Power Versus Boost

[ugy]

Wondering if somebody could explain why some cars get the same power with less boost?

For example my car has around 285rw (give or take five) and running 15psi. Yet I have seen other tunes doing around the same rw with around 12psi.

Why I want to know is because they say the less boost you run the better for the engine.

Thanks for any replies

[blueboost]

is yours 15psi at peak power?

David

[qik1]

alot of it has to do with the hardware your using. The other person at that power level could be running a full exhaust with a bigger dump pipe. This alone can make a difference.

[Panda Eyes]

some cars are freaks too. theres a thread on rwkw people got from thier stock xrt's, and it ranged from 180- 215.

mine had 210...

the different dynos may be calibrated differently as well.

you may find that yours makes 'more' power on the same dyno that the car with 12psi was measured on.

[Redback]

Boost PSI is usually sensed at the manifold where it is most convenient to tee into. Depending on your intercooler/pipe work setup and pressure drop across it your turbo may be producing 18psi at the turbo comp housing to make 15psi at the manifold.

Don't confuse psi to flow rate as well. You can still get 15psi of pressure through a straw and through a hose, which one is flowing more air. Another vehicle set up with an effiecient exhaust and intercooler is producing 12psi at the turbo comp housing to make 12psi at the manifold with no pressure drop and better air flow (it is now using a hose not a straw to blow through).

Now at 12psi the turbo is spinning slower and the air is being compressed 6psi lower. Remember that 6psi of pressure is like applying 2.5kg of weight to one square inch, it's a big difference! The more you compress air the hotter it gets. Hence the less efficient your combustion process becomes. Colder air has a higher oxygen/nitrogen ratio than hotter air. Inect more colder air/fuel and the bigger the bang.

That is why your car pulls harder on a cold night. It's almost like you're injecting a small dose of Nos/fuel. You can run more advance timing charts when you have cooler air which enables a more complete combustion process avoiding detonation.

Sorry to rammble on but to answer your question other cars that are making more power at lower boost are basically using a more efficient intake/exhaust setup. Also like forddriver 1 said not all cars are the same, depending on tolerances from factory one car might have a slighlty higher compression ratio which will in turn need lower boost to make the same power (volumetric efficiency). Sorry for the essay answer but I hope this helps.

Edited 19/07/09 01:36 AM by Dagabond

[ugy]

  blueboost said:

is yours 15psi at peak power?

David

Here's my Dyno sheet. It was done on a club dyno day hence the shoot 8. Dont know how hard it is to change to shoot 6f but it was done in shoot8

[ugy]

  redbackalarms said:

Boost PSI is usually sensed at the manifold where it is most convenient to tee into. Depending on your intercooler/pipe work setup and pressure drop across it your turbo may be producing 18psi at the turbo comp housing to make 15psi at the manifold.

Don't confuse psi to flow rate as well. You can still get 15psi of pressure through a straw and through a hose, which one is flowing more air. Another vehicle set up with an effiecient exhaust and intercooler is producing 12psi at the turbo comp housing to make 12psi at the manifold with no pressure drop and better air flow (it is now using a hose not a straw to blow through).

Now at 12psi the turbo is spinning slower and the air is being compressed 6psi lower. Remember that 6psi of pressure is like applying 2.5kg of weight to one square inch, it's a big difference! The more you compress air the hotter it gets. Hence the less efficient your combustion process becomes. Colder air has a higher oxygen/nitrogen ratio than hotter air. Inect more colder air/fuel and the bigger the bang.

That is why your car pulls harder on a cold night. It's almost like you're injecting a small dose of Nos/fuel. You can run more advance timing charts when you have cooler air which enables a more complete combustion process avoiding detonation.

Sorry to rammble on but to answer your question other cars that are making more power at lower boost are basically using a more efficient intake/exhaust setup. Also like forddriver 1 said not all cars are the same, depending on tolerances from factory one car might have a slighlty higher compression ratio which will in turn need lower boost to make the same power (volumetric efficiency). Sorry for the essay answer but I hope this helps.

I now have a better understanding of how it works.Thanks for that

At the moment I have a 3" exhaust with factory dump

Also a hyperflow IC which uses the factory crossover (which in itself is a restriction) so really I should be looking at a better flowing induction system to have a better chance of lowering the psi

[Redback]

Your UBP is also a restriction. Also porting the wastegate will help run a more consitant pressure without boost spikes. Something I need to have done.

[blueboost]

auto or man

[koppers]

It's all about efficiency. Plain and simple.

Just to rub it in, the ute makes 370rwkw @ 15lb peak through an auto

Edited 19/07/09 05:45 AM by koppers