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Ferabel73 04-08-2013 01:36 PM

307 built
I have an stock 307, and was wondering if I bore the cylinder to .40 will this increase the HP or it will remain the same as it is right now

69 widetrack 04-08-2013 01:58 PM

I'm sorry to say that the only noticeable horse power gain you will get by boring it out .40 would be because of the new rings and pistons compared to the older used ones in it now...the 7 or 8 extra cubic inch isn't going to make that much difference. If you want the 307 to have more would need to start at the heads and the the valve train, from the cam shaft up.


techinspector1 04-08-2013 02:51 PM

Agree with Ray.
The reason that a fellow would bore the cylinders is usually because they are imperfect for installing new pistons and/or rings. The cylinders do not wear evenly side to side or top to bottom and can be egg-shaped as well as funnel-shaped or both, so you want to bore and hone the cylinders to make them perfectly round again, like they were from the factory. At the same time, you would hone the cylinders with a certain grit number of stone, depending on the material the piston rings will be made from, in order to allow the rings and the cylinder surface to "wear-in" together and form a smooth surface with each other to seal in the combustion gases and make power.

Ray already knows this stuff, but we'll have a little math lesson for ferabel while we're at it.
.40" or .400" or 0.400" would be read as four hundred thousandths of an inch, or nearly half an inch.
0.040" would be read as forty thousandths of an inch and would be an acceptable overbore dimension. The reason for adding a zero in front of the number is to tell the person looking at it that the dimension is less than an inch, so that there are no mistakes when using the number to calculate other dimensions from it. For instance, 4.040" would be the cylinder bore diameter of a 350 Chevy cylinder block after boring it 0.040".
Also, you have to think about this....When cutting the cylinder bore, you would only take out 0.020" (twenty thousandths of an inch) on the radius of the cylinder, because as the boring bar turns to take material out, it is cutting then entire diameter of the cylinder larger, so 0.020" on a side (the radius) equals 0.040" finished bore (the diameter) increase.

0.004" would be four thousandths of an inch....
0.0004" would be four ten thousandths of an inch, also expressed as "four tenths".
0.00004" would be four one hundred thousandths of an inch, also expressed as "four hundredths". Automotive machine work does not get into hundred thousandths, I'm just showing this so that you can begin to get wrapped around the numbers.

Ferabel73 04-08-2013 02:52 PM

Ok, I forgot to mention that I got a new set of heads world S/R with 64 cc chambers and 2.02 intake valvs and 1.60 exhaust

techinspector1 04-08-2013 03:00 PM


Originally Posted by Ferabel73 (Post 1664295)
Ok, I forgot to mention that I got a new set of heads world S/R with 64 cc chambers and 2.02 intake valvs and 1.60 exhaust

So, are you planning to tear the motor down and do a rebuild?

vinniekq2 04-08-2013 10:36 PM

350s are cheaper to build, if you want a 307,think of it as a 283 stroker

Ferabel73 04-09-2013 08:28 AM

Sorry I couldn't replay to any of the posts yesterday, the casting of the heads is 42660, as for the camshaft it's an ERSON E10026 int.214 EXH.224 ,valve lift it says .443 int. 465 EXH with a duration of .050

Ferabel73 04-09-2013 12:20 PM

No much room left money wise , I got a new camshaft it's an ERSON E10026, as for supercharged I don't think I'll go that far no budget for it, all I want as for power maybe 330 or 350 HP.

spacytracy 04-09-2013 01:33 PM

Wish I could absorb most of the knowledge that F-Bird has. I follow his posts exclusively just to learn. Do yourself a favor and follow his recommendations exactly!

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