Beneficial to put CJ valves in a 390 GT Head?

[dozz302]

Hello, just wondering if anyone has ever done a comparison on putting the larger CJ valves in a stock 390 GT head.

[Urgefor]

Hello, just wondering if anyone has ever done a comparison on putting the larger CJ valves in a stock 390 GT head.

I have put larger valves in a set of c4 6090g heads with no other work.  Flow numbers before and after were in essence the same.

Also, this question would probably be better suited for the fe technical forum versus private classifieds forum.

[dozz302]

Thanks

[My427stang]

From a flow perspective with no other changes, no improvement

However, you gain a fresh seat surface and with a modern multi angle seat cutter you gain a little. 

With some rubbing depending on casting the gains climb to 40-50 cfm

[bluef100fe]

There’s gains to be had if you do some bowl blending, guide shaping, and short turn massaging. Also as Ross mentioned you gain some fresh material to land a good 3/4/5 angle valve job on. A word of caution, it’s really easy to do a bunch of grinding in this area of the FE head, and either not gain anything or potentially make the head worse. I’ve been farting around with iron FE heads and 385 series heads for 25 years and have gone backwards plenty. Just part of the game until you learn the shape each head likes and where not to grind lol. Good luck.