340 pistons in a 360?

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don-vee

don-vee

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So, I have heard of a few guys doing this in the old days, using 340 pistons in a 360, I think they called it the Hoover engine. Anyway, I have a nice set of 340 standard-bore pistons laying around (I think, more on that in the second question), and a 360 that's itching for 'em. I was going to have the entire rotating assembly internally balanced anyway. So, besides the .040 overbore, anyone know how I'd go about this, and what issues I might face?
Now, I was just TOLD they were 340 pistons when I bought them at the swap, but how do I check and make sure? What are the differences? Maybe the guy sold me 360 stuff instead, it's happened to me before.
 
The piston height would be longer due to the difference on crankshaft stroke. The piston height is the measurement from the piston pin centerline to the top of the piston. If I remember correctly the 340's length is approximately 1.8 something and the 360 is about 1.6 something.
 
I think your refering the old 360 crank into a 340 block stroker trick.
Equals 367 before overbore, 372.6 @ .030, 378 @ .060 over.

You can look up piston heights at places like KB or Federal Mougal.
 
The Compression Height of a 340 piston won't work with a 360 crank. The piston would be sticking way out of the top of the block.
 
don-vee said:
So, I have heard of a few guys doing this in the old days, using 340 pistons in a 360, I think they called it the Hoover engine. Anyway, I have a nice set of 340 standard-bore pistons laying around (I think, more on that in the second question), and a 360 that's itching for 'em. I was going to have the entire rotating assembly internally balanced anyway. So, besides the .040 overbore, anyone know how I'd go about this, and what issues I might face?
Now, I was just TOLD they were 340 pistons when I bought them at the swap, but how do I check and make sure? What are the differences? Maybe the guy sold me 360 stuff instead, it's happened to me before.
Click to expand...

The Tom Hoover 360 used OEM low compression 340 pistons. The replacement TRW versions (don't have the # handy) may work too. But they had to do a lot of machining on them - milled the tops down, chamfered the outer edge and a cut under the wrist pins to clear the crank. I believe he used 340 +.020 pistons. But this was done before 360 pistons were common. The labor involved today would not be worth it unless you can do it yourself. But you would still end up with OEM cast pistons, not as strong and probably a bigger overbore (+.040") than you need to clean up. I don't recall if or how much the block was decked

The 10.5-1 compression pistons will not work because they have too much compression height and the needed cut would result with a VERY thin top or with holes.
 
don-vee said:
So, I have heard of a few guys doing this in the old days, using 340 pistons in Now, I was just TOLD they were 340 pistons when I bought them at the swap, but how do I check and make sure? What are the differences? Maybe the guy sold me 360 stuff instead, it's happened to me before.
Click to expand...

Check compression height (center of pin to top of piston):

68-71 340 1.840
72-73 340 1.740
71 360 1.584
72-86 360 1.591

Although a machinist ruler would be preferable, I think even a Stanley tape would be enough to detect the difference.
 
High compression 360 pistons have a compression height of approximately 1.67" still almost .1" shorter than a low compression 340 piston.

Doesn't seem to be worth the effort when you can get a high quality hyper eutectic piston such as a KB107 for the 360 for around $200 a set.
 
Aw, nah., I guess these won't work. They're 11.5:1 dometops. I'll measure the skirt, and if they're 340, my best solution would probably be to barter them for the pistons I want. I'm sure someone on here would love to have these 340 slugs.
 
I've done several of these conversions but... You have to use 8.5 72' and later 340 piston. In stock form the piston exceeds the deck height by .020-.030 thousands. It all depends on block and how squared it is or isn't. I tapered the piston edges and had to cut deeper valve reliefs to put in a 500 lift cam. I also did alot of head work to increase the pocket to allow the piston not to make contact with head. With all this work it still had tooo much compression and couldn't truly run full advance. Seriously it could of run on alcohol. My advice is Dont do it. Pay the money for some kb's. You would make more power with less compression running full advance not to mention the cost of racing fuel vs. regular pump gas.
 
Used to be that you could not get any high compression 360 pistons...so as said tom hoover, used the 72+ piston, milled the top of pistons and cut the skirts to work in a 360 block....

now there are high compression 360 pistons that drop in with no extra machining...so why bother with all the extra stuff...
 
340sFastback said:
The Compression Height of a 340 piston won't work with a 360 crank. The piston would be sticking way out of the top of the block.
Click to expand...
Yes and no.
It really falls into the " why the hell would you " file , but a shorter rod would certainly work.
Different rod big end width and pin bore aside , there is nothing that can't be done if your dedicated or foolish enough. LOL
 
it works in my 65 cuda
13.91s @101.80s
only problem is it needs good gas 100 octane
or the head gaskets do not hold
head gaskets last about 3 years
 
grave-digger.jpg


I wish KB 107/167s were $200 a set! Man, can you believe the price increase over a span of 5 years!? True sign of an economy in the toilet.

And yes, the compression distance of a 340 piston on a 360 crank will net you a - number above deck.
 
Inkjunkie I am going to contact you before I make a serious move from now on. Perfect point check the date..
 
DaveBonds said:
I wish KB 107/167s were $200 a set! Man, can you believe the price increase over a span of 5 years!? True sign of an economy in the toilet.

And yes, the compression distance of a 340 piston on a 360 crank will net you a - number above deck.
Click to expand...

30 over KB107's $266 at Summit Racing.
 
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