Choosing a Compressor map, Need help!

[Speckid14]

I got really bored over the past weekend and thought I would try and to calculate the numbers I needed in order to make 650hp (flywheel) on a compressor map. However, I think I went wrong somewhere in my calculations. Please inform me if I did something wrong.

Motor and #'s I used:KA24DE or 146.456 cu.inchesS13 Cams 7200rpm redlineHp goal: 650hp96lb injectorsnon-intercooled temp: 175VE: 95%AFR:12Sea level: 14.7psia

First:Calculate BSFC (Brake specific fuel consumption)96*4 650BSFC=.59lb/hr or .0098lb/min

Then I used the BSFC to calculate actual airflow that I would need to make 650hp(flywheel):

Actual Airflow (WA)= HP*a/f*bsfc(lb./min)where:-HP: 650hp-a/f:12-bsfc(lb./min): .0098

so: 650*12*.0098= 76.4lbs/min = WA

Second:Then I tried to calculate the required manifold pressure to meet hp(650)This is where I think I went wrong as I believe the final number I got (in bold) is way to high.

MAP= WA*R*(460+Tm) VE*n/2*volwhere:-WA: actual airflow 76.4lbs/min-R: Gas Constant or 639.6-Tm: Intake manifold pressure(Farenheit) I used 175 which is a low temp on purpose because I wanted to get as close to intercooled as possible w/o using intercooler temps. non-intercooled: 175-300-N/2: engine speed/2 or 7200/2 I used 7200 which is max rpm with S13 cams-vol: engine displacement (cu.inches)

So:MAP=76.4*639.6*(460+175) .95*7200/2*146.456

MAP=61.95psia or 47.25psigThat means that I would have to produce 47psi (at the gauge) in order to make 650hp at the flywheel, that is insane when I know ivan has made over 700hp at the wheels on 42psi

Lastly:To calculate pressure ratio there are 3 steps

a.) compressor discharge pressure (P2C)note: depending on the flow rate the plumbing pressure drop can be estimated. On a well developed system rumor is that this is 1psi or less, on an OEM system this can be 4psi or greater. I used 2 just as a "middle man"

P2C=MAP+Plosswhere:-P2C: compressor discharge pressure(psia)-MAP: manifold absolute pressure(psia)-Ploss: pressure loss b/w compressor and manifold (psi)

so:P2C=61.95+2P2C=63.95psi

b.) Compressor inlet pressure (P1C)note: i just used sea level for ambient air pressure

P1C=Pamb-Plosswhere:-P1C: compressor inlet pressure(psia)-Pamb: ambient air pressure(psia)-Ploss: pressure loss due to airfilter/piping(psi)

so:P1C=14.7-2P1C=12.7

c.) calculate pressure ratio (IIc)IIc=P2C/P1C

so:IIc=63.95/12.7IIc=5.035!!!!!!

The two most important numbers on here are 76.4lbs/min of air and a pressure ratio of 5.035. While 76lbs of air a minute is definately possible and I know my calculations are right, a pressure ratio of 5.035 is absolutely insane This pressure ratio won't register on any compressor map, not even a T-88. Also I know that other cars are not needing 47psig to make that kind of power so my question is how did these numbers get so high. Or am I not calculating for other power that the motor puts out. One thing I did not like what I was told is that a 4valve motor generally has a 95% VE. I think that is way high my guess is more like 85%, which would make my psig go even higher because the motor loses effieciency. I'm totally lost and if you could give me a hint as to where I went wrong that would be fantastic.

Again:76.4lbs/min: OK5.035 Pressure ratio: Not OK

Also, has anyone heard of running an HX40 turbo on a KA24DE, thought it would be a good idea, 3500rpm spool up with up to 650hp+Thanks, Speckid14

[crzycav86]

What are the units you have for the gas constant?

I've done something like this before, but I used metric units. I have it in a spreadsheet that I've attached. The purpose of the spreadsheet was to make get a PW and duty cycle fuel maps given a VE and desired AFR map. It also has a "real time simulation" tool that should give you power, torque, duty cycle, etc.. given temperature, pressure, rpm, and bsfc.. similar to what you did.

I input your parameters and got an absolute pressure of 330 kPa, or 33.8 psi gauge... much more reasonable...

Doing this kind of analysis requires keeping track of units, otherwise it's hard to troubleshoot units. Plus, English units are a pain in the ***.

Here's the excel file, apparantly we can't post attachments on nico: http://www.houston240sx.com/fo...60127

[Speckid14]

I used a gas constant of 639.6, not sure of the unit as my formula does not have units (stupid).

This is the equation I have including units:

To calculate required manifold pressure to meet hp:

MAP=WA*R*(460+Tm) VE*n/2*vol

where:MAP: manifold absolute pressure (psia)WA: Actual airflow (lb.min)R: Gas constant or 639.6Tm: Intake manifold temp or 175 (farenheit)N: engine speed or 7200 divided by 2 ex. 7200/2 or 3600vol: Engine displacement or 146.456 (cubic inches)

Also, what did you plug in for the cc/min number in red??? Did you use a VE of 85, or 95? Has anyone calculated the real VE of a standard KA24DE using actual cfm and all (just curious)? What did you use for manifold absolute pressure, and why?

