Compression ratio vs Chamber cc
09-26-2006, 09:57 PM
#1
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Compression ratio vs Chamber cc
Im looking to be around 8.7 : 1 compression ratio on a blower motor
What combo is better ????
a larger piston and a large chamber
or a smaller piston and a smaller chamber
Also what pistons are better for a blower motor. Flat top or inverted dome????
What combo is better ????
a larger piston and a large chamber
or a smaller piston and a smaller chamber
Also what pistons are better for a blower motor. Flat top or inverted dome????
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09-27-2006, 10:47 PM
#2
Platinum Member
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Re: Compression ratio vs Chamber cc
wow. another question with many affecting factors.
If you are talking BBC on premium pump gas, then you have to be prepared to accept some compromises.
Each "fixed" factor closes you in on your options.
Here's what you base it on.
You want a squish area around .032-.036"
You want a chamber style that gives good tumble to the incoming charge.
You want the minimal surface area in the combustion chamber.
You have to keep dynamic compression under boost to a level that keeps you from detonating with the fuel choice.
You want to be able to run efficient levels of ignition lead (around 34 degrees).
Flattop pistons are "best", but when combined with popular chamber sizes that tumble well with good flowing valves, and a good squish, you end up with too much static compression.
Flatties with large chambered heads and proper squish will get you sitting prettier, but you'll almost have to get your own chambers cnc'd.
So dished slugs are an economical compromise that lets you use off the shelf chambers, set yoru squish properly, and keep compression down.
A .030 over standard stroke 502 (4.500 bore), 119cc chambered heads (decked for flatness to 116cc), a zero deck block (cut .020"), running a .038" stainless marine gasket, and a set of -11cc dished blower pistons will net you 8.6:1 static compression. Bout right for your app.
Same setup with 126cc heads decked to 123cc and .030" flattops (4cc valve divots) will give you the same 8.6:1. If you run it w stock bore flatties, you drop to 8.49:1.
mc
119cc chambers, decked to 116cc, a zero deck block, and dished slugs
If you are talking BBC on premium pump gas, then you have to be prepared to accept some compromises.
Each "fixed" factor closes you in on your options.
Here's what you base it on.
You want a squish area around .032-.036"
You want a chamber style that gives good tumble to the incoming charge.
You want the minimal surface area in the combustion chamber.
You have to keep dynamic compression under boost to a level that keeps you from detonating with the fuel choice.
You want to be able to run efficient levels of ignition lead (around 34 degrees).
Flattop pistons are "best", but when combined with popular chamber sizes that tumble well with good flowing valves, and a good squish, you end up with too much static compression.
Flatties with large chambered heads and proper squish will get you sitting prettier, but you'll almost have to get your own chambers cnc'd.
So dished slugs are an economical compromise that lets you use off the shelf chambers, set yoru squish properly, and keep compression down.
A .030 over standard stroke 502 (4.500 bore), 119cc chambered heads (decked for flatness to 116cc), a zero deck block (cut .020"), running a .038" stainless marine gasket, and a set of -11cc dished blower pistons will net you 8.6:1 static compression. Bout right for your app.
Same setup with 126cc heads decked to 123cc and .030" flattops (4cc valve divots) will give you the same 8.6:1. If you run it w stock bore flatties, you drop to 8.49:1.
mc
119cc chambers, decked to 116cc, a zero deck block, and dished slugs
