School me on 307 blocks

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DeezNutz
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School me on 307 blocks

Post by DeezNutz »

So I picked up this car last year and after doing some research I found out that it has a 397020 casting 307 with a 3.75 stroke crank. Kind of an oddball, but I guess it was built out of some leftovers from an Engine Masters deal around 2003. It is just a little 11 second footbrake bracket car at this point.
I have read that some of the 307's can go to a 4" bore. This sure would make pistons easy when its time to freshen this thing up. I know that it will need a sonic check to be sure.... but what is the real world experience on going 4" bore on this casting?
mag2555
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Re: School me on 307 blocks

Post by mag2555 »

Take it to a shop to have one Bore sonic tested if you do not get a clear cut answer here.
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
pdq67
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Re: School me on 307 blocks

Post by pdq67 »

I CAN'T PROVE it, but I have a feeling that the later, still small journal, 283 blocks MIGHT bore to 4.030" over but I would sure sonic check it before I went that far.

I say this because of the early, small journal 302" engine. The '67 302 engine here.

I have a good .020" over '66 283 block out in my garage just for maybe another old, "Junk 301" build.

pdq67
Walter R. Malik
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Re: School me on 307 blocks

Post by Walter R. Malik »

DeezNutz wrote: Thu Jan 30, 2020 12:01 pm So I picked up this car last year and after doing some research I found out that it has a 397020 casting 307 with a 3.75 stroke crank. Kind of an oddball, but I guess it was built out of some leftovers from an Engine Masters deal around 2003. It is just a little 11 second footbrake bracket car at this point.
I have read that some of the 307's can go to a 4" bore. This sure would make pistons easy when its time to freshen this thing up. I know that it will need a sonic check to be sure.... but what is the real world experience on going 4" bore on this casting?
WHY ...?
4" bore blocks are plentiful and ruining a 3 7/8" bore block is not the thing to do in my opinion.

If it is the engine I am thinking of, it was built by John Beck, not with just leftovers, and did quite well in that 1st contest pitting 366 maximum cube street engines.
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Ericnova
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Re: School me on 307 blocks

Post by Ericnova »

pdq67 wrote: Thu Jan 30, 2020 3:29 pm I CAN'T PROVE it, but I have a feeling that the later, still small journal, 283 blocks MIGHT bore to 4.030" over but I would sure sonic check it before I went that far.

I say this because of the early, small journal 302" engine. The '67 302 engine here.

I have a good .020" over '66 283 block out in my garage just for maybe another old, "Junk 301" build.

pdq67
The '67-68 small journal 302 engines weren't built by Chevrolet using overbored 283 blocks....they just dropped the 3.00" stroke crank into already 4.00" bore 327 block castings.
The late production 283 blocks are less likely to successfully bore to 4.00" than some of the earlier blocks
DeezNutz
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Re: School me on 307 blocks

Post by DeezNutz »

Walter R. Malik wrote: Thu Jan 30, 2020 5:30 pm
DeezNutz wrote: Thu Jan 30, 2020 12:01 pm

WHY ...?
4" bore blocks are plentiful and ruining a 3 7/8" bore block is not the thing to do in my opinion.

If it is the engine I am thinking of, it was built by John Beck, not with just leftovers, and did quite well in that 1st contest pitting 366 maximum cube street engines.
This is not "the" engine that was in the competition. I found that it was built with leftover parts from what was not used on the engine that competed.

Sure its pretty easy to just transfer everything to a 350 block....this is a low buck bracket car so I am just wondering if its fact or fiction about the 307 being capable of going to a 4" bore....
Do you know?
Thanks
Monza355
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Re: School me on 307 blocks

Post by Monza355 »

This is an interesting engine for sure. Do you want to share more information about the engine and the car setup ?
DeezNutz
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Re: School me on 307 blocks

Post by DeezNutz »

Monza355 wrote: Thu Jan 30, 2020 7:03 pm This is an interesting engine for sure. Do you want to share more information about the engine and the car setup ?
I dont know any real specs. I do know that it has GM fastburn heads, an edelbrock 2925 intake, and a pretty mild hydraulic roller cam have not dug into the engine at all. It runs fine on 91 octane. It came in a 73 Nova that I have slowed down to run in Summit sportsman bracket class, - 12.0 and slower, no electronics, no trans brake, no 2 steps. Pure footbrake car. TH400 and 4.10 12 bolt. Cal-tracs and QA1 single adjustable shocks
Really simple deal.
Car has run 11.60s at 115mph. I put a 600cfm dp carb on it and bolted in some weight to slow it down to 12.0xx.
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