Power Valve Selection
All this tells me is you don't know how to set ignition timing at idle on a Mopar. The proper procedure to set ignition timing at idle is to set the factory spec with the vacuum advance DISCONNECTED. Then you hook up the vacuum advance.
I can't tell you if he knows this, but I can tell you he's
been told a bunch of times.
It's also the same for many other makes and models - its a method widely used.
Even the '65 Pontiac FSM provides initial with vac adv disconnected (where it differs from Mopar and also many
others is connecting vac adv to manifold vac. instead of
port above the throttle plate)
I really want to know if you've ever tried to hot start a 440 with 35° of advance at idle.
Hell he said he made his own
custom adapter to make a GM distributor mount on a 440.
Look, I said it was a guideline, and it is. To say it isn't "founded in engineering" is just being overly dramatic, it's an accepted guideline that still appears in Holley literature regardless of its origin. Is it perfect? Of course not, I didn't say it was. And again, the OP does not have a radical cam.
You're welcome to your opinion, and I'm welcome to mine. The engine needs to go rich when the load increase gets the combustion so hot that NOx production shoots up. If we want to find a relationship between more aggressive cams and vacuum at idle, we can find plenty of data that shows more aggressive cams tend to lower idle at vacuum. This would result in selecting a lower power valve opening when in fact most hot rod/race engines will need enrichment at less throttle and higher vacuum.
There's a reason that most Holley's come with a 6.5 PV, because most gasoline engines will work well with that PV. If you have a more aggressive cam, then you need to LOWER the PV rating so it's not open more often than it should be.
Sorry you got offended by my characterization of Holley's guidance, but the engineering (such as in Larew's book) shows the opposite.
In the Holleys that Chrysler used in the late 60s HP v-8s, an 8.5 PV was specified.
The original 3310 (yes for a Chebby) came with a 10.5 PV on the primary side.
IMO Holley in recent years is like MP was in later decades - the people there only repeated what they had been told or heard - the techs and engineers who knew their stuff were long gone.
I agree the XE274 is not extremely radical, but it is more radical than factory. Therefore it could use a bit more initial timing than factory.
Here's a set of guidelines
Factory V-8 Engine and Cam Specs by Year 1965-1975
I agree an AFR gage is not needed. I also agree a vac gage is not needed, but can be helpful in testing what is happening before the PV opening point. I think we agree the goal is tune for performance. Performance being whatever calibrations produce the strongest power for the condition being tested.