.
The slant six had a unique 30 degree slant for a lower hood line and easier arrangement of accessories; it also allowed the intake manifold to have a ram effect.
Dan Stern strongly suggests, on applicable vehicles, bypassing the OSAC valve and cutting out the EGR if possible and legal; on 1974-75 models, replacing the Holley 1945 with a BBS or Holley 1920; and switching to NGK ZFR5N extended nose plugs (on 1974 and later vehicles, be sure to take off the metal washers first).
From mid-1961 to 1963, 50,000 225-cid Slant Six engines were produced with an aluminum engine block. These were discontinued because production was slower, more expensive, and not as reliable as with the steel blocks, according to various allpar.com interviews.
A special Hyper-Pak was available for the 170 and 225 slant sixes, with a radical cam; a Carter AFB four-barrel carburetor mounted on an intake manifold with long ram passages; steel tubing exhaust headers; higher compresion pistons and a special tuned exhaust system. Advertised at 195 hp (gross output, for the 170), Hyper-Pak engines are often said to put out even more power. They were the rulers of the lower stock classes at the drag races. The Hyper-Pak was available as a dealer-installed or user-installed option.
Hyper-Pak specs:
You can quickly and easily bolt on electronic ignition from later slant sixes, or you can order a kit from Mopar Performance (MP) - whose catalog and parts are available from any Chrysler dealer.
Click here for information on a modern Hyper-Pak type package.
Clifford Performance sells headers, blueprinted heads, revised cams, and other performance slant six parts.
Doug Dutra creates “Dutra Duals,” manifolds that support dual carburetors and are less prone to cracking.
A former Chrysler engineer wrote: “A 170 CID slant six HyperPak would deliver a comfortable 182 Hp, and turn 8000 RPM if you kept the cam lobes lubricated. I am sure there was more available, but it is anyone's guess what would break first. My suggestion would be start there and progress slowly. When it blows go back a step. Have a few engines handy, a ready wallet, a good dynomometer, and lots of patience.”
KE4DGI pointed us to a team that ran 9.85 @ 132 mph in the quarter mile at Bristol with a turbo slant six using fuel injection.
Al Toews pointed to his own supercharged-slant-six project, using multiple-point fuel injection.
Upgrading to a 'super six' intake, with a 2bbl carb, should give better performance and gas mileage. (Dan Stern:) It was released for marine/export only in 1967, and was found in North American cars and trucks starting with its 1976 release on the "Super Six" Volare/Aspen.
It's best to get both the intake and exhaust manifold together, as it's a headache separating these and putting them together again; also the throttle linkage is different, so be sure to get everything between the gas pedal and the cylinder head. The Carter BBD is a good 2-bbl carb, easy to rebuild and tune, and will give great performance. This is also how to spot the super six; the air horn is bigger than a 1bbl, so the old air cleaner won't fit. If you're not sure what it looks like, go pop the hood on any 2bbl V8 mopar, where it's the standard item. (The carburetor was somewhat different from the one used on V8s).
If it's performance you're after, another thing you should seriously consider is swapping the rear end to a shorter ratio- 3.23 was standard, though 2.79 was an option for highway mileage (unlikely with a 170) and 3.55 was an option for performance. Both these two are not uncommon in the 7 1/4" rear ends which are standard behind /6 cars. My 1965 B'cuda had a 3.55 rear end, and while the tradeoff is a lower top speed, the reason it was used was to leverage the slant six's torque. It's amazing how many people think right away of hot rodding their engines when a rear end ratio swap will make such a greater effect on their seat-of-the-pants power.
[Dan Stern noted:]
As far as an 8 3/4" rear, it's unneccesary behind a slant 6- unless you are going to compete in drag racing. A V8, with greater torque, can break a 7 1/4" rear, but it was standard behind 273 cars. The only other advantage the 8 3/4 gives you is the ability to swap gear pumpkins to 'quick change' the ratio from street to strip. Other than that, my advice is to run your 7 1/4 until you break it- if you manage to do that, then consider upgrading- or maybe just get another 7 1/4. A shorter (3.55) ratio will give you more durability anyway.
Adding a fatter exhaust system helps performance and reduces heat build up that hastens the demise of the exhaust manifold. I have replaced mine at least a dozen times for gasket leaks, cracks, etc. 2 1/4" seems good with a turbo type muffler. Doug Dutra does some good work making custom manifolds, reproducing Hyper-Paks and dual exhaust for the slant six (by cutting the manifold in half you reduce the tendancy to crack due to length and heat build up).
The next best thing I did was buy a high output coil. For $35 I eliminated the miss that most people said never existed. It idles much steadier and runs better. Of course the new ballast resistor was a good buy as well.
The stock distributor was pricey at $175 but definitely worth the long term investment. I have been getting by on cheap rebuilt parts as long as I can but they tend to fail often. The carbs fall apart after two years but one day I will shell out for a new Holley for $300. This week I am going to rearc and add a leaf to boost the rear springs (another $300). The sway bar did not come on my car so I added them front and back. Buying the original shop service manual has also been a move I will never regret.
Blocks made before they started the thin castings are most desirable. I think the break point is 1973, but not sure. Headers are a waste of money on a slant 6 intended for street use and take away the heat riser, making cold engine drivability pretty bad.
If you go with a 4 bbl setup, you want the smallest Carter carb for it. Anything bigger will give you problems unless you are very careful about opening the throttle very slowly at low speeds. A Holley carb may make the car a little faster, but they require nearly as much tinkering as an English motorcycle.
Fancy, expensive ignition systems are a waste on these engines because, with their long stroke, it is not safe to run them fast enough for them to make any difference. A modified cam will give a lot of power increase per dollar, but don't get crazy with this because you quickly start losing low end performance as the cam gets more radical.
The 170's relatively short stroke allows it to rev high. Both Russ Shreve and Steve Remington - a Valiant engineer and a Valiant expert - agree that the 170 is the engine to use if you will turn over 6,000 rpm frequently. According to Russ, a 170 CID slant six HyperPak would deliver a comfortable 182 hp, and turn 8000 RPM if you kept the cam lobes lubricated. He also said that:
It had a shorter stroke than the 225, but the same head and valves. Low end torque was less, but ultimate power was the same. In addition, with the lower block height it was a sturdier engine, and with the shorter stroke could rev higher with less chance of an rpm failure. The Achilles Heel was the cam lobes.
If he [someone upgrading their six] is going for higher power and RPM he is going to need the HyperPak clutch and special clutch bolts. Otherwise he is most likely to have a clutch explosion. I also recommend an explosion shield. A clutch explosion can cut a car in half.
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