PsYcHo_Pilot

I am a fan is the supercharger in particular the centrafugal type. i have been looking into the power generated by this and the power losses in driving it,

I have read that a boost of say 7.2 psi, will give about a 50% (excluding an aftercooler) overall power increase, but the SC can guzzle ( a MAX) of 20% of pre-boost power.

if anyone cold give me more info on normal operating boost pressures of SC's and power production of the SC & aftercooler in comparison to that of the Twin turbo& intercooler set up.

what can the Renisis (or any other rotary) handle these 20psi boosts i've read about, or is that just for recriprocating 5L's and over...
some assistance in this would be appreciated, SC site

PsYcHo_Pilot

and yes, thats an old 13b, with a SC on it

lOOK UP

CraziFuzzy

The choice between a SC and a Turbo depend mostly on what you want out of the car. A positive displacement SC will allow you to keep the almost linear power band that is so drivable about the RX-8's renesis, but you lose a lot of efficiency... The Centrifugal SC will be a lot more peaky with the power, and have more efficiency... a turbo will probably be the most efficient, but will, of course, add in a little to a lot of lag depending on the arrangement you end up with, sacrificing drivability.

wakeech

:D superchargers seem to be a hot topic:

http://www.rx8forum.com/showthread.p...0&pagenumber=1

that's a good thread where i highlight the kinds of tradeoffs that you need to make when dealing with superchargers, and the sorts of advantages and disadvantages there are with alternatives (like turbos).

as for after/inter coolers, the greater the volume of air you have between your compressor and the combustion chamber, the more "lag" you'll experience as the entire volume needs to get to pressure to boost the engine. but yes, it is important for higher boost applications, as the more you compress something the hotter it gets (as the energy it has in it is "concentrated", not to mention the engergy added to it by your spinning impeller or what-have-you).

as has been said before, the RENESIS has been reported to be built to "take boost" (from the horse's, er, Mazda engineer's, mouth)... how much?? we dunno, 'cause no one has to try it out with.

Sputnik

The picture you have shows a roots-type SC.

In my opinion, a centrifugal SC would not be very practical for a high revving engine. A centrifugal has a very narrow band where it is efficient to begin with, and putting it on an engine with such a high rpm range further limits the "sweet spot" where the engine will be strong. Outside of that "sweet spot", there will be little gain from a centrifugal, and way outside of the "sweet spot", it will actually hurt performance. A roots type SC would also be limited, but not as much as a centrifugal SC.

Yes, there are people who put centrifugal SCs on engines like the S2000. But those are perfect examples of what I'm talking about. You have a high "peak" HP number to brag to your friends about, but the actual improvement in power is limited to a very narrow band (which is annoying in daily driving and traffic, and isn't all that beneficial in racing either), and you lose power down low.

If that's what you want, then cool. But don't expect too much from it.

---jps

wakeech

oh?? i thought it was the other way around... ah well. good deal.
exactly what i was getting at (in the other thread i linked to).

PsYcHo_Pilot

thanks for the replies.

I have heard that the "Screw type" is the best, but this was off a piston engine site,
i believe that the centragugal would be a good option (from my limited knowlege of the subject)
I personally dont want a drag car, i DO want a car with great all round acceleration, and Very good handling chareristics.

-75% thermal efficiency (and there was a mention of greater volumetric efficiency),

-negate the weight, cost , and hastle of an intercooler.

-instant power

as has been mentioned before, the low torque at low speeds in the RENESIS, would be overcome by this.

and the rotary is a naturally high reving engine, so i guestimate it would decrease lag, increase boost pressure allowance, and my good old favorite, save weight, but i may be misinformed.

would anyone be able to hazzard a guess as to the weight difference between a TT and intercooler set up, as opposed to a sc.... ?? ??

but i guess we'll have to wait and see what mazdaspeed has to say about things.

so its a bit of a toss up... go with the fad, or try get the most out of things..

Sputnik

There's no "best", it depends on your application, and what you want out of it. It doesn't really matter between rotary and piston in this manner.

Quote:

...i believe that the centragugal would be a good option (from my limited knowlege of the subject) I personally dont want a drag car, i DO want a car with great all round acceleration...

That's the thing, with a narrow power band, the centrifugal SC will NOT give you great power in all rpm ranges (which is what I assume that you mean by "all round acceleration"). A Roots/Lysholm type wil be better over alll, but at the cost of thermal efficiency at higher boost levels, and "peak" numbers.

Quote:

-instant power

Again, if you punch the throttle at 3k, you will NOT get instant power from a centrifugal SC. You will have to wait until the engine gets higher in the rpm band before the boost really comes on. You will have it on tap with a Roots/Lysholm type (again, with the same tradeoffs).

Quote:

...and the rotary is a naturally high reving engine, so i guestimate it would decrease lag, increase boost pressure allowance...

??? What lag? What do you mean by "boost pressure allowance"?.

---jps

PsYcHo_Pilot

1st off, i want to fix the low torque at low speeds problem. so an SC is ideal for that, I just happened to stuble across the centrafugal type, and by the specs i saw, it looked like the better option,

thats my problem, i WANT instant power, at low speeds, without screwing around with the gearbox.
so thank you for bringing that to my attention. i'll take a look at the other types for an alternative then.

the answer :


the fact that the rotary is naturally higher reving, and the SC is belt driven, straight from the engine, it could spin the SC to the required RPM faster, than a piston engine could.. therefore decreasing the "Lag time"

thats what i mean by lag


Because of the high RPM, and the fact the rotor sosent reciprocate, would in my mind, indicate thsat the rotary can handle more pressure, than a reciprocating engine, "the bigger the bang, the fasdter she spins" and the higher the pressure, the bigger the bang, to a certain extent anyway.

but again, thnx for the info on the Centrafugal SC