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Messed up: 307 with 350 crank and 400 rods?!

17788 Views 11 Replies 6 Participants Last post by  Super Streeter
Can't remember how I even came across this combo--it was late at night and I had a couple brewskies--but I saw someone claiming on another forum you could turn a 307 into a 328 by using a 350 crank, 400 rods, and the stock 307 pistons. Or that'd be a 334 with the same stuff +30 over. Will this, in theory, work?

This is another "way out there" idea, but could you do a similar build with a 350 crank, 5.7 rods, and 4.0L Jeep inline six pistons? You'd need to machine for the pins a tad, but would it work!? Those pistons can be found here:

I know in theory how all the math works here, but I'm always confused by compression height. Looks like it could be a fun and cheap way to run a "different" SBC. And then impress guys with what a "307" could do. ("It's a stock 307 bottom end, man--just check out the casting numbers!") I'd bet it would even get pretty decent mileage.

Thanks for any help you can give me on this one. I would think this could actually be done on the cheap, too!
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But WHY ???

Most everything costs the same ( or more ) ... just build a BIG engine .

Just something different

Ok, I know it'd be easier to build a 350 or 383 or even a 377. In ways, I agree with that. But have you seen those in guys' cars before? Me too. Haven't seen a 328 yet, though! It'd be fun. And a conversation piece. It's like a flathead ford. Certainly aren't gonna make the most power, but they are atypical and have a street cred of their own.
I did an "on paper" build using a 307/327 LJ sbc crank, 400 rods, 305 block (.014" oversize), 265 (3.750" bore pistons). Came up with something like 290 cu in. Using 305 HO heads and a mild cam, it might be an nice engine for a street rod or or something simlar.

307malibu said:
Ok, I know it'd be easier to build a 350 or 383 or even a 377. In ways, I agree with that. But have you seen those in guys' cars before? Me too. Haven't seen a 328 yet, though! It'd be fun. And a conversation piece.
But the 328 weird combination engine ... still looks like every OTHER SBC ... :(
Build a BIG engine and claim it is a 328 ... :rolleyes:

If you are limited by bore size for a certain racing class or restriction ... I could see it's usefulness ... but for a street car ... :confused:

I built a 400 block with a 3 inch stroke crankshaft ... for a guy who had cubic inch limits in his racing class ... but it was a race only type of deal.
It can be done and if I had a 307 block and pistons, a 350 crank and a set of 400 rods laying around and needed an engine REALLY bad or had nothing better to do I might be tempted to throw one together just because I have a "fetish" for assembling pieces of metal together to make something whether they should be put together or not but I sure wouldn't go out and buy the stuff to do it. However if somebody gives you the stuff or pays you to haul it away go for it. ;)
And to think, I've got a 307 (complete minus the factory 2bbl intake) with around 30,000 miles on a stand in my garage. I'm going with a simple rebuild on the factory 305 for my '78, but that '69 307 may be a better bet. Fresh pistons, and 305 H.O. heads, and it might be done cheaper than a 305 rebuild. Either way, I like your idea of being different.

In a while, Chet.
schnitz said:
'69 307 .......... 305 H.O. heads,

Now THAT I can see doing. :cool:
right on!

Seriously, you can pick up the components for a build like this for next to nothing. 400 rods are virtually throw away. And the small cube chevys by themselves are not weak. Check out this 305 build:

Lots of things have been done with a 350 or 383. Call us (schnitz, I'm including you with "us") crazy, but the idea of a small cube motor ripping the colon out of something bigger is pretty appealing.

So will this work, anyway? Does the compression height and all figure OK?
It seems like it would work on paper.this is the same trick that allowed guys to build 383's using 400 cranks and stock 400 rods in 350 blocks with 350 pistons,and was the way you did it before the aftermarket taught us anything different.Just like the early 383 buildups,the thing to watch is clearance between the crankshaft counterweights and the bottoms of the pistons skirts.If this isnt a serious race buildup and is just for fun,you should be able to make it work even if it means boogering up the bottoms of the pistons with a die grinder to make it all fit.Just remember to bevel all the edges on your handywork so that it doesnt scuff the bores.This combo should really be balanced,but if you could find a 350 crank with the junk rods and pistons available,and could weight the old junk parts,and get the new mix and match parts to weight close to the same,there wouldnt be any harm in running it on the street for a while like that.My personal opinion is that even if everything was a little lighter then the old stuff{like within about 20 or 30 grams} but all the components weighed the same,you wouldnt have an issue with durability even on a pretty hot street engine.If you did this with a stock 350 crank stock 400 rods and the stock 307 block and pistons,it wouldnt need to be a high budget deal,and worst case senerio if you whooped it up for a while and it finally puked because you never balanced it you would have wrecked a bunch of parts that are next to worthless anyway.

Now it would be even neater if you could find a way to low buck a 400 crank into that 307,but nothing comes to mind just yet.Maybe 1/8" over 305 pistons in the 307 block or something.Good luck.
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The 307 with a 400 crank was done by John Beck in an Engine Masters' challenge a while back. See

But the custom pistons required for that would make the cost pretty steep.

Again, part of the point of this build would be cost factor. Using a bunch of nearly-free parts to make a motor that would perform.
I am thinking that the buildup you are talking about used something longer then stock length 400 rods.Thats why I mentioned 305 pistons with a huge overbore.Since the 305 shares the 3.48" stroke and 5.7" rods with the 350,and all these engines have the same deck height,it would seem that if you used a 400 crank and 400 rods in the 307 and used 305 pistons,the deck height would be correct,but the 305 bore is way small,so you would need pistons for a much bigger bore.I dont rememebr all the sizes of these little engins off the top of my head,but I am thinking that a .125" over 305 piston would fit a standard 307 and would allow the use of a 3.75" stroke wih a 5.56" rod.Of course I dont kow what kind of market there would be for 125 over 305 pistons.
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