JM Performance

I know that a .48 housing will spool faster than a .63, and I know that the .63 will make more power up top, but why?

Evil DOHC

For low boost you will see more usable hp with the .48. Once you reach 12 - 15 psi you can take advantage of the bigger hot side. With a .63 hotside you will see more advantage up top if you car is moving air. In an ls motor breathes less cfm than a stock gsr. I wouldn't waste the money upgrading the turbo, because you will only see a 4-5 hp difference up top with your setup.
EVIL

JM Performance

ok, but why? what about the size makes a difference?

Evil DOHC

The size makes a difference but do you want all your power to be from 5k to 7k? Or do you want full boost at 2800 all the way to redline? U tell me? Look at both compressor maps for both turbo's. Are we talking about the B or the E housing? Why are u using a stage 2 wheel? But to answer the general question, the bigger wheels pushes more air = more power.
EVIL


[Modified by Evil GS-R, 3:07 PM 1/10/2003]

JM Performance

Right now I have a T04B/T3 w/ the s-3 compressor wheel and the stage 2 turbine wheel in a .48 housing. But I'm still not following how the size of the exhaust side housing effects power. and yes more air = more power, but 9psi is 9psi, what changes between turbos is efficiency (heat), no?

BlueShadow

I think it's the same concept as your exhaust system. A larger A/R will have less turbine backpressure and be more free flowing, a smaller A/R will be the opposite.


[Modified by BlueShadow, 11:27 PM 1/10/2003]

turbohonda

The AR has nothing to do with the turbine wheel size. It determines the amount of clearance that is between the turbine blades and the housing itself. The bigger the AR, the less back pressure in the exhaust manifold.

MiraiZ

Someone made a great analogy in a past post. 9psi is not the same 9psi in all turbos. You can produce 9psi blowing through a straw, but you can also produce 9si through a 3" pipe....but which is going flow more air? The 3" pipe is...same difference with turbo sizes.

lazerus

well actually 9 psi is 9 psi as long as the air temperature is the same. If you are maintaining 9 psi in the intake manifold at 100 degrees farenheit, it doesen't matter if a t25 is doing it, or a t-78 is doing it.

And as far as the exhaust housing, work with a specialist and decide how much hp you plan to make to get the best turbo for your application.

MiraiZ

anyways...that turbo is not your bottleneck...its your MF2...go standalone and you can probably squeeze another 20-30+HP out of your stock parts

tony1

Actually, it's not the same. There's a thing called volume... Pressure is just a measure of restriction on the intake...

bangin'gearz

Imagine spraying water at a pinwheel with a garden hose. When you spray the water on the pinwheel, the flow of water through the hose is good, but the velocity of the water coming out is slow so the pinwheel takes a while to spin up to speed. Now imagine putting you finger over the end of the hose to restrict the flow of water coming out of it. Pressure builds up in the hose, but the water comes out faster. This thin, high-velocity stream of water spins the pinwheel much faster...but with a trade-off. There is more "backpressure" in the hose from the restriction (your finger, in this case) and the volume of water the hose can flow is reduced.

It's a simplified example of how a/r works.

A large a/r turbine housing has good flow, less backpressure, and will ultimately make more top-end horsepower (by increasing volumetric efficiency) but it also causes the turbo to spool slower. On the flip-side, a small a/r turbine housing will flow less, and have greater backpressure (and decrease volumetric efficiency) but the exhaust gas will have a higher velocity and allow the turbo to spool-up faster.

First and foremost, I'd be concerned with picking the proper turbine wheel for the application, and then fine-tuning it's spool-up characteristics with different a/r turbine housings.

MiraiZ

damn!..awesome first post!...lets hear it fro the rookie!

MotorMatrix.com

to the rookie for real!!! nice analogy!!!

bangin'gearz

If you're under the impression that 9psi is 9psi regardless of whether it's from a t25 or a t78, it might be worth your time to learn how to read a compressor map and compare the efficiency and volume of air those two turbo's will flow. It's not even close.

As the poster above stated, boost is just a measure of restriction (or backpressure, if you will) that has built up in the intake manifold. It say's nothing about the volume of air being forced into the combustion chamber.

Back to the water hose analogy, imagine a how much water a 1" diameter water hose will flow (with 9psi of pressure) versus the volume of water a 12" diameter water hose will flow with the same 9psi of pressure built up inside of it...

Food for thought.

DIRep972

iTrader: (1)

are u sure about that tony? will an aem bypass valve make boost cause isnt that a restriction in the intake?



[Modified by DIRep974, 1:49 AM 1/11/2003]

JM Performance

I'm not sure if thats all exactly right. The turbo may be able to pump out a large volume of air at a certain psi, but the volume of the engine and the intake manifold (everything on that side of the throttle plate where the map sensor is) is still the same. At a certain volume of space with a certain pressure, the only other thing that can effect the amount of air is temperature. The lower the temp, the denser the air. That is why all the maps are about efficiency. Nearly all turbos can put out the amounts of pressure we need, but the maps are about at what temperature the air comes out; about how effectivly the compressor can compress air w/o heating it.


[Modified by 00SilverLS, 2:47 AM 1/11/2003]

falcongsr

yeah and a smaller turbo will flow less air before getting outside of its effeciency range.

the pinwheel/garden hose analogies are spot on.

BlueShadow

The maps are also about how much air the compressor can move, when you compare a T3 40" at a 11 PSI and a T76 at 11 PSI you'll see a difference of 13 LB/MIN vs 55 LB/MIN.

So does 11 PSI = 11 PSI, yes (does one pound of rocks = one pound of feathers?)

But does the airflow from 11 PSI on a T3 = the airflow from 11 PSI on a T76? no

I dont know if that's relevant to the argument at hand...but I just thgouth I'd throw in my .02 cents.

JM Performance

your talking about two different environments. at open air, the bigger one will flow more, but when talking about inside an engine, there is a fixed amount of volume. It doesn't matter how mucht the turbo can flow, its gettiing shut off as soon as you reach your set 9psi.

BlueShadow

The 2 turbos will flow the same volume of air yes, but their density will be different. The larger turbo has the ability to cram more air molecules into the same amount of space that the T3 could.




[Modified by BlueShadow, 12:17 AM 1/11/2003]

JM Performance

density has to do with temperature. and cramming air molecules into a space is creating pressure. its all about at what temperature (which effects density) the compressor can cram the air.

BlueShadow

EDIT: Are you saying pressure has nothing to do with air density?

The density of the air is ALSO affected by the compressor...air temp as well as the pressure from the compressor affects density.

http://www.dictionary.com

DENSITY:

b. The mass per unit volume of a substance under specified conditions of pressure and temperature.


[Modified by BlueShadow, 12:31 AM 1/11/2003]

DIRep972

iTrader: (1)

i think the garden hose analogy is right on when it comes to ar and turbine trim.

compressors really confuse me. but when i think about it there are only 3 things that i picture happening.

u got the turbo pushing air. it pushes more air into the motor then the motor can take in and u get pressure. thats simple enough, but i get confused when the compressor actually compresses the air. i guess some compressor's can compress air cooler and denser then others at the same pressure and flow and thats where efficiency comes from. ???


[Modified by DIRep974, 12:32 AM 1/11/2003]

BlueShadow

Actually the turbo, or the compressor to be precise compresses the air AS it pushes it. The air between the compressor and combustion chamber is all compressed (assuming the compressor is turning, BOV is closed and TB opened).

c'mon man! this is day one stuff!!! j/k dood


[Modified by BlueShadow, 12:42 AM 1/11/2003]