Turbo's... Output Power... Hmmm

[justin911]

ok peoples

I've always been curious as to this after reading peoples upgrades/mods etc etc

Lets say you have 2 turbo's. Ones a big one.. the others a small one...

Now lets say there both running 14psi or something..

If they both go into the exact same car how is it possible one turbo will make more power than the other if there both running the exact same boost level ???

I understand that the smaller one will make boost earlier.. and the larger one would hold the boost stronger.. i guess.. but I dont understand how 14psi from one turbo makes more power than 14psi from another turbo ???

14psi from 1 turbo would be the same volume of air as 14psi from a smaller turbo right???

hmmmmm

thanks

[justin911]

grr i saw some guy writing a reply for like 30 minutes i was all excited... but u didnt post it in the end

[paulr33]

pressure does not equal volume. 35psi in car tyre is not the same amount of air of a truck tyre at 35psi. the bigger turbo will make more power as its exhaust housing is bigger, thus it can flow more air making the engine more efficient at the same base manifold pressure (boost)

[linxus40]

this is my impression im sure other will correct me if im wrong. a small turbo will hit boots at low rpm but the boost trails off and becomes lower at higher rpm. so at 2k you might be at 14 psi but at 6k it might have fallen to about 10ish. a larger turbo will hold the psi for much longer.

[justin911]

oooh ok i think i get it now thanks

so like.. if you attached e.g a balloon to both turbo's there both filling it with 14psi, but the larger turbo would fill the balloon quicker ???

pressure does not equal volume. 35psi in car tyre is not the same amount of air of a truck tyre at 35psi. the bigger turbo will make more power as its exhaust housing is bigger, thus it can flow more air making the engine more efficient at the same base manifold pressure (boost)

<{POST_SNAPBACK}>

[saliya]

ok peoples

I've always been curious as to this after reading peoples upgrades/mods etc etc

Lets say you have 2 turbo's ones a big one.. the others a small one...

Now lets say there both running 14psi or something..

If they both go into the exact same car how is it possible one turbo will make more power than the other if there both running the exact same boost level ???

The easiest answer is 'RPM'.

Power = Torque x RPM / (some factor > 1)

Assume that both turbos can make their boost target at some point in the engine's RPM range,

and that the smaller one cannot hold 14psi to redline.

Assume they both make the same torque for the same airflow - the one that can hold that

same airflow (torque) to a higher RPM will make more power according to the formula. So if

the smaller turbo can't hold it's 14psi as high in the rev range as the larger one, that's less power.

The next easiest answer is 'efficiency'.

Assume that the smaller turbo _can_ hold the 14psi to redline, but that it's well out of

its efficiency island. That is, that the air comes out of it much hotter than out of the large one.

All other things being equal, the hotter air has less oxygen to burn - meaning less torque

at the _same_ 14psi and the _same_ RPM. According to the formula, that's less power.

_edit_

As pointed out by PaulR33, the turbo itself is a restriction (like a muffler). A larger turbo

should offer a lower restriction at the same RPM, thus allowing more airflow for a given

input pressure. More airflow == more torque at the same RPM, so that's more power.

I'm sure that others can express this better than me or correct deficiencies

Regards,

Saliya

Edited November 6, 2005 by saliya

[paulr33]

psi means nothing. airflow makes power not psi

boost is a reistriction to air. decrease the restriction, ie bigger exhaust, bigger dump, bigger cat, bigger exhaust housing the lesser the resitriction, the more air, the power. at the same psi boost level. this is because there is less restriction

[saliya]

psi means nothing. airflow makes power not psi

boost is a reistriction to air. decrease the restriction, ie bigger exhaust, bigger dump, bigger cat, bigger exhaust housing the lesser the resitriction, the more air, the power. at the same psi boost level. this is because there is less restriction

<{POST_SNAPBACK}>

I think you mean 'boost is a measure of restriction' (the way I say it is 'boost is a function of

the engine's inability to deal with airflow). And I agree, it's airflow (not a given pressure) that

results in the ability to burn fuel and make torque.

But on the same motor, the restrictions should be the same (with the exception of the

turbo itself). He's not talking about changing other properties of the system to

permit more airflow at the same boost level...

Regards,

Saliya

[justin911]

cool thanks guys

[The Mafia]

an engine is just one big air pump... Bigger pipes... bigger pump (turbo) at the same pressure means more air is going to flow through it...

You can blow 14psi through a straw you know... Or you can blow 14psi through a 10 inch pipe.. Which one is going to let more air through?