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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old May 9th, 2017, 01:05 AM
401bluebird 401bluebird is offline
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Default 478 GMC V6 Forged pistons

I remember a few years ago talk about forged pistons for 401 V6s. somebody mentioned that the size of the larger 478 piston was greater than forged piston blanks which the piston builders machine into the required configuration.

Even though large pistons are being made now for aftermarket blocks which increase the bore centers to 5.3 inches (the Big 3 big blocks are all under 5 inch B.C.). Maybe these new forgings can accommodate a 5.125 bore (or +0.30 at 5.155).

I know that the Reno Air Races have dozens of rolls Merlin V-12 engines. I see that a standard bore R-M V-12 is 5.4 inch diameter. Maybe these forging blanks can be used for a slightly smaller piston diameter.

Custom pistons are never cheap but to build a higher compression 478 will require custom pistons.

Anyone know of any piston manufacturer who sells a 478 +0.030 high compression piston?
thanks,
-Andy Carlson
Ojai Ca
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  #2  
Old May 9th, 2017, 03:54 AM
bigblockv6 bigblockv6 is offline
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Default Re: 478 GMC V6 Forged pistons

No piston manufacturer presently makes pistons for the 478 V6 but they can be custom made from one or two of these piston manufacturers. Try Ross Pistons, J&E, Arias or Wiseco
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Old September 25th, 2017, 03:36 AM
Firepower Firepower is online now
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Default Re: 478 GMC V6 Forged pistons

A couple thoughts from a potential 478 builder:

With CNC equipment becoming far more common, billet pistons aren't as big a deal as in the past. Pullers are knocking out similar slugs.

Aircraft engines in 5.125 and 5.250 (any sonic check data out there?) aren't uncommon and lower cost pistons pop up a lot. Of course pin height and size are off, but if offset grinding the crank and swapping lighter/stronger rods, one may as well get the 550 inches or more.
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