I make government pay (AF Captain)... so the 3.2 will probably be my promotion to Lt Colonel present
. Next steps for me are an MSD unit, interior stuff, and chasing electrical demons.
From what I've seen in my research, a 3.2SS using 98mm P&Cs @ 9.5:1, single plug (usually MSD), '74 style exhaust (usually SSI), and a bit of tuning will get you in the 200 - 210 range. Adding 964 cams and some mild head work (port & polish) will bump up the power to the 230 range. For the most part, much of the labor in this is part of a rebuild anyway. If your P&Cs are Alusil then you have to replace them anyway.
The advantage to the 964 Cams is that they still play nice with CIS, have a streetable power curve in a 3.2, and run out of breath around the redline dictated by the mostly stock internals. If you go to carbs, you have a bit more freedom with the camshaft.
250RWHP is doable, but the costs start to spiral up. Specifically:
- going higher compression necessitates going to a twin-plug setup. There are multiple options, but none are cheap. You don't have to do this, but its one way to get a few more horses. Even with access to race fuel, its not a good idea to go high compression without twin plugs.
- going to higher revs. I'm not sure what the magic number is, but the stock rods & rod bolts aren't good for much beyond the original SC redline. You also have to worry about the valvetrain. Power being torque * rpm (divided by something based on horses
) and agressive camshafts mean this is the best way to get power.
- too much torque and you risk grenading your 915... so you need to mod that as well. Of course this is true with the 3.6 conversion too. The bearing retainer plate and possibly differential plate to keep from warping the case and oil cooling to keep the internals in check. This can of course be limited by running a higher revving engine, but then you've got the previously mentioned issue.
As for total parts / labor cost... baseline would be whatever a full rebuild goes for these days (haven't looked recently) + parts cost. If you decided to twin-plug there's also the cost of head work. Ditto for regrinding your camshaft (if its possible).
Your best bet would be to search the engine rebuilding forum and/or post your question there. There are several professional & amateur engine builders who post there from time to time and are willing to give advice.