Compound charging
Turbo Mini Forums

Looking at flow maps for chargers they all seem to be rated in Volume rather than the Mass of turbo maps, so this has got me thinking about what happens when you chuck boost into the input of a supercharger,

Take the following scenario for instance, a 2 liter engine with 8psi boost from an eaton M45, flowing about 280 cfm or 20 lb/min....

If we now chuck 10psi into the input of the eaton from lets say a turbo, we are effectivly running 18psi boost into the engine and 26lb/min, however, as the air coming into the eaton is already compressed, what is around 380 cfm at the inlet of the turbo looks like about 200cfm to the eaton,

does that sound right or am i talking boolocks?

maybe im out of my depth here but to me if the charger is capable of 8 psi then putting 10 psi in, i would of thought the charger would be restrictive then?

one day boost will be mine!

That's the way I understand it.

You have to remember there are 2 different types of supercharger. One is a positive displacement type - like the eaton, the other is aerodynamic - like a turbo only shaft driven.

The aerodynamic will have very different characteristics to a positive displacement.

In fact I would say that you could apply a low boost (5psi maybe more) into the positive displacement type. The side effect would be a lot more heat generated and a lot more wear internally on bearings and rotor tips.

not Mini related Joe but a good build to read anyway, we have a friend in Califonia running a compound charged Elise that Simon mapped - theres lot of build blogs/video's of it in action - look for Ronin, Franks using the stock M62 + big blower together.

JK

If Carling made Mini engines
it would probably be like this one!

You're nearly there Joe.

The final boost will be dependant upon the volume of air being forced into the cylinders rather than being an addition of boost. To size the supercharger, you need to factor the air coming out of the turbo by the density to get an equivalent volumetric flow at NTP.

A sample calc that I did before I realised that there are better ways of doing it:

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

John,

Very interesting car, filtering though all the keybord warriors is a nigtmare though!

Its exactly the sort of thing I had in my head, big turbo blowing through a charger, charger spools the turbo, turbo is amplified by the charger.... bang!

Paul, Ok, I think that makes sense, I just have to think about it in my head the other way.... NA engien consumes 6lb/min but the charger delivers 10lb/min so you get a density ratio of 1.6:1.... likwise with the turbo and charger,

so that backs up my assumption, with an engine you can force more air through it essentially making it behave like a bigger engine, and the same is true of a charger, stick a bout 5 psi into a M45 and it flows like a M62...

Erm Joe...

Do you have enough room left under your bonnet to get a supercharger in?

In the 13's at last!.. Just

Yes, but you could do it more efficiently with a turbo alone.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

LOL this isnt for mine, I'm perfectly happy with where my compressor efficiency is at 30 psi...

A guy at work has etonised his 2liter golf, but wants more pep, but dosent want to lose the low end, so was aking me about compound charging.

I think his eaton has a built in bypass so it may be possible to do an easy compound to turbo only comparison before ditching the eaton altogether.

anyway its just idea's being kicked around at the moment, but I reckon he needs to be looking at putting about 40 psi in to make it worth while.

So does a supercharger multiply what you put into it then?
So it will achieve 8psi with atmasperic pressure air, but if you feed it with pressure it will futher compress that air to achieve a higher psi?

one day boost will be mine!

If you have a supercharger with a 2 litres displacement for every two revs of the engine feeding a 1 litre engine, then, ignoring the effects of volumetric efficiency and temperature, you will see around one atmsophere of boost, approx. 15 psi.

If you feed the supercharger with air from a turbocharger at 2:1 pressure ratio (15 psi boost), then it will effectvely try to pass the equivalent of 4 litres of air into the engine. This will give around a 4:1 pressure ratio (45 psi boost). So the supercharger effectively multiplies up the pressure ratio.

This is a simplistic explanation. the effects of temperature will be significant and will raise boost even higher.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Not sure the compressor is able to keep very high pressures. It would leak.

For the rest this kind of systems should work. It's just another stage of compression, with one more opportunity to cool before compressing again. A turbo engine is a 2-stage compression system, here you have 3 stages. But overall energy efficiency must be lower as every compression stage adds losses.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

my eaton m90 has a displacement of 1ltr per revolution and on a 1330 it kicked out 16psi.

balls to the blower!!!



1330,stage3 head, gt1549, canems ecu, S/C box and drops

I had a Saab 93 as a hire car this week. It was 1.9 TTid. Under the bonnet were two turbos, one tiny little one and then one normal sized one. I could not work out the plumbing though but I don't think that they were compound. Quite fancy though and never off boost. (oh its a fiat engine apparently)

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

Staged turbos are getting common. But they never use an I/C between two turbos, the goal is to smooth the torque curve and not to make more power.

I believe the Lancia Delta S4 was a staged compressor-turbo design.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm