Bill Dedman said

Norm, here sre some more thoughts on how to go about this project as regards engine choice:

You really can't make a mistake here RE: engine choice, no matter which you choose. The 318/360 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 the 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.
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 will likely need 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 B-Body 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 A body car is like falling out of a tree. A decent set of headers, some 11:1 pistons, a slightly-warm, hydraulic roller cam and an Air Gap/ manifold and a 750 Holley, and you’re there!

The 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 12.90-second e.t. with a stock cam, pistons, rods, and cylinder head, using a 2.76 ring and pinion. I THINK he had installed an aftermarket intake manifold and a Holley 4-bbl carb . The turbo was a used Buick Grand National unit from a junk yard V-6. But, he used 18 pounds of boost to accomplish that, and that wouldn't be a viable, ongoing, scenario for a stock piston/rod motor because of eventual reliability issues.


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.

I posted a video of that car, running 127mph, earlier.

You probably need something in between those two.

My recommendation for the slant 6 motor would be to put a set of Wiseco forged pistons and K-1 rods in the motor, a 2-bbl 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 (even the 500hp ones)don’t like rpm’s much over 5.500, so they last a long time.

A PISHTA-design J-pipe will work well in the absence of a real header, for mounting the turbo.
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 header-back exhaust system is necessary. I have both on my Vortech-supercharged 360 Magnum-powered, ’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. The V8 won't perform well on both the highway and the drag strip on the same set of gearing. That means setting up two center sections, and swaping them for highway-trips or runs down the drag strip. That necessitates an expensive A-body 8.75" housing for drop-out convenience.... $$$$$$$

Needless to say, your pump gas, 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.

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.

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… with pictures of my engine and the J-pipe (PISHTA-design) I mentioned... keeps you from having to weld on the original cast-iron manifold to adapt the turbo to the exhaust system.

Whatever you decide, good luck!!!:cheers:

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