pre and post turbo pressure measurements
 

Hi, kinda new on this forum

I own an MY99 impreza since last december.
and started modding immediately.
Since I like to know how well upgrades really are I started measuring stuff.
My first real engine modification is a full 3" decatted exhaust.
Revolution mid-pipe and back box and H&S downpipe.
next to this I have an Techedge Wideband O2 (AFR)
rest of the engine is completely stock.

I started to log the boost (using the logging capability of the techedge)
and came up with this graph:

http://members.home.nl/bogink/boost_vs_rpm.jpg
I expected the boost to fall after approx. 5500rpm, but this continues fall to only 1.6 bar (abs).

Can somebody confirm if this is seen on all near standard impreza's?

Next I measured the inlet pressure (using old honda map sensors)
I measured directly before the inlet of turbo.
and came up with:

http://members.home.nl/bogink/inlet_pressure_vs_rpm.jpg

This is offcourse with WOT.
However 0.12 bar loss on behave of the inlet seems like Huge to me.:eek2:
anyone cares to comment?
and again can anyone confirm the results?

[fixed links]

Cant see the graphs need log on name and pass word

Boost target is 1.68 bar (abs) from 6200 RPM.

For 230BHP, say you have approx 8.6m^3/min airflow.

In a 1m long, 58mm diameter induction pipe with the equivalent of 3 x 90 degree bends you would expect a 0.016 bar pressure drop, about 2/3 of this from the bends. This will be a low estimate with changes in diameter/shape etc.

The pressure measurement is probably flawed if you measure directly in front of the turbo as there will be an affect from the air passing over the hole in the inlet pipe.

I thought the effect of passing air would only cause a pressure if the hole has a slash cut. if it was straight, like this hole the effect shoud be minimal?

John: if the length of tube is not the major cause of the pressure loss, is it the stock resonator box?

anyhow I will do some more measurements tomorrow on different spots in the inlet tubing, and let you know the results. Maybe it can be concluded that there is an major restriction somewhere..

ps. I read an article on autospeed on this subjest and they also did these kind of measurements also on a liberty rs.

they had these results:
Subaru Liberty RS

EngineRPM - Before Filter - After Filter - After Airflow Meter and Resonant Chamber
3000 5 6 7
4000 12 17 20
5000 19 26 31
6000 26 31+* 31+*
7000 31 31+* 31+*
[editted to clearify the table]

pressure is in inches of water 1 inch/water = 2.5 mbar

there measurement max'd out at 31 inch. Although I don't know if the liberty inlet can be compaired to the impreza's but they concluded that the resonator box is the major restrictor.

I can't remember if the MY99 resonsator requires the air to go through it, or if it is like a T off the side. I think it might be a better design than the old through flow Legacy/Liberty RS?

I can tell you that you can pull about another 100 BHP's worth of air through that standard inlet tract on a MY99 though with a VF28, uprated TMIC, exhaust and reflash.

I would try measuring at the large end of inlet pipe on turbo. You will create a vacumm any time you constrict the flow and speed it up. what is not clean from compressor maps is where they measure the inlet pressure, is it in the free air or right by the compressor blades?

Paul

I believe it's an T-off design.

The additional 100 horses will result (if my measurements are correct) in an additional pressure loss of approximately 0.06bar . This means in inlet pressure of 0.82 bar.
this will still be possible I guess, Although the point is:
If the inlet could be further optimised, the resulting chargetemp will be lower hence even more power. And since this is not that expensive to do....:luxhello:

Since I like to know. I will do the additional measurements tomorrow.

measurement points:
- just after the MAF
- just before the MAF
- just before the filter

Providing the current turbo is operating within it's sensible range, a 0.06bar change in the turbo inlet pressure will make no difference to the power output of the engine, assuming the factory boost control maintains the same pressure at the inlet plenum.

Paul

fixed links. should be visible now...

new messurments
 

Did some more measurements today.

now measured just after the MAF and measured just before the air-filter (stock) in the filter housing.
put it into one figure together with the first measurement just before the turbo.
http://members.home.nl/bogink/inlet%20pressure_2.jpg

The first measurement repeats itself with the measurement just after the maf.
the measurement within the airfilter housing shows only half the pressure loss.

So I conclude:

- stock filter and MAF do cause a pressure loss of max 0.06 bar
- The stock resonant chamber also result in an pressure loss of 0.06 bar.

I guess there is a lot to improve on the stock air inlet.

For me this is another reason to leave the MAF an go for the MAP based ECU's
An combine this with an good cold air intake.

Interesting results, but this information may be useful:

With APS induction kit in the wing, then the MAF sensor, then MRT turbo inlet pipe onto a TD05H-20G turbo on MY00 Euro spec Impreza Turbo I had 434 BHP and 395 lbft on a Maha dyno with 90% Optimax and 10% methanol. This was backed up by a 121mph quarter mile trap speed (and several others just behind) with full interior, tools, Goodyear F1s at standard pressure, and an extra gearchange from a 6 speed box etc. AP22 got a 124.9 mph trap speed before the uprated 5 speed broke.

Subsequently I switched to a larger turbo and never got figures off the same dyno, but I did try a larger filter and without the MAF sensor and the power plots on Delta Dash Road Dyno were virtually identical.