measured the 7a cams again

[repo]

Ok, pls back up this cold air expanding spoolup theory with some article or writeup from an authority. Thanks.

[quattro84]

I can't publish confidential papers based on FEV test results. All i can say is that it came from the development process of the new BMW IL6 engine (N55). http://www.bmwblog.com/2010/01/02/tw...ign-explained/
Perhaps some papers are available through SAE, i don't know.

The expanding air theory is very old and is commonly used on turbojet engines.


Most modern jet engines are actually turbofans, where the low pressure compressor acts as a fan, supplying supercharged air not only to the engine core, but to a bypass duct. The bypass airflow either passes to a separate 'cold nozzle' or mixes with low pressure turbine exhaust gases, before expanding through a 'mixed flow nozzle'.

http://www.ueet.nasa.gov/StudentSite/engines.html



Back to cam timing for the IL5's. What amount of overlap do people run with what A/r turbine?

[Audi_CQ]

About working or not, it is currently used on newer engine designs with different flame front propagation, squish areas to enhance exhaust scavenge flow, high CR, and adjustable camtiming to reach highest VE's from idle RPM (that are not found on the IL5).
The reason why is obvious and previously mentioned, wanting instant boost means small turbines and therefore high back pressures and sick temperatures.
Far fetched or not, it works. It's umluft. Currently tested by different OEM's without the extra fuel.
Sure these turbo setups are a complete different ballgame compared to our IL5, but it's all possible and coming. Even umluft.

With adjustable cam timing you change overlap to what is best, but we're talking about old Audi engines with fixed cam timing here. As you state: It's a complete different ball game

[lind4hl]

Repo, next step for you!

Audi 5cyl 20V V-tec

[quattro84]

Billman asked 'is this crucial on a turbo engine' , not my so i was talking about it in general.

Some kind of Porsche Vario Cam could made possible.


Audi has it's own VTEC these days on the FSI engines.

[repo]

1.8T engines use similar intake cam timing system as porsche, but I think it's being used mostly for emissions.

2.7T engines use it for performance.

If You mean Vtec like in Hondas, no way, if You ment Vtec as a synonyme for adjustable cam timing, yea, a variocam type of setup might be possible to construct.

I am quite sure the benefit got at low rpm, by advancing the intake cam in 2.7T does not come from enhancing the spoolup, but reducing the backdraft immediately after BTDC, and therefore making the engine itself do better.

[rash]

Repo you are allright!

2.7t got a variable inlet cam timing for better torque at low rpm...

...in power setting (high rpm) the inlet cam timing is set to "late" and in tourque setting (low rpm) the inlet cam timing is set to "early"...

...responsible for this behaviour is the point of inlet close - there is an adjustable angle of 22deg...

4.2 in RS4 B7 has variable cam timing on inlet and exhaust cams... ist is used for power and torque setting like 2.7t AND additional for reducing emissions at low rpm by forcing inner backflow of exhaust gas by valve overlap...

PS the new TTRS R5T uses the same technology on inlet and outlet...

...and only with direct injection you can use a wide angle of variable cam timing (TTRS 42deg on inlet and exhaust cam)...

[rash]

PS I think you misunderstood the turbofan:

Turbofan engine
In turbofan engines only a small part of the thrust is generated in the core engine, i.e. compressor, combustion chamber and turbine. The major part is produced by the bypass flow through the fan and the low-pressure turbine. The fan feeds large air volumes downstream which surround the engine like an envelope and thus reduce the engine noise. With increasing bypass ratio, i.e. ratio between internal and external airflow, operating cost, emissions and noise are reduced. Bypass ratios of turbofans for modern airliners are now about 6:1, i.e. the bypass flow through the fan and around the engine is six times the airflow through the core engine.

source: MTU Aero Engines

[Nik0las]

So then scales tend to be used stock cams instead 7A? I'm asking because I have plan to use such in my new project around 450hp. It will be stock Head. Any recommendation on this subject ?

[repo]

Definately stock cams for 450hp.

[rash]

Any recommendation on 550 PS ??

[Kieron20V]

The expanding air theory is very old and is commonly used on turbojet engines.


Most modern jet engines are actually turbofans, where the low pressure compressor acts as a fan, supplying supercharged air not only to the engine core, but to a bypass duct. The bypass airflow either passes to a separate 'cold nozzle' or mixes with low pressure turbine exhaust gases, before expanding through a 'mixed flow nozzle'.

I don't understand what application your referring to on a modern turbofan. If you are suggesting that the expanding hot exhaust stream is somehow pulling the cold stream through some sort of scavanging effect then you are wrong. "Jet" thrust is a result of mass flow. The main function of a mixer nozzle is to reduce noise output caused by the shear layer between the very high velocity core exhaust, and the relativly slow moving bypass stream. A byproduct of this is a slight increase in thrust, for the same reason, having one large stream moving at simillar speeds, rather than a dougnut of low speed air and a thin stream of very high speed air.


Regards cam timing, I know very little so Ill keep quiet, I was just interested in your jump fro mcam timing to jet engines.

-Kieron.

[repo]

Any recommendation on 550 PS

Yea, stock ones.

[Audi_CQ]

Any recommendation on 550 PS ??

Both 7A cams advanced 5 deg.
For track use: go mechanical as hydraulic lifters can struggle to keep up when used over some time on track and starts ticking. If mechanical go for no more then ~220deg @1mm lift for 550hp.

[20Vcqdriver]

In theory, using the 7A exhaust cam alone improves mid and top end performance for a slight loss of torque at 2000rpm. depends what you are after..