small block Q's from a noob

[jveik]

i have been entranced with chevy smallblock v-8's ever since i bought my truck with a 350 in it a couple years ago and now i have come to realize that the more i try to learn, the more i realize i don't know. heres some stupid questions lol...

when they measure the size of the engine do they take the total volume of the cylinder from the top deck of the block to the end of the cylinder or do they measure from the top deck of the block to the top of the piston at it's lowest point in the cylinder? (then obviously times it by 8 lol) im assuming that the volume of the combustion chambers is not used in measuring engine size, since the volumes of them vary...


also... since the 302 has the same 4 inch bore as the 350, is the block for a 302 cut shorter than one for a 350? seems like common sense stuff, but hey you never know how stupid i can be lol

[victimizati0n]

Originally Posted by jveik

when they measure the size of the engine do they take the total volume of the cylinder from the top deck of the block to the end of the cylinder or do they measure from the top deck of the block to the top of the piston at it's lowest point in the cylinder? (then obviously times it by 8 lol) im assuming that the volume of the combustion chambers is not used in measuring engine size, since the volumes of them vary...

to figure out engine size, you do this formula:

Bore x bore x stroke x .7854 x #of cylinders (8 in your case)

the bore of a chevy 350 is 4.000" and the stroke is 3.48" (it may differ somewhat depending on its year) and the 302 has the same bore, like you said, and a shorter stroke of 3.000"

also... since the 302 has the same 4 inch bore as the 350, is the block for a 302 cut shorter than one for a 350? seems like common sense stuff, but hey you never know how stupid i can be lol

The block is the exact same, the difference between the engines is the crank. You can put a crank from a 350 in a 302, and your 302 now turns imto a 350, its called stroking the engine (you have probably heard of the 383 stroker)

[tom3]

A little simpler. The engine size is it's displacement. The area of the cylinder - bore - multiplied by the distance the piston actually travels - the stroke - times the number of cylinders.

And the different engine sizes all use the same block external dimensions in the early engines, all are interchangable for the most part. The difference in all but the 400 is the wrist pin location in the piston. A longer stroke would have the wrist pin higher in the piston. A 400 small block uses a shorter rod, but again the outer dimensions of the block are the same.

[victimizati0n]

Originally Posted by tom3

A little simpler. The engine size is it's displacement. The area of the cylinder - bore - multiplied by the distance the piston actually travels - the stroke - times the number of cylinders.

And the different engine sizes all use the same block external dimensions in the early engines, all are interchangable for the most part. The difference in all but the 400 is the wrist pin location in the piston. A longer stroke would have the wrist pin higher in the piston. A 400 small block uses a shorter rod, but again the outer dimensions of the block are the same.

just pointing out, that changing the rod size does not change the engine size.

[jveik]

ah ha i see now. i never thought of the movement of the pin... lol now its off to my next quest of finding someone that can sell me a tachometer that goes up to only 6000 rpm, instead of the huge gawdy 10,000 rpm ones that i prolly wont even get over 5500 rpm with my future engine combination... i think that the huge 5 inch diameter guage would look absolutely rediculous, at least in an otherwise stock looking pickup truck lmao

[richtazz]

Actually, the 262, 265, 283, 305 and 400 blocks are different from all the others. All factory displacement smallblocks use a 4" bore except the ones mentioned above. The 400 has such a big bore (4.125"), that they had to remove the coolant passages from between the cylinders. It is commonly referred to as a "siamesed" block and is easily identified by the lack of the center freeze plug on the side of the block. It also has such a long throw crank, that it couldn't be internally balanced. The Harmonic balancer and flywheel have counterweights for the extra balance needed. The 305 engine has a smaller bore (3.736"), and is useless for performance applications. The bore stroke ratio is so stupidly out of whack, that you can't really do much with it. The 283 has a 3.875" bore, the 262 is 3.670", and the 265 is 3.750" just for reference purposes, and these are pretty much useless for performance as well. The piston pin placement in relationship to the top of the piston is how they compensated for the different crank strokes. All smallblocks except the 400 use a 5.7" long connecting rod. The 400 had to use a shorter rod (5.65" I think), because the piston pin would have been in the oil scraper ring groove to keep it from coming out the top of the block with the standard 5.7" rod. That is why 400's are good for low RPM, but not high RPM. The connecting rod angle at mid-stroke, created by the short rod, puts a lot of strain on the crank.

[Blue Bowtie]

And for just a little more confusion, early 265 and 283 blocks (and a fistful of 302s) used a smaller main journal crank than the later engines. Conversely, 400s used a larger main journal crank than the "regular" SBCs.