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Old 01-09-2011, 01:24 AM
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combustion chamber size?

About to buy my AFR 195's but idk if i should go with the 1034's 65cc or the 1036 75cc. any insight? shooting for 10:1 static compression. block zero decked, pistons have not been purchased yet.

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Old 01-09-2011, 02:10 AM
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Zero decked block with a 2 valve relief flat top piston, .041" gasket and 75cc heads gets you 9.95-1, close enough to your 10-1 spec??. Flat top piston will also be the cheapest to get, because it is easier to make, takes less machining than reflector dish or dome.

Also leaves you open to raise the compression ratio in the future, just mill the head at that time. Only difference in most SBC aftermarket heads chamber cc volume just depends on how far they mill the same basic casting before they ship it to you, they cast it with extra material on the deck surface and just mill it to achieve the chamber cc the customer orders.
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Old 01-09-2011, 02:12 AM
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So in theory if i wanted the smaller chamber in the future i could just mill down the 75cc chamber until its at 65 or smaller?
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Old 01-09-2011, 02:17 AM
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Quote:
Originally Posted by 383_Gladiator
So in theory if i wanted the smaller chamber in the future i could just mill down the 75cc chamber until its at 65 or smaller?
Yep, thats how the manufacturer does it, in most cases. If you think you may need to mill that far in the future you may want to ask AFR if that is how they do it, they may have a different head casting(since they have so many different heads) but I don't recall it being that way(2 castings).
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Old 01-09-2011, 02:39 AM
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is there any benefit to running a smaller chambered head with a dished piston vs a larger chamber and flat top? vice versa?
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Old 01-10-2011, 12:53 AM
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Quote:
Originally Posted by 383_Gladiator
is there any benefit to running a smaller chambered head with a dished piston vs a larger chamber and flat top? vice versa?
Depends on the use and how much you are chasing hp. current Nascar is small dish/small chamber, but they use splayed valve heads where the small chambers don't interfere with valve flow due to the valve angle(talking about valve shrouding. With 23 small block heads you can reach a point in chamber size small enough to crimp port flow.

I'd think you wouldn't gain anything noticable from a dish/small chamber set-up in your case. It's one of those "last 10 hp, chasing 800hp target" kind of things.
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Old 01-10-2011, 09:41 AM
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Quote:
Originally Posted by 383_Gladiator
About to buy my AFR 195's but idk if i should go with the 1034's 65cc or the 1036 75cc. any insight? shooting for 10:1 static compression. block zero decked, pistons have not been purchased yet.
My preference for a normally aspirated engine is tight chambers, there are a lot more active in getting oxygen and fuel molecules mixed together that are large chambers. Then I use a D dish piston to dial in the compression based on the needs of a dynamic compression for the cam, gearing and vehicle weight. The higher efficiency of a tight chamber more than offsets valve shrouding and goes a long way toward adding mechanical octanes to the engine which delays the onset of detonation which lets you also push the limits on ignition advance and fuel mixtures.

For nitrous and supercharged engines I go with an open chamber head, here there is so much product being dumped into the cylinder that unshrouding the valves becomes the more important feature vis-a-vis forcing close associations between oxygen and fuel with a tight chamber as this is being done by the mass of stuff being dumped into the cylinder. The short coming of this approach is a street driven machine where either the nitrous or the blower is a part time thing, these engines force a less than optimum efficiency when just cruising around.

There are a lot of Dynamic Compression Ratio (DCR) calculators out there, make use of them as your cam will negatively affect the Static Compression Ratio so the (SCR) needs to be well adjusted for that event at the time of selecting part. Keep in mind that large ports slow the low RPM flows an event the engine will react to like running a bigger cam at slow speeds, so this combination if used on a street engine with mild gears will want tight chambers to invigorate the mixture and more compression to overcome the lack of low speed mixture density in the chamber. This effect will be present at all RPMs under the max torque peak and will be increasingly apparent the further under the torque peak the engine is operated.

Bogie
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Old 01-10-2011, 10:16 AM
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I would get the smaller chambers and use the piston volume to help you hit your target as I think Bogie is suggesting (assuming an NA setup with part time street use).
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Old 01-10-2011, 04:49 PM
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the truck will be driven daily as a commuter while i do a motor swap in my other truck. i estimated a 10:1 static and 8.2 dynamic with my cam. i have 4.56 gears.
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Old 01-10-2011, 06:13 PM
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Quote:
Originally Posted by 383_Gladiator
the truck will be driven daily as a commuter while i do a motor swap in my other truck. i estimated a 10:1 static and 8.2 dynamic with my cam. i have 4.56 gears.
When I lived at Snoqualmie pass a billion years ago I had a Ford 4x4 with a Lincoln 430 stuck into it with big rear gears. It could climb trees with that much torque.

Bogie
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Old 01-10-2011, 06:16 PM
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well i'm hoping all this torque will clean out the tread lugs pretty good in the mud bog races. 37 inch tires are quite heavy
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