Let's talk Cubic Inches

SPEAKSUP

SPEAKSUP

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Nov 12, 2008
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Just wondering what size increases you get.

.20 over .40 over 6.7 piston's in a 5.9

6.7 crank in a 5.9

What cubes are you getting all around. I forget I think there was a good base line for every .10 over but I forget.
 
4.25" bore(standard ring size) with a 6.7 crank yield 415 CI or 6.8L.
 
(bore) x (bore) x (stroke) x 0.7854 x (# of cylinders) = cubic inches

4.02 x 4.02 x 4.72 x .7854 x 6 = 359.44
 
4.02 x 4.02 x 4.72 x .7854 x 6 = 359.44 stock 5.9
4.21 x 4.21 x 4.88 x .7854 x 6 = 407.59 stock 6.7

4.23 x 4.23 x 4.72 x .7854 x 6 = 397.98 5.9 crank, .020 over 6.7 pistons
4.25 x 4.25 x 4.72 x .7854 x 6 = 401.98 5.9 crank, .040 over 6.7 pistons

4.02 x 4.02 x 4.88 x .7854 x 6 = 371.63 6.7 crank, stock 5.9 pistons


someone double check my math.

-jp
 
you measurements are a 10th off, it is .020 and .040 over the ticking time bomb is .060 over.
 
jlibert said:
someone double check my math.

-jp
Click to expand...

I asking yall for the math :lolly:

Helping a friend do a rebuild he is going .20 over just wondering what increase. Figured I write down all of it for future needing's.
 
SKYNYRD said:
you measurements are a 10th off, it is .020 and .040 over the ticking time bomb is .060 over.
Click to expand...

So if you need to go more then .40 over start looking for a new block or go to sleeves?

jlibert said:
I'm not asking you to double check it. :stab:
Click to expand...

Yeah. Now that I see you formula it will be easier to figure out in theory:lolly:
 
SPEAKSUP said:
So if you need to go more then .40 over start looking for a new block or go to sleeves?



Yeah. Now that I see you formula it will be easier to figure out in theory:lolly:
Click to expand...

No need to go to sleeves @.060 over, that spec is in the cummins repair manual...it's perfectly fine.

Besides a bigger bore can do nothing but help, because it increases airflow in and out of the bore's. Sure it makes the cylinder wall thinner, but what does .030 add up to when your over all thickness is over .300....

6.7L Specifications:
Displacement: 409 cubic inches, 6.7 liters
Configuration: Inline 6 cylinder
Firing Order: 1-5-3-6-2-4
Compression Ratio: 17.3:1
Bore: 4.21 inches
Stroke: 4.88 inches


5.9L Cummins ISB Specifications:
Displacement: 359 cubic inches, 5.9 liters
Configuration: Inline 6 cylinder
Firing Order: 1-5-3-6-2-4
Compression Ratio: 16.3:1, 17.2:1 (high output version)
Bore: 4.02 inches
Stroke: 4.72 inches

To answer your questions...
.020 6.7 piston with a 5.9 crank = 397.98 CI
.040 6.7 piston with a 5.9 crank = 401.75 CI

6.7 crank and stroke with a 5.9 stock 4.020 piston = 371.63 CI

Hope this helps!
 
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