Boring out an engine?

[85MudMonster]

I waas just wondering, aren't the 305 and 350 blocks basically the same just the 305 has a smaller bore? so how much can you bore out a 305? Factory is 3.736, and I wanted to go .130 over to get 327ci, but the don't make pistons for that, so I was wondering if there is actually a difference in the blocks that makes it so you can only bore a 305 .080 over....

I hope all that made sense.

[Blue 82]

Yes ther is a difference in blocks (bore size)

You can make your 305 into a 334 by changing the crank

A .030 overbore with a 3.75" stroke crank = 334 Cu In.

here's some pistons
http://cgi.ebay.com/ebaymotors/KEITH-BLACK-PISTONS-FORGED-SBC-334-DISH-10-00cc-909_W0QQitemZ230218731081QQcmdZViewItem

[85MudMonster]

well, I wasn't really looking to change out the crank in it. I just wanted to bore it out as big as a 305 will go, but I don't know how big that is, After it's done it's gonna get put into a '71 Opel GT.

[Blue 82]

got something like this in mind?

[bmaier]

that is one crazy lookin opel, where did you ever find that 

[VileZambonie]

Overboring the 305 is a waste of $. For the cash you'll spend on machine shop work just to get .060" max you could pick up a good seasoned 350 block.

[78 Chevyrado]

You'd have to/ take the block to the machine shop and have them check it for bore thickness and such.  All blocks are a little different so max bore varies (not much, but a little).  The main thing about 305 blocks is that aftermarket heads are harder to find because of the odd bore size (3.736 inches).  327s and 350s share the 4.001 inch bore size and 350s are about as common as trees or grass, so everybody makes heads for them.  Otherwise they are the same as far as bolting everything up.  making a 327 if you can out of a 305 would give it a boost in power and more economy than a 350, and would be different than everybody else.  If you just want to reuse the stock 305 heads, you'll have no problems with anything else you want to add bolting up and fitting.  As far as pistons, to get the 327 you need 3.866 bore pistons.  With that said, if you cannot find pistons you might look into the pistons for a chevy 283ci (3.875 Bore) or 307ci (3.876 Bore).  I'm not sure what all is involved in swapping pistons as far as connecting rod compatibility, or factoring in rod length, etc so be sure it will work before you buy it.  Good luck!

Kenny

[HAULIN IT]

I agree with Vile, unless one is needed to use the "correct" block, as in a stock class of some race rules or for smog rules. The 350 block will cost no more & likely cost less due to being more common. It's good to see someone thinking off the beaten path in our hobby, that's how new things happen. I this case, you can't beat a reliable 350 block. Lorne

[Stewart G Griffin]

i thought 305/327/350 blocks were basically the same also.  So, what is the difference?

Actually, i thought all SBC's except the 400 were basically the same block.

[VileZambonie]

They're all similar in casting but each engine is cast with the intended bore in mind when they are born. They are not the same.

[85MudMonster]

No, It's gonna be an expensive build anyway. But I've got the 205 already, so when it is built is will be a 351 SBC, and best estimates from my Engine Dyno Pro software says about 500HP and 550Ft/lbs of torque (but that's a computer program so it's just an estimate not actual numbers) It's gonna get the works done on it, but this will be after I'm done with the 350 and it is put into my truck, I was just wondering what the difference was and how big I could go...Thanks.

[HAULIN IT]

If your planning to spend big bucks on a build, Why limit yourself to the "I already have it excuse"? Not to be a downer, But how did you come up with 500hp/550ft.lbs out of a bored 305?!!! You had mentioned you were leaving the stock crank, changing it would be the start of getting the torque up, Sorry I just don't see it. Short of a pro-stock type build, you would be lucky to get much over half that! Are you planning on this being a street engine? As stated earlier, the cost is the same (maybe less) with a 350 block. As the saying goes "No misplacement for displacement". Now if you said "I want to spend some bucks & end up with a 500/550 383", I'd think that is very doable. Just my two cents, Lorne

[85MudMonster]

Well we'll see. I'm gonna build it and then I'll have to dyno it and we'll find out how good I did. That 305 will work just fine. If I wanted another engine why would I get a 350 anyway, when I could get a 400, or just go crazy and cram a BBC into it.

[gezn2]

Well we'll see. I'm gonna build it and then I'll have to dyno it and we'll find out how good I did. That 305 will work just fine. If I wanted another engine why would I get a 350 anyway, when I could get a 400, or just go crazy and cram a BBC into it.

Before you dive too deep into the machine-work you'd be smart to get that block sonic tested to see just how much overbore it will take.
The 267s and 305s used different casting cores than the bigger displacement engines, you're probably not going to have enough 'meat' in the cylinder walls to safely punch it out to 351 CI without sleeves
Like the others have said, it's *your* money, but you can get a *lot* better bang for your buck with readily available 350 parts

[VileZambonie]

305's are great if you own a boat and a thick chain.