TorqStorm Supercharger build advice needed
Well as our buddy
@TT5.9mag argues and correctly, there's more than one school of thought. None of them are necessarily right or wrong, just different. My experience is with roots type blowers such as 471, 671, and 871 and the small B&M roots blowers like the 144. I've built several and they seemed to respond better with lower compression. That doesn't mean higher compression cannot work, but it can mean you have less "wiggle room" for detonation. Everything has to be perfect. As you say, I think you're about right with your projected effective compression ratio with around 12:1 with the blower on a 9:1 engine.
Now this part is my personal opinion and the WHY of why I do not like to run much higher than about a flat 8:1 on a blown engine. All of these timing retards pull timing out based on boost. What happens to an engine when you pull timing out? The power drops off. That kinda defeats the purpose of a blower, doesn't it? A lower compression engine will pull much less timing out. In fact, On the 144 blower engine we built, we didn't even have a boost retard on that engine and ran about 7 PSI. That engine was blueprinted "somewhere" under 8:1. I don't remember the exact specs, as this was probably about 1985 or 1986. This was with a small block Chevy (stock stroke 350) and in fact at B&M's suggestion that we did not need a boost retard if we ran the engine on premium. That's what we did and never had detonation. We used closed chamber 350HP heads and a dished piston we got to zero deck, so there was a small amount of quench with the about 1/2" wide ring around the outside of the piston that saw zero deck height, so it worked.
I'm not advising that you throw the boost retard in the ditch. Just tellin what worked for us. We did have boost retard on the others, although only pulling a small amount of timing. I've just never been a proponent of pulling timing out of an engine, nor water injection. What's water to to a fire? LOL I guess it's the old man in me. lol Technology has come light years ahead of where we were back then. So I would certainly take advantage of it and will when and if I build a blown slant.....and I'm probably going to at some point before I kick off.
But I want something stickin through the driver's side of the hood. lol