Hi ToonRBoy,
Thanks for taking a look at my slightly crazy conversion :-)
I have to disagree with you on a few points though..
Rotary like a 2 stroke....Nope I'm afraid not, it's a 4 stroke. My numbers were not calculated for the rotary anyway, that was meerly eye candy showing a past project :-). Besides, you assume because I have built a rotary that I don't work on 4 stoke piston engines. I do, In fact I have sized many turbos for people and am quite accurate at predicting lag, torque and power outputs at particular boosts, including but not limited to my latest project, a 6cyl RB25 DE, with turbo setup, 8:1 comp, forged internals, 400hp, and bugger all lag. I know how to size a turbo ;-).
In fact on the rotary I ran a GT3540, as apposed to the GT3071R I plan to run on this setup. The nissan motor also runs a GT3071R....but of course it has higher mass flow and therefore lag is less of an issue at this sizing and we can also get away with a couple less psi and a few more rpm.
Probably the missunderstanding here is that I am quoting flywheel, real hp....not rubbish power figures that are run on the dyno at the wheels and then multiplied by a factor inversly proportionate to the users old fella. I get tired of magazines unknowingly publishing peoples imaginary hp figures...but thats a another story.
Bottom line, on a 2L 8v single spark Alfa motor, she will need 25+psi to get 400 true engine hp on pump fuel at 7300ish rpm.
As for graphs of Turbos showing rpm....the only rpm you'll even see on a graph is the turbo shaft rpm, as the x axis (flow) is a function of rpm, and cannot really be anything but that.....a 4liter engine at 6000rpm makes a lot more mass flow that a 2liter engine at the same rpm, all things being equal. I assume you were refering to the turbo shaft rpm anyway.
As for the turbo being too small,
without going into all my figures, I actually get the lb/min to about 38 (you mention lb/hr...typo?), which at a PR of 2.7 lands me on the upper right hand side extent of the peak efficieny island for this turbo. That means that the turbo will run up through the meat of the peak eff island (I've checked this)...you could not ask for anything more than that. All of this by my calcs still only gives me 380rwhp at 24psi on 100 octane pump fuel.
You also say concentrate on cfm. I use lb/min, and talk in terms of psi as its something everyone can understand simply. That said, if I divide by density of air at sea level (0.076) I get cfm anyway, so no biggy.
Now if I go for what the other guys are suggesting here, I actually need to reduce the size of the turbo potentially. That is, they suggest running the scharger the whole time. This will mean I now only need to genrate max 15psi from the turbo and the remianing pressure rise of 10psi from the scharger. So in actual fact I will give serious consideration to revising the turbo selection on this basis. That said, it still looks pretty good at 15psi and PR=2 which is a bonus as it would allow me to run this turbo for both scenarios (I am thinking I will try both configurations and see which works out better).
What I will agree with you on is that the engine will need more reinforcing, and I am working on that as we speak, having measured up the block ready for some stress anlysis.
For turbo nuts out there, this is a VERY handy catalogue curtesy of Garrett Honeywell
http://www.turbobygarrett.com/turbob...007Catalog.pdf