IKnowNot'ing

That means the Axial s/c will be even more compact in size! Good!

Kev_UK

There aren't any pictures of the unit on the 8 yet, and there won't be for a while im guessing. Go back a few pages, or even to the start of the thread and read some - you'll notice he's only at the beginning of testing.


Keep it up Richard

s2je77

i'm sorry for asking a noob question..

but what's wrong with more pressure?
y would u have to remove a stage?

more pressure = more air = more fuel = more power... isn't it?

s2je77

Hymee

iTrader: (1)

Equals more stress on the internals. There are so many unknowns yet. It depends on what application you want it for. Who knows if a 12PSI kit requires more fuel flow than the stock injectors can supply? Not enough fuel = too lean = detonation = bang = here is the check for a new motor. Thanks for coming.

Some people, with such new cars will only want "bolt-on". Down the track, sooner perhaps, people will be prepared to do internal mods to keep up with higher boost.

One other thing - More pressure = more heat, there is no escaping that law of physics. Too much heat = need an intercooler = more cost. Intercooler = boost loss = need more boost = more power to drive pump = chasing your tail.

So in certain respects, less boost is better. It is, as they say, "Horses for Courses".

Cheers,
Hymee.

s2je77

thanx hymee,

Is 12 PSI a alot? cuz i'm interested in FI for my 8
and this S/C does sound a lot better than the turbos i have in other cars...
in my VW GOLF.. the it goes up to 5 bars... how many psi is that? is it a lot?
y would my dad's porsche only go up to 3 bars?

s2je77

ranger4277

5 bar is 73 psi and 3 bar is 44 psi; i guarantee neither car was running that much boost. Am I misunderstanding the "bars" you're talking about here?

86rx7

umm,.. 5 bar is ~75 psi,.. I HIGHLY doubt that,.. you sure its not .5 bar? or 7 psi? same for the porsche, as 45 psi is way way to much aswell. 12 psi is a decent amount of boost. the max I've usually seen on rotarys is 30, with most street cars in the 10-20 range. The rx8 has high compression though so i'd expect 6-12 psi max of a street car..

Richard Paul

iTrader: (5)

A bar is equal to 14.5 psi or 29.5 in hg.
This is the euro idea of a normal day. They are probably right.
We use the standard corrected number of 29.92 in. hg or 14.7psi.
This is the labrotory correct number for sea level dry air at 60 f.

Also note that this is the number we correct dyno hp to.
Then there is the SAE correct number. I might not have this exactly right but memory says 29.38 at 75 f.????

Now I know if that is not correct to the .001 someone is going to tell me the right number. And that is OK by me. Just pointing out that this is a rough room, alot of real good studies here. I like that also.

Richard

shelleys_man_06

I took a more mathematical approach when it came to making power. Read my first post in this thread:

https://www.rx8club.com/showthread.p...=ideal+gas+law

Did you mean by more fuel, more fuel consumption? A/F ratios are critical to optimum performance, especially in forced induction applications. More pressure can lead to more power, but it depends on the method. For example, an equation for power, which I will call W[dot] follows the equation

W[dot]=m[dot]*[(Integrand)pdV]

I wish I had mathtype .

m[dot] is the mass flow rate
[(Integrand)pdV] is the integral from the initial specific volume to the final specific volume, multiplied by some specified pressure p.

For those who haven't had any experience with calculus, the formula for W[dot] goes to

W[dot]=m[dot]p(v[2]-v[1])

v[1] is the initial specific volume
v[2] is the final specific volume, which are both measured in ft^3/lbm or in SI units, m^3/kg

Note: Mass air flow rates are usually in lbf/min, or in kg/s. It is okay to mix units, as long as you convert between English and SI.

Yes, increasing the pressure will increase the power. Unfortunately, the internal strength is weakened, since the mass flow rate is both pressure and temperature dependent. This will explain a lower modulus in the material.

With ideal intercoolers, the temperature drops, but the pressure is to remain constant. Cooler operating temperatures will lead to more power. Why? Going back to the Ideal Gas Law for the mass balance,

m[dot]=p(AV)/{R[G]T}

you can observe that lowering the temperature will lead to a higher mass flow rate, thus increasing W[dot].

Hymee

iTrader: (1)

It depends what you call a lot.

5 bar of boost is a lot though. 1 bar ~ 1 atmosphere ~ 14.7 PSI.

