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.

[e philpott]

If you do the appropriate bowl work with the larger valves it should pickup flow, I have no before or after but most of us clean up the ports and open up the throats accordingly when you go bigger valves, I did that on some 2.10/1.65 valves for C1AE's in my 63 Fairlane 390 with mild cam 237/247at .050 with 559/579 lift Lunati solid lifter and 3x2's (not the best intake) run a nice 12.50 at 108 good air and 12.78's hot and humid at Kilkare now called Dorona Xenia in Ohio and real driveable on the street

[dozz302]

Thanks for replies, but I would not touch the heads in any way other than increase valve size. Bone shock engine. If I replaced valves, is there any downside to larger valves? I am thinking no.

[My427stang]

No downside if you have radial valve clearance at the reliefs, which on a stocker I bet there is a ton of vertical clearance and you'll never get close to the piston anyway.

Basically you are doing a seat saver valve, no noticeable bad, no noticeable good.

[pbf777]

. . . . .  but I would not touch the heads in any way other than increase valve size.

     Part of the responsibility, in a reasonably proper "valve-job" requirement, this for the installation of "larger diameter" valves, and beyond just establishing seating surfaces and a certain sum of bowl blending, is also to consider the combustion chamber shrouding clearance; as this is often where the tradeoff in the value gained of a greater valve diameter can become compromised due to the resultant greater shrouding effect.  So, it is often also advisable to "open-up" the valve pocket in the chamber . . . . . some.   

     Scott.

[Joe-JDC]

Your low lift flow numbers will increase, but above ~.400" it will actually decrease or stay the same with the 30* seat and valve face angle.  A 45* seat and valve angle will increase the higher lift numbers and lose a tad on the bottom if you don't blend and do a bit of bowl work.  BTDT for Stock Eliminator flow testing.  Going from a 2.030" to 2.090" may not give you a seat area enough to get rid of any seat deterioration if the valves have sunk much.  You may want to look at going to 2.125" or larger to get the most from any change. JMO.   Joe-JDC

[pbf777]

        Remember, that although the "Flow-Bench" numbers are often the "measure" for the performance potential that a port might possess, the actual real-life function of the port as in service 'is' quite different.  So although many, my self included, will be lead down a path set forth by the flow-numbers (yes we have an SF-600  ), sometimes we find that the best power is being produced by those examples which defy explanation without the use of "some" conjecture.   

        Scott.