Slant six engine - Performance upgrades
 

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.

You can quickly and easily bolt on electronic ignition from later slant sixes, or you can order a kit from MOPAR

Factory-performance slant sixes

Beginning in mid-1961, the 225-cid Slant Six engine was produced with an aluminum engine block. Exact production dates are unavailable. There is no record of the number of these blocks produced.

A special Hyper-Pak was available for the 225 Slant Six. A competition engine, the Hyper-Pak featured a much more radical cam; a Carter AFB four-barrel carburetor mounted on an intake manifold with long ram passages; steel tubing exhaust headers; higher compression pistons and a special tuned exhaust system.

Advertised at 195 hp, Hyper-Pak engines actually put out in excess of 275 bhp (gross). They were the rulers of the lower stock classes at the drag races. The Hyper-Pak was available as a dealer-installed option.

Hyper-Pak specs: (Hyper-Pak 225 Slant Six) Overhead valve. Cast iron block

* Compression ratio: 11.5:1.
* Brake hp: 195 at 5200 rpm.
* Four main bearings.
* Solid valve lifters.
* Carburetor: Carter AFB 3083S four-barrel.
* Tuned exhaust headers leading to tuned exhaust system.


Modern Hyper Pak
Click here for information on  Hyper-Pak type package.
 

 A 170 CID slant six Hyper Pak would deliver a comfortable 182 Hp, and turn 8000 RPM if you kept the cam lobes lubricated.

One thing you can do for your 170 right off the bat is to upgrade to a 'super six' intake, with a 2bbl carb. This will give you not only better performance, but better gas mileage as well. It was at first an uncommon option appearing in the early '60s, but was later frequently used in the late 70s.

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. How to spot the super six; the air horn is bigger than a 1bbl, so the old air cleaner won't fit.


However, 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.

While the trade off is a lower top speed, the reason it was used was to leverage the Slant 6's torque to get it to get up and move so much more. It's amazing how many people think right away of Hot Roding their engines when a rear end ratio swap will make such a greater effect on their seat-of-the-pants power.

As far as an 8 3/4" rear, it's virtually unnecessary behind a Slant 6 unless you are going to compete drag racing, you really don't need it. A V8, with its 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,  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.

These two swaps, 2bbl and 3.55 rear, will give you a great increase in get-up-and go performance, all for under maybe $200.

Adding a fatter exhaust system helps performance and reduces heat build up that hastens the demise of the exhaust manifold. 2 1/4" seems good with a turbo type muffler.

The next best thing is buy a high output coil. Eliminated the miss that most people said never existed. It idles much steadier and runs better. Of course the new ballast resistor is a good buy as well.

 Buying the original shop service manual is the best move you will never regret.
There are a number of sources of parts to increase the power of the slant 6.

Blocks made before they started the thin castings are most desirable. I think the break point is '73. These are plentiful in most bone-yards, but be careful that you don't accidentally get a 170 because the block is too short to use the 225 crankshaft.

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.

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.


For high performance, the 170 may be the best choice because its relatively short stroke allows it to rev high. The 170 is the engine to use if you will turn over 6,000 rpm frequently. A 170 CID slant six Hyper Pak would deliver a comfortable 182 hp, and turn 8000 RPM if you kept the cam lobes lubricated.

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.

If someone upgrading their six is going for higher power and RPM  is going to need the Hyper Pak clutch and special clutch bolts and an explosion shield. Otherwise you could most likely to have a clutch explosion.