Originally Posted by Trudge

It depends on what you intend to use the car for - Street, track, daily driver, show? It also depends on you budget and your mechanical expertise. If you want to simply drop-in a new engine, then stick with the straight six and find an original 2.4 liter from a 240Z or a 2.8 liter from a 280Z or 280ZX. If you go with a 2.8 liter then do some research because, while the block is the same on all 2.8 liters engines, heads and intake manifolds are not and they have an effect on horsepower.

The easiest approach would be to go back with a 2.4 liter from a 240Z but they might be hard to find. Your 240 is already wired and piped for that engine so this would be the quickest solution.

The next best approach would be to drop in a 2.8 liter. However, these engines are fuel injected and require a fuel management computer which your 240Z does not have. So, when you purchase the engine also purchase the computer and wiring harness. I recall that there are also issues with the ignition and cooling systems.

V8's require modified motor mounts, tranny mounts, and a custom built drive shaft. A weak point is the rear diff and half shafts. You can get by with the stock rear differential and half shafts but they WILL eventually fail under the additional V8 horsepower. The V8 conversion is expensive and a bit complicated. The 240 frame rails cannot hold up to the torque of a V8 and you will eventually have trouble with the frame rails. Bottom line, the 240 chassis was not build for the torgue of a V8.

There are many Z club websites and many of them have articles covering this topic so I'd suggest you read all the articles you can find and then decide.

If you are going to truely restore your 240 then go back with original otherwise it will not be considered a restoration and at car shows you will compete in a modified category. Also, true ZCar enthusiasts/puresists frown on V8 conversions.

I restored my 1977 280Z and I decided to go back with a well built 10.5:1 compression fuel injected 2.8 Liter engine with a mild street cam, competition clutch. I built the engine myself and had a lot of fun doing it! It is as much fun to drive as my 01 Corvette Coupe and it will light up the tires and it will put you back in the seat.

You can get a lot of performance and HP out of those straight 6 engines.

Good Luck!