You can only get to a rough estimate with the math as there are many intervening factors that might effect your VE.

4.5 psi is .3 bar.

If say an SC with SSI and sport muffler can make say 200hp you would multiply that by 1.3 for about 260hp. For .5 bar multiply by 1.5 for about 300hp.

However, as noted it takes some HP to drive the supper charger. Say 10-20 at low boost. My guess is you would make about 250chp for 5psi.

About the same as a 3.2 with sport exhaust and chip but you will have a bit more low end grunt.

You will be working against some limiting factors. Assuming you are keeping the CIS it might be able to work fine upto 250hp but shoot for 300hp and you would probably require some very special mods.

The other is SSI's seem to be ok to about 250chp. After that they will probably start reducing your gains.

Then there are the losses from compressing the air. As noted if you start getting near .5 bar you may not see as much gain as you hoped for unless you fit an intercooer.

Now the fun stuff.

There is 5 psi and then there is 5 psi!

A turbo can get to 5 psi by say 2400rpm and stay there till red line.

A supper charger boost is rpm dependent. If your red line is 6500rpm and you configure your pulley so you make 5 psi at red line, you will make 3 psi at 3250rpm. Half the rpm, half the boost.

However, what is often done with supper chargers is to use a pressure relief valve to limit boost. This way you might us a different pully and shoot for 5psi at say 4000rpm and then keep it at your boost target to red line. This might also let you turn up the boost at a later date if say you want to run a tank of race fuel or something.

Good luck.

Air to Water Intercooler

Looks heavy and the pump is not a proper unit. They say no warranty on the pump and describe that where the saving come from.

A properly deigned and built air.air intercooler will require zero maintenance, has no moving parts, and is very efficient and reliable.

bell can make a very nice cooler for you with any end tanks, offsets and many cooler sizes.

I have no idea what he will end up spending here to get some unknown hp and some unknown reliability. But a 3.0 or 3.2 with ssi and a chip would give him 225hp. If he spent more and switched p/c for higher compression with the above he could be at 240hp. And there is a lot of knowledge out there so he does not just flush his money down the toilet and end up with a lump of aluminum.

I strongly advise against supercharging an air cooled flat six. You would be much better served turbocharging your car. I have owned tons of cars that had both methods of forced induction (still do) and the turbo cars I own far outperform the supercharged cars.

I have also done aftermarket supercharger kits on project cars as well with larger CNC custom intercoolers re-programmed EFI and trick piping and slick exhaust systems, in the end the results were disappointed compared to the effort involved.

Turbocharging is where its at! There is a reason most companies are getting away from supercharging even Mercedes and AMG which spends $10M per week on R&D are going away from supercharging and all their new top of the range engines will be twin turbo'd.
Yasin