cherry_camaro

My boyfriend and I are having an argument. Are the 305 and 350 blocks the same? Thanks to anyone with an answer.

spinish

No!

cherry_camaro

He wants someone to elaborate now. He's still not a believer.

2 z28s

the 350 and 305 have different bores but the same stroke, no they are not the same block

mnerat

bore the 305 and yeah they would.......right?

PontiacCowboy

They ARE the same block, the bore is different and the pistons are different. EVERYTHIG ELSE is the same.

84firebird

the 305 and 350 are the same external casting, but they are different internal castings. the original 305 will have a bore that's respectively smaller (3.75") to only produce 305 ci but the same stroke (of 3.48"), the crank journals are also different sizes so the mains in a 305 are also different...

as for boring it out...

you'd bore it an extra 1/8" off the wall making up for the 1/4" smaller diameter bore... which is entirely possible, just more heat, so it would take a while longer than boring a 350 .030" oversize, as you'd be taking off .125" vs. .015"...

issues, would include but not be limited to....


305's were mostly made in the late 70s and 80s when the castings would be foreign made, these early foreign castings and later foreign castings as well have different characteristics in the metal itself, and the boring of the cylinders may end with elliptical cylinders after it's bored, or even after being run for a while, considering how much it is being bored

the more you bore any engine the hotter it will run, anything over .040 in a 350 is usually pulled off the street because it overheats easily

boring so much will put the cylinder walls closer to water jackets, which i dont know the location of in a 305, but they may be very different than in a 350, like i said the interior casting is not a 350 interior casting, so they need not be anything alike (however with that said, they are extremely similar)

the heads on a 305 were 57-59 cc area (they say 58 cc but these were also foreign made, cc em for yourself and see what you think, i'm being generous saying that they were all within 2ccs of eachother)
put 350 pistons under those heads and compression is gonna go through the roof, need to use turbo style pistons with big dishs in em.....like a cereal bowl size would be nice

lol, you wouldnt want anything over 8.9-1 compression in this thing, with cylinders bored that much, you're just looking for trouble, why play the compression game

1.84/1.45 i think were the valve sizes, need to open them up to atleast 1.94/1.60 and i've heard of 2.02/1.60 but that would require unshrouding the valves in the chambers... also port and polish them for awhile, 305 heads didnt flow nice

otherwise your cams are similar grinds, and interchangeable, torque will be lost with the smaller diameter cylinders

and that's all i can think of for the moment

angel71rs

No way a 305 block can take that big a chop. A few engines can take a 1/8 overbore like some 455 Olds, some BBCs, 350 diesel Olds , but not modern lightweight castings like the 305.
1/4...

And no, the 350 and 305 blocks are not the same. They are both SBCs, but have different jacketing.

blackztpi

i thought for sure that the cranks in the 305 and 350's were interchangeable. ??

84firebird

son of a..... they are interchangeable, lol I shoulda looked into it before i posted, yea 305, 307, 327(later blocks) 350s are all large journal, only small journals were 50s-67 283s and 327s..... for some reason i thought 305 was small journal too : /

sorry for the mix up.... but yes 350 and 305 crankshafts are actually 100% interchangeable so long as they are the correct rear main seal

84firebird

I did mention that right? but yea, different internal casting means anything besides what the outside looks like is up for grabs..

so taking that big a chunk out of her would expose jacketing then? I was just measuring on the top of the block, and the cylinders wouldnt touch, but that's about your best selling point lol

jg95z28

Externally the same, and they share some of the same components, however they never shared the same castings.

Engine Block Codes for CID 305

Casting Years CID HP Main Notes
355909 1976-79 305 2
361979 1978-79 305 2
460776 1978-79 305 2
460777 1978-79 305 2
460778 1978-79 305 2
4715111 1980 305 2
10046164 1986 305
10243878 1996-97 305 2 Vortec truck, roller cam, one-piece rear seal
14010201 1980-85 305 2
14010202 1980-85 305 2
14010203 1980-85 305 2
14016381 1980-84 305 2
14016382 1979-84 305 2
14016383 1980-85 305 2 Truck
14088551 1986-87 305 2 one-piece rear main seal
14093627 1987-91 305 2 Roller cam, one-piece rear seal
14094766 1986-up 305 2 One-piece rear seal
14102058 1987-91 305 2 Roller cam, one-piece rear seal

Engine Block Codes for CID 350

Casting Years CID HP Main Notes
140029 1980-84 350 2
366245 1978-82 350 N\A 4 Bowtie High Tin
376450 1978 350 175-220 4 corvette uncertain
460703 1978 350 175-220 4 corvette uncertain
3858618 1968-76 350 2 unverified
3892657 1967 350 295 2 Camaro
3914678 1968 350 295 2 Chevy II/Camaro
3932386 1969 350 300/350 4 Passenger/Chevelle/Chevey II/Corvette/Camaro
3932388 1969 350 300 4 Passenger/Camaro Rare? See FAQ on site
3956618 1969 350 250-350 2/4 Passenger/Chevelle/Chevy II/Corvette/Camaro
3970010 1969-69 350 255-350 4 Truck/Passenger/Chevelle/Chevy II/Corvette/Camaro
3970010 1970-80 350 145-350 2/4 Truck/Passenger/Chevelle/Chevy II/Corvette/Camaro
3970014 1968-79 350 only 200 & 255 2/4
3970014 1970-75 350 2/4
6259425 1969-76 350 2
10036033 350 4 Goodwrench crate motor, 2-piece rear seal, "Hecho en Mexico"
10051184 1986-up 350 N/A 4 1 piece rear main seal. BOWTIE
10051184 1986-up 350 4 Bowtie, 4.00"-4.155" bores, 1 or 2-piece rear seal
10054727 1986-up 350 2/4 one piece rear seal, some "Made in Canada"
10066036 350 2/4 Target Master/Goodwrench crate motor, 2-piece rear seal, "Hecho en Mexico"
10066038 1994 350 4 Goodwrench crate motor, 2-piece rear seal, "Hecho en Mexico"
10090511 1990 350 375 2 LT-5, ZR1 Vette, 375hp
10125327 1992-96 350 300 & up 2/4 Gen.II LT-1, reverse flow cooling
10125327 1996-96 350 300 & up 2/4 Gen.II LT-4, reverse flow cooling
10153558 1991-92 350 375 4 LT-5, ZR1 Vette, 375hp
10199001 1993-95 350 4 LT-5, ZR1 Vette, 405hp
10243880 1995-00 350 2/4 Gen.I crate motors and "ZZ4", roller cam, one piece rear seal
14010207 1980-85 350 190 & up 2/4 corvette
14010209 1980-85 350 4
14011064 1982-86 350 N\A 4 High Tin
14011148 1987-89 350 Roller cam, one-piece rear seal
14016379 1977-79 350 up to 225 2/4 corvette and others
14079287 1986-90 350 Truck
14088526 1987-89 350 Roller cam, one-piece rear seal
14088548 1986-88 350 205 & up 2/4 corvette and others
14093638 1987-95 350 2/4 Roller or flat tappet cam one-piece rear seal
14101148 1988-up 350 205 & up 2/4 1 piece rear main seal. Late model roller non LT1
14101148 1987-90 350 4 One-piece rear seal

Z28SORR

And what this means folks is they are NOT the same. The 305 casting is lighter and will not take the HP of the heavier 350 block.
And by lighter I mean the actual wall thickness, the cylinder walls, the water jacket, and the lower webbing are all thinner. The cylinders can not be bored to the same extent that the 350 can. This is why people don't normally make 350's out of 305's.