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Author Topic: mixing and matching cranks  (Read 4866 times)
Flowjoe
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« on: May 10, 2006, 11:24:00 PM »

OK, Say you have a 307 block  and a 350 crank (large journal)...can you drop that crank into t he 307 and get a 329 CID (if my calculaatins are correct) motor?  Are there problems I'm not seeing?  Isn't that the same as dropping  aa 400 crank into a 350 block and getting a stoker motor?  Or the same way the 302 was created (283 crank into 327 block)?
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RAfbody
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« Reply #1 on: May 11, 2006, 07:46:50 AM »

The crank should bolt in the block ok but you would have to get some custom pistons or shorter rods to compensate for the difference in stroke.
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Russ
Flowjoe
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« Reply #2 on: May 11, 2006, 08:43:00 AM »

I wouldn't think the rods would be a problem since they are the same for all small blocks of that era.  Pistons might prove more difficult...hadn't considered that...how do they handle stroker motors built around a 350 block?   I mean, they throw all kinds of non-350 cranks into 350 blocks...perhaps we are talking custom pistons on t hese apps.
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red69
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« Reply #3 on: May 11, 2006, 09:15:08 AM »

What you would have would be an over bored 305. If you really wanted to do this you should look to see if someone makes that piston in the 307 bore size. 307 was 3.875 bore 3.25 stroke. 305 was 3.736 bore 3.48 stroke. Hope this helps.
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Flowjoe
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« Reply #4 on: May 11, 2006, 09:39:51 AM »

I hadn't considered where the 305 sat in all of this...strictly looked at old school bores and strokes (plus I have a good 350 crank and a good 307 block...thought it might make something).  Good suggestion...I'll look and see.
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pdq67
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« Reply #5 on: November 27, 2009, 03:44:31 PM »

Check Speed-O-Motive out.

pdq67
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Stingr69
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« Reply #6 on: November 28, 2009, 07:05:26 AM »

Throw that block in the trash. The pistons will need to be be $$$ custom made. The bores will shroud the valves too. You will never get any HP improvement and it will cost more to build too.

350 blocks are inexpensive. Not quite as inexpensive as a 307 block but still.....  Smiley

-Mark.
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hotrod68
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« Reply #7 on: November 28, 2009, 11:51:12 PM »

The biggest problem would be the bore/stroke ratio. 307s and 305s were slugs for a reason--the bore was way too small for the stroke. The 302 screamed because it had a large bore--4"--and a short stroke--3". The 307 with it's 3.875" bore and 3.25" stroke crank created a lot of internal friction and the 305 was even worse. While this was adequate for a smog motor that never saw more than 4000 rpm as a rule, it's a disaster for performance. And as Mark said, the small bore will shroud the valves as well. Pretty much all a 307 block is good for is a boat anchor. Good luck!
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HotRod'68  1968 SS350 coupe undergoing frame-off resto/rod. 386/350/4.11s
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« Reply #8 on: December 04, 2009, 05:10:59 PM »

Bore the 307 block to 4".I've never done it but heard that the blocks are "USUALLY" thick enough.Then you have a std bore 327.
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JohnZ
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« Reply #9 on: December 05, 2009, 11:01:30 AM »

Bore the 307 block to 4".I've never done it but heard that the blocks are "USUALLY" thick enough.Then you have a std bore 327.

Nope. The 307 block won't take a .125" overbore.
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'69 Z/28
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« Reply #10 on: December 06, 2009, 12:09:12 PM »

I agree with Stingr69, throw it in the trash. I would use a 327 small journal block and a 283 steel crank. 2 bolt main will be fine up to about 400hp if you build it right.

Buddy
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