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FE Power Forums => FE Technical Forum => Topic started by: dozz302 on November 03, 2025, 12:21:06 PM

Title: Beneficial to put CJ valves in a 390 GT Head?
Post by: dozz302 on November 03, 2025, 12:21:06 PM

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

Title: Re: Beneficial to put CJ valves in a 390 GT Head?
Post by: Urgefor on November 03, 2025, 01:04:31 PM

Quote from: dozz302 on November 03, 2025, 12:21:06 PM

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.

Title: Re: Beneficial to put CJ valves in a 390 GT Head?
Post by: dozz302 on November 26, 2025, 07:52:27 PM

Thanks

Title: Re: Beneficial to put CJ valves in a 390 GT Head?
Post by: My427stang on November 27, 2025, 07:53:33 AM

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

Title: Re: Beneficial to put CJ valves in a 390 GT Head?
Post by: bluef100fe on November 29, 2025, 08:40:28 AM

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.