bigger turbo, more power question.

[kevin.s]

A few friends and I were just haveing a heated discussion on how a bigger turbo creates more power. My thoughts are if a smaller turbo is running 2 bar through the boost pipe system and is swapped for a bigger turbo on the same boost pipe system at the same pressure, the power will be the same. The only difference would be that the bigger turbo wouldnt have to work as hard to produce that pressure.

For the bigger turbo to produce more power at 2 bar, it would have to go on a bigger boost pipe system so more air is displaced through the pipes as they are bigger and can hold more air at that pressure.

For the bigger turbo to produce more power through the smaller boost pipe system, it would have to run more presure through it.

Am i right in thinking this or are they right in saying bolt a bigger turbo on at the same pressure and thats it job done, more power.
im no expert on this but it just sounds like common sense to me.

 

[T.Trophy]

Mate your way of the mark, without going into detail a bigger turbo will flow more air at a given pressure, for example my car with a gt2560r turbo made 267bhp@21psi I swapped turbos to a gt28r and it made 341bhp@14psi

 

[Cupman29]

The bigger turbo will flow far more air. Pressure is about resistance not flow.

The smaller turbo will reach a level of power where it will not be able to supply enough air to the engine but will spool faster than a large turbo that will flow enough air to feed the higher power level but will spool later.

 

[Martin_172]

am i also right in thinking bigger turbo running half the pressure will have cooler air temps?

 

[kevin.s]

so its more to do with the volocity of air that the turbo pushes through, i understand how that makes more power, just thought that this would cause an increase in pressure as more air would be being pushed into the same amount of space.

 

[kevin.s]

am i also right in thinking bigger turbo running half the pressure will have cooler air temps?

from what ive heard, yes.

 

[Yellow Dave]

surely this depends on where you are measuring boost pressure from? 2bar in the inlet would be different to the turbo reading 2bar?

A bigger turbo putting out 2bar would have more airflow but if it were going into the same size pipework as the smaller turbo then would there also be a boost increase at the inlet compared to the smaller turbo

 

[kevin.s]

surely this depends on where you are measuring boost pressure from? 2bar in the inlet would be different to the turbo reading 2bar?

A bigger turbo putting out 2bar would have more airflow but if it were going into the same size pipework as the smaller turbo then would there also be a boost increase at the inlet compared to the smaller turbo

the measurement is taken from the inlet manifold but thats what i was saying, if the pipework is the same size how does it cause more air to go through without an increase in pressure.
i probly sound really stupid lol.

 

[Iceberg_172]

its not just down to having a bigger turbo. Its down to the compressor housing/wheel sizes and A/R ratios etc. These determine how quickly the turbo will spin up and how long the pressure will hold for.

Also. the boost pressure can be the same but the temperature of the charged air plays a massively important part in power figures aswell. the less the turbo has to work, the cooler the air willl be.

Then you have to take into account, turning up boost pressure without correct fuel mapping causes Pre-detonation (knock) this can cause alot of issues in power figures aswell as damaging the engine, less knock = more power safer

 

[Cupman29]

Pre-detention is caused by inlet temps being too high and fuel combusting under pressure much like a diesel engine and is not the same as fueling issues. Pre-det causes pistons to be forced down when they are trying to come up and vice versa and is a cause of engine failure by bearing failure, snapping a rod and even making the rod leave the block.

Knock can also be caused by poor fuel grade or quality.

Fueling issues such as running rich (to much fuel) or lean (too little fuel) can cause various issues such as melting pistons (lean), poor fuel consumption (rich) and emission issues (rich).

There are other reasons for knock but high boost pressure with adequate cooling will not cause pre-detonation but may run very lean.