2.5LGT flow chart?

[JL LGT]

I became uncontrollably bored at work, so I decided I'd attempt to learn about flow chart for both my engine, and a few turbos that I have in mind.

From the collective info I've gathered, I was able to put the chart below together....somehow! HaHa!

So tell me.....for those who understand this stuff.....does this chart make sense....or am I out in left field?

NOTE: The far left point is at 700RPM, while'st the middle "elbow" point is at 3500 and the far right point being at 6500RPM w/ a VE of 80%. I used the boost levels because that's where I *think* I'm gonna be looking..... but then again....I'm not that learnded yet! ;NutKick;

http://img.photobucket.com/albums/v509/Warwick_5S/2.bmp

[doctorstupid]

Well the first thing you need to know is that the pressure ratio is NOT Bar ;)

1.0 PR = 0PSIg = 0 Bar = ~14.5PSIa (at sea level)

And congratulations, you have the made the first flow chart that (somehow) crosses over itself :)

[doctorstupid]

Here, this page should help:
http://stealth316.com/2-air-fuel-flow.htm

Usually I do all my charts in CFM, because the mass/minute rate has several variables that can and DO change between manufacturers, and that information isn't always on the flow map. So if needed, I'll convert over to lb/min or kg/min, but cfm is a good starting point to go to any other unit.

[JL LGT]

Here, this page should help:
http://stealth316.com/2-air-fuel-flow.htm

Usually I do all my charts in CFM, because the mass/minute rate has several variables that can and DO change between manufacturers, and that information isn't always on the flow map. So if needed, I'll convert over to lb/min or kg/min, but cfm is a good starting point to go to any other unit.
Yep....that page right there....kicks ASS!

I knew something was wrong with that chart. Gotta hit the drawing board again.

As far as the PR....I thought you could calculate it using (BOOST + 14.7) / 14.7.

So.... going with (0psi + 14.7) / 14.7 = 1. What I read anyway.

[doctorstupid]

At this elevation, pressure ratio is PR x 12 - 12 (the numbers I use anyway, to keep it realistic)

1 PR = 0 PSIg boost
2 PR = 12 PSIg
3 PR = 24 PSIg
etc.

The pressure ratio is based off absolute pressure, 12 PSIa (absolute) is 0 PSIg (what you see on your boost gauge), for this reason you have to subtract absolute pressure above. 3 PR is 24PSIg or 36PSIa.

Makes more sense? :)

[-=[Juztin]=-]

At this elevation, pressure ratio is PR x 12 - 12 (the numbers I use anyway, to keep it realistic)

1 PR = 0 PSIg boost
2 PR = 12 PSIg
3 PR = 24 PSIg
etc.

The pressure ratio is based off absolute pressure, 12 PSIa (absolute) is 0 PSIg (what you see on your boost gauge), for this reason you have to subtract absolute pressure above. 3 PR is 24PSIg or 36PSIa.

Makes more sense? :)
The links you posted were very interesting reads that I gotta go over and take some time thinking about and learning. I was curious, on your 2pr & 3pr, how did you get the 12 & 24 psig #. would 2pr be 14.7psi x 2, so say 28psi, then subtact the base atmosphereic (14.7) to get the psig figure. But are you like rudimentarily taking away an add 2 psi for pressure loss thru piping and ic? If that was the case, would the 3pr have even less psig due to higher loss at higher boost levels?

[Skaterkid]

The 2 psi drop should be accounting for normal air pressure up here. Doc Stupid is just trying to be realistic with the ambient conditions we are faced with.

[doctorstupid]

The 2 psi drop should be accounting for normal air pressure up here. Doc Stupid is just trying to be realistic with the ambient conditions we are faced with.
Bingo. At seal elvel nomral atmoshpheric pressure is close to 14.7 PSIa, up here it's close to 12PSIa. Of course normal absolute pressure varies with weather conditions and such, but it's normally close to those figures. Pressure drop through the charge piping and IC should be subtracted from your PSIg figures if you so desire.

Another great read from Stealth316 for those learning about this stuff is http://www.stealth316.com/2-3s-compflowmaps.htm
It has a lot of compressor maps, as well as a primer on how to use them, and gets super technical with things like adiabatic pumping effeciency.

[JL LGT]

I wasn't calculating for this altitude. I was taking it slow.

I've got the wrong numbers down on the chart for the desired levels of boost @ idle.

Now that I've got a better idea of what absolute pressure is here at our altitude.... I can go back and ATTEMPT to make a proper chart for my engine.

Now for the impossible.....locating a friggin flow chart for the VF40 bolted to my plant!

Trying to decide whether I want an 18G wheel or 20G..... since it's a rather large burden to go twin scroll with the USDM LGT.....damnit!

[doctorstupid]

I wasn't calculating for this altitude. I was taking it slow.

I've got the wrong numbers down on the chart for the desired levels of boost @ idle.

Now that I've got a better idea of what absolute pressure is here at our altitude.... I can go back and ATTEMPT to make a proper chart for my engine.

