checked using an .815 wheel.

I just received an email from Crane

Intake 183@.200
Exhaust 178@.200

It’s odd that if the two lobes are from the same lobe family, that the longer duration exhaust lobe(@.020 and .050) would have 5* less duration @.200 than the intake.

Or....... it’s a typo on their part(intake is 178/ex is 183)which would make more sense.

Either way, the .200 numbers aren’t anything unusual for that .050 number.

The Comp .420 lobe with 266@.050 is also 183@.200.

Looking through the Crane lobes..... since you’re having an upper rpm issue..... I’d get this:

LH2 series lobes:
R268/432 intake lobe(298/268/181, .432 lift)
R272/440 exhaust lobe(302/272/186, .440 lift)

Then test it before changing anything else in the valvetrain.