Figuring engine displacement - Chevy Impala SS Forum
 
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post #1 of 6 (permalink) Old 01-09-2010, 10:52 PM Thread Starter
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Figuring engine displacement

Something that I have been wondering or a while, how do figure out the displacement of an engine that was bored out? About 10 years ago my father and I rebuilt the engine in our 87 lesabre (don't laugh, it was an excellent learning experience). We attempted to hone it out ourselves but screwed it up and and had a shop bore it out to fix what we did. The engine is a 231ci 3.8l V6 bored out 20 over (going by the receipt from the shop that I manged to keep).
So what size is this engine now? And did we gain any HP or anything good from this?

1996 DCM SS 201k
1996 Black RMW 158k
1995 DCM Roadmaster Wagon 110K
1995 LDM 1A2 Caprice Wagon 205K
1994 9C1 Caprice 151k
1992 Olds CC 5.3l LS swap 174k
1996 Black/Black FWB SOLD
1975 Impala Coupe

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post #2 of 6 (permalink) Old 01-09-2010, 11:34 PM
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Volume of one cylinder = Pi x 2R x S

Where Pi equals 3.1412
R is this the radius of the engine times 2
and S equals the stroke

Multiply the volume times the number of cylinders and you have the total displacement.

There are lots of online calculators that can do this for you.

Without knowing the stroke, I can't say for sure but you probably picked up 2 or 3 cubic inches.

Sharkx

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post #3 of 6 (permalink) Old 01-10-2010, 12:12 AM
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Pi = 3.1416

Jim B.

'95 9c1, pcmperformance.com 93 tune, Dynomax Ultraflo catback, K & N box filter, LT4 KM, 160 stat, 3.08 Posi.
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post #4 of 6 (permalink) Old 01-10-2010, 05:06 AM
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Wiki specs

The bore was enlarged to 3.8 in (96.5 mm), identical to the Buick 350 and Olds 307 V8s, yielding 231 cu in (3.8 L) displacement.

bore of 3.80" and a stroke of 3.40"

larger 252 cu in (4.1 L) version of the 3.8 L LD5 V6 was produced from 1980 through 1984 and marketed as an alternative to a V8. The bore was enlarged to 3.965 in (100.71 mm)

For your 3.8 rebuild:

New bore 3.820"

R = 1.91"

R x R = 3.6481

3.6481 x 3.14159 = 11.46083" area of cylinder bore

S = 3.4"

38.96683 cubic inches volume per cylinder

233.8 CI total

Try "running the numbers" for the original published dispalcement (231), which is often rounded up or down from a true calculated displacement--see what it actually measures to know the real difference from boring the cylinders .020". Use bore 3.80 and stroke 3.4

Since the engine was bored, can we assume that new pistons were used?

The amount of increase in displacement by itself would have minimal effect on power output--MAYBE a couple of HP.

Bill Harper
ISSCA #127
inov8r@windstream.net
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post #5 of 6 (permalink) Old 01-10-2010, 10:11 AM Thread Starter
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Cool, thanks for the info guys. And yes, new pistons were installed.

1996 DCM SS 201k
1996 Black RMW 158k
1995 DCM Roadmaster Wagon 110K
1995 LDM 1A2 Caprice Wagon 205K
1994 9C1 Caprice 151k
1992 Olds CC 5.3l LS swap 174k
1996 Black/Black FWB SOLD
1975 Impala Coupe

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post #6 of 6 (permalink) Old 01-10-2010, 12:57 PM
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This is easy to remember......
Bore x bore x .7854 x stroke x # of cylinders
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