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Old 04-08-2013, 01:36 PM
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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

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Old 04-08-2013, 01:58 PM
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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 power...you would need to start at the heads and the the valve train, from the cam shaft up.

Ray
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Old 04-08-2013, 02:47 PM
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The 307 is a good engine to hot rod and responds well to typical hot rod upgrades.
Like cam, compression ,, valve size, head port flow,, induction and exhaust system upgrades.
But increasing the bore size in of it self will not add power in any meaningfull way.

If you are going to bore it for new pistons then do that for that purpose.

As said get better heads for your 307. ALL the stock 307 motor heads suck.
So lots of good choices there.

check the cylinder head casting number, between the valve springs on your 307 heads.

What other SBC heads do you got kicking around? (casting numbers)
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Old 04-08-2013, 02:51 PM
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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.
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Old 04-08-2013, 02:52 PM
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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
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Old 04-08-2013, 03:00 PM
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Quote:
Originally Posted by Ferabel73 View Post
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?
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Old 04-08-2013, 03:02 PM
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S/R or S/R torker heads? they are different.

The S/R torker 64cc head is a good head for your 307.

When using this 2.02x 1.60" valve head on a 307 then boreing the engine by .040" is a good thing as it allows for more valve space.
( DO not bore to 4") +.040" over bore for +.040" flat top 307 pistons is plenty.

Then, you want to mill the 64cc heads to get the chamber smaller for good compression on your 307.
(and deck the block too). Do not assume the "64cc heads" are actualy 64cc.
Measure them. I bet they will CC bigger than 64cc. Getting the real compression ratio correct is essential to getting the high perf 307 SBC build right.
You got some good hard parts to work with. Will really shine with the right tweeks.

This is a very good engine to supercharge (but with a low compression ratio).

The S/R torker head gets even better when hand ported. (makes big power)

How do you plan to use this 307? ( consideration for cam/compression/intake exhaust choice.)
It will make very similar power to a 327.

What is the casting number/part number on your S/R heads?

for a high perf 307 you want to get the chamber volume down to about 58cc. ( flat top +.040" over 307 pistons and 10:1cr)
getting the compression ratio right is critical.

Do not bother boreing this block to 4".. You can build a rocking 313CID small block with a +.040" bore and the stock 307 crank.

One of the keys to building up the 307 is don't dummy it down. It like the same things as a high perf 327 SBC.
And will perform very similar when done right.

Last edited by F-BIRD'88; 04-08-2013 at 03:17 PM.
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Old 04-08-2013, 03:20 PM
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This is a very good engine to supercharge (weiand 142 blower)(with a low compression ratio)
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Old 04-08-2013, 10:36 PM
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350s are cheaper to build, if you want a 307,think of it as a 283 stroker
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Old 04-09-2013, 08:28 AM
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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
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Old 04-09-2013, 10:56 AM
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The chamber spec on those heads is 67cc, not 64cc. You have to cc the heads to see what they really are.
Not a lot of replacement pistons available for the 307. The ones that are available have a modified lower pin height which drops the engine compression ratio. "rebuilder piston"

A bad thing for a naturally aspirated performance engine. (you want around 10:1cr),,, A good thing if you want to build a supercharged 307.
(You want a low engine compression ratio for supercharging 8.5:1 or less)
You can get this easily with what you got there.

Are you interested in that?

(camshaft: its a real bad idea to re-use a flat tappet cam when rebuilding a engine.)
get a new cam and new lifters.

Question? Does this 307 really need new pistons? (cylinder bore wear)?
How much power do you want? Whats the budget?

Last edited by F-BIRD'88; 04-09-2013 at 11:08 AM.
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Old 04-09-2013, 12:20 PM
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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.
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Old 04-09-2013, 01:23 PM
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Well when forced to stick to a stict budget I would not spend any moeny on stuff that won;t help that much.

I would freshen up the 307 with new rings and bearing and a cylinder hone job.
(do not bore for new pistons.) If the 307 crank is not pristine get it turned .010- .010

I would find, hand home port and use a different cylinder head with a small combustion chamber (53 to 58cc) on that 307 and use the SR torkers on something else.

Otherwise the engine is going to have a low compression ratio using those 67cc heads.

Use the 4416 heads off your 305, on the 307. (If your 305 has the good #4416 or #601 heads, use 'em)
Port them, Don;t be shy here add 1.94" intake valves and get a valve job and some perf valve springs.
CC them and mill to 56 to 58cc actual measured.
use a felpro 1094 steel shim head gasket.

750 carb dual plane RPM style manifold,,, headers... recurved HEI

get some gears for the car and a converter. A 10" "3500+ stall" is not too much behind a 307. (actual stall will be closer to 3000 rpm) 4.10's is great.

The erson cam will work very well in your 307 if moddied like I outlined. You want as close to 10:1cr as possible.

It will surprise you in how well it performs. But the details matter.

Use the 67cc 2.02 S/R torker heads on a 350 or .... The chamber is just too big for a 307. (unless its a supercharged 307)

Last edited by F-BIRD'88; 04-09-2013 at 01:43 PM.
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Old 04-09-2013, 01:33 PM
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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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Old 04-09-2013, 01:46 PM
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before you rip the 307 apart measure the stock piston deck clearance @ TDC (you need to know this)
Before any thing do a simple engine compression test on it.
(It may not be that bad)(if its got compression and oil pressure you can probably resurrect it with a re ring and bearing job)
"Krylon rebuild"

When you don't got much money to throw at it you got to be resourceful and spend the doe where it will do the most good.

You can "rule the streets" with this budget hopup 307 motor and a 150hp basic plate nitrous system. (potential 11sec ET's)

Last edited by F-BIRD'88; 04-09-2013 at 01:52 PM.
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