333pg333

My head is starting to hurt and I notice my eyes crossing.

Actually within reason I agree with RPH in that so long as you don't put on something that is way out of proportion for your engine, it's not going to make that much difference. Unless you're testing back to back. I know currently I have a turbo that is too big for my engine. (Vitesse stage 5 on stock 2.5L) However you just learn to dance with what you've brung. The S2 r & p offsets this a lot, but the turbo should be really a pig on this car, but it isn't. In fact I like the combo as you really have to plan your moves, but it has a nice kick at 1.5 bar on E85. So assuming you do a better match up than I have ,you can't be that far off the mark really. If you're hunting that 100% efficiency, you may just chase your tail forever?

Dave951

RPHarris I too have read the Corky Bell book many times. And I agree the major reason why I even bothered doing to calcuations were the two you listed. I defintely did not want to be on the left side of the surge line.

For thoose are of you how have heard of the book we are talking about its called. Maxiumum Boost by Corky Bell. Available at Amazon Link. The author details how to calculate the pressure ratio, and a few other necessary things so you can make use of the compressor map. Its a really good book if your into figuring these things out.... which you should be your modifiying your car for performance reasons.

When I get home tonight, I'll see if I can pull out some of the eq's and post them.

333pg333 100% efficiency.... I wish. Take a look at some of the maps. Percentages in the area of aprox 70% is where you are going to realistically fall.

I've been playing around with the turbo calculator over @ Squirrel Performance. Its a pretty nice calucator as it will plot a nice curve right on the compressor map. Now I'm trying to feed it some slighly more acccurate data. I'd like to have some real data from people who have collected it for:
IC Loss (psi) *Please note what intercooler you are using weather it be stock, or something else*
Vol. Efficency
Intake Temps
Dug up a old thread from NZ951 and found some data he collected.

Ambient for test: 10*C
The typical cruise was consistently +6 degreec C over ambient
The MAX degrees C was 39 or 21 over ambient

944obscene

I messed around with the calculator a little. Interesting stuff! Looks to me like a k26 is on its face right around 320-350hp, but a k27 does beautifully. Or maybe I did that wrong?

blown 944

Patrick here is a fun little site the hp is not exact but I have found that using `~ 85 dropping to 75 ve works pretty good. I just wish they had some other maps. try putting in 15psi at 3000 rpm and then scroll through the maps and you will see why too large of turbo doesn't work. Then try putting in 25psi (at higher rpms) and you will see why too small of a turbo doesn't work

944obscene

Surge and gulping... or out of breath and a really good hair drier (HOT).

95ONE

Turbo's should be around 70-78% peak efficiency. But a well planned Intercooler set-up brings that up a notch or two to the 90's. Cryo spraying can of course take it to over 100.

Dave951

95One Please explain how a turbine can run ABOVE 100% efficiency?

As I understand it 100% efficiency would imply that the turbine would suffer no major or minor losses caused by friction, heat or any other force that would otherwise hinder its performance. Considering that is completely impossible to eliminate all friction between contact surfaces I don't see how this would be achievable.

I found another interesting site that has some good links about turbocharger theory.

95ONE

A turbine can't.

An intercooler takes away it's inefficiency. (heat) And then Freezing the air brings it to a much denser charge.

Dave951

95ONE So then what efficiency are you referring to if your not referring to the turbo itself? Or saying it another way, what components are you including in a system that on net is going to generate above 100% efficiency?

I'll agree that adding an heat exchanger to a system will help reduce the volume that the same amount of air will take up, thus allowing for more air molecules to enter the cylinder. Same theory would apply to cryo.

95ONE

100% efficiency regarding heat. Nothing more. 14.5 psi = double wheel horsepower. 150 Stock = 300 @14.5 psi. See it a lot.

Man I'm being lazy today. I'm being so damn general. Don't make me break out Corky bell's book.

100% efficient is still heating up the air according to physics. Can't get around that - yet? But how much less efficient than a perfect compression of air is the turbo... 20-22% typically.

RPHARRIS

Isn't efficiency just measure of heat added to the charge? 100% efficiency meaning the temperature of the charge coming out of the compressor is the same as that going in? 50% efficiency would mean the temperature of the charge (in kelvins) is doubled. AKA, 75% efficiency means that for a given pressure ratio ratio, the charge density exiting the compressor is 75% of that of the atmospheric air because of the heat added. <----wow that's an awkward sentence

One thing I have always wondered is whether you can compare the relative efficiency of two different compressors using their maps. For example could you determine if it is better to be in the sweet spot of an inefficient compressor, or on the fringe of a more efficient one ...its hard to explain what I mean without posting some actual maps

RPHARRIS

Over 100% efficiency would mean that the charge temperature is REDUCED. Which is possible with meth/water injection because of the enthalpy of vaporization ....or something like that.

95ONE

No. Air compressed = heat. physical law. a perfect compression will still net you a hotter charge.
There are currently no compressors that can compress air perfectly. But if there were. (Please don't make me go look up the exact formula) 50 deg F intake temps. and it went through a compressor at x amount of pressure. If it were 100% efficient. The outlet temps will be higher.

95ONE

correct.. Charged air.

thingo

A lot of interesting stuff in Jeff Hartman's book is a bit more current than Corky Bell with a lot of pics, including our cars.