I dynoed a SBC dirt modified motor for a customer a few years ago.
They had been running the car for several events but it just wasnt competitive, so they brought it in to have it tested to see how it stacked up.
It ran beautifully, sounded real good, and had pretty good throttle response...... But it was way way down on power...... Like 100hp or so.
These are pretty bread and butter combinations. If you use A,B,C, and put it together right they all make about the same power. Something has to be pretty screwed up to be off 100hp.
I suspected the cam was in wrong, but the builder(whom I'd worked with quite a bit over the years) assured it was degreed in properly.
"Normal" cranking pressure for these is over 200psi.
I tested one cylinder quick and it was only like 150-160.
After some discussion and exchange of ideas, I tested a few more cyls.
The pressures were all over the place. A couple close to 200, a few down near 100.
I leaked it down........ It had a bunch of bent valves.

Took the motor off the dyno and they took it home. They pulled it apart, and after disassembling the heads found almost all the valves were bent. Some a little, some a bit more.

They can run just fine with bent valves....... But they won't make any power with bent valves.

I will say this, If I hadn't tested that motor myself and saw how good it ran, I never would have believed it could have run so good with the valves so screwed up.