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Old 01-02-2008, 10:33 AM
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Piston surface volume

Having stock dished 350 pistons with 4 valve reliefs what is my approx volume in CCs.

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Old 01-02-2008, 11:48 AM
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Take a read of this.
Quote;
Piston shape also plays a big role in compression. A pure flat-top piston does not affect compression—but rarely occurs in the real world. Even a “flat top” piston incorporates valve reliefs in the piston top that add volume. A typical small-block, four-eyebrow piston contributes roughly 4 to 6 cc’s worth of volume. This is the same as adding that amount to the combustion chamber size.
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Old 01-02-2008, 12:17 PM
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Quote:
Originally Posted by BadA$$37
Having stock dished 350 pistons with 4 valve reliefs what is my approx volume in CCs.
Replacement pistons run from 14 to 25 cc depending upon exact application.

As in example small chambered head with 8.5 compression will have a 25 cc dish. Large chambered head with 8.5 compression will have a 14 cc piston. The factory also varies head gasket thickness from about .018 to .060 inch. So without taking the engine apart and measuring, you can never get to exactly what the compression will compute.

Bogie
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Old 01-02-2008, 12:29 PM
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I have the piston pulled and in hand, It is a replacment piston and its 60 over. How would I get the volume from it.
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Old 01-02-2008, 12:36 PM
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I googled the numbers from piston top, 423np 060. appears to be a sealed power piston but havent found the volume, any ideas??
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Old 01-02-2008, 12:54 PM
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Quote:
Originally Posted by BadA$$37
I have the piston pulled and in hand, It is a replacment piston and its 60 over. How would I get the volume from it.
Get something thats graduated in CCs or MLs like an old veterinary syringe, an eye dropper, or graduated 100 ML cylinder. Try a chemical supply or kitchen supply store for something graduated in Cubic Centimeters or Milli-Liters. For reference there are 14.4 CC/ML to a cubic inch and 25.4 mm to a straight inch. A CC or a ML is the same volume.

Mount the piston in a vise so the crown is level in all directions. Take the graduated whatever and draw a measured amount of fluid, rubbing alcohol works well, and proceed to fill the depression in the piston crown. If it helps you, taking a piece of Plexiglas with a 1/4-3/8 inch hole in it and sealing it to the piston crown with Vaseline can be a helpful pouring guide.

Bogie
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Old 01-02-2008, 12:57 PM
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Well if you can accurately measure the shape features you could mathematically calculate it. You will need the formula for volume of a torus then divide by 4 for the bottom radius.

On the other hand if you can accurately measure the form, I could draw it up on Solidworks and check mass properties which will give the volume.

The best bet would be to take a picture and import it to paint or something like that so you can label the features with dimentions. Don't need to be neat or formal it's just information to me.
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Old 01-02-2008, 02:46 PM
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Quote:
Originally Posted by bentwings
Well if you can accurately measure the shape features you could mathematically calculate it. You will need the formula for volume of a torus then divide by 4 for the bottom radius.

On the other hand if you can accurately measure the form, I could draw it up on Solidworks and check mass properties which will give the volume.

The best bet would be to take a picture and import it to paint or something like that so you can label the features with dimentions. Don't need to be neat or formal it's just information to me.
Bentwings thanks for the help,

maybe you can start with this info

The diameter of the dish is 3.112 and .057 depth.
I will work on the relief
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Old 01-02-2008, 02:48 PM
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I usually add 5cc to the chamber volume to account for the valve reliefs in a 350, 4 valve-relief piston.

This is in addition to the value I get when calculating the volume amount from the deck clearance and head gasket volume.

tom
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Old 01-02-2008, 03:23 PM
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That should have the same volume as a H859Cp piston plus 5 cc for the 2 extra valve reliefs. I am not sure what that is, I just know the pistons are very similar. (except for the valve reliefs).

They are 9.6:1 with a 64cc head,
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Old 01-02-2008, 03:31 PM
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how would 9.6.1 be on pump gas? I am not a motor guy and trying to build a 350 for a roadster. I have a 350 thats bored 60 over, i have a set of 60cc 305 heads(416) and a set of 76cc 350 heads(882s). Dont want big HP, just something I wont have to be tweaking all the time. I want to use what I have and not spend any money, suggestions???
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Old 01-02-2008, 03:58 PM
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Pretty shallow depth.
Assuming a 3/32 radius at the bottom and tangent to the bottom, and a full circular dish, You have 6.89 cc so far.

If it is D shape all I need is the distance across the circle to the flat.

For valve reliefs I need the number, the diameter, the length of the cut perpendicular to the face of the cut and the angle to the top of the piston. Either side of the angle will do, I can use either. Instead of the angle you could give me the length of the machined relief... ie the distance from the straight side to the diameter. I may be able to position this so it works out.

EDIT Try to give me the spacing of the valves as my car is miles from me. thanks

I can try and paste a picture if you give me this stuff.
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Old 01-02-2008, 04:17 PM
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Ok I've got a valve relief plugged in but I need "real" dimensions.
Also let me know if the valve reliefs are different or if it is a "slash" type of relief.

Thanks for giving a retired eng something to do. haha

enjoy
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Old 01-02-2008, 06:17 PM
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bentwings

I dont mean to take your fun away, but I used a syringe my RN wife had and we dropped water on the head and came up with 15cc.

Im not sure how I can even measure the relief?
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Old 01-02-2008, 06:56 PM
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Good going!! Medical supplies for automotive understanding. I like it.

I think the pistons I mentioned earlier are 12cc so you could expect 10 to 1 compression with 60cc heads.

As long as the pistons are less than .015 below the deck at TDC then I would say go with the 60cc heads this will give you around 10:1 which should work with pump gas. The 76cc heads will drop your compression to like 8:1 which will give you horrible performance, That street rod would run the best with the 416 heads and premium gas and if the compression was a little to high you could back off the timing or add a 4 dollar bottle of octane booster when you filled up the tank.

Unless you were planning on adding a supercharger then you would want that 8:1 compression.

There are a lot of possibilities when building a motor and all the parts have to come together just right to make decent power on a budget. But it is not unreasonable to expect good numbers, run on pump gas, and not break the bank building it.
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