360 block help thank you

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Bigboy 68

Bigboy 68

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I’m not that familiar with the 360 engine my question is I know the crank is different can I use 340 pistons and rods in the 360 block the 360 I picked up as a standard bore block and I believe it needs to go 40 over to clean up the rust Any help appreciate it thank you
 
std bore on 340 is 4.040 and yes the pistons and rods will work. The CH is taller on the 340 piston and should run around .018 above deck. Use gasket thickness to set quench and desired static compression.
 
I think that if you are using factory 340 pistons, they will hit the counterweights of the crankshaft when turning the engine over. Can they be clearances? Not sure. I have a old article to modify the TRW replacement pistons for the 73 340 for use in a 360
 
Unless you yourself are a machinist, it will be cheaper to buy 360 pistons for what you want. In order to put 340 pistons in a 360, you will need to cut the top edge of the piston decks at a 45 degree angle, to I think .200 wide....IIRC? Then you need to mill the skirts to clear the counterweights, as mentioned above. Then you have to mill the piston tops too. Tom Hoover came up with all this back in the mid 70's when there were no 360 pistons available. Today, there are 4011 choices of 360 pistons.
 
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No, you cannot if you use the 360 crank. The 340 pistons have a much taller compression height and will stick out of the block by over .150" if used on a 360 crank!

You can only put the smaller stroke of the 340/318 crank in if you you use the 340 rods + pistons. But, the main bearing diameters are smaller for that crank than the 360 crank mains. So you have to get what is essentially a shortened stroke 360 crank. I do believe that SCAT (or someone) makes that animal.

And then there is the matter of balance. Stock type 340 pistons are not even close to balancing with a 360 crank. There may be some lighter 340 pistons that will work out.. it has to be computed. But that does not solve the stroke and rod+ compression height issues as mentioned above.

The rods completely interchange and are the same rods.

Are you trying to re-use the old 340 pistons? Tell us what is the use/goal for this engine so we can perhaps help better with alternatives.
 
OK wait'
what would be the point of boring a 360 to fit 340 pistons and then installing a short stroke 318/340 crank, on spacers I'm guessing, or a big journal crank?
Not too many years ago; we used to read about this all the time, and a friend of mine, whom I have no reason to doubt, claims to have done this exact thing; namely 340 pistons into a 360 with the 360 crank, and open-chamber heads. Yes, he owned a machineshop at the time, 20 years ago. And yes it was quick.
However,to be accurate; I did not see the project go together.
In today's market, I don't see this as in any way feasible. Do-able yes. But there's way cheaper, and far better ways to rebuild your 360.
The cheapest way I have seen; is to just slam the tallest hypers in there on bushed rods. Done deal,you can take it apart as often as you think necessary, with re-useable gaskets.
My KB107s came in at .012 below deck. Add an .028 gasket and a closed chamber head and yer done. If you have to clean up the decks, then cut her to zero and use the FelPro .039s. Depending on your total iron chamber volume, cam selection may be troublesome. With alloys, give her to the max.
 
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Correct the 340 piston will stick out of the deck about .150....you are going to need a head gasket .185 thick...aint going to work...plus the skirts will hit the crank.....

Tom Hoover 360 thing was great back went there were no 360 pistons available...now there are more 360 available then 340 pistons since there were millions of 360 made...1971 to 2002...
340 made from 1968 to 1973....do the math...

Buy a set of 360 pistons....bore the block the minimum needed to clean it up
 
It can be done but with late 340 8:1 pistons not the 10.5 ones but these days it's cheaper to buy the right [much lighter] piston.
 
