Hey all,
So, it's still a possibility that I'll end up building a new engine for this '75. If I was going to future proof it against sometime getting hardware to stuff more air down it's throat, what might my considerations be in the present with engine building specs?
I'm assuming compression ratio would play a part at least.

 

If you want to boost it, lower initial compression allows you to stuff more into it - say 8.0 - 8.5:1. Depending on your desired HP, you'll want to beef up the bottom end too.

 

Hmmm.... initial spec was 9.5:1 but will be modded to AL heads and +4cc in the chambers so that will go down a bit. Guess I could swap gaskets. Might get to 9:1 or so. Been a while since I had to boot my brain up

 

For a great all round performance street car, force feeding via turbo or supercharging is unbeatable. You can have a docile car which the wife can go shopping in (if she stays off boost), and you can tear up the bitumen on race day under full noise at will. Great combination.
If you can drive around without spooling up into boost you can return similar gas mileage as a stocky....

With 9:1 compression you won't be able to run much more than 6~8psi without consequences.
But that amount of boost will give you a substantial gain.

Conrods and crank are put under a lot of stress with boosted applications, so forged components would be a good thing.
Pistons too are subjected to higher temps, and if you have any tuning issues during setup, they can fail very quickly.

If you can drop compression lower, you can obtain some awesome power gains by running 12~15psi, which would certainly make for a very lively ride. A good intercooler is essential to provide consistent power gains in higher boost apps, as intake charge air temps get very high as more boost is provided.

You don't need big duration cam grinds, so off boost torque is NOT compromised. Good cam lift is your friend though, to get as much fuel into chamber as possible when pushed under presssure.
Having a good free flowing exhaust is also important, especially in turbo apps. Boost control is the hardest aspect, especially if running old school carb and ignition. Computer engine management makes light work of setting up force fed engines for best performance, driveability, reliability and economy.

Centrifugal superchargers are quite good for providing easy power gains whilst maintaining good manners when not on boost, as is the case with turbos, although there is a bit more work involved for exhaust plumbing.

For outright grunt though, nothing beats a positive displacement blower... the torque/power gain is available at any rpm.... no need to spool up to get the added power.



My everyday driver is a turbocharged Ute (sports truck) with a few mods...
It's a 4 litre 6 cylinder running 15psi max boost with a huge intercooler and puts out 400 honest horses and 550 lbft torque at the rear wheels. It may weigh close to 2 tons, but it's good for low 12's on street rubber, and 11's with slicks, and returns 28mpg (imperial gallons) on trips.
It's a great parts hauler across the country, and it goes pretty hard at the local strip on a Saturday night.

Force fed engines do require a bit more fiddling to get right, but when they're setup properly, they provide a very big grin factor!