Thread: BBC crank application

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Hello guys,
I have been working hard so it has been a few weeks since I was on the page. A friend of mine has a question that I cannot answer so I thought of you all. He has a 454 block that is supposed to be a "high nickel" block. It is marked Hi Perf pass but Mortec only shows the block as a 454 with some CE blocks four bolt. The block is a two bolt. How can we tell if the block is "high nickel" and even if there is such a thing. Block #3999289,HI PER F9 ON REAR,FRONT HI PER PASS E 10.
He also bought a forged crank that the numbers show to be a 396 piece. They told him that a 396 crank would work on a 454. That would mean that all the BBCs have the same stroke? Or is there a rod length difference?

Can't say on the high nickel content, but the cranks are different on a 396 and 454. Basically a 427 is a bored out 396, and a 454 is a stroked 427. The 396 stock bore is 4.094", and the stroke is 3.76"; while a 454 stock bore is 4.250", and the stroke is 4.00". The length of the rods has nothing to do with the stroke, but contributes to the "stack" to get to the right deck clearance/squish. Your friend will be running a 427 if it's a stock bore 454 block and a 396 crank.

Welcome to CHR!

Your block is a very common casting. Used in cars and trucks from 1972-78 it was the base for 215, 235, 240, 270 and 275 horsepower engines. The fact that it’s a 2 bolt should not disappoint as a 2 bolt block and cast crank can easily live with 450 horsepower.

I have seen a wide variety of casting identifiers in big blocks, i.e., "HI PERF", "HI PER P", "TRUCK", "PASS", "MARINE", and "TRUCK". As you have attested, it may be different front and rear. HI PERF or HI PER was used on most big block blocks and is not an indication of four bolt main caps or that it was destined for a high performance application.

Look at the front of the block, in the timing gear location. If you have a 010 stamp the block contains an additional 1% tin - 020 stamp means additional 2% nickel. They’re fairly rare and unless you’re a real serious racer, you’ll never get to the point in your build that it matters.

All stock big blocks use a 6.135” rod. As such, if you build with the 396 crank, you’ll want to use 427 pistons – I’d look to get a 4.00 crankshaft and make a true 454.

Hopefully Pat McCarthy will chime in as he is the big block master guru of the world (seriously, he is the best!)

Again, Welcome,
Glenn

Thanks Guys !!

Roger touched on "stack". Let me embellish that a little.....
Pistons have what is called a compression height, the distance from the centerline of the wrist pin to the crown of the piston (the crown is the flat part of the piston that is adjacent to the cylinder wall, just above the top ring). Depending on the crank stroke of the motor, pistons are made with a different compression height so that they will end up with the crown at the top of the bore at top dead center.

The BBC block deck height (measurement from the centerline of the main bearing bore to the block decks where the heads bolt on) is 9.800", so we must choose components that add up to close to that figure in order to have a working motor.
http://jamisonequipment.com/sites/de...s/BHM-24-1.gif

If the radius (half the stroke) of a 454 crankshaft is 2.000" and the 454 connecting rod is 6.135", then we must use a piston with a compression height of around 1.640". Adding those 3 values together would yield a stack of 9.775", leaving the piston crown 0.025" below the top of the block with the piston at top dead center. This 0.025" piston deck height added to the head gasket thickness comprises "squish". A squish of 0.035" to 0.045" is considered by many to be ideal, so in this case, we might add a shim head gasket measuring 0.020". The piston deck height of 0.025" added to the gasket thickness of 0.020" would give us a 0.045" squish.

Now, if a fellow were to use aluminum heads, they don't much like solid shim steel gaskets, preferring a thicker composition gasket so that they can move around a little without cracking or fretting. Problem is, with a piston deck height of 0.025" and a ~0.040 composition gasket, the squish is 0.065", too wide to be effective in controlling detonation on pump gas. What we might do in this case is to cut the block decks down by 0.020", creating a new block deck height of 9.780" and a new squish of 0.045".

Using a 396 crank in your 454 block, as Roger and Glenn said, would make a 427. The crank radius would be 1.880", the rod would be 6.135" and you would use a piston with a compression height of around 1.765" to make a stack of 9.780". Many fellows will cut the block decks to "zero", meaning that the crown of the piston comes exactly even with the block decks with the piston at top dead center and there is no piston deck height. In that case, you would use a composition gasket and the thickness of the gasket would become the squish figure. If you used a 0.040" gasket thickness, then the squish would be 0.040".

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I knew I was on this site for a reason! Thanks for all the info!

Hey Tech inspector!
I just wanted to let you know that I copied your dissertation above and shared it, with due notation, with my sons Fire Academy class. Apparently firemen are mostly motor heads. They wanted me to let you know how much that resultant discussion and learning was valued. Well done my friend!