sbf 383

[Guest]

[383notch]

Newbie here, I have 74` 351w.  It has a stock bore.  I plan on boring it .030 and putting in a 6.125 rod with a 3.750 stroke. Stock deck height is 9.503.  I want a piston to deck clearance of .005.  After the calculations, I came up with a piston compression height of 1.498.  I could not find any pistons close to that.  Is there any thing else that I can change, besides the rods, to come within spec of the pch.  Could head gasket thickness be the answer? Does cumbustion cc or shape affect it as well.
The rods are carrillo with carr cap screws that i got for under 150.00.  This will be a s/s engine on a budget.  Any suggestions on the top end combo will also be appreciated as well.

[frop]

Find a piston you like shorter than that and cut the block to match.

Nik P

[trickcat]

  please post your location on your profile. Why do you want a piston to deck clearance of .005, Have you chosen a head that requires a piston to deck clearance of .005?

[383notch]

No  i have not chosen a head yet.  I read on a site that said that .005 was the desired number.  So It is as simple as getting the block milled to compensate for the difference!

[trickcat]

You need to figure out what head you are going to run, that will determine the pistons to use at a given compression. Mine is -19cc with a 58cc head I got 11:1 compression

This is from an article:
The formula for determining deck clearance volume is similar to displacement:
DC = Bore x Bore x 0.7854 x Distance between Piston and Deck at TDC
If the piston in our example at TDC is 0.020 down in the bore, then the equation works out like this:
4 x 4 x 0.7854 x 0.020 = 0.2513 cubic inches

Gasket volume is almost exactly the same. It is simply the volume contained in the compressed height of the gasket. Properly torqued between the head and engine block, a compressed gasket is normally between 0.005- and 0.015-inch thick. The compressed thickness value can be provided by the manufacturer and is usually found in the catalog. Calculate gasket volume exactly the way you would deck clearance volume except use the figure for the compressed gasket thickness in place of your value for the distance between the piston and deck at TDC.

Another variable is combustion chamber volume. There is no doubt this is the area that has the most effect on compression ratio. Most combustion chambers for racing small-blocks are between 60cc and 90cc, which is huge compared to the 5cc dishes in the piston. Manufacturers will tell you what the chamber volume should be, but that number is rarely accurate once the head has been worked. How deeply the seats are cut,cutting on the chamber walls to unshroud the valves, angle milling the head, and decking the surface all affect the volume.

[trickcat]

More Piston Considerations:
When we were researching the effects of compression, Bob Koch of Race Engineering gave us some points worth considering. Race Engineering is a top provider of custom and off-the-shelf pistons to engine builders and Koch deals with compression ratio problems daily when designing pistons.

"You almost always want to make changes to the cylinder head rather than the piston when trying to influence compression ratio," he says. "First,because it is so much easier to change compression ratio by simply decking the cylinder head. If you start trying to get a specific compression ratio by making piston changes, you are going to get into custom pistons. A piston manufacturer isn't going to make custom pistons in anything less than groups of four. That means you either have to go without a spare and take your chances or buy four extra. Neither option is smart financially.

"Cutting the deck of the head also helps keep the piston weight down, which is a major consideration when you are trying to reduce your rotating mass. A lot of people aren't aware of this, but a large dome generally adds less weight to a piston than a small dome--which is what you would use if you are trying to influence compression. From 0 to around 7 cc, a positive-displacement dome is going to be solid. You can count on about 2.85 grams of added weight per cc of volume. Multiply that by eight and you can get a significant amount of weight. If you go larger than 7 cc, piston manufacturers can begin to hollow out the area underneath the dome to save weight, but that is always something you need to be concerned about.

[SteveL]

What is the pin size for these rods??  As in, are they Ford rods, or
chevy rods.  I'm asking because I didn't realize Crower made a Ford
pin rod in a 6.125" lenght...

[383notch]

These are Carrillo rods that I am going to have to get resized.  So my first step in this process would be to select:

1.Select the head and cc that I want to run

2. Select the  pistion with the corresponding  comp. that I want to have

3. have the block decked to get the  desired piston to deck clearance.
 
Is there any thing that I am overlooking. 

[Is1BadFord]

These are Carrillo rods that I am going to have to get resized.  So my first step in this process would be to select:

1.Select the head and cc that I want to run

2. Select the  pistion with the corresponding  comp. that I want to have

3. have the block decked to get the  desired piston to deck clearance.
 
Is there any thing that I am overlooking. 

Most people run 0 deck in performance applications, and use the gasket for the quench area.  Felpro 1011-1 and 1011-2 have .041" and .039" respective crushed thicknesses.  I prefer the 1011-2's of those.

On the pins...you didn't say what the size was on the little end.  That will play a large part in piston selection.  Whether it be ford, or chevy is irrelevant, as long as you select the proper piston to match.

Cris

[Ammosteve]

The problem is you are trying to build an engine around a rod. 

You should figure the stroke you want to run and the piston and ring package that fits the application and what ever is left is your rod.

What parts do you actually own?

Steve

[Ammosteve]

A couple of questions for you.

What is the actual deck height of your block?

What will it take to square deck it?

Do you have a cubic inch limit?

Typically a 383 uses a 6.250 rod. 

Steve

[383notch]

The block has never been touched.  never squared.  I want to keep the 383 cubic inch size.  The reason that I chose the  6.125 rod was for the use with the 3.750 crank that i had bought.  I saw a piston on Keith black site that was suppossed to fit, but I am not sure of it since it was a chevy piston,  KB pistons KB385 for 9:1 compression and KB225 for 10.5:1 compression.  I own the  rods and the crank now. 

[frop]

Try looking for a piston in the 1.490 range.

Nik P

[Lightnin McQueen]

You can use a 3.75" stroke and use a 6" rod with a 1.6 compression height piston all you have to do is make sure that the counter weights clear the skirt . This will leave the piston in the hole .025" and you can either leave it alone or deck the block. I have done this I wanted the shorter rod. What compression ratio are you looking for?

[Ammosteve]

You need to have your block measured to find out what the actual deck height is and what it will take to square it. 

Blocks castings are + or - that 9.503 measurement. Find out what you actually have and then go from there.

Steve