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Old 12-14-2005, 09:10 AM
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open/closed chamber heads

what is the difference between open and closed chamber heads? also i just rescued a 68 L36 convertible vette. 4 speed. everything is there but... its kind of a basket case without the basket. however, the frame is solid no rust. i would like to make it original, but hurricane charlie turned the 427 to a ball of rust. i haven't tore into it to see if it salvageable. if i can't make it original i am going to hot rod with modern stuff, you know, put more into it than it's worth. any way i have a 1987 454 targetmaster truck engine 2 bolt main 2.19 valves is it worth putting @ $1,000.00 of machine work into plus all the other stuff. just looking for opinions. thanks jim

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Old 12-14-2005, 10:28 AM
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Closed chamber heads have a combustion chamber that resembles a bathtub, has quench area on both sides of chamber. Open chamber heads have the spark plug area of the head laid back to the edge of the cylinder to form a larger combustion chamber. This promotes better flow in and out of the chamber and lowers emissions because of the lack of quench area on one side.
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Old 12-14-2005, 11:59 AM
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Here's pictures of Ford Cleveland open and closed chamber heads. (ignore the arrows)
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Old 12-14-2005, 02:14 PM
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open chambers have bigger combustion chambers (118 to 123 cc) and tend to flow better due to unshrouded valves and slightly larger oval ports.

closed chambers have smaller chambers (100 to 112cc)

Closed chambers were needed to get the compression up on the smaller 396, 402, and 427 engines. A 454 can build compression with open chambered heads using only modest domed pistions due to the larger displacement of the 454.

Most 396. 402, and 427 replacement domed pistons are designed to work with closed chambered heads. And 454 domed pistons are set up for open chambered heads.

Go with the 454. I perfer the 454 over the 427 based on the theroy, more cid will make more hp and torque.
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Old 12-14-2005, 02:38 PM
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You can build compression by cubic inches alone? Man I may need to re-think things then. Seems to me that a 118cc head will need the same height dome to get the same compression no matter what the bore size is.
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Old 12-14-2005, 02:56 PM
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Quote:
Originally Posted by BBCMudbogger
You can build compression by cubic inches alone? Man I may need to re-think things then. Seems to me that a 118cc head will need the same height dome to get the same compression no matter what the bore size is.
More cubes pushed into the same size space = more compression.

.030 overbore isn't much..... 1/4 inch stroke is a lot !!!!!!
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Old 12-14-2005, 03:29 PM
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Yep, more cubes will make more compression when the combustion volume is constant.

For example, build a 427 and 454 with the same cc heads and same domed volume in the piston. If the 427 is 9.0:1 cr then the 454 would be 9.5:1cr.

Then why not just use a bigger dome? Bigger domes slow flame travel. It is always better for flame travel to make the desired compression with the correct sized chamber and flat top pistons.
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Old 12-15-2005, 05:44 PM
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Is it safe to assume that by rule of thumb rectangular port heads are open chamber and oval ports are closed chamber? In some limited research I have generalized that oval ports are limited in their RPM potential by lack of flow as compared to rectangular. I have this 402 and was considering having a set of pistons made with the open chamber design in order to get the rectangular flow up to 7000 rpm.........unless there is a good oval port closed chamber aluminum head out there. Budget won't support a new block!
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Old 12-16-2005, 08:10 AM
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No, you really can't assume that. Here is a site that might help.
http://www.nastyz28.com/bbcmenu.html

Both rectangle and oval ports came with open and closed chambers.

The "good Oval Ports" (049 and 781) will flow as well as the rectangle ports up to 0.550" lift. And in most cases, the ovals will out perform the rectangle ports especially if a little head work is done on the ovals.

Open chamber heads flow a little better than closed due to less material around the valves.

I recently had some bigger valves install in a set of stock 402 heads and did a little bowl work. The heads flowed 250 cfm on the intake at 0.500" and 199 cfm on the exhaust. Should be enough for 500hp. The stock 402 heads you have might be enough with some modifications.

For the cost of a custom set of pistons you could buy a complete 454 in need of a rebuild (500.00). Just look for 049 and 781 casting numbers on the heads before buying it.
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Old 12-17-2005, 06:26 PM
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Took the heads off today I saw the 781 on the underside of one of the runners....is that the number I want? Do you know the chamber size so I can compute compression?
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Old 12-19-2005, 09:08 AM
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I have seen 781 on the bottom side of my 781's like that. But the number you are looking for is the casting number under the valve cover. Look at the last 3 numbers in the casting number, .......781, ......049.

781's typically have 120 to 123cc's combustion chambers with 260 to 265cc intake ports.
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Old 12-19-2005, 09:40 AM
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I did confirm the last three numbers in the casting are 781. No wonder I can't get any compression with the puny .110 dome on my pistons the chambers are pretty big. World has an aluminum head with an 80cc chamber that should work with the piston I have to get around 11:1
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