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Old 07-29-2001, 10:18 PM   #1
Scoob
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Question How much HP do you get from 1 PSI of boost?

Anyone got any ideas/references/data?
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Old 07-29-2001, 10:22 PM   #2
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1 psi? why whould you do that. probably not worth it considering the costs to install for little difference in hp/torque
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Old 07-29-2001, 10:32 PM   #3
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Clarification... An additional 1 PSI on top of what we already have in the WRX. I don't anticipate upping 1 PSI only. Just wanted to see what the increments might have been.....
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Old 07-29-2001, 10:33 PM   #4
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With everything else staying constant (EGT's from turbo and such).. I have heard about 10hp from every 1psi.
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Old 07-30-2001, 10:23 AM   #5
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Well if that were true... I have approximately 25 extra horsepower? with just a boost controller?

would be nice nice though..
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Old 07-30-2001, 10:41 AM   #6
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1 PSI is completely relative to the amount of flow you are getting for that PSI.

In other words.... 1PSI on a VF22 may be 20 HP (just for example) and 10 HP on a TD04 (just for example).... and again.. it's all inclusive... you won't make any power if you don't have fuel and timing to back the extra air flow.

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Old 07-30-2001, 10:59 AM   #7
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RiftsWRX, so I get this right, Not only is the pressure important, but also the ability for the turbo to push enough air volume into the cylinders. The same thing goes for other high pressure air applications, high pressure low volume vs. low pressure high volume.
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Old 07-30-2001, 11:18 AM   #8
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In essense...

Stand in front of a little table fan and put it on high... damn doesn't that thing have to spin fast to really cool you off..

Now stand in front of an industrial size warehouse fan... WOW that thing blows you over at half the RPM!

Get it?

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Old 07-30-2001, 11:21 AM   #9
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Quote:
Originally posted by RiftsWRX
1 PSI is completely relative to the amount of flow you are getting for that PSI.

In other words.... 1PSI on a VF22 may be 20 HP (just for example) and 10 HP on a TD04 (just for example).... and again.. it's all inclusive... you won't make any power if you don't have fuel and timing to back the extra air flow.

Jorge (RiftsWRX)
www.ProjectWRX.com
All very true Rifts.

From the dyno sessions Ive been around (4 cylinder FWD cars), it seems that generally 1 psi of boost nets about 8-10 more hp at the wheels. Id says this is a safe assumption to use.

Of course, as the turbo gets pushed into lower efficiency ranges, the power gained per psi drops.
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Old 07-30-2001, 11:25 AM   #10
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Good analogy Jorge!! I am gonna have to steal that one from ya next time someone asks me how to explain turbo sizing/efficiency. I usually went the techie route, but your analogy is just so much more funny, but still gets the point across.

Mike S.
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Old 07-30-2001, 11:27 AM   #11
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I'm a I.T. Director... I had to learn through the years to explain things to the execs in a non techie way !

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Old 07-30-2001, 11:57 AM   #12
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Ah, it is so clear now. The bigger fan takes more time to speed up , thus the analogy, bigger turbo means longer spool up time.

Thanks guys

Rifts, i can totally relate to the IT-exec translation skills!
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Old 07-30-2001, 12:00 PM   #13
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If one assumes that all turbos, regardless of size, impart the same number of BTUs to the intake air while rasing its pressure by 1 PSI at some RPM, then the horsepower increase will be identical, regardless of turbo size or speed. Turbo size/speed only matters when discussing whether or not it is actually possible for a turbo to raise the intake pressure by 1 PSI at some RPM.

For instance, it may not be possible for a single large turbo to increase intake PSI by 1 at 2800 RPM and it may not be possible for a small turbo to increase intake PSI by 1 at 6500 RPM. However, in the RPM range where both turbos can increase intake pressure by 1 PSI, the resulting increase in horsepower is identical.
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Old 07-30-2001, 12:29 PM   #14
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With all that being said, what kind of HP does the wrx put out at 6500 with 15psi of boost. I was think that with the fbc inplace I was only running like 7-8psi at 6500 rpm, but now I am at 15psi. I didn't have my scan tool when I had the fbc inplace, so I don't know what the timing was then vs what it is with the mbc I have in place now. For the sake of this conversation, lets say that the fuel and time are the same, and that the actual volume of air is ok (not being overheated, but maybe NOT AS GOOD as a better turbo), dod you like that 7-8hp/p\1psi is a good number? With that being said, then would the Hp is 6500 be about 275 or so? Then if we get into better turbos with the mbc or ebc going, 300 should be a problem.


Russ
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Old 07-30-2001, 01:00 PM   #15
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Well I conservatively estimate my WRX to be around 250 hp at the crank (an increase of about 23 hp over stock). THis is just with a boost controller set too 17.5psi max.

If you went off of what I said before 1psi ~ 10hp then I should, theoretically, be getting about 40hp more BUT since I am pushing that much boost (out of efficiency range for turbo) and throw in the fact I live at 6000ft. above sea level (turbo further out of efficiency range + less cooling from intercooler becuase of thinner air).

I adjusted the theoretical 267hp down to 250hp. But who really knows... only the dyno knows right =).
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Old 07-30-2001, 01:22 PM   #16
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Quote:
Originally posted by Jon [in CT]
However, in the RPM range where both turbos can increase intake pressure by 1 PSI, the resulting increase in horsepower is identical.
Only if the compressor efficiencies are the same.

Or, if youve got a good enough intercooler, it doesnt matter anyway
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Old 07-30-2001, 06:52 PM   #17
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This is a ridiculous, unrealistic question! Unless you live in a vacuum.

i.e.
If I you add 1 psi, assuming there is no RPM variable and the turbo housing material volume tt and impeller efficiency, solenoid, leaking bov and engine coolant effectiveness are not factors, along with exhaust gas velocity, temp consistency, wake effect and turbulence, and supposing a statical pressure differential between exhaust and intake plus ignoring IC efficiency and inhg loss, heat source proximity, advance, flow rate, fuel delivery, cam degree and flame front consistency are not factors, _THEN_ ! and only then! would psi still never be enveloped in an HP algorithm.



SLR-
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Old 07-30-2001, 07:01 PM   #18
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Luckily, I'm working on a special "PSI to HP" calculator based on SuicidialLabRat's algorithm, which should be done in a WRX dash-matching color in a few weeks. The days of poring over this heinous mathematical problem are soon to be over. SLR is a frickin' genius.
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Old 07-30-2001, 07:59 PM   #19
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Were gunna be rich kid!

Actually, I would settle for some mendo. rally at guru's; whats up rock star!? Hook me up!






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Old 07-31-2001, 07:27 AM   #20
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Default The Answer

http://www.turbofast.com.au/TFmatch.html
Just fill in the blanks... note the "units of measure required"
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Old 07-31-2001, 11:52 AM   #21
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Gas
1 Turbo
Intercooled
2000cc
6400rpm redline
12psi boost
= 227HP

Thats our HP, but that is not our engine...shy 600rpm max and 2psi of boost.
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Old 07-31-2001, 12:18 PM   #22
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I should also mention that they ask for "redline" it should be asking for the "peak power RPM" not redline

You know when you see a graph of horsepower. The peak power is about 1000 RPMs shy of redline
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