question about a chevy 305

Jim
3/30/06

Yes' Mr. Bowtie. I have a question about a 305 chevy motor, what I would like to know is what all I would have to do, to trun a 305 cid motor, into a 350 cid motor? I am not sure that I can take a 305 cid motor, and make a 350 cid motor out of it? Could you let me know if I can do this, or do I have to pick up a 350 cid motor to put in my chevy car. I am hoping that I can do this, because I have a 305 cid motor now to put in my car, but I would like to have a 350 cid, not a 305 cid? If I can do this, what all would I have to do, to change it over?. thanks' for helping me with this matter, Jim.

Mr. Bowtie

Jim, You may be able to turn a 305 into 350 cubic inches with a stroker crankshaft, oil pan rail casting grinding for crankshaft clearance and an overbore on the cylinders, and grinding the bottom of the rods and or rod bolts so they do not hit the camshaft, however I would not do it, due to the weak bottom end casting on a 305 block, which under high horsepower use will blow apart. It will be incredibly cheaper just to purchase a good new or used 350 block to begin with. Save a ton of time, and lots of money by getting a new Dart 350 cubic inch block.

Jim
3/30/06

Thanks, Mr. Bowtie, on the question of the 305 cid. I just thougth that all I would have to do was to use the heads,bore the cylinders,rods and pistons for a 350, and put then in the 305. I did not know that the 305 cubic inch engine had a weak bottom. I just thought the main thing I would have to do was a lot of boring to the blocks. I also thought that all the blocks from 265 thru, 350 was the same. To move from motor to motor size, was to bore out the size of the cylinders that you would need? once a agine, Thanks' for helping me with this matter, Jim.

Mr. Bowtie

Jim, Just for your information Eagle has just released a new lower engine rotating assembly which makes a stock 305 Chevrolet block into 331 cubic inches, which I am told is the maximum amount of cubic inches you should attempt with a stock GM 305 block, before you run into cylinder bores which are too thin and may run hot and crack the engine block. The 265–350 Chevrolet engine blocks are not all exactly the same, and through the years the castings were improved and changed.

The stock GM 305 and 350 engine blocks use the same 3.48 inch stroke crankshaft. However the 305 cylinder bore is only 3.735 inches, and the 350 has a cylinder bore of 4.00 inches. You simply can not overbore the 305 block to 4.00 inches like the 350, due to the lack of cylinder thickness in the casting of the 305 block. The cylinder bore thickness would be reduced to a cylinder bore which is too thin on a 305 block if overbored to 4.00 inches. Also under perfect conditions when the block is cast new at the foundry the bores are supposed to be straight top to bottom in relationship to one another, however in the real world back in 1976–1994 when the 305 blocks were cast, the bores tend to move around, and each and every cylinder are not exactly parallel to each other from top to bottom, thus one or more bores may be cocked at a slight angle to the other bores. This is ok in a stock bore cylinder, however when you go to overbore the cylinder to a larger size you reduce the thickness of the stock casting and you can easily go through the side of the bore due to this „cylinder core shift“ when the block was cast as new. If you go through the bore when boring a block, obviously the stock 305 block is scrap. This core shift, and core thickness in every cylinder bore is checked on every engine block, by highly reputable machine shops, before any machining work is attempted, to save you time and money and a scrap engine block. Every engine block has a maximum limit to which the cylinder bores can be overbored, and in the case of the stock 305 Chevrolet block, your safe limit would total 331 cubic inches.

I hope this helps explain the reasons a little more clearly.

Pete Demitraszek
4/16/06

what is the max over bore for the 305?

jack
1/28/12

My 56 corvrtte has a stock 283 cu. with a cracked block. instead of looking for another 283 block I have an overbored 305 block in perfect condition. can I use that?

Otto
1/29/12

Check out the crankshaft journal specs on the 283 vs 305.

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