Flow chart, help me interpret it

[StockyMcStock]

this is a lysholm 2300 (marketed as whipple) flow chart. give me opinions on what sort of final pressure i would be looking at for an RB25/30 combo engine (standard head + cams, 8.3 compression ratio and standard bottom end) if the engine revved to 6,500 rpm and the blower was driven at 2x crank speed to keep the rev ceiling at 13,000rpm.

just after opinions if anyone can interpret the flow chart better than i can! i expect the engine to produce roughly 400-450 horsepower at the crank.

[Sydneykid]

Simple stuff.........

*You need ~10 lbs of air per minute to make ~100 bhp.

*So if you want 485 bhp (450 + 35) you need ~49 lbs of air per minute

*At sea level etc , 45 lbs of air per minute is around 17 cubic metres per minute

*Go up from the 17m3/m pont on the bottom axis and it's most efficient area (65%) is 1.75 pressure ratio (~0.75 bar boost).

*The air is going to be 100 degrees C (the red line) and that's hot, so you will need some cooling of the charge ie; water injection, intercooler etc

*It is going to be running at 86% efficiency (the purple line)

*Note that the supercharger itself is going to need 34 bhp (25 kw) from the engine to run it (the green line). That's why I used 485 bhp above.

*So you will need around 8,000 rpm, plus 14%, say 10,000 rpm

*At double cranksahft speed that means max power at ~5,000 rpm, not bad for an engine with a redline at 6,500 rpm.

Hope that was of some help:cheers:

[Lithium]

Nice - that cleared a few things up for me as well, thanks

[StockyMcStock]

yeah good stuff - wasn't sure on the conversion stuff (BHP to airflow particularly) so that's nice work. i'm thinking if running the blower at 2x crank speed and venting the excess air via a turbo external wastegate in the induction piping somewhere, so i can vary the boost if i want to. the charge will be heavily intercooled, yes, i am using a good front-mount and thinking of running a custom water/air after the other intercooler which i can pack with icy water for dyno runs/drag runs.

[Sydneykid]

venting the excess air via a turbo external wastegate in the induction piping somewhere.

I think a BOV would be more applicable than a wastegate, too slow and way over engineered for inlet air. Use a positive boost controller (like the Jaycar IEBC) to control the BOV opening.

[StockyMcStock]

how? the BOV only has a fitting on the top, to help it open under vacuum obviously. wouldn't you need something like a wastegate which has a pressure fitting such that compressed air will force it open against the spring pressure?

the only way i can think of doing it with a BOV is by altering the spring rate till it was just right, but i doubt it would work properly?

[Sydneykid]

how? the BOV only has a fitting on the top, to help it open under vacuum obviously. wouldn't you need something like a wastegate which has a pressure fitting such that compressed air will force it open against the spring pressure?

the only way i can think of doing it with a BOV is by altering the spring rate till it was just right, but i doubt it would work properly?

The better BOV's have two air supply inlets. One for vacuum and one for pressure. Use the pressure inlet (under the diaphram) and it will open the valve when air flows. Leave the vacuum inlet open to atmosphere. Then use a boost controller to open a solenoid and allow air flow (boost pressure) to the BOV when the target boost is reached. You can of course by supercharger blow off valves, they come with a box of springs, so you can adjust to your boost target. But I like the idea of of eletronically controlling the boost.

[StockyMcStock]

ah, that's pretty much exactly what i was going to do, with a turbo external gate. i am already using a garrett 32mm wastegate as a bypass valve for the blower i have now, i was thinking about getting a second one and doing exactly what you just described. however hiding two wastegates in the piping could be somewhat interesting, at least the coppers wouldn't know what it was.......

p.s. i've personally never seen a BOV with two fittings like that, and i suspect they'd be expensive? can you throw me a brand or a link or something?