3 Bar boost = 1 atmosphere + 3 more. Effectively 4 times the N/A volume of air going in.

But those numbers are more like PSI for factory/production cars. I would believe 5 PSI for the Golf (without any other specs on hand).

You will find some Dragsters run at 30+ PSI.

The 12 I mentioned was just a figure I plucked. It is a fair bit for a street car. I was making a point about the fuel system keeping up with a fairly aggressive level of boost.

Cheers,
Hymee.

Hymee

iTrader: (1)

What is your definition of a turbine???

Good info here I reckon, RAP has even posted pics of the components, and papers he has written!

What do you want?? Oh, I forgot. Rome really was built in a day.

Cheers,
Hymee.

Richard Paul

iTrader: (5)

Oh boy, I for myself will step aside on this one. There are some real intelects on this thread who can do better then I, and will.
My only point is that second year engineering students always know everything. Hell, I did.

Just warning you, like I said before. This is a rough room.

shelleys_man_06

I know there are some real smarties in this forum. In addition, I know they're smarter than me. I just enjoy using mathematics to make my point. Concepts are more important than any math.

Hymee

iTrader: (1)

Sir,

With all due respect, I must object to those statements. Like RAP said, this is a rough room.

If the charge is cooled, its pressure drops. You can't get away from that ideal gas law you mentioned.

X molecules of "air" always ways the same mass. Once the air has gone through the supercharger, there is X molecules there. No more, no less. No amount of heating or cooling will change the number of molecules in there.

And I didn't say an intercooler is not any good. But it is not a panacea.

Cheers,
Hymee.

Hymee

iTrader: (1)

I love the math and theory behind it as well. But my calculator doesn't go down the 1/4 mile very fast.

You need the calculator to help get things close to right, but the practical experience is what puts results on the board.

Cheers,
Hymee.

shelleys_man_06

Mathematical analysis is a model for reality. Of course, these results are going to be skewed in the real world. In addition, I believe I mentioned an ideal intercooler, and not an actual intercooler. I am quite aware that real intercoolers have significant pressure drop. Just read the specs off the 2004 Garrett catalog. The pressure drop probably comes from the transience of the working fluid. That's what correction equations are for. You do make a point Hymee. The best results are the ones on the track, and not the lab. Also, you can use these to make your car better. It's that simple. Experience always weighs more than mathematics.

Hymee

iTrader: (1)

Thanks SM6.

Don't forget there must also be a pressure drop because we reducing the temperature, whilst keeping the volume and mass constant. The temp only affects spark timing / detonation risks. No matter what the temp, once you have stuffed more air molecules into the intake under pressure, there is more of them to get into the combustion chamber.

Cheers,
Hymee.

shelleys_man_06

Indeed Hymee. Also, after observing the design of an axial-flow compressor once again, I would believe the efficiency would be far greater than positive-displacement, or even centrifugal superchargers. I would support the manufacture of this product, since it provides another alternative of adding power. Unfortunately, the only way to really prove whether the axial-flow compressor is sound is to test and win.

shelleys_man_06

I certainly enjoy these forums because we can exchange knowledge from the comfort of our own homes. Learning is fundamental .

Hymee

iTrader: (1)

And test I intend to do!!

s2je77

the cars are all the way down in the garage... so i don't wanna hike down there and check the units....

i'll take ur word for it that i'm reading the wrong numbers....
then do k27 and k37 mean n e thing?
cuz k27 is the one in the golf and the k37 is in the 944

i'm probably getting off topic... so u can ignore me and go back to talking about the S/C

jeff

Hymee

iTrader: (1)

I walked all the way down to this interenet site http://www.turbos.bwauto.com/en/products/commercial.asp

The K27 is 150-330 kW range.

The K37 is 230-265 kW range.

Actual boost pressure is a function of the displacement of the engine it is installed on. (I.e. how much air it requires, v's how much is being "pumped".

Cheers,
Hymee.

shelleys_man_06

Neat. I've been looking for Borg-Warner's webpage for quite some time. Thank you Hymee.

Hymee

iTrader: (1)

I googled for "k27 k37 turbo".

It is the first page, so I could have clicked "I'm feeling lucky".

Glad I can help with the really hard problems.

Cheers,
Hymee.

shelleys_man_06

Hey !! J/K. Actually, I was looking for the page with the chart of turbochargers.