It could be from the cylinder wall but the two guys I was working with could never nail it down.
We thought the steeper seat angle should have allowed the air to be “stood up” for lack of a better term.
In fact, this all started because I was doing a bunch of 50 degree stuff and some 55’s and I was at another shop. I was heading back to the dyno but I stopped in the assembly room to visit with the owner a bit.
And there on the floor was a cylinder head from HRD (I can’t think of the name of that guy now but I think his last name was Dixon) and without measuring it I said those heads have the same 55 degree seat I’m using.
He called BS so I ran back to the shop and grabbed the cutters and it was the exact same.
He wasn’t going to flow them because they were late getting there so I said I’ll grab one and flow it for you.
When I gave him the report his wasn’t happy with the dip. I said I know it’s there, but I haven’t figured out how to get it out yet.
Then he pulled out the report from the heads before they went back to HRD for upgrades. And the 45 didn’t have it. He then flowed them and the dip was there.
Certainly there is a reason for it. We collectively spent way more time to sort it out than we should have. Even HRD (at that time) didn’t have an answer for it
That was when we both bought different tooling and tried to get rid of it. When we did it lost power. Every time.
It may be sorted out by now but I haven’t really tried to figure it out since about 2004.
Oh yeah, lol we had the brain storm of top cutting the valve. I forgot about that one. I tried a bunch of different angles and widths and I found a couple that looked like they’d be killer and it got rid of the dip.
That was worse than changing the valve job. I think that engine was making 2.2-2.4 HP/CID at 9k plus. And top cutting the valve killed power everywhere.
We started talking about changing cam timing and the owner of the engine was on the phone with Comp looking at different loves and such. I took the head back to the bench and reverse flowed the head with the top cut valve and without it.
The reverse flow was staggering. Now that I think about it fuel consumption went up and power was down.
We decided that it was easier (more cost effective) to shelve the cam timing tests and just not top cut the valve and live with the dip.