They will go mid 300’s if you work them. Took me a good bit of time to get mine there. And some welding.
Like I mentioned, if I was doing another set I wouldn’t pick up a grinder until the seats had been changed out, the spring pockets welded up and the guides replaced with a .500 OD piece that wasn’t the junk they come with.
If you get a 2.125 valve in there I’m confident they’d get 400 or close to it.
I had a 2.100/1.600 in mine and no way would I use that big 1.600 valve again. In fact, you may be able to get a 2.150/1.500 combo but it starts getting tight.
