340 blocks

[Scat Pack Fever]

Hello!

If I am going to build a 340 for the street, does it matter what year of block I buy? THere is a 1971 340 block for $350 in my area and was wondering if that was a good deal or if it really matters what year of block I go with. I know the heads make a difference, but I wasn't sure about the block.

[wart1de]

1971 is meant to be a good year for blocks but it'll need to be sonic tested if you are going for big power.

[MEK-Dangerfield]

1971 is meant to be a good year for blocks but it'll need to be sonic tested if you are going for big power.

 

     

You also need to know how much it has been bored, if at all. If it's 60 over, I don't think I would bother.

[Aussie Challenger]

Just check and make sure that it doesn't have a later crank in it, they were cast, many things have been changed on rebuilds over the years.   

[Scat Pack Fever]

Actually it is a bare block. What is sonic testing?

Thanks,

Robert

[Aussie Challenger]

An electronic devise that measures the thickness of the bore, it can show if the bore casting is central or there are thin spots which can crack or even break through when motor is bored.

[HemiOrange70]

Sonic testing should run no more than $100. Also get the cylinder bore measured-If it needs no boring than 30 over is fine other than that I would pass.

[Scat Pack Fever]

I'll have to find place around here to do it then. Cool! Thanks for the info. I want to build a 340 to kill the G.M. cars

[rilko]

So are all 340 blocks the same? I understand they changed in '72? Was the compression drop in '72(and HP reduction) a result of the different heads or ?. Besides
smaller intake valves was the combustion chamber larger in the '72 heads? How do I turn my '72 340 Challenger back to the 275 HP  earlier version  - with J heads with
bigger valves and ?

THANX!

rilko

[burdar]

340's got a drop in compression in 72 as well as smaller intake valves.  The main reason for the difference in HP numbers is the fact that the rating system was changed in 72.  HP was no longer measured at the flywheel.  Starting in 72, engines were rated with all the accessories installed...with exhaust manifolds and trans installed.  This is the main reason for huge HP differences between 71 and 72.

To the OP...you could buy a complete 360 for the cost of just the 340 block.  You can dress the 360 to look just like the 340 and no one will know but you.