I kind of forgot about this thread for awhile, but I did indeed get out my calculator so you could see how the numbers work out as far as bore size and how it affects compression. Enjoy-

I will simplify a few things for math sake, but the principle is the same.

Some assumptions:
1. Zero deck height.
2. Chamber volume=64 cc
3. Flat top pistons with no valve reliefs.
4. Head gasket thickness=.040 in, also same size as cylinder bore.
5. Stroke constant for both engines.
6. CC's=cubic inches x 16.387

Compression ratio=(swept volume + deck height(0) + head gasket volume + chamber cc(64) + piston domes or dishes(none)) / (deck height(0) + head gasket volume + chamber cc(64) + piston domes or dishes(none))

FIRST ENGINE=4" bore, 3.5" stroke:
1. Swept volume=4.00 X 4.00 X 3.5 X .7854=43.98 c.i.=720.70 cc's.
2. Deck height=0 cc's
3. Head gasket volume=4.00 X 4.00 X .040 X .7854=.50 c.i.=8.19 cc's.
4. Chamber volume=64 cc's.
5. Top of piston volume=0 cc's
COMPRESSION RATIO #1=(1+2+3+4+5)/(2+3+4+5)=10.98:1

SECOND ENGINE=4.125" bore, 3.5" stroke
1. Swept volume=4.125 X 4.125 X 3.5 X .7854=46.77 c.i.=766.42 cc's.
2. Deck height=0 cc's.
3. Head gasket volume=4.125 X 4.125 X .040 X .7854=.53 c.i.=8.69 cc's.
4. Chamber volume=64 cc's.
5. Top of piston volume=0 cc's.
COMPRESSION RATIO #2=(1+2+3+4+5)/ (2+3+4+5)=11.54:1

Obviously, a bigger bore with everything else constant does indeed yield a higher compression ratio.


------------------
'93 2wd truck
408 sb, vortecs, 454 TBI, Comp Cam, dual exhaust


[This message has been edited by SCRA rules! (edited March 31, 2001).]

[This message has been edited by SCRA rules! (edited March 31, 2001).]

 

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hey SCRA, guess you got me, i found out where i was making my mistake. I made a slight math error on my calculator when i wrote the program. i don't know why that was stuck in my head but i can except being wrong. thanks for correcting me.

sorry it took so long to reply but i was gone over the weekend.