Building 340 short block

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Kenflo

Kenflo

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Have a 68 340 in the shop, had it magged, cleaned up and shot blasted. Looks like a good builder, need to go 60 over so I need some help with piston selection. I am going to have the block filled with epoxy block filler (recommended by the shop). They recommend diamond forged pistons for $1200 ?? I looked on summit site and they have some cheaper options like
KB 243 (cast hypertectic), sealed power cast, silvolite cast, all can be had for around $400. The top end will be edelbrock aluminum heads so compression will need to be 10.5 to 11. Is their a need for the expensive forged units? I'm going for more street rather than strip with the build.
 
The KB cast pistons will work fine it you are not going to use nitrous, turbo, or supercharger. Just make sure the ring gap is set to KB specs. You using "Edelbrock 360" or the "340" heads? Best set up would be the 360 closed chamber heads with pistons set to zero deck. If you don't have the heads already go with the closed chamber 360 Edelbrock heads so you can build a quench combustion chamber.
 
Why is the block being filled? What is this engine going to be used for?
 
It is being filled due to the large over bore to strengthen the cylinder walls. The goal for the engine build is high performance street, not for track.
 
Kenflo said:
It is being filled due to the large over bore to strengthen the cylinder walls. The goal for the engine build is high performance street, not for track.
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If its for the street, no way I'd fill the block.
Why not just sleeve the cylinders? Or use a different block. All that said I know it been said before, why not use an LA 360 roller block? You'd be miles ahead with a roller and 360s are easy to find plus cheaper.
 
1200 bucks for pistons??? I have CUSTOM made Diamond pistons in my stroker that were no where near that expensive....sounds like they are trying to make a BIG profit on you.

For a mostly street application, you don't need them. JMO.
 
moper said:
Why is the block being filled? What is this engine going to be used for?
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Really need to think about these questions and ask yourself what your usage and purpose intended for this build. Using sleeves may be your best bet if you are only thinking about building the 340, as opposed to the 360 roller build suggestions?

Also are you aware that the max overbore limit for a 340 block - according to the factory service manual specs - is .040 overbore? Going further with overboring increases your chances of overheating, among other things?
 
The cheapest way out would be to have the block sonic tested. there's a decent chance that for a 340 based build it's fine at +.060. You cannot fill a block you intend to street drive much. Well - you can - but it won't help you much because in order to maintain the cooling system you can only go about 1/2 way, and the highest stressed areas are mid way up and higher. The sonic test would cost you a little more than the filler and labor to do it.
 
My 340 is .060 over with no issues and it's a 72 block. I do suggest Sonic testing your block to be sure as every block is different.
 
By the time you sleeve eight holes and all the associated machining that goes with doing it right , you should have just done up a 340 resto block or an R piece.
Unless you NEED that block number , I am not going to go north of 1000.00 in block prep.
You should have it sonic checked and magged first thing.........O.K. , hot tanked , then sonic and magged.
There are more than one shelf piston in a forging that comes in cheaper than 1200.00.........I am sure of that with out even looking.
I am not a big fan of the hypers , but they are a good value for what they are. I always look to the future , where I might want to try spraying it or other enhancements.
Piston weight and a good balance job will be where you should be thinking.
No on the fill for a street motor......unless you are building a limited use serious piss pounder. For a car you want to drive and enjoy whenever you want , I'd pass on it.
 
I talked to the machinist at the shop today and he said the block filler is to strengthen the cylinder walls, maybe necessary and maybe not, he claims he does it for assurance. He fills half way and said there will be no cooling issues in fact in some cases cooling is improved? As for his recommendation on the pistons he said them hypers are junk and have seen many fail. I've been looking for 60 over pistons on the web and there really is not many choices for the 340 with stock stroke. Block filler is going to run around $400 and a sonic test could cost about the same, it already magged good and it cleaned up very good. Time to decide what to do......
 
Oh yeah! Machinist also said with the block filler in, being a street application we shouldn't need to sonic test the block.
 
