The Stovebolt Site Forums The Shop Area Engine Shop Boring out a 307

I am thinking of boring my 307 out to make it a 327. I have heard that these blocks were thin-walled and weaker than some of the other blocks. Does anyone know if you can safely bore a 307 out to 4", otherwise I will just start looking for a different block.

Aaron

Just get a good 350 block and put the 307 crank and a set of 327 pistons in it. They have the same main journal and piston pin diameter.

If you do as suggested above, don't forget to have all parts that are attached to the crankshaft balanced . This includes flywheel/flexplate, harmonic balancer, rods and pistons.

This goes along with the 283/327 questions I asked awhile ago. I think Chevy did the following to get the 283-302-327-350 displacements:

Put 283 crank in small-journal 327 block and get a (Chevy)302.

Put a larger stroke crank in a redesigned 283 block and get a 307.

Put a larger stroke crank in a large-journal 327 and get a 350.

The stock bore on a 283 is 3.876". The stock bore on a C302-327-350 is 4.0" Assuming a 307 has the same bore as a 283 and a 3.25" stroke (same as 327), you'd have to bore it .124".

This is impossible, because you'd hit the water jacket before you can cut 1/8" out of the cylinder walls. Find a 327 block.

chevyman may clear this up further...

chip

Boring a SBC past .060 requires sonic testing to determine if the cylinder walls are thick enough. Older '50's blocks were a little thicker around the cylinder walls and could go .125 over. That's what the rodder's were doing at that time to get a 327. Eventually, GM cought on and started making 327's (with 4.001" bore standard). From there, you can go another .060...... Watch for heating up, though, if you do it.

Stock 283 cranks had a 3.00" inch stroke. You'd have to bore a 283 more than .125" with a 3" stroke to get a 327. And the 327 didn't come out until '62 or so, so the '50's hot rods must've used a different stroker crank to give 327 CID. Anybody know what crank that was?

Chip

Thanks for the responses. I didn't really think that they left enough material in there to bore it out 1/8th of an inch, but I wanted to know for sure.

Aaron

The 307 crank has large journals. The same as a 350. all of the 327's i have looked at had small journals.

Chiphead, you are right. I forgot that minor detail.........whoops :o
I think they turned down the rod journals to increase the stroke, but I don't know what rods were used and that would change the deck height on the pistons, so........I'm not sure what was done to increase the stroke. Probably some combination of both?

Grinsha, after '67, all 327's had large journals. No 327 engines produced after 1970 as far as I know .

Every one has side stepped the two posts from Grinsha. All the parts from the 307 that 65chevy20 has, will fit into a 350 block. I don't know any one that needs more than 15 minutes to find a good 350 block. Stock 327 STD-30-40-60 are not as cheap today as 350 pistons, but $150 should do it.
I don't remember ever hearing of anyone building a 327 out of a 283. Not that it couldn't be or never was done. What was very popular, was to bore the 283 to 4" and make a 301 (4" Bore x 3" Stroke). In the '60s this was very popular, because off-the-shelf 327 pistons (4") were probably $40 (guessing here). This is the engine Chevy copied with their 302 (4" Bore x 3" Stroke). Ok, 301.44 inches. This is really a great engine. Rod to Stroke ratio is 1.9 and Bore to Stroke is 1.33. The 327 is also real good with 1.75 R/S and 1.23 B/S. You can't get that with any other small block without aftermarket long rods.
The whole idea of mixing and matching parts is to save money.

I was wondering if you could de-stroke an early 350 with a 327 crank/rods/.030" pistons and get a 331. (327 bored .030")

That may be the way to go, as a 350 block and 327 bottom-end are still easy to find. Add a set of camel-hump heads, an Edel Performer intake, a Holley 650, and a Comp Cams XE-262, and you'd get 320 HP easy.

chip

so who's building this dream motor anyway?

Richard and Chip, that is exactly what I am planning to do now that I know my block is out of the question. I am already running 283/327 Power Pak heads with the 1.94/1.50 valves and I have the Performer intake on my engine too. I was planning next to get a Performer or other similar cam kit. Now I just need to get the 350 block and some pistons and I am good to go. Thanks for the help.

Aaron

Hey Fellas,
Correct me if I'm wrong, but I seem to remember that conrod length was the same for all SB in that era and various displacements were achieved by piston pin heights and crank stroke.I think the PowerPak heads were first used on the '56 or '57 injected Corvettes and by using these heads, a Crane "Fireball" cam, extractor headers and a Quadrajet carb on the 307, you get a nice high-revving engine without a lot of expense. Just my 2c.
OLD 42

Richard, I didn't disagree with Grinsha; I only pointed out when large journal 327's were produced.

327 and 307= same stroke, 3.25" early 327 had 2.30" mains until '68 when they were increased to 2.45". Rods were 2" until '68, then went to 2.20"

350=stroke 3.48"

What about building a 9/16" (3.5625") stroker from a 350? Now that would be unique

Yes, or pretty nearly yes. All Generation I small block rods are 5.7" except the 400 small block, which is 5.565".

gmc248
I'm not sure what you mean by "What about building a 9/16" (3.5625") stroker from a 350?". That stroke makes 358 inches and would require a custom piston, custom crank and the 5.7 rods should work. A better stroker is the very popular 383. It uses the stock 400 3.75" crank in a .030 over 350 block with the 5.7 (350) or the 5.565 (400) or the very popular 6.0" rod that all the aftermarket venders can supply.
What I think is much better, is a 377. This is a .030 over 400 block with a stock 350 crank (3.48"). Federal Mogul makes what they call a thick bearing for this combo. Pistons are made so that you can use 5.7 or 6.0 rods. You doen't hear of these very often for a number of reasons. 400 blocks are hard to find. 4 bolt 400's are harder to find and everyone thinks they have to have 4 bolts. A subject that has been discussed here in the past. The third reason is that most people have a real hard time giving up 23 cubes and having to pay to do it. The urge is to build a 408, 412 or even 427.
The reason for a 377 is a rod/stroke of 1.72 and a bore/stroke of 1.19 . This is real close to the 327. What you get is a very high revving, big inch, small block, that isn't a really big buck engine. Also, I should add that this gives up a lot on torque to the 383. The 377 is for a light car and the 383 is a better choice for a truck. That is unless you think that an old truck should have a six, then my choice is a 292.