383 PISTON INFO

[mopar Joe 65]

COULD SOMEONE TELL ME WHAT PISTON TO USE FOR A .030 OVERBORE ON A STOCK 68 383 WITH THE 906 HEADS. I DON'T WANT TO SPEND $ 800.00 OR MORE ON PISTONS. ANY INFO WOULD BE APPRECIATED.

 

[pomonamissel]

kb's hypereutectic 383 +.030 = 4.280 dia bore . summit had three sets for @ 400 bucks a set . add a few options like flooting pins and moly rings .

 

[mopar Joe 65]

THANKS, MY PISTONS ARE PRESSED ON , I'AM NOT SURE WHAT FLOATING PINS ARE ? DOES THAT MEAN THEY HAVE SNAP RINGS ?

 

[70bigblockdodge]

Floating pins are held in by rings,locks, etc. not pressed into the rod. No advantage unless you are planning to take your engine apart over and over. Get pistons with highest compression height or a step head (KB term) if available. It will keep your compression out of the 7:1 ratio range.

 

[mopar Joe 65]

THANKS, MY STOCK 68 383 SPEC'S SAY I HAVE 10.1 COMPRESSION WHAT DO YOU THINK I SHOULD SHOOT FOR ?

 

[70bigblockdodge]

Both of those suggestions will help you get headed towards that number. If you are having the block decked enough to zero deck the pistons follow your machinist recommendations. That 10:1 number is what they designed what it actually has will be lower, head combustion chamber and piston below deck will be bigger than listed from factory resulting in less than 10:1, try to keep it up and just live with where it ends up, will not make a big difference in power, or if this becomes a huge concern go with the $800 pistons in a relatively stock engine.

 

[pomonamissel]

flooting pins have been used to reduce heat and wear , chrysler used flooting pins in the eary hemi motors , not just for ease of disassembly n assembly . and if you set the piston @ .020 below deck it will drop that c/r . of course you will have to figger in your cam opening/closing for true c/r . for pump crapgas iron heads need less c/r then alum alloy heads .

 

[70bigblockdodge]

flooting pins have been used to reduce heat and wear , chrysler used flooting pins in the eary hemi motors , not just for ease of disassembly n assembly .

Yes but in the scope of his build it is not a advantage to offset cost to modify the rods, I'm assuming here because he does not want to spend 800 on forged pistons just to drive to Dairy Queen.

 

[moper]

None of the shelf part numbers will get you an actual 10:1 static compression without a complete blueprinting of the long block. So you can ignore that factory claim.
The KB hypers are your cheapest & best way to better static compression. The KB-400 domed version will work best for you if you are keeping the 906 head.
A few notes on them:
You (or your assembler) MUST pay attention to the literature about setting the top ring end gap during assembly.
You MUST have the rotating assembly balanced with these units.
You "should" have the connecting rods resized and good bolts installed in them prior to rebalancing and the piston install. As you note - pressed pins don't come apart easy. I believe the pistons have a groove for a spira-loc type pin retainer. So you could have the shop hone the pin end of the rod and buy locks for them and make them floating. On a mild application there is no worry about having to install a bushing in the rod to run them as full floaters.

 

[727]

If using KB Pistons be extra sure to gap the top piston ring as per instructions. Bad things will happen if the gap isn't large enough.

Speed pro makes a forged set for around $400 with moly rings. They are heavier than the KB's and they are flat top. Key word here is Forged!