The official FABO machinist/member collaboration, busted 340 thread

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I shipped the crank today. Good luck with the build!
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I'd really be stoked if @replicaracer43 could snap a picture of the main saddles oiling holes. And when he inserts the bearing halves.. how they line up on the saddle, or not so much... and the bearing needs massaged open towards the main feed hole. I'd like to see how many are like mine.
 
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Weighing out the new piston and rod combo is pretty interesting, but not at all suprising. This engine came with a set of ancient TRW flat tops, they weigh 732.5 grams, compared to 610.4 grams for the KB flat tops

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Rod weight for factory 340 floating rod equipped with arp rod bolts checked in at 751.6, the new scat floating I beam rods check in at 574 grams for comparison

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Those are some huge weight differences. That can't do anything but help.
 
I will say this though. There've been MILLIONS of those old heavy *** TRW pistons used through the years and they ran fine.
 
RustyRatRod said:
I will say this though. There've been MILLIONS of those old heavy *** TRW pistons used through the years and they ran fine.
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Exactly. I am building a 440 with the old TRW six pack pistons and rods.

Others talk about how heavy they are, and they are technically correct about the weight.

But does it really matter in an RV engine that won't spin north of 4500 rpm?

As long as you have a good set of rod bolts I say no.

Bottom line, for a 340 street engine if I had a set of the TRW forged heavy pistons would I use them? Sure. If I had to buy new pistons though the lighter ones (provided a rebalance is in the budget) are a no brainer.
 
mgoblue9798 said:
Exactly. I am building a 440 with the old TRW six pack pistons and rods.

Others talk about how heavy they are, and they are technically correct about the weight.

But does it really matter in an RV engine that won't spin north of 4500 rpm?

As long as you have a good set of rod bolts I say no.

Bottom line, for a 340 street engine if I had a set of the TRW forged heavy pistons would I use them? Sure. If I had to buy new pistons though the lighter ones (provided a rebalance is in the budget) are a no brainer.
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It sure didn't matter in A12 cars that were raced the hell out of either.
 
To say this block was in poor condition would be a severe understatement, even checking the decks in the block squaring fixture indicated one side unlevel front to rear, and the other deck unlevel and twisted... after decking the block to a true square condition, it resulted in the piston out of the deck far enough to push our compression ratio a bit high, so the solution was to mill the piston tops to end up at about 9.6 static with the iron heads. I'm going to call this thing "problem child" I do believe. But, we are making progress! Stay tuned!

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