vtec.dc2

With mild 4.5-5psi boost I plan to run, graph lines usually end up closer to bottom and further to the right.

As shown on the picture below, Is (D) where I want to be?
Does it matter if I'm more to the right where percentage is lower?

Thanks

(this is just a random graph, used as an example)

mos

You want to be at D.

vtec.dc2

Thanks

If closest graph I found matches (B), I undestand that it will not be as efficient.

I understand what surge is, but what happens If I choose the compressor closer to (B) or (C) point? What effects could it have?

noel

How do you calculate where you'd be with a certain engine at a certain rpm. I'm still kinda confused by those maps.

Noel

vtec.dc2

theres a bunch of things to consider, i'm still not 100% sure where I can explain unless looking through directions.. some links I found though:

http://www.majesticturbo.com/compression.html
http://www.bsmotor.com/turbo/tabell.html
http://www.turbofast.com.au/tfcalc.html
http://www.gnttype.org/techarea/turbo/turboflow.html
http://home.planet.nl/~jwq/turbo_expl.html

http://www.stealth316.com/2-3s-compflowmaps.htm
http://www.stealth316.com/2-adiabat1.htm
http://www.stealth316.com/2-turbotemp.htm
http://www.stealth316.com/2-air-fuel-flow.htm

and if anyone knows answer to above, please help

racerxadam

here is a helpful link https://honda-tech.com/zerothread?id=142398

vtec.dc2

thanks, that is a good link, and this explains my question.

vtec.dc2

thought I got it all, but now I'm not sure if Pressure ratio is the same thing as Density ratio.. as seen in http://www.majesticturbo.com/compression.html
or http://www.stealth316.com/2-air-fuel-flow.htm

I know how to calculate the pressure ratio, but what about density ratio? How do you calculate that?

Lets say I'm trying to calculate Volumetric Air Flow (VAF)

given:
C.I.D. = Cubic Inch Displacement
V.E. = Volumetric efficiency - Is there a formula for that? (example .80 percent)
D.R. = Density Ratio? - How do I calculate that?

formula:
VAF = .5 x C.I.D. x RPM / 1728 x V.E. x D.R.


[Modified by vtec.dc2, 10:37 PM 11/24/2002]

vtec.dc2

searched around a bit more, and found answers at http://www.aquamist.co.uk/rescr/faq/...s/airmass.html for density ratio..

the other thing remains is "volumetric efficiency" - how can I found out volumetric efficiency of my b18c5 engine?

Quick 200k Mile Motor

Ive played with compressor maps many times, and even this morning (because I had a dream). I could simplify it a little more..

Pressure Ratio: is located on the Y-axis (vertical) of your compressor map and is basically the amount of boost. For example, 9psi of boost will always be 1.714 on the axis. Same with any other amount of boost.. 14.7psi will always be 2.102 on the axis. It is not dependant on the displacement of your motor, the next factor is.

Air Flow: the X-axis (horizontal) and is basically the air flow your motor demands (dependant on Displacement, RPM, and VE).

VE is probably the most complicated factor. Some say peak VE reaches at peak torque. Some think its @ peak hp (still confuses me).
With production motors, VE can range from 80 to more than 100% (105 is the highest ive seen). I think of 80-85% VE as stock. And a little more over 100% (105) as modified.

Both RPM and VE, will change the value on the x-axis. A higher the RPM, or VE, will move your plot toward the right as the motor will demand more airflow. It can make you fall out of the sweet spot ("D" on your illustration), or make you stay in it. For example, a 1700cc motor can use a big .60 trim compressor. Why? Because of 100%VE, 8500rpm, 14.7psi of boost (2.102 pressure ratio).


[Modified by Quick 200k Mile Motor, 12:31 AM 11/25/2002]

SoulSurfer

I usually use 85% as stock VE as well. I don't know of any way to actually determine it and it gives you a good rough estimate.

vtec.dc2

found couple more links

http://www.installuniversity.com/ins...n_9.012000.htm
http://www.nightrider.com/biketech/c...mulas_page.htm

volumetric efficiency seems to be a tough one to figure out so far.

TurboMinivan

Somebody posted a link, and then quoted from it:

"If there was such a thing as a compressor with 100% efficiency then the air would not be heated up at all."

This statement is COMPLETELY incorrect. It is a physical law that compressing air heats it. Period. What the efficiency refers to is how much the air is really heated compared to how much the laws of thermodynamics say it should be heated. Were there actually a compressor with 100% efficiency, it would only heat the air as much as it "should" and not a degree more. The real world, however, isn't so perfect. Go for the best efficiency you can get!

To really choose a proper compressor, you can 't just map one point on the graph. You'll need to essentially plot the line which represents the majority of your engine's operating speed, then decide precisely where (along the plotted line) to place the point of peak efficiency. And no matter how little boost you run, consider a proper intercooler mandatory! You'll enjoy greater longevity while getting the maximum horsepower bang for your "buck" of boost.

BlueShadow

That's why I said <u>"If there was such a thing as"</u>....I said that because there is no such thing as a compressor with 100% efficiency. I shouold have said 99% instead to keep the nitpickers off my nuts.

Also for those of you that asked:

the VE% for an H22 is 102% and for an S2K (F20C?) it is 112%. All the other B series VTEC motors are probably around 102-105% at peak HP.

&lt;--BlueShadow who is digging up old topics from weeks ago.



[Modified by BlueShadow, 10:10 PM 1/8/2003]

SoulSurfer

Where did you find this...personal experience?

BlueShadow

http://www.autospeed.com/A_1127/page1.html

I asked around, and people said that the author was a pretty reputable source. IIRC the numbers actually came from an SAE paper.

Quote:

Some say peak VE reaches at peak torque. Some think its @ peak hp (still confuses me).

Most motors typically reach their peak VE at peak torque....the exception to this rule are VTEC motors. VTEC motors get peak VE usually at their peak HP.



[Modified by BlueShadow, 9:33 AM 1/9/2003]

SoulSurfer

Interesting...I was under the impression that rotaries were one of the few factory motors that run at 100+%. Could just be that I'm an idiot.

BlueShadow

lol!, I didn't know it either till I read the article, I assumed that because of the VTEC design the VE was really high like 95% plus....but I didn't think it was OVER 100%. You'd be amazed at what you could find on the internet when you do a few searches.

IN VTEC

iTrader: (3)

Wouldn't it be better to have a pressure ratio of 1.7? -where it could lie in the fattest parts of the islands to maintain greater efficiency through a wider spread of the rpm band. 10.29lb of boost.

BlueShadow

If you lower the boost you also lower the amount of airflow. So if you go down to a PR of 1.7 you will also lose a few LB/MIN of airflow and that equates to less HP.

If you're not smack in the middle of the "island" it's not the end of the world. Once you start going into the 50%-60% then you want to start worrying.