Compound charging

[foxdie]

Initially yes. But where's the fun in stopping there?

I didn't say stop there, I just think we should keep it realistic and set goals

First goal is to see if charging turbos with a centrifugal supercharger at least breaks even

[wintertidenz]

To be honest I think that just going for the third turbocharger might just be the easier and quicker way to go.

[scott.mohekey]

To be honest I think that just going for the third turbocharger might just be the easier and quicker way to go.

Yep, no way am I bothering with a supercharger.

[thfelipeth]

im interested to see where this is going. ignore me

[Jesus-Ninja]

To be honest I think that just going for the third turbocharger might just be the easier and quicker way to go.

It depends. Given a choice of either, a tub is better, I think, in terms of efficiency. But a centrifugal charger can be fitted as easily as a turbo but without any changes to the exhaust system and it requires no boost control. The only thing it needs is a pulley.

[Jesus-Ninja]

The difference between the first and second gives us the pressure ratio of the larger turbo, the difference between the second and third the pressure ratio of the smaller turbos, and the difference between the first and third, the overall pressure ratio.

No.

The difference doesn't give you the ratio. It simply tells you the difference. If your plan is to run the two pressures across a dual port wastegate, then it won't work. As the two pressures operate against each other you'll simply get the difference. Let me explain:

To make the numbers easy, we'll say that our twins are most efficient at 1:2. That is to say that with an inlet pressure of 1 bat (ie atmospheric pressure, NOT 1 bar boost), they will produce 2 bar absolute pressure (ie 1 bar of boost above atmospheric which is 1 bar)

If the big turbo hasn't spooled yet and the twins are on song, then the difference will be 2 bar absolute - 1 bar (Atmospheric) = 1 bar.

Lets now say that our big feeder has run up to 1 bar boost (ie 2 bar absolute) which the twins are now seeing. For them to still be in their same efficiency we want them to still run at 1:2. So they'll be taking that 2 bar absolute from the single and making that into 4 bar absolute - this will be a difference of 2 bar across the twins compressors and a difference of 3 bar between the plenum and atmospheric.

So - what you need is some electrickery that will read the pressure before the twins and after as absolute values and divide one into the other and make a decision as to whether to open a solenoid that will bleed boost off to the wastegates.

IF it was the other way round and the twins fed a third charger, AND that was a supercharger, then life would be much easier: Boost on the twins would be easy to regulate, as the inlet is ALWAYS atomspheric and you could operate the wastegate on pre SC pressure, and a supercharger doesn't need regulating in the same way.

[Jesus-Ninja]

I'm thinking... an Arduino could be used to monitor the 3 MAP sensors via AnalogIn, control the duty cycle on multiple wastegates via PWMOut through a Transistor / Darlington Array, and then perform some calculations and either output a MAF emulation signal (PWMOut again) or a MAP sensor signal (AnalogOut) to connect to an ECU

You'd definitely want an ecu to control it

AKAIK the diesel setups only have a wastegate on one tub.

[scott.mohekey]

The only thing it needs is a pulley.

And a place to put it.

[scott.mohekey]

No.

The difference doesn't give you the ratio. It simply tells you the difference. If your plan is to run the two pressures across a dual port wastegate, then it won't work. As the two pressures operate against each other you'll simply get the difference. Let me explain:

Ok, so my terminology was wrong, but with the three sensors as I described, and an ecu of some sort doing the calculations you mentioned and controlling the waste gates, I think it will work.

[Jesus-Ninja]

And a place to put it.

Very true

In the place of the aircon pump?

[Jesus-Ninja]

with the three sensors as I described, and an ecu of some sort doing the calculations you mentioned and controlling the waste gates, I think it will work.

Yes

[Jesus-Ninja]

Interesting read: http://www.yellowbullet.com/forum/sh...d.php?t=216811

[scott.mohekey]

That certainly makes the waste gate control sound a lot simpler.

[Kenneth]

There is no reason why you can't get pneumatic control of the wastegate and chances are it'll be a lot easier to manage. You can get fuel regulators which use a raising rate factor greater than 1, a wastegate is the same principle just slightly different in size and actuation.

alternatively you can use a standard external and control both sides of the diaphragm. While this will not exactly give pressure ratio control, you can still manage total boost ok. The thing with this setup is that as the big turbo spools up, it will start taking up more and more of the total compression requirements. Which, with the turbos available today, could be a good idea.

[roryfromnz]

This is an awesome topic of conversation. Im sure i had seen a Toyota 4agze 1.6l engine "Twin Charged" and running well over 300hp at the wheels.. The did have some tuning issues but perhaps the small toyota supercharger might be a fun place to start if going for the supercharger route. The were running the turbo into the charger im pretty sure..

[ILLEGAL]

single GT35R.. problem solved.. LOL grey hairs avoided.

[lancerevo3]

subscribed

[scott.mohekey]

So, I'm thinking one of the GT37 range of turbos from Garrett. I haven't really looked at the compressor maps etc yet to see if they're ideal or not, I'm mainly basing this on them being the smallest Garrett turbo with a twin scroll exhaust inlet, which I think would be ideal for the fact I'm going to be running the exhaust from the two smaller turbos into the larger turbo.

[Kenneth]

My understanding is that split pulse is to reduce cylinder interference (pulse interference from other cylinders) which reduces turbine efficiency, but usually comes at the cost of peak flow

This being the case, you would not need (or probably want) a split pulse exhaust housing.

[scott.mohekey]

Yeah, my thinking was to make it a bit easier to merge the two flows. I guess the back pressure caused by the turbine wheels on the smaller turbos is enough to remove the cylinder pulses?