Turbo questions

[ScuttleRX]

This one has bugged me for a while, why does the \'kick\' from second turbo feel so much stronger than the first one when the boost pressures are the same?

Surely 0.8 bar of pressure will be the same amount of air, therefore power, no matter what produces it? Someone enlighten me

[nikp]

This is purely a guess, but it hould be accurate.

Pressure is regardless of air volume. You can have 1 cubic centimetre of air at 0.8 BAR, and you can have 100 cubic metres of air at 0.8 BAR. Pressure is purely that: pressure. It has nothing to do with volume. This is all a fact. The guess is how it relates to the 2ndturbo, and that is: I presume that you get a \'kick\' because all of a sudden you are getting a larger amount of air into the engine - it\'s at the same pressure, but a lot more of it.

Anyone, correct me if I\'m wrong!! :p

[iaint]

If you look where the fd makes most of it\'s power you\'ll see the peak values on the 2nd turbo - the curve is also steeper on the initial engaging of the 2nd snail.

There\'s also the psychological aspect - you had acelleration then a brief respite and then it\'s back to give your kidneys a hammering!

Iain

[ScuttleRX]

See what your saying Nik, for some reason i was assuming the turbos were both flowing same amount of air. Obviously second turbo is flowing a larger amount of air but keeping pressure the same.

New to turbos so please excuse the incompetence!;)

[iaint]

Originally posted by nikp
This is purely a guess, but it hould be accurate.

Pressure is regardless of air volume. You can have 1 cubic centimetre of air at 0.8 BAR, and you can have 100 cubic metres of air at 0.8 BAR. Pressure is purely that: pressure. It has nothing to do with volume. This is all a fact. The guess is how it relates to the 2ndturbo, and that is: I presume that you get a \'kick\' because all of a sudden you are getting a larger amount of air into the engine - it\'s at the same pressure, but a lot more of it.

Anyone, correct me if I\'m wrong!! :p

The kick is because of more air but you missed mass (or density) out of the equation...

Pressure is a function of volume and mass - if you have a container that holds 1 ton of air at 1 bar then upping the pressure in the container increaes the amount of air in the container, more mass - this is how a gas cylinder works.  

To flow more air at the same pressure you need a bigger space for it to flow through.  To up the air flow with the same space you need more pressure.  

At high rpm the engine is using greater quantities of air so the 2nd turbo is needed to be able to flow enough - pressure is maintained at 0.8 bar.  IIRC the stock twins are quite small and are most efficient in the 0.8 - 1 bar region.  After this the size of the compressor side isn\'t big enough.

Iain

[bnaellis]

The kick is because below 4,500 rpm only the first turbo is working. at 4500 rpm both the 1st & 2nd turbo are working hence the big surge in power.

rgds

[Martiny]

Just to clarify one thing above. The primary turbo and secondary turbo are the same size.