Well, I've gotten to the point of building the engine for my 57 Plymouth.

I know a lot of the older Hot Rodders on this site have stressed choosing the right combination of parts when putting a car together so I though I try to put the thought process I used in picking the pieces I'm going to use on the 2 different builds on paper to give some of the newer hotrodders a idea about what we're talking about. Although the engines I'm building are early Chrysler Hemi's, the PROCESS is the same on any other car/engine combination.

Project : 57 Plymouth, 354 Hemi.

The goal of this project is to have a very streetable car capable of making long highway trips comfortably. I wanted the feel of a hotrod that could have been built in the mid-late 60's with a few creature comforts like AC and Cruse. Early on I picked up a very nice one off tri-power intake and also decided I wanted a 4 speed. The Plymouth is a relatively heavy car in the 3500-3700 pound range with the Hemi and full interior. After determining what I wanted the car to be/do the next step to determining how I was going to build the engine was to figure out the drivetrain.

The drive train:

After setting the basic parameters it was time to decide on the engine RPM range I wanted to operate in at 75 MPH (the speed the car will see a lot of). For ME I decided that I could live with a cruse RPM of no more than 3000 RPM (and preferably a bit lower) and that would match up with the capabilities of the intake nicely and should provide an MPG figure that I could live with. After running the calculations it looked like a 3.00 final ratio should do just fine with approximately 2800 RPM at 75 with a 28" tall tire.

There were a couple of options on how to end up with a 3.0 final ratio. The most oblivious is simply throwing a rear end with a 3.0 ratio under the car. With the weight of the car, a 28" tire and only 354 Cubic Inches (even if it is a Hemi 354 Cubic inches is still only 354 cubic inches) and a 3.0 gears it sure would not be a stop light terror.

The other choice is to use a deeper gear in the rear end and an overdrive transmission (the option I chose). It turns out that the A833 Overdrive transmission will effectively turn a 4.10 rear axel ratio into a final ratio of 2.99 when running in overdrive. It also has a 3.09 first gear (possibly a little too deep with the 4.10 rear end, but will have to see). This should make VERY responsive at the old stop light.

Finally the engine:

With the rest of the drive train sorted out I could now concentrate on building an engine to match the rest of the car. The first step on this is researching what works for the particular engine you've chosen. As an example those tricks that will work say on a small block Chevrolet may not necessarily hold true for a big block Ford or in this case a HEMI.

Compression: This will be a BIG factor in determining how enjoyable the car is to drive, especially in a street car on pump gas. The GENERAL rule of thumb currently used is that a normally aspirated street motor compression should not exceed 9:1 in order to prevent detonation and allow the engine to take advantage of a good advance curve. There are however a couple exceptions to that. One exception is aluminum heads which due to their superior heat dissipation can be run at 1/2 to a full point higher. Another exception are the Hemi heads that due to their design can also be run at 1/2 to 1 point higher. So basically on my build compression would be limited to 10:1.

Pistons: Unfortunately economical off the shelf pistons for early Chrysler Hemi's is some what limited. My personal preference would be to have a compression ratio in the 9.5 to 9.75 to one range. Short of going with a custom piston my choices were either 8:1 or 10:1 and as it is cast Hemi pistons what it would normally cost for Forged pistons for most other engines. Yes I chose the 10:1 pistons, (in part due to living at over 4500 feet which also tends to make a higher compression a little more forgiving).

CAM: Personally I don't concern myself so much with gross lift figures on a cam. I choose a cam based on the effective torque and RPM range (this really goes back to what works well in one style of engine being a dog in a different engine). As the intake was already chosen that should provide excellent low end torque and also very good top end power and the forgiving rear-end/transmission combination I could go with just a bit more radical cam than I would if I were building an automatic car with 3.00 gears. What I ended up with for this combination is a cam with a .450 lift and 290 duration ??? Believe it or not this is a fairy radical cam with a fairly good lope and should have the higher compression and deeper gears ( I would defiantly NOT run it in a 3700 pound car with a 3.00 gear and automatic). Ok why so small when in a small block Chevy you'd be running a cam in the .490/.500 lift range? Rocker arm ratios that cause the valve to open wider that it would with a cam of this lift in say a SBC, and larger valves and more efficient head design. Springs and lifters would then be based on the cam makers recommendations. Personally on street engines I go with hydraulic lifters.

Intake: After I choose the cam I would normally pick a compatible intake, in this case however the Tri-Power was a foregone conclusion. Were I to pick a different manifold for this engine (primary operating range 2500-3000 RPM and a redline of 5800 RPM based on the limits of the lifters) I would go with a good dual plane single 4 BBL intake.

Exhaust: This one is pretty straight forward, use/build the most effective (least restrictive) system as you can. Now normally this would involve using headers, but in this case I choose to go with the best Chrysler exhaust manifolds I could lay my hands on (they are very similar to SBC rams horns, only MUCH bigger) and will flow more than adequately enough for the size of the engine and RPM range.


So there it is, how I went about figuring how to build this engine. I'd be interested on input from the rest of you guys to see if your thought process is along the same line or not, or thoughts on this particular combination.