I’ve done it. It works if you want a cheap 360 with some compression, if you have some stock or forged pistons laying around. Watch the piston to head clearance, as said earlier the crank journal gets close to the bottom of the piston.
 
raymond said:
It can be done but with late 340 8:1 pistons not the 10.5 ones but these days it's cheaper to buy the right [much lighter] piston.
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The only low compression 340 pistons out there these days (like Silvolites) will still stick out the top of the deck by something like .137"...... still needs milling on the pistons. Now if you milled those by about .040" and use open chamber heads, and a .050" thick head gasket, then they would have decent head clearance. As noted, you'd have a really high compression 360..... works out to around 12:1 ! But if you then put in a big enough cam to run on pump fuel with this static CR, now the piston-valve clearance will become a big problem. So now more milling...... and at some point, you realize it is a solution that creates more problems than it solves.
 
KB107s, zero deck.

Aren't the 70 over KB107s used for the 340?
I remember reading that...
 
Jimacuda said:
KB107s, zero deck.

Aren't the 70 over KB107s used for the 340?
I remember reading that...
Click to expand...

wrong compression height. ....kb107 has ch of 1.67...piston will be down in the bore aways.
 
70aarcuda said:
wrong compression height. ....kb107 has ch of 1.67...piston will be down in the bore aways.
Click to expand...

Knew I forgot something...:)
From Campbell enterprises....
Kb 107 in 70 over can be used in a 30 over 340 with 360 crank.
Details....:D

Looks like they're on sale.
 
mderoy340 said:
std bore on 340 is 4.040 and yes the pistons and rods will work. The CH is taller on the 340 piston and should run around .018 above deck. Use gasket thickness to set quench and desired static compression.
Click to expand...
I think I milled .070 thousandth off the piston top and compression was still up there.
 
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RustyRatRod said:
Exactly. I love when people jump on the "no you caint" when "yes you can".
Click to expand...

Yeah but you can do a lot of things with the same result that are actually quite impractical and even irrelevant to the times we live in. Buy a set of pistons.

This question could have been answered in one reply, but someones always gotta get type happy and plant a seed of confusion, contribute guesses and or add more questions offshoot questions derived from confused accounts heard from a 3rd cousins brothers uncle daddy.lol
 
Up till the last couple of decades, you simply could not get decent off-the-shelf street pistons for a 360. Your choice was basically cheap replacement cast pistons that would end up .100 below deck at TDC or high-dollar forged 11.5:1 pistons. Today you can get zero-deck hypereutectic pistons for around $300. No reason to go to all the trouble Hoover went to way back when to turn low compression 340 pistons into ten+ to one 360 pistons. Unless you're just a glutton for punishment. . . .
 
MOPAROFFICIAL said:
Yeah but you can do a lot of things with the same result that are actually quite impractical and even irrelevant to the times we live in. Buy a set of pistons.

This question could have been answered in one reply, but someones always gotta get type happy and plant a seed of confusion, contribute guesses and or add more questions offshoot questions derived from confused accounts heard from a 3rd cousins brothers uncle daddy.lol
Click to expand...

I agree.....but "back then" it was about the only way since no one made high compression 360 pistons "YET".
 
AJ/FormS said:
The cheapest way I have seen; is to just slam the tallest hypers in there on bushed rods. Done deal,you can take it apart as often as you think necessary, with re-useable gaskets.
My KB107s came in at .012 below deck. Add an .028 gasket and a closed chamber head and yer done. If you have to clean up the decks, then cut her to zero and use the FelPro .039s. Depending on your total iron chamber volume, cam selection may be troublesome. With alloys, give her to the max.
Click to expand...
This ^^^^^^^^^^^^^^^^^^^^^^^
Though I’d run floaters, not pressed rod and pins.
I like zero deck it mostly due to the previous issue of no thin head gaskets at the time of my builds. You can get gaskets at most any thickness.

Jimacuda said:
KB107s, zero deck.

Aren't the 70 over KB107s used for the 340?
I remember reading that...
Click to expand...
With the 3.58 crank for the smaller journal 318/340 crank. I have said crank. It makes for a CID of 372/373 rounded up a few tenths.

Wyrmrider said:
like 305 chevy fishing weights
Click to expand...
Corrected in quote... LOL
 
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