307 sbc

cbracer14 · Post by **cbracer14** » Sun Oct 04, 2009 11:22 am

How much can these blocks be bored?

falcongeorge · Post by **falcongeorge** » Sun Oct 04, 2009 12:08 pm

You want to punch it an 1/8 & build a std. bore 327, right? I have heard of guys doing this, but I have never tried it myself. I would think sonic check is a must.

cbracer14 · Post by **cbracer14** » Sun Oct 04, 2009 12:39 pm

I was wondering if these castings are the same as the 2 bolt 4 inch blocks only with the smaller 3 7/8 bore. Also does anyone have any experience with a 3 7/8 bore x 3 3/4 stroke combination?

Wolfplace · Post by **Wolfplace** » Sun Oct 04, 2009 12:50 pm

cbracer14 wrote:I was wondering if these castings are the same as the 2 bolt 4 inch blocks only with the smaller 3 7/8 bore. Also does anyone have any experience with a 3 7/8 bore x 3 3/4 stroke combination?

=
No they are not

defrag010 · Post by **defrag010** » Sun Oct 04, 2009 12:58 pm

The first old rebuilder I worked at, they would "punch out" large journal 307 blocks to 4" and build 350's with them. They would build them with the used STD bore pistons that came out of core engines..

Wolfplace · Post by **Wolfplace** » Sun Oct 04, 2009 1:11 pm

defrag010 wrote:The first old rebuilder I worked at, they would "punch out" large journal 307 blocks to 4" and build 350's with them. They would build them with the used STD bore pistons that came out of core engines..

=
Kept a lot of repair sleeves in stock did he,,,

I built a number of 482's many moons ago before I even knew what a sonic tester was
I also put in a number of sleeves
Always wondered why the same combo was a complete turd one time & the next one ran good
And why I had to run shop rags taped to the breathers on one & the next was fine,,,,

Then I "discovered" sonic testing,,,

mallow415 · Post by **mallow415** » Sun Oct 04, 2009 2:28 pm

I ran a 307 block .060 over 2bolt studed with a 3.48 gm steel crank, alum rods, ross dome pistons roller cam and sportsmanII heads ported by Rons 2.08 valve. The motor was awesome had great torque. Ran that motor for 10 years and finally pucked a head gasket and it hydrulic on me and it was over. But it was was very impressive motor.

the nitro man · Post by **the nitro man** » Sun Oct 04, 2009 4:41 pm

i know a guy that put a 400 crank in a 307 block & it made like 359 cubic inches. it's a good combo in my opinion if your limited to cubic inches of 360 or less.

BrazilianZ28Camaro · Post by **BrazilianZ28Camaro** » Sun Oct 04, 2009 5:43 pm

the nitro man wrote:i know a guy that put a 400 crank in a 307 block & it made like 359 cubic inches. it's a good combo in my opinion if your limited to cubic inches of 360 or less.

Your friend had too much material removed to clearance the block ?

Alan Roehrich · Post by **Alan Roehrich** » Sun Oct 04, 2009 6:49 pm

You can bore them at least 0.040" safely. Some will go 0.060".

The best thing to do with a 307 block is to sell it to a guy who races a 305 in Stock or Super Stock. They sleeve a 307 block down to 305 bore to make a real stiff block. They'll usually pay enough for a 307 block that you can buy a complete 350 core with what you get.

I wouldn't give $0.50 for a 3 7/8" x 3 3/4" engine. There's no valid reason to fool with it. The bore restricts breathing so much you can't feed the cubic inches you gain with stroke. Reminds me of all of those 305 "conversions" with 400 cranks.

You can buy 350 blocks anywhere, and the market is full of rotating assemblies. If you don't like one piece rear seal cranks (and I don't) and all you can find is late model blocks, get a rear seal adapter and put a two piece setup in it.

stock z/28 · Post by **stock z/28** » Sun Oct 04, 2009 9:44 pm

As was said they are not the same casting as a 350 2 bolt.

I have probably bore around 20 of these to 4 in back in 70s and early 80s and used some form of std 4 in bore piston --302-327-350.

I have never had any issue with them, and a few are still running today.

I used to race a couple with used 302 z/28 pistons and the sealed up ok.
Used to use a spaced and a head land type top ring.

I would certainly check the cyl wall thickness with an ultrasonic tester now, back then I just used a modified caliper with a few tig welds and a dial indicator, that was slipped though a head bolt hole to try and get a thickness dimension.

Lot of better way to to do it now. I know I was probably lucky but no cracked cyl walls.

I would certainly use a 4 in bore block now.

Jeff

falcongeorge · Post by **falcongeorge** » Sun Oct 04, 2009 9:47 pm

Alan Roehrich wrote: I wouldn't give $0.50 for a 3 7/8" x 3 3/4" engine. There's no valid reason to fool with it. The bore restricts breathing so much you can't feed the cubic inches you gain with stroke.

I didnt want to say that for fear of starting a p*ssing match, but now that you have said it,well...

BrazilianZ28Camaro · Post by **BrazilianZ28Camaro** » Sun Oct 04, 2009 10:30 pm

HAVE SOMEONE HEARD ABOUT 307 BLOCKS BEING A LOW NICKEL CASTING THAT WEAR FASTER THAN OTHER SBC ???

THERE ARE CLEARANCE PROBLEMS STUFFING A 3.75 CRANK IN IT?

Alan Roehrich · Post by **Alan Roehrich** » Sun Oct 04, 2009 10:36 pm

The 307 blocks were made out of the same iron as the 350 and 400 blocks of that era. They wear just fine.

I've never had the slightest desire to even consider putting a 400 crank in a 307 block, so I have no idea whether or not it will clear. It probably will. Whether or not you'll hit water trying to get the rod bolts to clear the bottom of the cylinders at the pan rail is another matter entirely.

I suppose if you have a burning desire to build a 4000 RPM small block, putting a 400 crank in a 307 block may be the way to go. I cannot think of any legitimate reason to do it.

Just because you have some parts lying around does not mean putting them together is a good idea.

By the way, please, if you do not mind, turn "caps lock" off.

falcongeorge · Post by **falcongeorge** » Sun Oct 04, 2009 10:52 pm

Alan Roehrich wrote:
I suppose if you have a burning desire to build a 4000 RPM small block, putting a 400 crank in a 307 block may be the way to go. I cannot think of any legitimate reason to do it.