Konstantin

hello
anyone calculated this accurately? Many suggets to work with 0,85 but these is just a standard number and not sure how close to the true is this number.
I want to calculate the Engine WOT graph and put it in the Turbo map to see which Turbo works perfect for my application

Konstantin

Waterguy

I have back-calculated VE from dyno tests on stock cars. The best estimates I have come up with are as follows:

RPM __ VE_

2500 - 75%
3000 - 84%
3500 - 91%
4000 - 90%
4500 - 86%
5000 - 84%
5500 - 80%
6000 - 76%
6450 - 70%

Some of the dyno sheets posted here show definite VE improvements over stock. As expected, the biggest factor seems to be larger turbo hot sides and cat bypass. TonyG's car seemed to hit a VE of greater than 100%

HTH

Konstantin

what about the 1000 and 2000 rpm?
is this for a 2,5l or a 3L engine?
what kind of head?
did you calculated teh IC efficiency with 80 %
here the data of teh IC temps
http://www-public.tu-bs.de:8080/~y0003315/porsche1.html
A) Intercooler temp
1) Inlett temp
2) outlett temp
speed km/h inlett °C outlett °C
80 42 20
120 45 21
160 50 22
200 59 23
240 80 29

Konstantin

Waterguy

I haven't seen rear wheel dyno charts that low, so I haven't calulated VE that low. Based on what I have seen on dynos, I would say about 70% at 2000 rpm.

As I said, stock 951. 2.5L, stock 2 valve head, stock manifold, etc.

I was a bit more pessimistic and used 70% IC efficiency.

What was the ambient air temperature for those intercooler temperature results? It would be interesting to se if they fit a constant intercooler efficiency percentage. The formula I use is:

IC efficiency = 100% - (outlet - ambient) / (inlet - ambient)

I also used the K26 compressor chart to calculate the turbo oultet temperatures, and even at stock 0.75 bar boost, the turbo outlet temperatures I calculated were much higher than your measured IC inlet temperatures (about 100 C.)

Konstantin

THE temps on this hahrt are as you see on my web site a graph from an official Porsche papaer published in 85 when the 944 Turbo first came out.
It is in 5th gear.
It was either18 or 20 degree outside temp

that means almost 96% in low rpm and 82% in high RPM and WOT

Konstantin

TurboTommy

Why are you guys bringing the IC into this?

Technically, VE is: how much of the available pressure is entering the cylinders.
On a turbo engine the available pressure is what's in the intake manifold. Everything before the throttle body are devices and plumbing that are needed to create this available pressure for the engine to "see". We can maybe measure pressure drops and pressure gains (turbo) along the path from the air filter to the intake manifold, but these would have nothing to do with VE.

On a NA engine the available pressure is always ambient. So, in this case, the intake manifold better have the same pressure as ambient. Only here does one have the right to question the path upstream from the throttle body (or the throttle body itself), which would ultimately affect the pressure the cylinders will see.

TurboTommy

Konstantin,
regarding the IC effeciency data
Maybe I didn't look right, but I didn't see where they're refering to a 951 engine?

Tomas L

Tommy, I think the reason for the IC efficiency values is the way that VE is calculated from the dyno sheets. There is no way to separate VE and IC efficiency when all you have to work from is hp and torque curves.

The IC diagram Konstantin refers to is very strange. The inlet temperatures are way to low until you reach top speed where they get reasonable values.
The only thing I can think of is that those numbers are taken at constant speed or extremely slow acceleration. Otherwise the inlet temperature should be constant from the rpm where you get max boost. Since 240 km/h seems to be the only speed with full boost in these diagrams, it's also the only values worth something. And since 240 km/h will give a very good cooling airflow which will be much worse at lower speeds, I thing we can assume that 82% is a best condition case. Lower speed full boost efficiency will be much lower, perhaps 60%??

Tomas

Konstantin

hello
the data are from this page
http://www-public.tu-bs.de:8080/~y0003315/porsche1.html
I put some date for the 951 here.
yes the speed was low 80 km/h in 5th is not to much load and low rpm
the diagramm goes up to 260 km/h (full boost and full speed) This si the max load you can put to the engine
the outside temp was 20 degree
so on low speed with light load is almost 100%
at 260 km/h and full boost is 82%
check teh graph at the side and see your self.
or go to a University library and check for ATZ
German "AuTomobil Zeitschrift"
in 85 you wil find the paper about the 951 beeing a revolutionary engine with new technology new cat converter etc.
It is also translatetd in English in the same magazine.
It is about 5 pages long.
Then you will find all data you need and even more :-)

Konstantin

toddk911

"3000 - 84%
3500 - 91%
4000 - 90%
4500 - 86%
5000 - 84%
5500 - 80%"

So 85% is just about right.

Also, how much does the number used for IC eff. matter??

Because unless NASA built it not many IC's out there that have 100% effeciency

Konstantin

I remeber messured the air temp BEHIND the IC in winter.
with 15 Grad outside I had 13 gard!!!! behind the IC while driving at about 100 km/h
80 km is about 1800 rpm so not much load at 1800 rpm and the 100% sound right
an 260 km/h and full boost and full load teh ef. is only 82% so this sounds about right to me.
now if you have a lower speed with less air going through the intercooler the eff. would be lower but you get an idea what is the max (100%) and what is the worst case (82%) in 5th gear.
using IC cooling you can go over 100% and with lower gears higher rpm and less air through the IC you can go lower than 82%.
I think Porsche wanted to show with thsi graph what is the IC Efficiency whie cruising at the Autobahn at all possible speeds.

Like every Day driving at the Autobahn.
On the race track may be different.
someone who has two thermometers with a long wire and sensor can check thsi by him self. I will do this next week and let you know

Konstantin

Konstantin

BTW
here a dyno from my 968 Turbo S that also has lower RPM data
so you can calculate the the engine eff. for this car at low RPM

http://www.968turbo.de/968tsdyno.html

Konstantin

Tomas L

Where does these values come from. Since the efficiency depends very much on how you measure it these values mean nothing without knowing the conditions when they were measured.

Since we don't want max power when cruising at part throttle those values are not very interesting. Most of us want to use full power at a speed substantially lower than 260 km/h where the IC efficiency will be lower than the indicated 82%. And 82% will not necesarily be the worst case in 5:th gear, at full power you may get higher temp at lower speed.

Tomas