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://www.speed-talk.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.
GM 076 Head valve length and valve seat
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Re: GM 076 Head valve length and valve seat
Gary, not to dispute, but my CASTING numbers say 3946074 BUT are "D" port. I don't know how to post images?????GOSFAST wrote: ↑Thu Jan 04, 2018 2:05 pmJust 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".
Re: GM 076 Head valve length and valve seat
I will be using the Jessel Pro series 1.8 1.7 shaft rocker stands. .490 .460 lobes.
Re: GM 076 Head valve length and valve seat
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
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.
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
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.
Pete Graves
CPMotorworks,Inc.
Custom Engine Machining
Cylinder Head Fixture for Vertical / Surfacing Mills since 2008
CPMotorworks,Inc.
Custom Engine Machining
Cylinder Head Fixture for Vertical / Surfacing Mills since 2008