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Old 08-21-2002, 03:04 PM
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Lightbulb 307 performance

I am looking to beef up a 307 sb chevy engine. I have countless of testemonials of the potential of the 307 yet no one has informed me of the process of turning this 130hp sleeper into heavy-hitting contender...if anyone has any info that could be usefull please share <img src="confused.gif" border="0">

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Old 08-21-2002, 03:58 PM
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I don't know about a powerhouse, but I had a 307 in a 72 Chevelle, and it had 350 heads on it. These worked good and it brought the 307 from 130 to 230 horse. The 130 hp rating also included a 2bbl carb and all the emission crap. Once that is off you jump in horses a bit anyway. I'm sure that someone else would be able to recommend an awesome cam/crank swap.
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Old 08-22-2002, 09:12 AM
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okay this is right out of a HRM article: 307 is a stroked 283. same crank as large journal 327. use keith black #166 hypereutectics with a 4cc dome and then you need stock chevy 400 5.565 inch rods. mill the block .025 and piston deck clearance will be .005. with 30 overbore you have 311cid. with 64cc chamber heads and 4cc dome you have 10:1 compression and @350HP doesnt mention cams but whatever you can put in a 350 will work just the same.
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Old 12-25-2008, 11:33 AM
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are u guys sayin that the 350 heads will bolt up to the 307?
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Old 12-25-2008, 08:25 PM
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350 heads will bolt up physically, but you need to be aware of different combustion chamber sizes. Your 307 probably has ~70cc chambers.

Large-chamber (76cc) 350 heads will drop your compression ratio, which means power goes down a little, fuel consumption goes up a little, and you won't be able to realize the full performance gain from a camshaft upgrade. A camshaft upgrade with a compression ratio downgrade makes an engine weak at low RPM, and not as strong as it could be at higher RPM.

Small-chamber 350 heads (64cc), will increase your 307's compression ratio, and you might see a small power & fuel economy increase. The big payoff is when you go to a camshaft with more duration, which will raise the point in the RPM range where your torque peak occurs, and you'll see a significant increase in horsepower. The higher compression ratio will keep it from losing so much low-end grunt when you use a "bigger" cam.

Make sure the heads you get have the accessory holes in the ends like your current heads have, or you'll play hell mounting your alternator, power steering, etc. If they don't have the proper holes, you can't just drill and tap them and expect them not to break. Sometimes they don't, but I wouldn't chance it. '69 & '70 300HP 350 cars (not trucks) would be the primary source for small-chamber heads with accessory holes, but '96-'99 L-31 Vortec 350 truck heads are better, although they do require a specific intake manifold.

Bullheimer's right on target with using 283 pistons and 400 rods in a 307. The only available aftermarket 307 pistons have their height reduced as much as .020", and will decrease performance and efficiency, and increase the chance of detonation if you use low-octane gas.

Last edited by jimfulco; 12-25-2008 at 08:38 PM.
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