Packard Forum Index » Modification Discussion

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

Craig: Please correct me if I am wrong. If you increase the stroke of an engine by longer connecting rods the engine will have more torque.

John F. Shireman

Quote:

John, increasing the length of the rods has nothing to do with the stroke.

What longer rods do is basically give you a longer lever on the crankshaft, which gives you more torque. Google "rod to stroke ratio" to learn more. A longer rod will give you more torque over a shorter rod on the same stroke.

Also, a taller piston will be more stable than a short piston for the same stroke. Wrap yer head around that.

Craig is correct, anything can be made to fit anything. It ain't easy, it ain't cheap - kids don't try this at home.

FWIW, I've used a couple of different BrandX pistons in the Packard V8. The Mopar 413" and the Ford 370" truck pistons can be made to work, with much machine work and custom balancing.

However, I've found the cost of modifying the 402" GM pistons and custom rods to fit the Packard V8 exceeds the cost of custom forged pistons which fit with no hassles.

BTW, Quote:using the GM rods will require grinding the crankshaft to a smaller diameter.

I'm using Oliver 7.250" custom BBC rods with SBC piston pin bores in a hot street Packard V8. They are $1400 a set, but won't ever be a weak point.

As always, your engine, your money, your decision.

thnx, jack vines

Jack Vines wrote Quote:
<p>The mods to the 402 pistons is cutting off the small (0.200in) dome and adding another valve relief. There are no mods to the con rods which are "off the shelf" (see the manufacturer and P/N cited).</p>
Quote:
<p>Correct, from 2.250 to 2.200 (0.050) on the rod journals. No difference on the mains, of course. Off the shelf BBC rod bearings will then fit. Pontiac and other racers do this all the time.</p>
<p>The whole assembly must be rebalanced, but one would do this anyway for a "high performance" build.</p>
<p>I'm not defending this setup per se. I am only putting forth an alternative for someone who wants better than stock pistons and rods at what appears to be a reasonable price, even considering the machine work.</p>
<p>Craig</p>

Many thanks to Craig and Jack for their analysis.

For those not racing and thus for cost savings then why not use OEM or standard duty replacement Chevy 402 rods and pistons with modifications as Craig indicates??

i.e. Many of us do not want racing engine strength but do not want anything less than OEM Packard parts strength either.

PRoblem with custom made pistons (for use with Packard rod) is that they would have to be available in various oversizes AND SETTING ON THE car owners SHELF in those various oversizes. THis is especialy true for the racing crowd. Also using the Packard rod does not address the plain 'white box Taiewan' made rod bearings which may be of questionable quality.

Quote:


Wrong. When you buy custom pistons from any manufacturer of said custom pistons they start with a blank that fits your requirements and machine it to fit, IE, they put the ring grooves and the pin hole where you need it. MOST pistons are available if you know how to shop for them.

Bearings are another thing entirely. Although I have a sneaking suspicion that some main bearings can be used as Pack V8 rod bearings. I'll have to keep researching that one for a while, but any competent machinist can find bearings for you. Remember, what's undersize on a Packard might be standard on a Hupmobile, etc.

"When you buy custom pistons from any manufacturer of said custom pistons they start with a blank that fits your requirements and machine it to fit, IE, they put the ring grooves and the pin hole where you need it"

Yes. But it is MUCH easier and cheaper and FASTER to buy an off-the-shelf local parts store piston than arrange for pistons custom made.

Quote:

Depends on your definition of easier/cheaper/faster. A piston that was meant to fit will last longer than one that's made to fit every time.

Some of us will remember that a while back, we had a chance to have a run of OEM-style Packard V8 pistons manufactured. As I recall the minimum run length was 50 sets, the supplier was willing to keep the majority of them for his own stock. I pushed the topic pretty hard here, but we only generated interest in 5 or 6 sets. As I recall the price was $55 per, +/-.