stock bore stroker - Ford Mustang Forum
 
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post #1 of 13 (permalink) Old 07-17-2009 Thread Starter
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stock bore stroker

stroking a standard 302 with out boring the engine will bring it to what CI? i dont know if i wanna go head and bore it or not. i have the forged piston, and if i bore it out and stroke it i will have to buy new ones and im not made of money haha.
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post #2 of 13 (permalink) Old 07-17-2009
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What stroker kit did you get? for a 331 with a standard bore it'll be a 327, for a 347 stroker kit with a standard bore it'll be a 342. I would recommend to just save and get the pistons. You can't use the stock pistons on the 347 though because of how the piston is designed. If I'm not mistaken you can't do it for a 331 either.

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post #3 of 13 (permalink) Old 07-17-2009
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Yeah i dont think you can stroke it with the stock pistons. They move the pistons wrist pins up when you stroke it.


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post #4 of 13 (permalink) Old 07-17-2009
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You are limited on what you can do without special pistons.

The formula is 8*3.1416*bore*stroke= displacement

A 302 is 301.6 CU in

a .030 over 302 is : 8*3.1416*4.030*3=303.85 cu in

a stock bore 3.4 inch stroker is 3.4*3.1416*8*4.0=341.8 cu in

a .030 over 3.4 stroker is 3.4*3.1416*8*4.030=344.37 cu in

a .060 over 3.4 stroker is 3.4*3.1416 *4.060*8= 346.9 cu in.

People tend to exaggerate the advantage of boring the cylinders out. If someone bores .030 to unshroud the valve, they move the wall .015 inches away from the valve. This is not likely even measurable. The cu in change is .030/4.000= 0.75 %

Unless you really go huge in bore, to levels where a standard block will get weaker or fail, the extra cubes or valve unshrouding are just not worth it. This is why I bore ONLY enough to clean up the walls and fit a standard oversize piston of the smallest oversize possible on a stock engine.

Who cares about 0.75% more displacement or 1/10th % less valve shrouding when the block is 10% or more thinner on cylinder walls??? Bad trade off.

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post #5 of 13 (permalink) Old 07-17-2009
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Tom, that is one of the best ways to look at IMHO opinion. Also most of the better heads have an altered intake valve placement, which even further reduces the shrouding. This also depends on the amount of free drop the valve has. Canfield has an altered valve placement,IIRC its .200 toward the center of the bore, TFS TW does the same, but with a rotated valve also. AFR's have a stock placement valve, there flow numbers are inflated, due to the fact that they flow them on a larger bore. Most other heads use the standard .030 bore for flow numbers.

Valve shrouding in the combustion chamber is far more important I believe.

I have a set of Canfield 195's, they are 2.02/1.60 valves, its on a stock bore 302.

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post #6 of 13 (permalink) Old 07-17-2009
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No kiddin, I was tryin to think what else but my mind was kinda fried at 2 am. Good info Tom

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As a point of reference going from a 290 rwhp car to a 500 rwhp....

will be like riding a 500cc dirt bike and jumping on a "Busa......
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post #7 of 13 (permalink) Old 07-17-2009
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Some good stuff contain in this thread.....

Tom thanks for the great explanation......
post #8 of 13 (permalink) Old 07-17-2009
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I've never seen that formula before. I was taught this one and it's the one every engine builder I know of uses.

Bore x bore x stroke x .7854 x # of cylinders.

4 x 4 x 3 x .7854 x 8 = 301.59
4 x 4 x 3.250 x .7854 x 8 = 326.72
4 x 4 x 3.400 x .7854 x 8 = 341.80

4.030 x 4.030 x 3 x .7854 x 8 = 306.13
4.030 x 4.030 x 3.250 x .7854 x 8 = 331.64
4.030 x 4.030 x 3.400 x .7854 x 8 = 346.95

Which ever formula you use, as long as you get the correct answer.

As for wanting to stroke it but use the stock pistons, you can't do that because of the rod and the pin location in the stock pistons. Use the stock pistons with a longer stroke rod and it'll come up out of the bores. You must use stroker pistons even with a stock bore.

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post #9 of 13 (permalink) Old 07-17-2009
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This is why, a lot of engine builders, will say that a 306 or 357 are pointless, unless you have cylinder problems. I have a set of JE's that are .030. I could have used them on this build, but to use some high dollar pistons, on a basically stock bottom end it not smart.

The gains are minimal with just a .030 bore. As tom has said, when you start getting into the 4.125 bore range, your doing something then, but you paying to be able to do this.

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eagles formula looks more like the one i use. pie(3.14)x radius square x stroke x no. of cyl. .030 over 302= 305.9, 306 anyway, you can get stroker kits in std. bore size to have another rebuild/bore later but check cylinder condition before you order.
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post #12 of 13 (permalink) Old 07-21-2009 Thread Starter
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Thanks for the help, i believe what im going to do, is just stroke the stock bore.
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post #13 of 13 (permalink) Old 07-21-2009 Thread Starter
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using the 347 kit
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