please help me find a cam (sbc 350) - Hot Rod Forum : Hotrodders Bulletin Board
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Old 11-05-2008, 12:44 PM
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please help me find a cam (sbc 350)

Im new to this, i hope you guys can help me. I have a 350 bore .060 over with hyp. flat top pistons and vortec heads and will be running a performer rpm ari gar intake. i want a rough idle and as much power as i can get.(motor will be in a truck.)carb-650 vac 2nd.i was thinking of the performer rpm cam.
Thank you,
Ben

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Old 11-05-2008, 05:39 PM
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To choose the proper cam, you must first know the static compression ratio of the motor. Any cam ground will have a range of compression ratio where it will work. Outside of that, it will either make too little or too much cylinder pressure.

You might, for instance, choose a cam that works with 8.00 to 9.50 or one that works with 8.50 to 10.0 or one that works with 9.00 to 10.50 or one that works with 9.50 to 11.00 or one that works with 10.00 to 11.50.......yada, yada, yada.

These different ranges of cams have different intake closing points and compression does not begin in the motor until the intake valve closes. If you have a low static compression ratio and you choose a cam that has a late intake closing point (like most guys who are looking for the rump-rump sound), then most of the mixture that was drawn in on the intake stroke is blown back up the intake tract by the ascending piston before the intake valve closes and the motor is low on power. It might sound good to you, but it won't make the power you thought it would.

If you have a high static compression ratio and use a cam with an early intake closing point, then too much mixture is trapped in the cylinder and the motor makes too much cylinder pressure for pump gas. The result is a motor that detonates like shaking a can full of marbles. Under these conditions, the motor will disassemble itself in short order.

You need 5 values to determine the exact static compression ratio of the motor.
1. Cylinder volume
2. Combustion chamber volume
3. Head gasket volume
4. Piston deck height volume
5. Piston crown volume

The cylinder and chamber are easy from the info you gave, but unless you know the dimensions on the gasket, piston deck height and crown, you're shooting in the dark.

Welcome to engine building 101.
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Old 11-05-2008, 06:32 PM
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Thank you for the info. I was told by my local performance shop that with flat top pistons and vortec heads i am looking at 9.75:1 to 10:1.
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Old 11-05-2008, 07:11 PM
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for a truck I would go wih a Voodoo 262 cam. Unless you're willing to go to a solid, then you can make some serious power- but you need to adjust it every third oil change.
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