273 to 340 swap ?'s

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smlveightis

smlveightis

Confused in Confusion
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Going to pull the trigger on a 340, pretty sure it's a '73, and going into a '67 Barracuda with original the 273/904. Hoping to make this a plug n play swap.
Besides the motor mount/bracket on the RH side, will everything else just bolt on the 340? As in my original A/C unit, P/S pump, Alt brackets, and the exhaust manifolds. I am attempting this transplant on the "cheap". Any help/suggestions would be most welcome!!
I'm pretty sure this has 1.88" INT valve heads, due to the year of thie engine. Will I encounter any problems bolting on a set of 2.02" J heads? Also I have a LD340 intake to put on top of it, what size (CFM) carb would best fit this engine? As far as I know the engine is factory stock, and this is just a street machine.
Thanks, Steve~
 
The bracket you need to change is on the left (driver's) side. If it's a 73 cast crank engine, you're going to run into balance issues. Are you planning on keeping the 904?
 
Yes, was planning on using my 904, but the seller has a 904 that was previously mated to the 340. Figured that my 904 would just bolt up to it.
What type of balancing issues are there? I am aware of the externally balancer on these cast crank engines, but am unaware of any balancing issues.
 
You'll need a 904 converter that is balanced correctly for the cast crank 340. I'm not saying it's a huge issue. It's just one of the only things you're going to run into that isn't basically a straight swap.

I've done the 273-340 swap a few times, and it's pretty simple. You shouldn't have any trouble.
 
Thanks a million! I appreciate the info. I really had not thought of that at all. Maybe I should look into picking up the 904 that was mated to it! Again, thanks!
 
By the way, do you know what cgm carb I can put on this engine? One book I read (how to hot rod SBM), stated that a 750 could/should be used. Is this too much carb in a basiclly stock engine?
 
That's a question that can have people arguing for days.

Personally, I'd suggest that on a low compression 73 340, an 1850 600 cfm vacuum secondary carb would work very well. Especially since it's an automatic.
 
won't there be a big exhaust leak from the port mismatch with the 273 ex. manifolds ????
 
Thanks for the responses! I ended up not buying the engine, it turned out to be a 318! Someone had ground off the 318 casting # off the side of the block. Couldnt tell what it was. It had J heads on it, with the internally balanced crank balancer. Upon closer inspection, after scraping off the paint @ drivers side front of block, the I.D. for a 318 was revealed. So no deal was done. Again thanks for all who responeded. I will keep these responses in mind for future reference.
 
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