What are peoples thoughts on the large split duration of many off the shelf cams? Many Crane cams have close to 10 degrees more on the exhaust to help out the poor exhaust flow of stock gm heads, but most aftermarket heads have much better exhaust ports. Does less of a split, say 2 or 3 degrees work better on a good after market head?

In some cases, the custom cams have actually made less power and proven less reliable than a well designed/picked off the shelf cam.

Lot of variables on that i think. I think some of the custom cam guys tend to overshoot that concept. They start looking at exhaust flow numbers, that may be false. Like some heads advertise big flow numbers on the exhaust, but when you take the pipe off , they dont really flow much better than some other comaprable heads.

I think there's some merit in that, with better flowing heads. For instance, my cams were spec'd with less of a split than I was running previously with Merlin heads (now AFR 357 CNC). I also went went from a solid roller to hydraulic. I also had the benefit of running the solid roller with the Merlin heads and also the 357's. When I built the new engines last winter, they were basically the same (a few cubic inches "less") and I picked up a decent amount more power with the new cam and roughly 3 mph increase in my heavy old resin bucket.

What we did was work backwards from the Crane solid cams that I had in my engines and designed a hydralic cam that was similar in duration (converting solid to hydraulic) and maximized the lift profile, splits and LSA to work best with the heads.
https://youtu.be/xzefrv28RE0 https://youtu.be/lEqFPYBB6Vw

Sounds awesome!! Those 357cc heads must really turn on with some rpms.

Thats kind of what I was thinking with the split, but agree with Mild that there is a lot of other things going on. I'm will be running 4 degrees more on the exhaust with dart 308s, but my buddy will be running 10 degrees more (731 cam), but he has 188 heads.

I don't think custom cams should be bought untill YOUR actual heads have been flowed.

Advertised "marketing" numbers shouldn't be used.

You are correct flow numbers are for marketing purposes. When you start bumping elbows with the top cylinder head guys in the country they don't provide flow numbers for cylinder heads. Why? Cause flow numbers don't mean anything and that's not how a proper port is designed.

And yet almost every cam company/ cam designer, wants flow numbers to design your cam.

I have never had any issues ordering cams without flow numbers.

Really ? Ive had marine kinetics ask for flow numbers, jones camshafts ask for flow numbers, bullet ask for flow numbers, and even my controlled induction cam software wants air flow input to design a cam.

Sure, if you are using an off the shelf head where the cam guy has those numbers in his notes, its not needed. A custom ported cylinder head, i havent had a cam company tell me "flow data not needed "