Digging up twincharging again...

[myne]

So I've been thinking a bit about bolting a turbo onto my GZE

I've read just about every reference to 4agze twincharge setups eg : http://www.geocities.com/MotorCity/l.../20-valve.html
And the toymods parallell twincharging thread :
http://forums.toymods.org.au/index.p...art=0&count=60

I came up with a design (actually before I read any of that) and I was wondering what people would think.
Takai says it wouldnt work because the SC bearing seals would blow if its' inlet met boost, but the guy in the first link seems to have done it that way so I dunno.

My basic idea is this :


Under low load, the SC would be off, the system would experience vacume, and the SC bypass would be fully open. "Naturally aspirated"
http://www.users.on.net/~jvizard/myn...desprotvac.GIF

Under moderate load, the pressure switch would experience vacume, and be in the "on" position. The bog stock ECU would turn on the SC and the SC bypass would close as the pressure closed the actuator. "Supercharged"
http://www.users.on.net/~jvizard/myn...edesprotsc.GIF

Once the turbo spooled up, (and this would take a fair bit of tweaking) the SC bypass would gradually open as the pressure before the throttle built up. Once the pressure was at a pre-determined level (probably a couple of psi less than the SC) the pressure switch would trigger and the SC would turn off. "Turbocharged"
http://www.users.on.net/~jvizard/myn...desprottur.GIF

Details of intrest
* The Supercharger would not be intercooled simply for the sake of room. For that reason it'd only run factory boost. (Which shouldnt lose too much power since it will be turning off somewhere in the rev range) It's plumbed directly into the back of a "tvis" style manifold.
* The SC bypass will work similar to how a choke advances the throttle on a carburettored engine. Only in this case there would be 2 "chokes" pushing it open.


Thoughts?

[takai]

As said on IRC, i personally dont think this will work due to the design of the housing seals on the SC12 (and 14 afaik). The seals around the bearings arnt designed to be under a high internal pressure load from greater than atmo air being blown into it. Thats why there is, by default, a pressure regulator on them. But the pressure regulator woudlnt be able to equalise the pressure loads which a turbo would pump into the charger.

[Bahnugget]

so chuck in another butterfly (or 2, one in the input one in the output) to isolate the SC

[MWP]

The simplest way i can think of doing it is:

              ----ONE-WAY-VALVE---
              |                                 |
IN---TB------SUPERCHARGER--------TURBO----INLET_MANIFOLD

The one way valve would allow the turbo to suck air when it was needing more than the supercharger can give, but would close when the supercharger is moving air when the turbo isnt making boost.

[Earlyrolla]

As I understand it, the SC12 and SC14 have three vent pipes on the supercharger. One for each front bearings and one for the back gear housing/bearings. The purposes of these pipes is to allow manifold pressure (actually supercharger internal pressure which should approximately equal manifold pressure) to the outer side of the bearings, i.e. the side of the bearing facing away from the supercharger lobes. This allows for an approximately equal pressure on both sides of the bearings which should stop any pressure from pushing out the grease from the bearing races.

Based on this, provided you plumbed the vents correctly so that the pressure on both sides of the bearings was approximately the same, you shouldn't compromise the life of the bearings by blowing the grease out of them!

[takai]

Yeah, sure the holes are large enough to equalise out the pressure from heated atmo etc, but is it enough to equalise the pressure from 20psi being pumped into it?

[Earlyrolla]

The pipes only need to be small. I am sure you wanted to sit done and work out the rate of flow through the pipes based on a transient manifold pressure then I doubt that it would take more than a second for the the pressure to re-equalise on both sides of the bearings. Remember the only flow through the pipes is the mass of air required to change the pressure in the cavity on the other side of the bearing. The size of the pipe is not really related to pressure in the sense that you are implying (if I understand what you trying to get at).

[takai]

True, but i was under the impression that the pulley end of the charger vented to atmo, rather than to a sealed cavity.

[Earlyrolla]

I can't say for sure on the SC12, but on the SC14 that a friend has on his MR2 all three pipes connect to a common rail that then connects to a solenoid.

I don't see why the front would be different to the back, the idea is to maintain a close to equal pressure either side of the bearings, otherwise like you said the pressure would blow the lubricant out of the bearings.

The front has two pipes as there are two separate bearings where as the back only has the one pipe as the whole cavity behind the bearings is linked as a result of the gear set and back casing.

[takai]

Yeah, without having an SC12 here i cant see why it would be different, although instinct tells me that since the gearset is swimming in oil then it wouldnt be getting pressurised. However, something in my brain is also telling me that there is a hole drilled all the way through the shafts that the pressure equalisation pipes are connected to. Still struggling to remember though. Maybe once i get a good look at an SC12 or 14 again itll come rushing back.

[Earlyrolla]

In shouldn't matter about the oil to whether it is pressurised or not. The back gear cover has a full o-ring seal around it. The increased air pressure will not affect the way the oil lubricates the gears.

I can't say for sure either, a friends got an SC14 in bits in his garage so I will have to take a peek next time I am round there.

[takai]

Yeah, i was more thinking about the opposite, which is when the charger isnt turned on, but the engine is producing vacuum then you have a likely circumstance for sucking oil through the equalisation rails. Although, one would assume that the solenoid was there to minimise that, but my solenoid on the GZE never turned on or off, and several that i know of have been the same.

[myne]

Interesting. Can anyone confirm the operation of these breathers, and or the SC1x's ability to handle being pressurised?
That entire design seems to hinge on how the SC would handle non-operatational boost conditions.
If it can, and bearings wont fail, then to me, it looks like a winner, with only the finer points of how much boost the SC can efficiently deliver at low-ish rpm without intercooling, how the actuation of the bypass should be handled, and fabrication to be debated.

Oldcorollas, I'm waiting on your input if you've got any.

[Earlyrolla]

I am not sure exactly how the original system is configured but there is nothing stopping the modification of the system to suit the twin charged application. A passive system could be used in place of the solenoid with a bit of thought.

I don't believe there should be any problem using an SC1x for the twin charged application.

As for supercharging without intercooling it will depend on how much boost you are aiming for; as the temperature rise across the supercharger is primarily related to the rotational speed. Remember that even a low-ish pressure from the turbo as it spools up will aid the pressure generated in manifold by the supercharger greatly. Not to mention the obvious flow on effects of increased exhaust gas mass flow and hence faster spooling of the turbo.

Another question to ask is how often will the engine be in the band where the supercharger is active?

If this is through the band of normal driving then the supercharger may be active for prolonged periods of time, where by intercooling may be beneficial. If the control system is designed such the supercharger is only ever active for short periods during acceleration then compensation of fuelling and ignition advance could be made by the ECU to accomodate for increased intake temperatures resulting from the non-intercooled air.

[Valkyrie]

Hi,
Here is a picture of a twincharge set-up. Some might recognise it as the engine from the Lancia Delta S4 rally car.

This should give a clear picture for all viewers.

You are looking at a set-up similar to this without the second intercooler?

Notice the use of a second wastegate/blow-off valve.



Cheers