cumbustion chamber size for 8.5:1 on a 371ci shortblock - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 12 Old 02-08-2008, 12:17 AM Thread Starter
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Last edited by jfitts23; 04-02-2008 at 04:43 AM. Reason: forgot info
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post #2 of 12 Old 02-08-2008, 12:44 AM
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Are you sure you have the right pistons listed? 4x3.47 does not equal 371.


'67 coupe, blow-thru 351w S475, C4/C5, 8.8 6.38 at 110, 9.99 at 135
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post #3 of 12 Old 02-08-2008, 12:53 AM Thread Starter
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yea i copied and pasted from the website
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post #4 of 12 Old 02-11-2008, 11:33 PM
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A 4" bore and a 3.47" stroke would yield a 347ci engine:

D =((B^2 * S * (pi/4))*8)
D = ((4^2 * 3.47 * 0.7854)*8)
D = 348.84 ci

No clue what combination you'd have to have to come out at 371, but it's not gonna be just a bore size. The stroke would have to change.

I don't know about those CR numbers, either. With a -8cc dish and 58cc heads, I'm coming out with 11.75:1 CR...

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post #5 of 12 Old 02-11-2008, 11:44 PM Thread Starter
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here is more info on it.

http://www.jegs.com/webapp/wcs/store...0002_493767_-1

the bore is 4.125
the stroke is 3.5


jegs has it listed as a 375ci

but i think i'm just going to go with 70cc victor jr heads with this short block for a good turbo motor.
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post #6 of 12 Old 02-12-2008, 10:29 AM
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Originally Posted by jfitts23 View Post
but i think i'm just going to go with 70cc victor jr heads with this short block for a good turbo motor.
70cc heads w/ -8cc dish pistons and a .041" Head Gasket should net you a compression ratio of about 9.8:1 on a 4.125" bore engine. -8cc just isn't much of a dish.

For comparison, I'm building a 351 with -17cc dish pistons and 65cc heads. My compression ratio is 9:1.
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post #7 of 12 Old 02-12-2008, 09:03 PM Thread Starter
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i think i might have to rethink my shortblock because i would like lower than 9.8:1. might just get a dart block for i can can choose what ever compression i want instead of the already made world. that world just had me tempted because its such a good price. well thanks
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post #8 of 12 Old 02-12-2008, 11:09 PM
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Quote:
Originally Posted by jfitts23 View Post
i think i might have to rethink my shortblock because i would like lower than 9.8:1. might just get a dart block for i can can choose what ever compression i want instead of the already made world. that world just had me tempted because its such a good price. well thanks
To help you out some, you can figure your static compression ratios yourself using the following formula:

Compression Ratio:
CR = (V1 + V2)/V2
Where:
CR = Compression Ratio
V1 = Cylinder Volume (in cubic inches (ci))
V2 = Cylinder Head Volume (in cubic inches (ci))

V1 = (B^2 * (pi/4) * S)/1000
Where:
B = Bore (in inches)
pi = 3.1416
S = Stroke (in inches)

V2 = HV + DV + V3
Where:
HV = Cylinder Chamber Volume (in cubic inches (ci))
DV = Piston Dish Volume (in cubic inches (ci))
V3 = Slice (or Squish) Volume (in cubic inches (ci))

V3 = B^2 * (pi/4) * (G - DC)
Where:
B = Bore (in inches)
pi = 3.1416
G = Head Gasket Thickness (crushed) (in inches)
DC = Deck Clearance (in inches)

To convert cc to ci: cc/16.4
To convert mm to inches: mm*25.4

Hope this helps.
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post #9 of 12 Old 02-14-2008, 03:05 AM Thread Starter
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thats a bit tecnical for me. i'm at the beginners level on this stuff thats why i was asking.
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post #10 of 12 Old 02-14-2008, 10:54 PM
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thats a bit tecnical for me. i'm at the beginners level on this stuff thats why i was asking.
That's cool, but it never hurts to have information on hand

I'd study those formulas (and any others I could find) if I planned on building a custom engine. Things like compression ratio need to be worked out in advance so you don't blow it to kingdom come

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post #11 of 12 Old 02-14-2008, 11:00 PM Thread Starter
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i think i'm just going to get the heads i want probably afr 205 and instead of a 371ci, have a 363 built for what ever compression i need
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post #12 of 12 Old 02-15-2008, 08:15 PM
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Quote:
Originally Posted by jfitts23 View Post
thats a bit tecnical for me. i'm at the beginners level on this stuff thats why i was asking.


Try this...

http://www.race-cars.net/calculators...alculator.html

NEVER do business with Sam Rivera AKA Sam Wilson.
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