Now for the impossible.....locating a friggin flow chart for the VF40 bolted to my plant!

Trying to decide whether I want an 18G wheel or 20G..... since it's a rather large burden to go twin scroll with the USDM LGT.....damnit!
Boost at idle.....? You should be well into vacuum under idle conditions.

[JL LGT]

What I meant was.....the numbers at idle are wrong....which is why the chart so drastically crosses itself like it does. I prolly got cross-eyed somewhere during the process... remember.....I'm da n00b.

This process can become confusing at times and I've found myself on more than one occassion going back and fourth between several different pages to try and figure out where I could have gone wrong.....cause the figures just don't look right.

To make it even worse.....I plan on learning (or attempting to) the processes involved with actual tuning on a dyno. Reading fuel maps....IDC...etc.etc and their pertinence to the power pro.

Man.....do got's lots to learn. :cross-eyed:

[doctorstupid]

OK, here's the super easy dumbed down way to make a flow chart:

calculate air flow volume for desired RPM using this formula: VAF = L/28.328 x RPM/2 x VE x PR

Now multiply that number by the pressure ratio you would like to plot.

Go into MSPaint and plot that bastard.

So, for example, a 2.5L at 2,000RPM with 80% VE will intake 70.6CFM at 1.0PR (that's 2.5/28.328 x 1000 x 0.8 x 1.0). At 3.0PR, it's 211.8CFM. So you draw a line between (71, 1.0) and (212, 3.0). Then repeat using different engine speeds and VE and you end up with straight lines that go up at an angle and do not cross over eachother, it's as easy as that :)

And seriously, don't bother with idle, you don't make boost at idle, the throttle is shut, the turbo is simply 'idling' spinning along meaninglessly at low speeds, well off the compressor map. At this point it's nothing more than a restriction.

[JL LGT]

You could have just called me an idiot....or dip shit.

That would have worked too.....thanx.

[Conrad]

You could have just called me an idiot....or dip shit.

That would have worked too.....thanx.

Sheeeeesh do you know anything????? :rofl:

[JL LGT]

I'll get back to you on that one.

[-=[Juztin]=-]

Warwick's a pretty big dude, I'm sure he knows how to punch someone in the face ;) (j/king)

is there a way to calculate VE instead of relying on documents of detailed engine specifics that usually don't show the VE for the entire rpm band? (Least in nissan's case) I should probably go back and look thru that site to see if that dude mentions of a VE calculator. For example I know my car's displacement is 213 ci. I've read the heads flow 57cc

[Skaterkid]

Are you sure you don't mean CFM? To my knowledge the only way to find out your engines true VE is to actually run it on a dyno where the air intake is being monitored by a pitot tube or a mass flow meter. It changes with RPM, and the only thing you know for sure is that where your torque peaks is where your engine has max VE I believe. I haven't begun to research this enough to know rules of thumb, but following a torque curve of your stock engine I'd say it stays in the 80% range over the rev range and is in the high 90's near your torque peak. Just my .02 on this, I'm no expert,

[doctorstupid]

Are you sure you don't mean CFM? To my knowledge the only way to find out your engines true VE is to actually run it on a dyno where the air intake is being monitored by a pitot tube or a mass flow meter. It changes with RPM, and the only thing you know for sure is that where your torque peaks is where your engine has max VE I believe. I haven't begun to research this enough to know rules of thumb, but following a torque curve of your stock engine I'd say it stays in the 80% range over the rev range and is in the high 90's near your torque peak. Just my .02 on this, I'm no expert,
Kind of. The problem is volumetric effeciency is a really vague term, some people include the intake tube and headers in the equation, others do not; some won't count the intake manifold. You could decipher intake air volume going from MAF readings and compare those numbers to what the engine would flow at 100% effecoency, it would be challenging to get much more accurate than that, though trying to measure all that through turbos and intercoolers and loads of piping would only complicate it the comparison. 80 or 85% seems a reasonable assumption accross the board to me, in reality when it comes to plotting engine demand on a flow map you should not really have to worry about a few CFM. Unless you've selected a generally shitty turbo for your application, of course.

And on another note, did it suddenly get hostile in here? Did I miss something or what?

[doctorstupid]

Here, those of you nerdy enough to want to plot your engine demand should find this useful:
clicky clicky (http://www.antisheep.org/hosted/Intake.xls)

I'm not done with it yet, I have a lot of other figures to add for it, but for right now it's quite functional for plotting engine demand. Input into the yellow boxes, plot corrected flow along the X axis and PR along the Y. It's setup for my engine at the moment, I realize my VE is set way high, I split the difference for the accepted VE figures for this engine to account for my top end (which is very not stock).

Speaking of, does anyone here know how the hell I can define the X and Y axis on an Excel chart? I'm trying to make it graph the parameters, but for the life of me cannot figure out Excel's chart function. I can make some charts, just not what I want.....

And on an unrelated note, I'm working on another far more in depth spreadsheet for suspension kinematics, I'll post that in due time.