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Old 11-06-2006, 02:11 PM
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closed vs open chamber

What is the difference between closed and open chamber pistons? Can I use closed chamber LS6 pistons with my open chamber 781 heads?

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Old 11-06-2006, 02:31 PM
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It usually refers to the chamber design. Open chambers are typically large with no quench area. Closed chambers are typically smaller with some quench area.

Using one with the other usually results in either sky high compression or super low compression.

A good example is the Cadillac motors. The early high compression motors used a closed 76cc chamber with dished pistons. The later lower compression motors used 117cc open chambers with flat tops. Using early pistons with late heads makes about 6.8:1. Using late pistons with early heads makes about 12.8:1
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Old 11-06-2006, 03:50 PM
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A close chamber cylinder head has a much smaller combustion chamber as compared to the open chamber head. When a piston is domed, it must fit inside the chamber size.

So, you will run into problems if a domed piston for an open chamber head is used with a closed chamber combustion chamber.

Furthermore, it is not ideal to use a closed chamber dome with an open chamber head because the dome sticks up only on one side and will slow flame travel. This may make the engine require a little more ignition timing to get the job done.
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Old 11-06-2006, 05:45 PM
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are all dome pistons closed chamber?
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Old 11-06-2006, 07:47 PM
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No... Open chamber pistons come any where from dished (super charger apps) to around 14 to 1 just depending on the type of head and design of piston... Also closed chamber was phased out due to emissions and efficiency of the newer design open chamber...

Also on the question of which will work together... You cannot use open chamber pistons with closed chamber heads...

Yes you can use the closed chamber pistons with the open chamber heads (in most cases but not all)... Flame travel does slow somewhat but not that much... I infact am currently running a set of closed chamber pistons that are 12 to 1`s (ZL1/L88 pistons) with the closed chamber heads... But am running a set of 781`s which are open chamber and ended up with a compression ratio of 10.8 to 1 and with good cooling and 8 degree`s base timing (with a good curve too) and can run pump premium...

Things can be done if worked out correctly and make tons of power too... Just think of a 4000lb+ truck with a little 432 cui BBC running 12.53 @ 109mph (but with AVgas and more timing for the track) PS no Nitrous...uh yet...
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