new BBC big bore build ??



new BBC big bore build ??

Postby grumpyvette » May 15th, 2014, 11:17 am

albatross wrote:I'm back underway with my BBC chev build in which I've ended up with a set of (stored for 10 years but brand new) 6.135 h beam rods and a forged 3.766 crank. They go in a merlin block and merlin Ali heads with 119cc. I'd like to take the bore out to 4.600 in the block and use the crank and rods I already have.
Can I simply get a set of pistons for this, all the pistons I see for this crank and rods setup are for a much smaller bore. I need a comp ratio around 7-7.5:1 for my supercharged setup. If I use a set of Manley pistons 4.600 bore with 1.645 comp distance , -10cc inverted dome gives me around 7:1
Any reason why these pistons or something similar wouldn't work?


most 3.76' stroke cranks were used in 366-396-402-427 displacement bbc engines, and as such the cranks had counter weights matching those piston and rod weights, cranks generally have counter weights designed for a certain range of connecting rod and piston combo, your use with a larger heavier piston may require a good deal more MALLORY METAL (heavy balance weights) inserted in drilled holes in existing counter weights and that can get rather expensive when you balance the rotating assembly, you generally cant weld excess metal to the outside edge of the counter weight to get the wight required due to the need to clear the piston skirt needing to clear the counter weight passing under the piston skirt at bottom dead center on the stroke, (thats one of the reasons why 6.385" and longer connecting rods are generally selected on many longer stroker cranks, IE the need to clear both the longer stroke and larger counter weights required) and your block will need to be sonic tested , bored and honed with deck plates, a good machine shop should be where you start as they can measure and advise you on what to buy and the cost of the machine work and parts


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RELATED INFO
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you might want too read carefully thru these threads posted above and their sub links and play with this calculator I will link too below

https://www.uempistons.com/index.php?ma ... aaaf4455f4

youll quickly see that an increase in bore diameter alone tends to increase displacement, which if no other changes are made also tends to increase effective compression
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: new BBC big bore build ??

Postby grumpyvette » May 17th, 2014, 9:29 am

you may also find these related threads very useful


viewtopic.php?f=53&t=1168&p=41255&hilit=measure+deck#p41255

viewtopic.php?f=53&t=510&p=12279&hilit=measure+deck#p12279

viewtopic.php?f=53&t=509&p=12277&hilit=measure+deck#p12277

viewtopic.php?f=53&t=4630

viewtopic.php?f=53&t=852

viewtopic.php?f=53&t=5064

viewtopic.php?f=53&t=978&p=1711#p1711


most big block blocks will take a .060 over bore without issue some will take .100 but your almost sure to have very thin bore walls that won,t seal the rings well, and keep in mind many of those blocks have internal water passage rust issues after all many are 25-30 plus years old

bore x bore x stroke times 8 x .7854= displacement
example
a 4.310 " x 4.310" x 4.25" x 8 x .7854=496 cubic inches

read these links and sub links

viewtopic.php?f=69&t=1420

viewtopic.php?f=69&t=5123

viewtopic.php?f=69&t=6125

viewtopic.php?f=69&t=189

BUY A FEW REFERENCE BOOKS ITS MONEY VERY WELL SPENT

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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

User avatar
Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


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