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Old 03-21-2010, 07:46 AM
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305 vs 307 sbc

Ok guys if you had to buld one engine and had one 305 block with crank ( 3.736 bore x 3.48 stroke ) and one 307 ( 3.876 x 3.25 stroke ) using any haed-intake-cam combo and could switch cranks what would you do? .... what do you think

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Old 03-21-2010, 07:59 AM
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Longer stroke should have a bit more torque
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Old 03-21-2010, 08:09 AM
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right .23 stroke but would you use it in the bigger 3.876 bore of the 307 or the smaller bore of the 3.736 305
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Old 03-21-2010, 08:13 AM
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It really all depends if it's a roller 305 block, mileage, wear, what vehicle it's going in, it's planned usage and how much money I feel like spending. If I had both and only the block and crank to each, I'd be inclined to sell both of them and get something with a little more bore/stroke potential.

If I just HAD to keep them though I'd probably get a set of 059 vortec heads and build the 305 if it was going in a fullsize or truck and the 307 if it was going in a smaller car.
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Old 03-21-2010, 08:50 AM
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Hands down, 307
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Old 03-21-2010, 11:59 AM
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This is just the first page of 5 pages of results from puttin' "350" in Auto Parts in the Kansas City craigslist. You guys don't make any sense to me when you come on here and say what this poster has said. It's as it he's chained to a 305 and a 307 and just can't do anything else. HOGWASH. If a guy can't find a decent 350 to build for 100 bucks, he ain't lookin' very hard. List your 305 and 307 stuff on craigslist and sell it.
http://kansascity.craigslist.org/pts/1654169105.html
http://kansascity.craigslist.org/pts/1654143598.html
http://kansascity.craigslist.org/pts/1653767050.html
...out of a 2500...should be a 4-bolt main roller cam motor with Vortec heads and 1-piece rear seal...
http://kansascity.craigslist.org/pts/1653379610.html
http://kansascity.craigslist.org/pts/1652870018.html
http://kansascity.craigslist.org/pts/1650316195.html
http://kansascity.craigslist.org/pts/1649736578.html
http://kansascity.craigslist.org/pts/1647686311.html
http://kansascity.craigslist.org/pts/1646892115.html
http://kansascity.craigslist.org/pts/1646735071.html
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Old 03-21-2010, 01:14 PM
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im not looking to buy or find an engine. i started this thread because a friend and i were sittin around the shop and it came up. he said he knew a pro engine bulider that could put a 305 together that would run better than any307. i only wanted to know what you guys thought since the 307 has a larger bore. im not saying this is what i have to work with. or that i would not take a 350 over just wanted input thanx man
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Old 03-21-2010, 01:21 PM
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Quote:
Originally Posted by 66chevy pickup
im not looking to buy or find an engine. i started this thread because a friend and i were sittin around the shop and it came up. he said he knew a pro engine bulider that could put a 305 together that would run better than any307. i only wanted to know what you guys thought since the 307 has a larger bore. im not saying this is what i have to work with. or that i would not take a 350 over just wanted input thanx man
That's quite a subjective statement. I think your friend is blowing a little smoke, personally. Not that making a hot 305 or 307 can't be done, it just seems like your usual wrenching b.s. that people like to perpetuate.
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Old 03-21-2010, 01:45 PM
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Your rite valkyrite. and thats one of my most favored things i love to do. guess i wont do that here
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Old 03-21-2010, 03:37 PM
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Quote:
Originally Posted by 66chevy pickup
Your rite valkyrite. and thats one of my most favored things i love to do. guess i wont do that here
You might point out to your little friend that ultimately, HP is based on the ability of an engine to breathe. A larger bore breathes better than a smaller bore when the valve sizes are maximized for a bore diameter.

Honda tried to get around this in F1 motorcycle racing by building a 32-valve 4-cylinder 4-stroke engine that used an ovoid cylinder w/a ceramic piston- the NR500- to compete w/the then-reigning YXR-500 4-cylinder Yamaha 2-stroke engines that were stinking up the show (world champs of '78, '79 and '80- w/Kenny Roberts riding), but that's another story...

Honda did get a win w/Freddy Spencer in '83- aboard the much more traditional NS-500 4-cylinder 2-stroke, having abandoned the oval cylinder/piston concept for F1 motorcycle racing.
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Old 03-21-2010, 05:19 PM
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Bore size trumps stroke, any day of the week. More bore size means bigger valves and less shrouding, which means more potential hp.

If you want to do something out of the ordinary with the 307 block drop a 3.75"(383) crank and custom pistons into it making a 360 at .030" overbore and 366 at .060" overbore.

This stroked 307 was third or fourth place at the first year Popular HotRodding Enginemasters Challenge. IIRC he used Bowtie Vortecs on it, 2.00"/1.55" valve combo. Made pretty impressive power for what it was.
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Old 03-21-2010, 06:21 PM
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I'd just use the 305. But I guess you could use the 307 block with a 305 crank.
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Old 03-21-2010, 07:30 PM
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Quote:
Originally Posted by 94_C/1500
I'd just use the 305. But I guess you could use the 307 block with a 305 crank.
This makes 333 cu.in. at .030" overbore. Why would you go this small if it is going to require custom pistons??

Going longer yet than the 3.75 stroke would be even smarter since you have to buy custom pistons anyway. 3.875" would make a 371cu.in. at .030" over, 377 at .060" over.
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Old 03-22-2010, 11:23 AM
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Quote:
Originally Posted by 66chevy pickup
right .23 stroke but would you use it in the bigger 3.876 bore of the 307 or the smaller bore of the 3.736 305
Look at it this way, a 307 is a stroker 283 made using a 327 crank and a 283 block, two well respected engines.

The 305 is a overbore on the 262 block, a well respected crankshaft on an orphan block.

It's sometimes possible to bore a 307 to 4 inches making a 327 out of it using older blocks. It is not possible to bore a 305 to 4 inches.

The 307 even at its stock bore will accommodate 1.94 and 1.55 valves without having to carve on the upper cylinder bore. This is iffy on a 305 being dependent on guide center machining and overall position of the head on the block.

There is a lot of crap about 307s being made from cheaper iron, not true. It was nothing more that the need to provide the entry size V8 with more nuts as power take off loads for accessories increased so the venerable 283 got some stroke.

The 305 is a purpose made SMOG engine. It's basically a 1/16 overbore on the ill-fated 262 block with a 350 crank stuck in it. There was this theory floated in the late 1970's that a small bore and long stroke made for a low emission engine with a lot of torque. Chevy in particular and GM in general fell for this crap which is what you get when finance departments and the US EPA are running corporations instead of the engineers.

Example of design by government bureaucracy, I was at a company in the 1970s that added on to an existing facility. The OSHA mandated mens room had 26 sinks, 3 urinals and 3 stalls. Needless to say, we had clean hands and a long line.

Bogie
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Old 03-22-2010, 05:00 PM
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Quote:
There was this theory floated in the late 1970's that a small bore and long stroke made for a low emission engine with a lot of torque. Chevy in particular and GM in general fell for this crap which is what you get when finance departments and the US EPA are running corporations instead of the engineers.
I'm no expert on this but quite a few very hi output per cubic inch modern engines have a somewhat small bore and long stroke. Many late model Hondas do,like the 2 hp per cubic inch S2000. The Chevy LS V-8 has a smaller bore and longer stoke than the Gen1 SBC and makes more power.I would think that bore and stroke ratio is just one part of the whole package and does not by itself say the engine is a inferior design.
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