bob_series1

My brother in law has a 4x4 saph that is running a T4 (small) on 1.6 bar of boost. I ask why he does not use a smaller turbo?

His reply was due to the T4 having bigger exit pipe there would be a better flow rate of air.

He was saying that a T4 running 1.6 bar would produce more power than a T35 running 1.6 bar. Is this correct?

I thought that if the engine was running at full throttle, the inlet pressure was at 1.6 bar, then if you had smaller inlet, the air would just be travelling faster compared to a wider inlet where the air would travel slower.

Can someone clear this up.

Thank you.

Dicko&Vacant

iTrader: (3)

yes a t4 running 1.6 bar will produce alot more power then a t34 running 1.6 bar

xr2wishy

iTrader: (2)

i'm not sure to be honest, otherwise we'd all be running bigger turbo's.
i think the problem is not so much the size of turbo but how it all flows.
1.6Bar of air from what ever source would be the same, to get to 1.6Bar of pressure requires the same flow through the inlet.
i think the inlet temps have more of an effect, a faster spinning turbo with smaller compressor will generate more heat and thusly higher act's and less power.
also the exhaust housing will restrict gas flow out of the cylinders and thusly use more power from the engine making it less efficient.
so as for power, you want a big compressor wheel and housing, along with a big exhaust wheel and housing, but you'll possibly never reach boost in this case, so a compromise has to be made.

i welcome any thought/evidence that contradicts this, so i can plan my next upgrades wisely.

bob_series1

This is what i was thinking xr2wishy. However, if the turbo housing is smaller, but it still has to supply 1.6 bar I would expect the air to flow through the turbo at a faster rate. Narrow and fast = wide and slow theory. Thus, resulting in the air spending less time in the turbo and as a result, less heat is exchanged.

But like you said the turbo is hotter!!!!! In the end it is pumped through the inter-cooler so it is levelled out abit.

What do you think??

Any other thoughts???? I did not debate the case to much since I had a few beers.

RobertM

A good read:

http://www.motorsport-developments.c...AF240.tech.pdf

crazycage

pressure and flow are two different things mate and a t4 will flow much more air at 1.6 than the t34 at the same pressure.

p-s do you think a t2 from a fiesta turbo will do 500hp on a cossie if you could run it at 2 bar ?

xr2wishy

iTrader: (2)

/\ but at the inlet, a t2 wouldn't be able to maintain 2bar of pressure though.
pressure is a measure of force over area and therefore it will require resistance to gain the pressure.
since then engine would be the same then the same volume of air would be required to maintain pressure per second from wherever it's from.
i understand what you mean about a t4 flowing more than a t2, of course you're right.
but with a given resistance, i.e. inlet ports/cylinders/throttle body all pipework you need a given flow of air to maintain this pressure.
if you have more flow and resistance is the same, then the pressure would be higher.
i dunno, i'm not an expert in physics, did a degree though, although more to do with astrophysics really.
p.s. the T2 thing, if it could handle the revs, then sure it could make 500bhp, but you'd need a big exhaust housing to get the gas out and that's usually where the t3 has a limit in housing sizes as standard.

Chip

iTrader: (3)

A bigger turbo will flow more air more easily than a smaller turbo, as a consequence it produces less back pressure in the exhaust manifold, which allows the engine to breathe more easily, which results in more power.

So NO, you wont get the same power at the same boost on different size turbos generally.

Mitch01roo

Spot on.

bob_series1

So, it is the Volumetric efficiency that we are changing!! Not so much the amount of air flowing through the turbo.

Fitting the T4 results in:
Lower back pressure
Lower outlet temperature.

So the power is increased, but so is the lag.

RobetM - Thank you for an ace link.
Xr2wishy - "with a given resistance, i.e. inlet ports/cylinders/throttle body all pipework you need a given flow of air to maintain this pressure.
if you have more flow and resistance is the same, then the pressure would be higher." This is what I was trying to say to my brother in law but after a couple of pints I failed. LOL
Chips - Looks like you REALLY know your stuff. Did you read the PDF before posting?
Crazycage - If you could some how get a T2 to boost 2 bar, using an external power source, then yes you can have your 500bhp? Do that and your rich.

Maybe getting that new dyson electric motor and putting that in a T4 would be intresting. Spins fast enough but doubt it would have enough torque.
http://www.telegraph.co.uk/technolog...ew-vacuum.html

SS1

iTrader: (3)

Chips - Looks like you REALLY know your stuff. Did you read the PDF before posting?

Doubting Thomas

james kiely

iTrader: (5)

chip does less backpressure mean lower egt,s?

cheers james

Chip

iTrader: (3)

Yes generally it does, for example on Rob's astra we saw 80 degrees less temperature from fitting a larger backhalf housing on his GT30

Chip

iTrader: (3)

Not on this occasion but Ive read Stu's article before mate yes, and it all agrees with my own experience, as you would expect as lets face it stu knows what he is talking about

bob_series1

cheers all i have learnt a lot from this thread.