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Old 08-12-2008, 04:08 AM
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Piston CC's

I'm wondering who to listen too. Myself or Summit.

On Summit's site it tells me that the Sealed power H345NP 4 valve relief pistons are +5cc's (+5 meaning add 5 cc's to total cumbustion space). I've cc'd the valve reliefs myself and found that all told they are 12cc's total.

So herin lies my dillema for doing CR math. Do I go with the 5 or 12?

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Old 08-12-2008, 04:55 AM
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You will also want to check the compression height of the piston, if it`s 1.540 leave it with them, for a 350 chevy the correct height with stock rods is 1.560, the 1.540 "destroked" piston costs compression, quench and power.
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Old 08-12-2008, 01:08 PM
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Quote:
Originally Posted by Diabolicboy
I'm wondering who to listen too. Myself or Summit.

On Summit's site it tells me that the Sealed power H345NP 4 valve relief pistons are +5cc's (+5 meaning add 5 cc's to total cumbustion space). I've cc'd the valve reliefs myself and found that all told they are 12cc's total.

So herin lies my dillema for doing CR math. Do I go with the 5 or 12?
Combustion chamber measurement is the inverse of fishermen's measurement, the chamber parts are always bigger than advertised and compression is always lower.

Bogie
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Old 08-14-2008, 04:23 AM
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Quote:
Originally Posted by DoubleVision
You will also want to check the compression height of the piston, if it`s 1.540 leave it with them, for a 350 chevy the correct height with stock rods is 1.560, the 1.540 "destroked" piston costs compression, quench and power.
It is 1.56

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Originally Posted by oldbogie
Combustion chamber measurement is the inverse of fishermen's measurement, the chamber parts are always bigger than advertised and compression is always lower.
That's what I kinda thunk. If I use what information I have actually acquired myself, I come out with a near perfect CR.

Thanks Guys
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Old 08-14-2008, 04:36 AM
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how did you measure the 4 valve reliefs?
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Old 08-14-2008, 04:48 AM
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Well this is where I show my shoddy workmanship

Basically used the same tecnique (is that even a word?) as you would to CC other such stuff.

Smeared some grease around one of the reliefs, put my plate on and measured the fluid to fill said relief (this is where shoddy comes into play) and multiplied by 4.

I understand that all valve reliefs (unless machined) are probably not equal, but I just had to cc and find out... ya know?
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Old 08-14-2008, 08:01 AM
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You may want to try a different method to measure those reliefs. I've used it and I think it's an accurate way of doing it.
Get some modeling clay and press it down into the relief to fill it up. I'm assuming that you have a flat-top style pistons. Carefully shave the excess clay off the top of the piston. You now have an exact duplicate "plug" of clay that is the same volume as the relief.
Now carefully pry out the plug, trying not to deform it. Maybe a little silicone lube wiped sparingly into the relief will help keep the clay from sticking. Once you have the plug out, drop it into a container graduated in cc's filled with a known quantity of water. The increase in water volume will be your relief volume in cc's. If you wanted to be more accurate, you could do all 4 plugs, and not have to multiply, provided that you have a graduated container big enough.
I documented this on my project journal here:
http://www.hotrodders.com/forum/jour...ge=5&reverse=1
If you click on "view from beginning" it should be entry # 52.

Hope this helps,
Steve
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Old 08-17-2008, 02:57 PM
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Let's not forget that "piston volume" also includes crevice volume above the rings and the bevel around the top of the piston.

The only real way to measure it is with the piston in a cylinder.
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