Car got tuned today...

[Tosh]

ahhh thanks doc

[Tex]

My understanding is the same as Ben's. As another analogy (an exaggerated one to help illustrate the point), imagine two different-sized air tanks. One maybe the size of a Coke bottle, the other the size of the tank on the back of a petrol tanker.

Pressurise both to a given pressure, say 20psi.

They're both at 20psi PRESSURE, but the difference in VOLUME is massive.

[B-Man]

I always like the water tank analogy.

You got a big water tank full of water

you punch a small hole in the bottom of it with a nail - how much water comes out ?? Not much.

then you get a huge hole saw and put a 5 inch hole at the bottom - how much water comes out ?? Heaps

The pressure in each circumstance was the same - 1 bar (Atmospheric pressure I think is 1 bar)

[Tex]

Correct, 1 bar or 14.7psi IIRC is atmospheric pressure at sea level.

An interesting side note which many people don't think about is that as a result, when your boost gauge shows, for example, 1 bar of boost, the intake manifold is actually at 2 bar, because you're adding 1 bar of BOOST to the 1 bar of atmosperic pressure.

I guess that means drivers of NA vehicles could tell people they're running 1 bar through their motor...

[Duncan]

ok, but as the water dribbles (or pours) out, the question is, "is the tanker half full, or half empty" :confused:

[Silver-Arrowz]

Yes, just like if a tree falls in the woods, does it make sound??? :confused:

Back to the question from evl r33, don't look at numbers from differing dyno's and base everything on them. They are simply a tuning device. My car made 160kw on rwd but then suddenly made 180kw on 4wd at a different place? That's right, the transmission somehow makes power now... :confused:

[Roy]

Silver-Arrowz, what do those transmissions sell for, are they available in RWD,

Im ater a 7 speed that makes power, god knows my engine doesnt.

[Kinks]

Originally posted by fatz

kinks

give me 10 seconds and i will show you how to drive a GTR

then you will know how txo get it sidways

pete

I've been for a ride with you in the streets of mudgee, you took blackbart and I for a spin. Ages ago

Back to the topic at hand - Tex and I were debating this last night. When you're talking about how much power an engine's making in terms of the turbo side of it you care about two main things - boost pressure and intake air temperature. Remember that boost pressure is measured at the manifold, after the throttle body. Same with intake temp. At that point, everything else is constant because the heads are the same as before, the cylinder filling will be the same. This means that for a given manifold pressure you will get a constant VOLUME of air going into the engine whether your turbo is big small or spraypainted bright purple. With a bigger turbo, the air isn't heated as much and therefore because it's denser, you get more MASS air flow into the engine - which at the end of the day should give you more power.

As for why two stock turbos running 1 bar gives more power than two bigger turbos running 1 bar I'm not sure. It must come down to tuning differences or - more likely - dyno differences. Remember that dynos aren't comparable a lot of the time - you only have to see Secoh's "dyno proven" 195rwkW VW Beetle to know that dynos can tell fibs. (although I think that power figure was wind assisted)

[kabab]

You also have to remember a large turbo is going to give you a cooler charge of air aswell as an increased volume.

The cooler the air is the more dense it is.

So more cooler air = more power

Also another thing to note is peak power is not the only thing that matters the area under the power curve is what makes a difference to. The large the area under the curve you have a larger power band.