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Discussion Starter · #1 ·
I've been wondering for awhile and I've never received a good answer. If a 305 and 350 are identical externally why can't the 305 be bored to a 350? I'm guessing it's either how the coolant/oil passages are, or how they're cast. Is this true?

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kenny

85 El Camino 355ci
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The 305 block is cast with smaller cylinders. If you tried to bore it out to the 4" bore of a 350 you would bore through the cylinder walls, or at least they would be too thin and would crack. The 305 and 350 do have the same 3.48 stroke crankshaft.

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Kenny,
Before going one step further, THERE ARE NO DUMB QUESTIONS--------------THAT'S WHAT THE FORUM IS FOR!!!!!!!!!

That said, the reason that you can't bore a 305 to a 350 bore size is because the walls of the cylinders are not thick enough. If you tried to bore a 3.73in cyl (305) to a 4.00in cyl (350), one of 2 things would happen (or both). You would either be into the water jacket, or, the cyl wall would be nearly paper thin, thus no strength in the wall.

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Tom Parsons

[This message has been edited by DZAUTO (edited 12-24-2001).]
 

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If you tried to bore a 305 out to a 4" bore like a 350, you would cut into the water jackets. Remember, changing the bore of the block is not the only way to change the cubic inches of a motor. For example: I run a 383 which in short is a 350 with a 400 crank. I did have to bore the 350 block .30 over, but that is nowhere close to the 4.300 inch bore of the 400. After boring the 350 .30 over, the bore is 4.030. See how much bigger I would have to bore the 350 to get to 400??? The 400 has what are called siamese cylinders which eliminates some of the cooling passages so that the bigger bore can be reached.

I hope this helps.

-Nathan
 

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Discussion Starter · #5 ·
So it is the water jackets.

It's pretty dumb (to me at least) that they would have an identical sized block, same crank but 3.74 on the 305 and 4 on the 350, yet the 305 has thinner walls.

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kenny

85 El Camino 355ci
350 turbo - 4.11's
best run so far 12.92
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i thought a 400 had 4.125 in bores?
 

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?

The cylinder wall thickness is reduced for proper cooling. Even if the wall thickness wasn’t a factor. The cost of boring would greatly exceed the cost of a good used 350 block. The Chevy 350 is still the most common block on the planet.
 

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?, if you were really intent on making a 305 into a 350 you could bore out the 305's cylinder bores and then resleeve them to the 350 size - but man would that be a waste of money, as someone pointed out the 350 has to be one of the most available blocks on the planet.

Thomas

P.S. With the aftermarket paving the way, a whole lot more 400, 415, 427+ cube smallblocks will become common, just like the 383 smallblock combo currently.


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"Bomber" '67 El Camino, Beater comes back to life.
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Discussion Starter · #10 ·
I have no intent on ever using a 305. I was just wondering why the same size block (externally) isn't completely identical inside. I figured it was something to do with cooling but never really looked into it because I know a 305 isn't worth it.

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kenny

85 El Camino 355ci
350 turbo - 4.11's
best run so far 12.92
My Page
 
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