turbos
Turbo Mini Forums

Dave your totally right, I like them but I got two cars running them and about 3 spare t3s!

I havent got T2 maps anymore... so I can't give you the figures, but when I last looked I wasn't very impressed with the efficiency and turbine speeds from 18psi up!

Alex

AlexF

18 psi?

Well 16psi was enough to take my mini to many sub 14 sec 1/4 miles... why would you need more?

Also - did you happen to investigate how perfectly efficient a 40 trim T3 is at that boost as you were looking at the T3? Answer - Not efficient at all...
Sure, you can fit a larger compressor to a metro - just as you can to a T2, or just straight to a T25 compressor housing.


I am curious now - and have no experience in this niche area - but how many R5GT folks ditch the T2_ series and go straight to a T3?

This is true Dave... but people do run that.

But as you know psi isn't the be all and end all of power!

No idea what the R5GTT peeps do... but many Fiesta RST owners go t2 - t3!

Alex

AlexF

I'm still not getting this.

to make 'x' psi in 'y' volume at a 'z' temp wil require a certain ammount of air, nomatter what's pumping it.

And if on an identical engine you ran (say) a T2 and a T3 at 20psi, then the turbo which was most efficient at that psi would make the most power, right?

But is this to do with how much power the engine is making or how much the turbo is absorbing?

I need answers.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

i was totally lost after this:
06/08/2005 16:57:31

Now I've been thinking about this for a while now, well a few hours.

I agree with what Alex is saying. Whis is basically the better match your turbo is to your engine, the more efficient it will be and hense the less power it will absorb trying to make boost.

but I still think that the following statement holds true:

"Surley a t2 turbo, on a 1293 engine, at 6000 rpm at 20 psi would deliver the same amount of air as a t3, t4, or t5. If it could not supply enough air, then it would not give 20psi? "

In fact alex, your theory supports it!

It may be true that a T3 will pump more air at 15psi than aT2 (it's fact that it will). However it will make 15psi at much lower volumes of air too.

The wastegae does a good job of increasing the flow (and volume) of air at a set psi. i.e. the pressure will remain fixed as the revs rise, but the volume of air will increase.

As none of us are using a T3 to its maximum flow rate it makes little differance that a T2 won't pump as much air at 15psi.

This is because we don't need it to pump its maximum volume of air at 15psi. If we did it would never make the boost at the top end of the rev range, if at all. and they do, so they can't be to far out.

So the T2 must be the better choice of turbo as it will make th pressure at the volume of air needed, but it also will spin up quicker.

Touchey (spelling)

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

its correct sizing of the turbo to the engine displacement which drives the turbo into boost sooner! (ie less lag) at a given RPM

if the flow capability of a T2 is 180 bhp???
then if thats all you need then thats it, but......

if you need more BHP a larger flow rated turbo size is required. but you pay the penalty with more lag at lower RPM as we know!

a T2 seems to be about right! for the humble
A series

The T2 transformed the way my car runs, no going back for me.

How many people on here have fitted a T2, then reverted to a T3?

none i bet gibbo

i run a T3 at the mo with 8.4:1 cr and the lag IMHO is like the TITANIC getting up to steam

although! when you have finally got it spinning it does produce the goods ...but... the T2 does it sooner!

My next project will incorporate a T2 for sure

Edited by BENROSS on 10th Aug, 2005.

Lag is not an issue! YOU CHANGE GEAR!

If I'm not mistaken isn't the fastest turbo mini blown by a t3 hybrid?!

Alex

AlexF

It's a common mistake to confuse lag with boost threshold.

but I know what you are saying.

Am I about there with the pressure/flow.volume thing though?

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

give me a few mins to sup some more coffee and have another stab!

Alex

AlexF

Bigger is better. Isn't that right Jon?

“"Surely a t2 turbo, on a 1293 engine, at 6000 rpm at 20 psi would deliver the same amount of air as a t3, t4, or t5. If it could not supply enough air, then it would not give 20psi? "

In fact alex, your theory supports it!”

OK lets have another think about this…

The problem with your “same engine” scenario is that the moment you slap a different turbo on it, you TOTALLY change the engine.

