Don Terrill’s Speed-Talk

The owner of these heads wants to have them flowed, I also want to for my own curiosity. I won't be flowing them and grinding a little at a time though. I don't have a bench (yet) and the guy who flows my stuff is about 45 mins away. I'll probably just drop them off and they flow what they flow. I want to get my own bench so I can mess around with stuff like this. Would be nice to spend a day with the pitot tubes and some clay with those. I'm sure I would learn a lot, or just enough to get myself in trouble.

Mild port work is easy to kick those heads up to 325cfm range no problem at all.I’m betting you close now. A stock set of cc heads typically sit in 280-290 range.

Had them flowed with and without the plates. The intake port the plates hurt the flow, the exhaust port it helped the port carry a few more CFM past .500" lift where without the port backed up.

Thats what we typically do run the exh plate only. Ive built some of these to run in mud trucks. The exh plate will give you big gains in truck for whatever reason. The one i did we never Dynoed but it picked up significantly in mud pits. We have seen the same drop as you with plates on bench. I often wondered if you raised roof of port some to get the volume back you lose with plate would it help. The Clevelands have a deceiving port shape and while they look way oversize they actually work well even at modest rpm. The last pump gas Cleveland i did for mud bronco peaked on dyno at 5900.

Bench operator said that they were unstable or turbulent flow between .500 and .600 both with and without the plates. From what I've read on here and abroad that is common with Cleveland's and you can chase your tail trying to fix it. The factory valve seats have that undercut below the bottom cut and I wonder if that is some of it. The seat modification that was spoken of on this thread I wonder if it would not help this.

cgarb wrote: ↑Sun Dec 13, 2020 5:19 pm Bench operator said that they were unstable or turbulent flow between .500 and .600 both with and without the plates. From what I've read on here and abroad that is common with Cleveland's and you can chase your tail trying to fix it. The factory valve seats have that undercut below the bottom cut and I wonder if that is some of it. The seat modification that was spoken of on this thread I wonder if it would not help this.

We never gad to many issues with turbulence heres a set done for sons mud truck on 408 400 base engine. That engine made 560@6200