Alternative pistons and rods for V-8

Posted by Craig Hendrickson On 2010/1/21 17:09:28

In another thread, it was asked and minimally discussed if there was a way to use aftermarket rods and/or pistons in a Packard V-8 rather than the stock cast pistons and rods.

After retrieving some old spreadsheets from my hard drive and conducting some current research on the internet, I believe the answer is a qualified YES.

The original "stack up" of reciprocating components in a Packard V-8 is (inches):

Deck height (from crank centerline to top of deck): 10.60325
Rod length (center-to-center of big end to small): 6.78125
Crankshaft stroke (only 1/2 of stroke counts): 1.750
Piston compression height (centerline of pin to top): 2.072

Subtracting the last 3 from the deck height yields theoretical piston top height relative to deck level, i.e.,

10.60325-6.78125-1.75-2.072 = 0.000 (piston top at deck)

So, those are the dimensions we have to work with.

Also relevent is the bore size; a 352 is 4.000 and a 374 is 4.125. A 352 can be bored to 4.125 without problem. There are some other important numbers, but I'll get to those.

After some web research, I found that Chevy Big Block 402 pistons are 4.125 or larger with a piston comp ht of 1.77. The "low compression" version has a 0.200 dome on it, but this could easily be milled off flat. Also, Eagle SP makes a Chevy Big Block con rod in 7.100 length. I'll get to the adaption mods later. Anyway, adding up the stack heights, one gets:

10.60325-7.1000-1.75-1.77 = 0.01675

This is pretty darn close without doing any piston top milling or crank stroke grinding.

The good news is that the prices are very attractive. On SummitRacing, the pistons (UEM-IC9948-STD) can be had for $445. These are forged aluminum with either type pin. Also on SummitRacing, the rods (ESP-7100C3D) can be had for $600. These are H-Beam 4340 full floating rods which you'll never break in a Packard.

I'll wait for subsequent posts to discuss the minor modification details and what the extra rod length means.

Craig