GM 076 Head valve length and valve seat

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67 Nova
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Re: GM 076 Head valve length and valve seat

Post by 67 Nova » Mon Jan 15, 2018 11:09 am

Kenny,

You can get 380+ CFM out of the 2.250 valve. My 475" ZL-1 with cast intake FINALLY got some good dyno results. It's long and a lot of info, but check out my first post:

https://speedtalk.com/forum/viewtopic.php?f=1&t=48195

"- 1969 "074" heads ported with 2.25/1.94 valves, flow 380/278 on 4.350 bore fixture"

I'm more concerned with that BIG BIG lift cam?? Rocker studs get pulled out all the time, and with that much lift could very well be questionable of keeping the heads together at all.

Also that intake your using??? I've not ran one, but from what I have seen, the STOCK "198" might work better, or try a C427X!! Just some thoughts. Not many seem to like that intake FYI.

67 Nova
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Re: GM 076 Head valve length and valve seat

Post by 67 Nova » Mon Jan 15, 2018 11:13 am

GOSFAST wrote:
Thu Jan 04, 2018 2:05 pm
Kenny M wrote:
Wed Jan 03, 2018 12:25 pm
They are the D ports that had the tongue in the Ex port, but it has been removed. Again I'm looking to see if there is any problems opening up the stock seat for a 2.300 valve.
Just to (help) keep the record straight, the "074's" had round exh ports an NO "vanes". The "D" port and "vanes" come out after on the "077" castings. The G.M. part # was 014011076, the casting # on the head was 14011077. Photo below on the exh runners. We get an easy 350 CFM in and 260 CFM out staying with the OEM valve sizes (2.190" int x 1.880" exh), 3/8" stems!


The original "074's" and "077's" had 290/295 int runners, 2.190" int valves, and 1.840" exh valves!

These castings were designed at the time around the 396"/427" platforms, hence the smaller runners.

Going for memory I doubt very much fitting a 2.300" valve in the existing int seats!

Thanks, Gary in N.Y.

P.S. I can add this with respect to both the "074's" and the "077's", we see 500/550 HP on many of our 396" pump-gas builds. The "077's" do have an edge getting there over the "074's".
Gary, not to dispute, but my CASTING numbers say 3946074 BUT are "D" port. I don't know how to post images?????

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Re: GM 076 Head valve length and valve seat

Post by Kenny M » Mon Jan 15, 2018 12:22 pm

I will be using the Jessel Pro series 1.8 1.7 shaft rocker stands. .490 .460 lobes.

67 Nova
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Re: GM 076 Head valve length and valve seat

Post by 67 Nova » Mon Jan 15, 2018 1:27 pm

Kenny M wrote:
Mon Jan 15, 2018 12:22 pm
I will be using the Jessel Pro series 1.8 1.7 shaft rocker stands. .490 .460 lobes.
That should help. I had mine sent in for vacuum sealing and some cryo work as well. But I'm not running shaft mounts and only low .700 lifts with some easy ramp speeds.

Are you going to weld them all together like the big chief stuff??

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Re: GM 076 Head valve length and valve seat

Post by Walter R. Malik » Mon Jan 15, 2018 5:52 pm

The Jesel shaft mounted rockers I have used for standard B.B. Chevrolet engines only have the intake rockers on a common mount. The exhausts are still individually mounted so, different heli-coils should be installed to lengthen the thread depth within the head and use longer bolts holding the exhaust rocker stands in place to match the deeper threads.
Has Jesel designed a different set-up from that ?

A 2.250" intake valve diameter on 50 degree seats should be adequate for those heads and that application.
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Re: GM 076 Head valve length and valve seat

Post by cpmotors » Tue Jan 16, 2018 11:07 am

Kenny M wrote:
Tue Jan 02, 2018 9:22 pm
I'm Looking for a idea of what valve length would be used on the old GM BBC 074 076 heads with a valve lift of .870?
Also can the stock OEM intake valve seat be opened up safely for a 2.300 valve.? I will be going with a jesel valvetrain.

Thanks
On a 781 iron casting I used a Ferrea F5031/F5035 with 5.271"/5.425" OAL for .800" lift, PAC R505 retainer, for 2.000" IH.
Couldn't say on the seat ring.
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