Turbo /6 or v8

cinimod2 said
I'm debating whether I want to go with a tubo /6 or my 318 that I'd currently in my 75 dart sport. I'm looking for power. I've seen videos of 11 second /6s. My question is how expensive and how much would I have to do to the engine in order to turbo it and get somewhat of a nice street car for Friday night fights?

cinimod2 said
I'm not looking to be super-fast, just quick enough to compete with some v8s and turbo imports.

You really can't make a mistake here, no matter which you choose. The 318 is a great engine with lots of potential, and can be hopped-up to give some very satisfying performance on the street. But, if you're going to have to buy a V8 anyway, you can probably buy a 360 Magnum nearly as cheaply as you can buy a 318, and the additional 42 cubic inches will be nice to have, with most aftermarket speed equipment fitting both motors.

Does your car already have a slant six in it? If it does, and you choose to turbocharge it, it will have a financial start on the V8s for the following reasons:

You won't have to spend the money on a different basic engine to work with. You already have it!
There is a long list of things for a V8 swap that you won't have to buy if you keep the six.
Neither route is cheap, but a low 12-second slant six turbo car might well be cheaper to build than a V8 engine-swap car that will run low 12's.

I haven't done the slant 6 deal, but I have the V8. By the time you have modified a 318 or 360 (normally-aspirated) engine to make enough grunt to run low 12's in a 3,300-pound A-body, (say, 360 horsepower) it likely needed a cam with considerable duration (rough, higher-than-stock idle) and a set of headers. It won't have a lot of low-end torque, so around-town drive-ability won't be too good unless you have a loose converter, ($) assuming it's an automatic. A stick car with that engine will need some rear end gears that will allow it to have considerable torque multiplication to move the car off the line; something in the neighborhood of 3.90-4.10:1. That will make freeway driving stressful, if you try to keep up with traffic. Higher-than stock compression pistons will likely be needed to offset the loss of cylinder pressure that comes with a cam that has the kind of duration it takes to make one horsepower-per-cubic inch.

An 8.25" rear end will usually suffice in a car like this, but changing ratios is not a quick-and-easy job, like it is with an 8.75" drop-out unit. But, the 8.75”s are expensive... especially, for A-Bodies. You can use a cheaper B-Body 8.75" rear, but that requires careful measuring and a set of wheels with a custom back-spacing. The V8 car, if you want to use it for trips, AND “performance driving,” really needs the flexibility of the easy-gear-change rear, unless you know it just won’t be used on the freeway.

On the plus side, building a low-12-second (112 mph) 318/360 is like falling out of a tree. A decent set of headers, some 11:1 pistons, a good hydraulic roller cam and an Air Gap/750 Holley manifold, and you’re there!

The forced-induction slant six is a different story, because of the lack of hop-up parts (a nice, cheap, turbo header, for instance) makes it more of a challenge to build.

But, the performance available from these engines is pretty competitive with normally-aspirated small blocks.

Two examples I have heard about come to mind:

Tom Wolfe’s ’70 Dart was equipped with a 225 slant six (a well-used, high-mileage engine) and ran a 12.95-second e.t. with a stock cam, pistons, rods, and cylinder head, using a 2.76 ring and pinion. I THINK he had installed a Super Six intake manifold and two-barrel carb. The turbo was a used Buick Grand National unit from a junk yard V-6.

Here’s a video of that run:
[ame="http://www.youtube.com/watch?v=pPe_vHwZsF4"]Slant Six Turbo 1970 Dodge Dart 1/4 Mile pass - YouTube[/ame]
At the other end of the spectrum, is Ryan Peterson’s ’66 Valiant that runs a built-up engine with a 650 (?) Holley 4-barrel carb, a ported head, big valves, and a turbo cam. It runs 127 mph in the quarter at about 2,800-pounds, and has a 10.74-second e.t., with a 727 transmission.

Here’s a video of that car, running 127.
[ame="http://www.youtube.com/watch?v=7QzUfV8iTpQ"]Turbo Slant Six 10.74 @ 127 mph 7-19-10 - YouTube[/ame]
You need something in between those two.

My recommendation for the slant 6 motor would be to put a set of forged pistons and rods in the motor, a 2-bl Holley (500cfm) carb on it, a Snowperformance boost cooler (meth injector,) and an e-bay 65mm turbo, for starters.

The money you DON’T have to spend on putting together a car with this type of engine, will probably make it the cheaper of the two alternatives.

A stock cam will work fine, along with a set of 340 valve springs. These turbo motors don’t like rpm’s much over 5.500, so they last a long time.

Lots of folks just weld the turbo mounting flange to the cast iron stock exhaust manifold. Saves the cost of a header, right there.

The turbocharger homogenizes the sound waves to the point that a muffler probably won’t even be necessary.

No $500.00 TTI headers or $500.00 exhaust system is necessary. I have both on my supercharged ’72 Valiant, so I know what they cost.)

Slant six turbo motors, for some reason, “like” to be held back, so the rear axle-ratios for them that work well for them on the hiway, also work well for drag racing. Both Tom Wolfe and Ryan Peterson run 2.76 gears in their cars.

That means that a junkyard 8.25” rear end out of an Aspen or Volare or, ’73-up A-body) will be ideal for the turbo slant 6 car, and will be bought a whole lot cheaper than the 8.75” needed by the V8 car.

Needless to say, your low-12-second slant six car will have impeccable street manners, with its stock idle and tons of low-end torque, due to the stock cam specs. And a stock converter works fine.

You want to run 11’s??? Since you already spent the money for forged pistons and rods, just crank up the boost a few pounds, and ~voila~! 100 more horsepower. J

Not so easy with a V8.

You pays your money and you takes your choice! A V8 car can be built while you are THINKING about putting together a turbo slant 6. The choice is yours…

Hope this helps