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1939 Packard Six. Contemplating an engine swap. Suspect the stock rear axle would not respond well to torque and horsepower numbers in the 300+ range. Can the axle gears be replaced with others with a higher power rating? Or is the best option to just replace the axle with something like a Ford 9 inch? Any insight would be appreciated.

I would think you would want a different rear end with better gearing. They were geared for the power output of the original. motor and the speed of the original roads.

This is why people had or added overdrive.

You make want to use a later rear end with either a 3.23 or 3.54 gears.

Plus you'll want bigger brakes to pull the reigns on all those horses,,,

Big Kev,
Thanks for your suggestions and a reminder of just how much travel by car has changed. These older vehicles are definitely time capsules.

Flackmaster,
Thank you for pointing-out the limitations of older brake technology, I appreciate your comment.
This Six, a Business Coupe, was restored by a previous owner, and I am going to evaluate the effectiveness of those period hydraulic brakes. My desire is for this car to just be a cruiser - no racing about. Just getting on a modern two lane highway with speed limits of 65mph is going to be hairy enough.

All well and good -- but then I don't understand your comment about wanting a 300 HP engine. Highway driving is problematic for old cars more because of engine speed than engine power.

The 300 HP 1956 cars could hit 120 MPH, and since required power is times the cube of velocity, this implies you need only about 40 HP to cruise at 60 MPH. Of course you need more for hills. But still, more a function of gearing and having increased motor life from not flooring it, than a strict lack of power.

Point is you could swap in something marginally better, e.g. a 150 HP straight eight from the 50's, and the car should be just fine if you have an overdrive and/or a decent rear end ratio. Without needing to beef up or re-engineer the entire drivetrain.

I appreciate your well-reasoned comments. My target of 300HP is based on past experience of what that amount of power can do in terms of general performance. I did not mean that in a written-in-stone sense, just a base for conversation. My intention is to enjoy an occasional drive into town (less than 10 miles), likely fewer than 500 miles per year. Returning to my previous post, safely getting onto a busy two lane highway, specifically US 97, requires the power to quickly blend into traffic usually travelling well above the posted limit of 65mph. Out there, there is no margin for error. US 97 is the second busiest N/S highway in Oregon, and the most popular truck route, rivalling I-5. It is also something of a slaughterhouse; I should buy stock in companies that make flat-deck tow trucks. Using the relative performance of my 5.4L Triton-equipped F-150 as a unit of measure, 300 horses seems about right. The fact that this Packard's smooth-flowing body lines have street rod written all over it does not hurt. A shiny new V-8 crate engine seems the easiest way to meet performance requirements for modern roads and to stay safe. A straight 8 would definitely work, but I have no illusion about availability and pedigree of any such engine I may find.

My shop and most of my Packards are also "in the boonies" of Oregon off Hwy 97. Although I've not driven them there, when they were here in California as everyday cars, they had no trouble at all in highway traffic. In fact, the main problem was in town where other drivers would see an old car and pull right out in front of me no matter how fast I was going! Fortunately Packard brakes are good too.

Greybeard, not a fan of "retro rod/Frankencars," nor of Packard sixes, which i think should've been marketed as "Packardettes." That said, run some numbers. Your coupe weighs only 3,365 lbs. That's a lightweight in today's world, where even mid-sized "crossovers" creak the scales at 4,800 lbs. unladen.

The Packard 245-ci six is a husky, overbuilt engine, used in 141-inch wheelbase NY taxis 1948-on, in White trucks through the mid-'50s, in Chris Craft runabouts. You don't mention if your car already has overdrive. If not, it'll have a slightly taller rear axle. So carefully rebuild your six, port and polish, lighten the flywheel, then add overdrive and radial tires. Full synthetic 10W/30 motor oil, any name brand, DOT 5 silicone brake fluid. Well adjusted drum brakes will stop you fast as discs, unless racing through the Andes or Rockies. Unless you, friends, family Sumo wrestlers with a couple bags of cement in the trunk, that wee coupe will dance.

You'll find that's plenty of suds to merge onto freeways. But if still more oomph wanted, consider a twin carb set up. There are many out there. Saw a nifty '40 110 coupe with triple carbs, and the longtime owner drives it routinely in San Francisco, as hilly a town as Pittsburgh, PA or any burg you can name.

An inline six and straight eight are the only automotive engines with inherent balance. V-12s and V-16s the same with the firing impulses halved for less crankpin loading. That, and a rorty six has a nice exhaust patter. A lifelong Packard friend had as a teen a well-tuned '40 110 conv. coupe with a split manifold and dual Smithies that in the early '50s routinely trounced the usual tweaked Fords and Mercuries.

Only so much of that 300 hp will make it to the pavement, in any event, so hp just advertising crapola and cars 'n' coffee palaver for those who don't know torque, overall gearing, weight is the enemy.

Don't reinvent the wheel.

Cheers,

Silverbeard (if i go three days without shaving)

Thanks for your insight - I am reassured that I can expect my Six to handle everyday conditions with confidence.