I said earlier that an engine is just an air pump, the more air you can pump in and out the better. The key point in this case is that by changing the turbine you are changing how easily the engine can get rid of its exhaust gas. This is like the idea of two different size balloons… although you inflate both to 15psi if they are different sizes the volume of air will be different. As pressure is basically a resistance to flow, if its harder to flow air into an engine then there will be higher pressure, but that doesn’t mean there is more air going in.

I'm trying to do a worked example using t2 and t3 figures bare with me peeps!

Alex

AlexF

I know what you are saying....but......

If an engine is running at 6000 rpm at 15psi then the volume of air needed to get 15psi will be a set ammount at a set temp.

So what if the exhaust is a bigger restriction, this just means that more energy will be required to spin the turbine, thus less bhp at the flywheel. but the engine is generating as much bhp (energy) it's just using it to spin the turbo so you see less.

As I said, the turbo is absorbing the power rather than the engine not making it.

But still the same volume of air at 15psi on the inlet side.


Wil

Edited by wil_h on 10th Aug, 2005.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Arr

“If an engine is running at 6000 rpm at 15psi then the volume of air needed to get 15psi will be a set amount at a set temp.”

Yes that is correct. But by changing the turbo, you also change the flow characteristics of both the inlet and the outlet.

“So what if the exhaust is a bigger restriction, this just means that more energy will be required to spin the turbine, thus less bhp 'total'.”

Pressure = force / area

Pressure is created when there is a resistance to flow. For example, if you change the resistance of the exhaust so that it is greater (you fit a smaller turbine housing maybe) you will need less force to produce the same pressure over the (now) smaller area.

So by fitting a larger turbo you not only flow more air for the same pressure but also use less energy pushing the exhaust gas out on the exhaust stroke. It also means that the valve over lap will be of more help bring fresh charge in.

AlexF

"by changing the turbo, you also change the flow characteristics of both the inlet and the outlet"

Well yes and no. Whatever turbo you have if it is making 15 psi and x volume of air then as far as the engine is concerned there has been no change.

Changing the turbo only changes the resistance of the exhaust. The volume of air to create the desired psi remeins constant.

We'll never agree to agree.

Wil

I supect that we are saying the same thing

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

“Well yes and no. Whatever turbo you have if it is making 15 psi and x volume of air then as far as the engine is concerned there has been no change.”

But that’s the point! Its not the same amount of air!

You have changed the total restriction of the engine…. So you have changed the area the air can flow through.

Pressure = force / area

Think of force as air flow… if you change the area then to achieve the same pressure, the force (air flow) must change.

“Changing the turbo only changes the resistance of the exhaust. The volume of air to create the desired psi remains constant.”

So that statement can not be correct. The pressure a turbo creates is linked the resistance to air flow through the engine. Without some resistance to flow there would be no pressure build up. So by changing the restriction in the exhaust (turbo) you ultimately change the amount of air and engine can flow in and OUT. So the volume of air will change if you change the flow rate of the engine but keep the pressure the same.

Alex


PS This is fun!

AlexF

But the compressor is only trying to pump air into the cylinders not through the turbine (except on overlap).

The engine is trying to pump 'air' through the turbine. It has to be the energy created by the engine that drives the turbine and not the compressor otherwise we've discoverd perpetual motion.

Tis fun indeed.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Statically, yes... your right.

But our engines are dynamic... so the inlet and exh flows are in effect linked!

Alex

AlexF

Yes it's a dynamic system.

But I still can't see how the compressor can be considered to be blowing through the turbine.

This is nonsensical.

The air may be considered to 'flow' through the engine, but this is a mass of air moving through a number of different stages. it is not constantly influanced by the compressor.

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

What goes in must come out?

What goes in drives burns then drives the turbine which turns the compressor?

Alex

AlexF

I'm with Will on this one... It started off being the compressor alone discussed in the original statement - and now the turbo as a whole is being bought in?

Add in another factor - Take a T2 .48 turbine with a reasonably large trim - compare that to the tiny (and unique to the metro) .25 T3 turbine,,,
I know which my money is on as being less restrictive 'as a system'

Edited by turbodave16v on 10th Aug, 2005.

I'm not sure if you are agreeing with me or disagreeing?

And it will take a far more convincing arument before I start believing that the compressor is pumping into the turbine.

My final words on the subject. (hopefully)

Wil

Fastest 998 mini in the world? 13.05 1/4 mile 106mph