GM 076 Head valve length and valve seat

[Kenny M]

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

[mag2555]

I have never set up aBBC for more then .750" lift , but what I can tell you is your likely to need some dam long valves, like 5.494" overall with a installed height of over 2.100".
Your likely to need retainers that move the keeper groove up .050" to do this installed height.

It's a total waste of time and money to stuff in 2.300" valves into this head as even if you knew what you where doing porting wise to make good use of that size valve there just is not enough port wall thickness nor short turn height to get the most out of it!
Also not to mention that the amount of unshrouding needed in the chamber to not choke off that valve size would greatly cut into your compression ratio.
If your not planing on doing any porting to the Heads Intake side then stepping up to 2.250" valve if you have a 2.19" now with a proper detailed valve job will pick you up a nice chunk of flow, andif you have 2.06" valves now then going up to a 2.19" would be all you should go!

And by the way the Exh side of the heads like the ZL1 suck even worst then the standard 1.76" valve iron heads at low lift and there not really anything to write home about at high lift either!
They need the bigger valve of 1.90" to get killer low lift numbers along with somewhat better high lift numbers.

I believe David Vizard had a great book on BBC heads that I have yet to read , but I am sure that like all of his books there worth way more in good info then what you pay for it!

[Newold1]

Is there an important reason that you are now planing on using this particular iron head and asking about attempting what you are trying to accomplish??

[Kenny M]

These are the 1970s GM Aluminum Heads. They have a 2.250 valve in them now. 320CC port and flow 360cfm ported . I'm looking to get them to flow in the 375 range with a 340 CC port. They are for a vintage drag race class.

[mag2555]

They are round Exh port ?

I have seen where they have been ported into the 390 numbers on the Intake side with a 2.300" valve, with 280 out the Exh side which is not that great even if you factor in 4% more flow from tuned Headers your still at only 72%!

I would seriously concider having the Exh port floors built up to a far better D shape on those heads and rasing the roof to complement the floor and get those Exh numbers into the 310 cfm range

[Kenny M]

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.

[pdq67]

It might be in the old Hotrod book, "How to Hotrod BBC's", that say's that the 2.300" valves are too big even for the 494"/500"/510" CanAm engines so please think hard before doing this. Just because GM made 2.300" intake valves doesn't mean that they are that good to use!

pdq67

[mag2555]

Another question here Ken.
Why do need 400 cfm, how much hp are you looking/ needing to make?
Your gonna need a dam good / big Intake Manifold also!
Please give more details on your build if you would?

[Kenny M]

700+ With a very old well ported twisted Scorpion and a ported 4780..This is old school...496 4500 bore.14to1 285 290 112 870 800
I'm shooting for 380CFM. I'm very close now with the 2.250 valve.

I pick up air flow with a 50" valve job But I am concerned that if I open the seat up for a 2.300 valve and seat may get too thin.. That's my Main question, Not how to make HP.. But know one seems to have the answer, so I will figure it out. or stay with the 2.250

[Old School]

700+ With a very old well ported twisted Scorpion and a ported 4780..This is old school...496 4500 bore.14to1 285 290 112 870 800
I'm shooting for 380CFM. I'm very close now with the 2.250 valve.

I pick up air flow with a 50" valve job But I am concerned that if I open the seat up for a 2.300 valve and seat may get too thin.. That's my Main question, Not how to make HP.. But know one seems to have the answer, so I will figure it out. or stay with the 2.250

I would stay with the 2.250. I don't think your heads have enough for 2.30. I have a set of 074 that EPD did in 1979 that were on a pro stocker of the era. They flow close to your intake but less than your exhaust. I have had them on everything from 468 to 557 engines. I thought the exhaust was holding the power back,espescially on nitrous so I swapped them for a cnc set of Brodix 2x with much better flow numbers. The car ran exactly the same on engine and on nitrous.

Will this be a stick shift car? If so the cam should be fine. If an auto trans I would cut the intake duration back to the 278 range. For maintance sake I might also cut the intake lift back to the .830 area.

How fast do you have to run? What car and what weight? Rules?

[GOSFAST]

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!

An important note on BOTH these castings, they absolutely needed the longer bottom exh rocker studs installed as a precaution!

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".

[MadBill]

...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!

I have Oct 1969-cast round port ZL1 heads on my 495" BBC. When I stuck my thumb in a port during flow testing, it got quieter and picked up over 10 CFM, so I fabbed stainless steel D port-conversion 'tongues', which together with 1.92" exhaust valves brought the flow up to 270 CFM @ 0.800".

On the dyno, the inserts picked up over 10 lb-ft. @ 4500 RPM and then turned inside-out from the heat.

[Kenny M]

My mistake... These are 077 Heads.

[mag2555]

If your running 14 to 1 then 330 cfm should net you well over 700 hp if you have enough port area!
For a 2.300" valve to function well with a 50 seat your Throat size should be 2.07" and the port circumference ( not area ) behind that should be 6.499".
I have made 750 hp many times on 14 to 1 500 cid motors with only 340 cfm passing thru 2.19" valves!

[randy331]

even if you factor in 4% more flow from tuned Headers your still at only 72%!

So why would that matter ??

Randy