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Old 06-12-2003, 07:51 PM
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Open or Closed?

I've got a set of SBC 441 heads that I had on a 350. I'm thinking building another 400, keeping the compression ratio between 9 and 10. Since the 441s were fairly recently rebuilt and they have bolt holes, I thought I'd just have them drilled for steam holes. However, my son says the closed chamber heads produce better power than the open chambers. Any thoughts/experience out there?

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Old 06-12-2003, 08:25 PM
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the (closed chamber?) smaller cc. head will raise your compression ratio above your stated amount, use the 441 heads they flow fairly well, (actually one of the better 76 cc. heads) and will keep your compression ratio at a reasonable level.
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Old 06-12-2003, 08:45 PM
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m12600 the 441 castings will work just fine they are early 70's castings, they will out flow most of the early closed chamber castings because of less valve shrouding however open chamber castings are more prone to detionation than closed chambers, so higher comp. ratios are harder to obtain especially on pump fuels.
high comp. can be compensated for with higher duration and overlap cams however more cam is needed with open chambers than with closed chambers when using the same comp. ratios, also high flowing heads dont mean squat on most street engines that dont see high rpm's , you really need to look at how the car will be driven and what rpm range and type of fuel before you can properly pick a head, small chamber heads also make comp. higher than large chambers sometimes to much, a 400 with most flat top pistons will have around 9.8-1 comp with open chamber (76cc) heads but have 10.2-1 with (67cc) early small chamber and around 10.6 with (64cc) 305 big chambers and almost 11-1 with (58cc) small chamber 305ers witch probably will dissapoint you on the rpm side because of realy bad valve shrouding, anyway good luck hope i could be of some help. c ya mikey
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Old 06-12-2003, 08:58 PM
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you said, open chamber castings are more prone to detionation than closed chambers, is this due to sqish? cause Ive never heard this before, but it would make sense...
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Old 06-12-2003, 09:17 PM
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This is probably a stupid question, but what exactly is the difference in a closed chamber head and an open chamber head? What defines them as open or closed chamber heads?
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Old 06-12-2003, 10:29 PM
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I've currently got a set of Vortecs on a 406 with 12.5cc dished pistons. According to TRW, it should be about 10:1. The engine only has about 1000 miles on it, but I'm apparently going to have to pull it because of a problem with #6 cylinder. I'm a little concerned about the durability of the Vortecs.
I was going to build another 406 as a backup. The only 64cc heads I've got are 3-4 sets on 461/462s, but they don't have the bolt holes. I do have a set of 041s, but they'd need a complete rebuild.

To stfinney: I've been told the 64cc heads were "closed" and the 76cc heads were "open". I don't know if the "squish" area is the cause of the terms.
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Old 06-13-2003, 02:46 PM
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The combustion chamber shape of the 64cc heads promotes more efficient combustion. Not as good as a Vortec, but better than the 76cc heads. Squish, quench, squench, whatever, is something else that also affects combustion efficiency & detonation resistance. Check out David Vizard's book How To Modify Small Block Chevy Cylinder Heads. He can explain it much better than I can. Given equal compression ratio, etc., the small chamber heads, even though flowing a bit less, were good for 20 or so more HP. More efficient means better mileage, too.
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Old 06-13-2003, 04:59 PM
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I do know that its better to use a flat top piston with a smaller chamber than a dome with a large chamber.Cause with a dome the flame has to travel over the hump.
Stick the 441s on with a flat top and call it a day(Hows that for technical??) .You'll be about 9.1:1
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