To my understanding block filler is only used for drag race applications where the engine doesn't run for long periods of time. It does strengthen the block, but I would be afraid cooling would be an issue.
 
My understanding of the block filler on a street engine as it was explained to me is that we fill the block to the freeze plugs, where on a drag engine it would be filled to the top. When the filler only goes to the freeze plugs it leaves just over half of the cooling capacity still in tact on the block. Another point that I was told is that most of the heat will be near the top of the block as well.
 
Its your money. I would find a 360 roller block unless its # matching block. I think you are going to have overheating problems. How many small block Mopars has this machine shop done and filled for street use?
 
Kenflo said:
It is being filled due to the large over bore to strengthen the cylinder walls. The goal for the engine build is high performance street, not for track.
Click to expand...

They're stupid. Find another shop. 340s are thick. They can routinely go .100 over and not look back. Sounds like they build chevys.
 
Vs29H1B said:
Really need to think about these questions and ask yourself what your usage and purpose intended for this build. Using sleeves may be your best bet if you are only thinking about building the 340, as opposed to the 360 roller build suggestions?

Also are you aware that the max overbore limit for a 340 block - according to the factory service manual specs - is .040 overbore? Going further with overboring increases your chances of overheating, among other things?
Click to expand...

I have personally sonic tested a lot of 340 blocks and 71-73 360 blocks. I can tell you from first hand experience that they are consistantly thicker than the rest. By a good margin too.
 
Vs29H1B said:
Really need to think about these questions and ask yourself what your usage and purpose intended for this build. Using sleeves may be your best bet if you are only thinking about building the 340, as opposed to the 360 roller build suggestions?

Also are you aware that the max overbore limit for a 340 block - according to the factory service manual specs - is .040 overbore? Going further with overboring increases your chances of overheating, among other things?
Click to expand...

The max bore of the block should be determined by the cylinder wall thickness. NOT what the book will say. The past limits were printed for a reason and so is the current thinking and working measures of going beyond the past printed limits.

Overall, it will depend on power level sought by the builders wants.

1970Duster said:
If its for the street, no way I'd fill the block.
Why not just sleeve the cylinders? Or use a different block. All that said I know it been said before, why not use an LA 360 roller block? You'd be miles ahead with a roller and 360s are easy to find plus cheaper.
Click to expand...

Sleeveing the cylinder or cyclinders can be expensive over a cheaper block filling. Cooling will never improve with this method but it is not impossible to have a high HP engine running well in the street with half a block filled. Improvements in the cooling system maybe needed.

To the OE poster, what kind of power are you seeking?

The hyper-U slugs are fine for a lot of builds. $1200 is way to much for slugs. As said above, you can have a 1 off custom set of forged slugs made cheaper.
 
He adds block filler for insurance on a street engine? I'm not sure I'd trust him if he's that concerned. He is right - filler does strengthen - at a cost. That cost is both financial and cooling system efficiency, plus more maintenance and and faster engine wear (the oil gets hotter too). It's entirely up to you but what he's telling you (yes, in terms of piston choice too...) is of an "extreme" nature. He's "seen" too much in terms of destruction and he's planning too much for it. If it were me I'd find another builder. You'll get a better product for less money.
My advice - sonic test the block - and it should cost less. $400 is robbery. Then buy a set of pistons based on use. There is nothing wrong with hypers provided the builder follows directions in terms of piston to wall and ring gaps.
 
Wow, all good points, Thanks! I think I'm going to seriously reconsider the block fill at this point. I know that they build Chevys, but who doesn't? I think all machine shops build a lot of Chevys they out number Mopars 10 to 1!!! For my build I'm hoping for a 400 hp street friendly engine. I certainly don't want to sacrifice cooling. I may pull it out of the shop And take it somewhere else.
 
$1200 for pistons, $400 for a short fill of block filler, $400 for sonic testing.....:wack:

For a 400hp street motor: KB hypers would be fine $359, short fill of hard block $79, sonic testing $150 or less is common.....That is a savings of $1412!!!

RUN AWAY (don't walk).....JMO
 
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