Thread: 305 crank

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Hi:

I have a 305 engine and a 350, I am rebuilding the 350, I am gonna use the heads and the question is CAn i use the 305 crank on the 350?

thanks.

in theory you can, i'm not sure why you would though. It wouldnt come out to 350ci. I'm sure someone knows the bore and stroke for this combo. Also, from what i read of your post it seems that you are going to use the 305 heads on the 350. I have heard that these heads arnt very good and dont flow, just my .02

305 and 350 use the same stroke crank, 3.480".

And techinspector what do you think about the cylinder heads?? I think they are the same too.

thanks.

I thought they had different counterweights. Anyways, it will be way out of balance because the 305 has smaller pistons than a 350 and you will have to spend a lot of money getting the rotating assembly balanced. It may be cheaper to get a 350 crank balanced for a 350 and just use that.

Physically, they'll bolt on. The 305 heads have smaller valves and ports and a smaller combustion chamber (58 - 60 cc's) than the 350 heads (64 - 76 cc's depending on the head). Lots of guys have used 'em on a 350 and swear by 'em.

Here's my take on it:
With the small ports, velocity will be up and make for a great low-rpm torque motor. Flow at higher rpm's will be down due to stalling of the port, you can only move so much air through any port and the 350 will want to pump more air than the 305 port can handle at high r's.

With stock-type flat-top 350 pistons with about 7 cc's of valve relief and the block cut for zero deck, a 0.030" overbore, 60 cc chambers and around 9 cc's of gasket (0.039" compressed), static compression ratio will be at 10.56:1. With the zero deck and 0.039" gasket, you should still be able to operate on premium pump gas without detonation, assuming you de-burr the chambers, piston tops and spark plug electrodes to eliminate hot spots and use a cam with the proper intake closing point to bleed off a little of the cylinder pressure.

The cam is the next point of contention. If you're building a motor that will have good low-rpm response, but will lay down on the top due to port stalling, you'll want to optimize the combination with a fairly short cam. There's where the problem comes in. If you use a short cam with an early intake closing point to accomodate the power at low r's, you will build too much cylinder pressure to operate on pump gas. If you use a longer cam to accomodate a lower cylinder pressure to use pump gas, you've given away the power at low rpm's where you need it to accomodate the small 305 ports.

If I'm makin' this sound like a bad idea, you're right, I think it's a bad idea and a total mismatch of components.

If I were going to do this at all (which I'm not), I'd opt for dished pistons to lower the static compression ratio to around 9.00:1 or 9.25:1 so I could use a short cam and have a decent low-rpm puller. Same specs as above with Keith Black #KB193 12 cc pistons would yield 9.26:1. Then I'd use a cam something like this
http://www.cranecams.com/?show=brows...tType=camshaft

wow, yeah, i was just kiddin bout the crank thing anyway good one tech

So the best recommendation is to use the 350 crank and cylinder heads??

yep

The 305 crank will be balanced completely different than the 350 crank would be. You either have to use a 350 crank, or have the complete rotating assembly balanced and hope that it can be balanced correctly. Probably cheaper and less trouble to just go with a 350 crank.

The 305 and 350 cranks are the same casting. But, the 305 is milled through the counterweights. The only way to use one in a 350 is to have your machinest add mallory metal. Why would you do that? Much more expensive than buying a good 350 core. Your machinest will most likely have one or two on hand.

And I agree about the 305 heads.

With gas prices going up a 305 does not look like a bad deal.

Bib_Overalls : What do you mean by the gas prices. If I put the 305 heads will use less gas? And the performance? No extra problems?

thanks.

Most 305 heads are the light casting and prone to cracks. I avoid using them.

depending on the year of the 305, the heads may be the same. what year blocks are you working with? if you dont know, get your casting #'s and go to www.mortec.com and look them up!!

It a 78 305 something like that and the 350 is 82 something like that.