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Old 10-13-2019, 12:53 PM   #1
tismy55
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Default BBC 290's Heads

I have a set of casting 290 Heads they are suppose to be closed chamber heads, and it looks like a machine shop has slightly opened them. My question is slightly open good or bad? Thanks for your help
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Old 10-13-2019, 01:42 PM   #2
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One 'good' would be that it's an easy way to lower compression if it was too high. Much easier than changing pistons. One 'bad' is that it forever ruins a good set of closed chamber heads.

I forget the number right now but there is a factory BB head that is known as "semi-open". I prefer closed chambers myself but some guys think those things are the greatest. The work done on your heads resembles that.
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Old 10-13-2019, 01:48 PM   #3
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Would they be worth anything ? with slightly open chambers,and does it help the flow any say like with a turbo etc

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Old 10-13-2019, 03:29 PM   #4
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Quote:
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I have a set of casting 290 Heads they are suppose to be closed chamber heads, and it looks like a machine shop has slightly opened them. My question is slightly open good or bad? Thanks for your help
Those 290's aren't considered "semi-open chambered" from G.M., they are closed-chamber pieces.

That "relief" you're looking at by the spark plugs is how they came from the factory!

They were used on most of the smaller BB builds, both the 396" and the 400". You would find them on the Chevelle's, Camaro's, Vette's (454"/390 HP), Nova's, and the "passenger" line (Impala's).

Thanks, Gary in N.Y.

P.S. On many of our 100% stock-appearing builds with those castings we can make 450+ HP on the 396"/400" platform and 500+ on the Vette's (554"). All on "pump-gas" and all with OEM exhaust manifolds and Q-jet carbs! They are a good number among the resto guys! I have a few sets on the shelf.
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Old 10-13-2019, 03:42 PM   #5
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Would they be worth anything ? with slightly open chambers,and does it help the flow any say like with a turbo etc
Yes, of course they are worth something. Someone that is having pinging problems on a closed motor would love to have that set over a full open chamber.

The closed vs open argument started right after the open heads first came out. Arguments started when GM put out a bunch of propaganda bs claiming a great benefit by having open heads vs closed. Turned out that some guys were losing power by running them though. Kinda funny that GM was getting pressure by the EPA people then to reduce smog by changing the chambers. GM had no choice but to go to a full open to make better smog numbers, so the propaganda was put out there to entice people to buy. A sales pitch.

Hard to answer your second question, mostly all depends on the motor combo.
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Old 10-13-2019, 03:44 PM   #6
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Thanks I appreciate the info. The engine came out of a doner 1970 Monte Carlo.
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Old 10-13-2019, 03:54 PM   #7
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And closed is closed,



Semi-open is between the two,



And open is open,

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Old 10-13-2019, 09:20 PM   #8
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I don't think those 290's have heat treated exhaust valve seats. Anyone know what the first year for that was? Small and Big Block.
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Old 10-13-2019, 10:42 PM   #9
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Induction hardened exhaust valve seats started in 1971. Along with a general lowering of compression ratio on all engines.

One of the biggest problems with open chamber heads or even semi open is compression ratio. Example even a big engine like a 502 needs a domed piston to have a decent compression ratio even with 110cc heads.
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Old 10-15-2019, 11:31 PM   #10
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Induction hardened exhaust valve seats started in 1971. Along with a general lowering of compression ratio on all engines.

One of the biggest problems with open chamber heads or even semi open is compression ratio. Example even a big engine like a 502 needs a domed piston to have a decent compression ratio even with 110cc heads.
Thanks, I wasn't sure when they changed that.
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