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Old 06-26-2008, 01:22 PM
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Originally Posted by Ed ke6bnl
My 72 el Camino is using oil like the Valdez in Alaska. It was a no history 350 motor from someones 67 nova was good for several years, I still have the maybe original 307 that was
in the truck when I got it
and I have the chance to get another 76 el Camino 305 for the motor,to swap into my 72. Is one with the 305 versus the 307
better then the other. Fuel economy is now an issue not when I first put the 35o in a few years back. Your thoughts thanks Ed
These can be though of as the 307 being a 283 stroked with a 327 crank and the 305 as a debored 350.

The 305 has a 3.48 stroke and the 307 a 3.25 stroke. The difference probably isn't noticeable. Both engines were an attempt in time to put the torque peak at a lower RPM on a smaller engine to give it more mid RPM punch without resorting to more displacement.

There is no guarantee that a smaller engine will get better gas mileage in a larger vehicle. It takes X amount of power to make it go. Whether that power is coming out of a 305, 307 or 350 it's the same. The difference is how much throttle opening is used, the smaller the engine the more throttle opening used at any given RPM.

An example, my S15 originally had a 151 Iron Duke and a 5 speed. It now has a 350 with a 4 speed auto, overall the fuel consumption hasn't changed much. Unless I get on it.


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Old 06-26-2008, 10:33 PM
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Close your eyes and pick one...then put vortec heads on it and never look back!
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Old 06-27-2008, 03:08 AM
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The larger bore of the 307 makes up for its shorter stroke. Torque is for the most part a function of displacment.

The 307 has the advantage of flat-topped pistons, as opposed to the 305's dished and possibly bevelled-on-the-edge smoggers.

My personal opinion on why GM started making the 305 is that it was cheaper to build, since the 307 required a different crankshaft casting from the 350. They made all their 267-305-350 cranks from the same casting, and simply machined a little extra metal off the counterweights to balance the smaller engines.
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Old 06-27-2008, 05:17 AM
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What about a 305 crank in a 307? I f you were going to change pistions you might as well get the extra cubes. 333 with a .030" overbore.

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Old 06-27-2008, 11:28 AM
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the difference in torque production that the .23" longer stroke will maek is negligable as soona s you consider that the larger bore of the 307 will have less shrouding and better quench with flat top pistons. I would go with the 307 because of the larger bore and better piston design- really they're pretty equal but the 307 has a slight advantage.

Its like comparing a 348 to a 350, the 348 has the larger bore and better rod ratio which usually makes a difference in both torque in HP- its why people go through the trouble of building a 348.
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