Thanks for your help, its hard to find someone around that likes to do this stuff like me, lol.

for crzycav86 - nice link, whoever made that is the bombAny word on use of an HX40, with 33.8psi it is even more possible.

[crzycav86]

I made that spreadsheet last month for a discussion on another forum. I'm glad you find it useful.

I should have mentioned that you don't touch the numbers in red - those are outputs. You modify the stuff in black to meet your parameters. the red cc/min thing is injector flow-rate for a given base pressure (where the injector is rated at 43.5 psi base pressure)

What I did for your case was set the temperature to 175 degrees, and set the bsfc to .59. Then I adjusted the manifold pressure until i get 650 hp at 7200 rpm. It turned out to be 34 psi.

Anyway, with some headwork and cams, you can probably get .95 VE at peak horsepower.

[Speckid14]

well now that the psi is sorted out, thanks for your help, what about the pressure ratio. A pressure ratio of 5.035 won't register on any compressor map, lol. I haven't been able to find any other formulas to find pressure ratio either, lame.

^^^Look at the P2C/P1C=IIc in my first post^^^

thanks for your help, I wish I knew more people that knew how to do this, as I know no one.

Also, what did you use for fuel density, I am only coming up with 507hpwith a manifold absolute pressure of 234.42 or 34psi

Thanks again, Speckid14

[crzycav86]

Uh-oh. i made a mistake in thats spreadsheet. Where it says "manifold absolute pressure", that should say gauge pressure.

it looks like your numbers are correct, but you might want to reduce bsfc to .5 - that will improve your hp numbers and allow you to reduce the boost. thats probably how ivan got his numbers - good tuning, and probably water injection to get the intake temps very low.

[Speckid14]

well now that we got that out of the way, how do I take this data, and apply it to a compressor map??? I really really want to know how to read these correctly and be able to apply them to any application. I'm really wanting to get into the business of doing this eventually.

Thanks, speckid14

[crzycav86]

after you figure out your air flow and pressure ratio, you plot it on the compressor map. the compressor map gives you the compressor efficiency for that operating range. the compressor efficiency will tell you how much the air is actually heated beyond a perfectly efficient isentropic compression.

i wrote this on another forum, so i'll paste it here. it has an example using a t3/t4 at 4 psi. he was asking if it would be worth using an intercooler at 4psi:

here’s how we answer your question.

Use this formula. It’s from thermo for an isentropic compression. It describes how air will heat up as it is compressed.

T2 = T1* (p2 / p1)^.286

T1 and T2 are inlet and outlet temperatures in Kelvin. P1 and p2 are atmospheric and manifold(absolute) pressure in atm. the .286 is from the ratio of specific heats at constant volume and constant temperature. it's generally constant.

The actual temperature gain is (T2-T1) / compressor efficiency, which is what you get after plotting the compressor map. On a 57 trim at 4 psi, yours is around 68-72% from 5000-6500. If there is a significant temperature gain, then you can benefit from an intercooler.

So lets say it’s 75 degrees outside. That’s 297 K. atmospheric pressure is 1 atm, 4psi of boost is 1.272 atm absolute. Compressor efficiency is 68%.

T2 = (297)*(1.272/1)^.286 = 318 K.

Temp gain = (318 – 297) / .68 = 30.8 Celsius = 87.5 * F

So the temperature inside your intake will be up to 162.5* Farenheit. Not extremely bad, but since ambient air is 75 F, you could cool a lot of that down. A good intake temperature is less than 130* F.

hope that helps!

EDIT:

Actually, your real intake temperatures will be higher if it's taking air from underhood. lf the underhood temps are about 100 degrees, you can do the same thing to find the actual intake temps:

T2 = (310)*(1.272/1)^.286 = 332 K.

Temp gain = (332 – 310) / .68 = 32.5 Celsius = 90.23 * FSo an intake charge 25 degrees hotter increased the pressurized air by 3 degrees.

[crzycav86]

i thought you might be interested in reading this thread, it's current and related. a lot of the stuff here is repeated from a different point of view: http://www.ka-t.org/forums/vie...d5ccc

[Speckid14]

wow, that lovehorsepower.com website is sex, lol. Thanks alot for the help, Im going to have a local guy help me out with plotting the points as that is what I am seeming to struggle with, for some reason i am having trouble calculating rpm and then putting onto a compressor map. I am interested in an HX40 just because of the quicker spool, but am also thinking about T-61.

Thanks, Speckid14

[carmo]

This is one the most worth while threads I have read to date. Like you said Speckid, it's hard to find anyone else interested in this stuff. I'm a newb at it, so alot of the jargon is over my head. But, there are good links here for good research. Thanks guys.

[Speckid14]

Yeah this thread is awesome. Thanks for all the help.

However, I am still having trouble graphing points according to rpm. Any help would be appreciated. Or do I just change the rpm in the flow calculation formula from redline to anywhere in the powerband???Can't figure this out

Thanks, Speckid