Ten Hours, 800 RPM, Full Throttle: How Chrysler Used To Test Engines

Murilee Martin
by Murilee Martin

Now that I’m scouring eBay Australia for crazy Detroit Down Under cars— maybe even as crazy as a 4-71-blown six-cylinder Torana— I’ve been dragged once again into the Whirlpool Of Arcane Internet Car Knowledge. You know how that goes: you go to look up the Australian Falcon on Wikipedia, a reference to the Valiant Charger leads you to the mother of all Chrysler-related online time-sucks, and then your whole day is used up. This time, Allpar sent me to Valiant.org, and that’s where I found the page on the Chrysler Hemi-Six engine. There you’ll find a description by a Chrysler engineer of how his Australian counterparts tested their new (American-designed) engine:

They couldn’t get an engine to run lab endurance for more than about 20 hours or so without dropping a valve or putting a hole in a piston. Well I suspected right away in the States what it was, and when I got there, sure as hell, they were running wide open throttle lab endurance (their schedule was probably different from ours, but ours consisted of 10 hours each, and I may forget one, but the first 10 hours were 800 wide open – can you believe that? – then 1600 wide open, then 2400, 3200, the fifth 10 hour cycle was 3600, and the last was 9 hours at 4000 and the last hour at 4400, all wide open throttle. And their engines were failing in the second 10 hours due to pre-ignition or valve overheating.

Now, the Aussies were using hot spark plugs, which is the reason they were killing engines, but let’s get back to that standard Chrysler endurance test, circa 1966: ten hours WFO at 800 RPM! That’s like dragging a flat-tired trailer full of dead horses up Grapevine Hill, in top gear, against a 60 MPH headwind (granted, the cooling system on the test stand was probably beefier than the one in a Valiant VC, but still). Just another day on the job for a Chrysler pushrod engine! With that philosophy, it’s no wonder the Slant Six and LA small-block V8 were so tough.

Murilee Martin
Murilee Martin

Murilee Martin is the pen name of Phil Greden, a writer who has lived in Minnesota, California, Georgia and (now) Colorado. He has toiled at copywriting, technical writing, junkmail writing, fiction writing and now automotive writing. He has owned many terrible vehicles and some good ones. He spends a great deal of time in self-service junkyards. These days, he writes for publications including Autoweek, Autoblog, Hagerty, The Truth About Cars and Capital One.

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  • Moparman426W Moparman426W on Feb 01, 2012

    I'm short on time right now, but when I return sometime this evening I will explain some of the reasons that chrysler engines, the slant 6, small and big block engines were so rugged. And Gslippy you couldn't be more wrong, they weren't worn out by 100k they were just getting started.

  • Moparman426W Moparman426W on Feb 02, 2012

    The reason the bottom end of the slant 6 was so tough was because it was originally meant to use an aliminum block. Weaker aluminum required extra materil to be rigid, so that was how the tooling was designed. They started out building both cast iron and aluminum versions, because the reynolds aluminum company couldn't yet meet the supply. The aluminum version required a special type of antifreeze, and it was supposed to be changed every year. Most owners neglected to change it and it would cause the deck of the block to erode between cylinders, so chrysler dropped the aluminum version. Since it would have been costly to make new tooling for the cast iron version they stuck with the original tooling. The result was an extremely beefy bottom end with an excessive amount of cast iron, with a skirt that went about 4 inches below the crank centerline. It used a forged steel 4 main bearing crank. When the bearing size is adequate a 4 main crank is stronger than a 7 main because it has alot less twists and turns, the slant 6 had hemi sized main bearings which gave it plenty of bearing area and a beefy crank. In mid 76 they switched to a cast iron crank. In the chrysler tradition the block also had a very high nickel content. The small block chrysler also had a high nickel content in the block, much more than a small block chevy. They also used beefier rods than chevies, in fact the lowly 318 used beefier rods than the mighty LS6 454 chevy. Another important thing is that the rods were longer in the chrysler engines. A longer rod makes for a more stable piston for less side loading of the cylinders reducing wear. A shorter rod pulls the piston inward as it nears the bottom of it's travel, causing more thrust loading and as it gets ready to travel back up that short rod kicks it out toward the outer side of the cylinder wall. That's why many builders of chevy race engines over the past 20-30 years use aftermarket 6 inch rods in them, the factory rods are 5.7 inches. A few years back Rick Ehrenberg at mopar action was discussing the mopar long rod adavanatge and he said "the next time your chevy buddy starts bragging about his "long" 6 inch custom rods you can proudly point out that the factory rods in your lowly 318 work truck are 6.18 inches long. The small block chrysler also has a beefire bottom end than the small block chevy, with thicker webbing, bigger main caps and bigger cap bolts. That is why mopars don't need a 4 bolt block in the majority of performance applications. They did make 4 bolt block 340's for the AAR cudas and T/A challengers, but they were considered overkill and unnecessary. The big block chrysler has pretty much the same advantages over the big block chevy, much higher nickel in the block, beefier and longer rods and the bottom end is skirted making for an extremely rugged engine. All chrysler engines used wider cam lobes with .904 inch diameter lifters compared to .842 diamter gm lifters resulting in a greater wear surface, along with a better hardening process of the cam. That was why you almost never saw a mopar with a bad cam, something that was very common in chevies. All mopars back then also used shaft mounted rockers. They were expensive to build and added about 4-5 lbs. of weight. But they kept the rocker arm stable for consistent valve lift. The ball stud setup on cheveis let the rocker arm move around altering vale lift, and it progresses with higher valve lifts and rpm's. That is why most big time chevy racers convert to a mini shaft rocker setup. As good as the mopar shaft setup was it was expensive to build, that was why they changed the design on the magnum version of the small block in the early 90's. They came to a compromise. They came up with a pedestal design, very much like used on the ford cleveland and 429/460 and 73 and later AMC engines. It's not as good as the old shaft setup, but better than the slip-n-slide ball stud setup used on the chevies, and much cheaper to manufacture than the shaft setup.

  • CanadaCraig You can just imagine how quickly the tires are going to wear out on a 5,800 lbs AWD 2024 Dodge Charger.
  • Luke42 I tried FSD for a month in December 2022 on my Model Y and wasn’t impressed.The building-blocks were amazing but sum of the all of those amazing parts was about as useful as Honda Sensing in terms of reducing the driver’s workload.I have a list of fixes I need to see in Autopilot before I blow another $200 renting FSD. But I will try it for free for a month.I would love it if FSD v12 lived up to the hype and my mind were changed. But I have no reason to believe I might be wrong at this point, based on the reviews I’ve read so far. [shrug]. I’m sure I’ll have more to say about it once I get to test it.
  • FormerFF We bought three new and one used car last year, so we won't be visiting any showrooms this year unless a meteor hits one of them. Sorry to hear that Mini has terminated the manual transmission, a Mini could be a fun car to drive with a stick.It appears that 2025 is going to see a significant decrease in the number of models that can be had with a stick. The used car we bought is a Mk 7 GTI with a six speed manual, and my younger daughter and I are enjoying it quite a lot. We'll be hanging on to it for many years.
  • Oberkanone Where is the value here? Magna is assembling the vehicles. The IP is not novel. Just buy the IP at bankruptcy stage for next to nothing.
  • Jalop1991 what, no Turbo trim?
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