Diggin' a little deeper.
This all pretty similar to what Bill does for the 289 heads that have to run FIA prep in vintage (ie: stock castings)?The difference most of the time is what you're working on. They both have there place 5/16 is more of a race part. 8mm is more OEM type. (Keeper and retainer packages can be wildly different). Its all about what you are used to.
OEM Performance Replacement stuff is typically a day away at half price. But if you cant find something that will interchange with what you're working on than custom or race parts are what you need. SBF has always been an easy swap with some kind of chevy valve. Our Y Blocks not so much, they need +.200 with a 1.94 diameter and that is just not a common part so we buy those deep. Its all about what you're working on.
The FIA european spec 289's that we build will typically have either production 289 head castings or the better C6FE heads, depending on the chassis engine is going into. We run 11.25 CR compared to EMC max of 10.5. FIA mandates correct vintage heads and blocks, flat tappet cam and lifters,stock type rockers-- NO ROLLERS ALLOWED!The only intakes allowed are the stock Shelby's,performer rpm,or webbers. Obviously, this makes it tougher to make reliable power. Typical output is 380 tq and 450 hp with production passenger car heads and 20+ more with the GT-40 C6FE heads. In USA 289 engines we are allowed to use the better 351W and C6FE heads and high compression ratio.500+ hp common. Some sanctioning bodies like SVRA allow aftermarket iron heads and roller valvetrains.580+ hp achieved with proper budget B production 289's .Performer RPM intake still required.T/A 310 cid versions 600+ with dual plane, 620+ with Vic Jr. Because of the way the rules are written, we never build any 289's with C5AE production heads and roller valvetrains. If we did, power in the 500 neighborhood is possible. Peak hp would occur at a higher rpm than scored by EMC though.
Since we are on 289 heads... Here's mine... ported these right before all the aftermarket stuff came out. (Well, the AR SBF was out, but I couldn't afford those. lol) These were daily driven 100 miles to college, then 40 miles each way back and forth to work from there. Ran 10.63 @ 126 in a 3300 lb 1966 mustang with a stock Toploader 4-speed... and a 200hp nitrous plate. Went 7.48 @ 92 in the 1/8 n/a. SFT 236/248 @ 0.050 @ 110 (Comp 282S intake, Comp 294S exhaust) Daily driver street car that embarrassed a LOT of cars street racing that should have beat it on paper back then... as ALL small block Fords were slow before aftermarket heads came out. lol
An intake bowl eventually cracked, so I drilled a hole to clean/epoxy the water jacket side of the crack with JB Weld. (see first picture) Ran the heads for YEARS after that without issue. After they had been run for 12-15 years with the occasional freshen-up, I sent one of them to get flowed. With the old valve job, they went 217 intake and 176 exhaust. May have the full sheet somewhere. I don't have a flow bench, and did these decades ago as a kid. Just an amateur compared to most of you. I did take them off every year or two to touch up the port job. Would use the carbon tracks to see where the dead areas were.
Chambers are probably too big, and the exhaust ports had the ugly air port... C6 castings... and likely ended up too big as well. 1.94"/1.60" valves. The left side of the intake port has an S curve in it. I make it a straight shot to the valve, and try to center the guide in the port the best I can. (Do NOT try this on a 351W head... or you will find water. lol) Intake ports ended up at 155cc. Stock is supposed to be 126cc. Takes a LOT of grinding. I also make the exhaust roof a straight line from the roof of the port exit to the top of the bowl... grinding out all the valve guide and boss that sticks out. Dove rockers and very little guide wear over the years.
I did these with STONES and a 2500 rpm hand drill. No carbide. The longer stones were hard to find before the internet. Hours and hours and hours... lol
It became an addiction. lolYour story reminds me of alot of my first 289. Valve sizes, porting ideology, and tons grinding time. Even your 351w learning, I bet I've put holes in those heads right in the same places. I'll bet your engine impressed you enough to want to keep playing with engines though. The 351W heads never impressed me for 289 and 302. A whole point of compression lossed was hard too swallow.