twincharging prototypes needing constructive critisism (SC14 + turbo)

[Cameron_Datto]

The best guy to talk to is "Warpspeed " on skylinesaustralia forums ,, here is a link worth reading ,
http://www.skylinesaustralia.com/for...hl=twincharged

Btw i kept the twincharged system i made simple with out bypass valves on boost or the magnetic clutch switching off , i only use a Bypass valve at idle speeds , iam more than happy with the result ,

[2JZR31]

I came up with a very simple an easily tunable SC bypass ages ago. You just get a small TB connected to the accelerator pedal and in parallel the SC, and get it to open and close in the opposite direction of the main TB. (check my 30second MS paint diagram)

In response to stockystock and warpspeeds reduced back pressure theory. I disagree. It has been proven time and time again that turbos make power more efficiently than superchargers. This means that the power loss associated with the backpressure of a turbo is less parasitic then the drive system of the supercharger. In a twin charge system where the SC turns off at higher RPM, the backpressure of the turbo can easily be reduced further than in a straight turbo application by using a very large exhaust side on the turbo. There SC will get rid of any lag normally associated with large exhaust housings.

[MWP]

I came up with a very simple an easily tunable SC bypass ages ago. You just get a small TB connected to the accelerator pedal and in parallel the SC, and get it to open and close in the opposite direction of the main TB. (check my 30second MS paint diagram)

I hope you would have a decent sized bov in there otherwise youll blow the intake pipeing/tb apart.
As far as effiency and ease of use goes, having the TB before the supercharger always makes more sense... ie, the stock Toyota setup.

[brett_celicacoupe]

good input


i think this design will work fault free and be very smooth.

note: for this post i will assume the SC makes a solid 10psi

with valve 1. , a normal turbo type wastegate actuator can be used. it will need to begin to open when the pressure is ~1psi higher than what the SC would naturally create on the engine.

so.....whilst the SC is on and the pedal is flat to the floor, a constant pressure will be held- for the air entering the engine. when the turbo is making say 2 psi, the post-SC pressure will try to be 12psi (10+2), but because of the wastegate actuator, opening at approx 11psi, the bypass TB will have opened enough to reduce the pressure back to 11psi. this should be about as smooth as the wastegate operation on any turbo

this pressure will continue to be self regulated by the bypass TB until the pressure either side of the bypass TB is equal(ie turbo making >10psi) . when this happens, the bypass TB will experience pressures that wont be able to be relieved by just opening so the wategate type actuator will just open 100%...... great, bypass ready to let 20psi through.


during a gearchange where the SC is on, theoretically there would be a massive pressure spike - because of no TB before the SC. but, the wastegate type actuator will just open fully with pressures greater than 11psi. to add to this however, valve 2. will open with with vacuum and help to vent any of this pressure.


so the added feature with this diagram is valve 2. it is essentially a plumback BOV that only opens with vacuum. this will serve 2 purposes;
1. to help vent pressure when TB is snap shut during gearchanges - when SC is on
2. to provide a free air path past the SC whilst cruising. when cruising along, there should be enough vacuum to hold this valve open. so the air from this and the small amount of air that can come through the SC blades when its off should be adaquate


here is the new diagram






any care to exam it to find any possible faults? i want to hear them

[2JZR31]

I hope you would have a decent sized bov in there otherwise youll blow the intake pipeing/tb apart.

I don't think you understood the idea at all. The small TB opens in the opposite direction of the main TB. IE when the main TB is closed, the bypass TB will be open and vice versa. The operation will be totally linier and you can adjust the sensitivity with throttle cams etc. The BPTB only needs to be very small. (IE cheap from a wrecker)

[brett_celicacoupe]

I don't think you understood the idea at all. The small TB opens in the opposite direction of the main TB. IE when the main TB is closed, the bypass TB will be open and vice versa. The operation will be totally linier and you can adjust the sensitivity with throttle cams etc. The BPTB only needs to be very small. (IE cheap from a wrecker)

i see a problem with your design where you floor it but only 85% to the floor. this would leave the other TB 15% open which would let a lot of air escape

[2JZR31]

care to exam it to find any possible faults? i want to hear them

I can't see any this time

[brett_celicacoupe]

should be relatively simple to get parts for as well. just need;
-wastegate actuator
-large TB
-bosch vacuum only operated BV

[2JZR31]

i see a problem with your design where you floor it but only 85% to the floor. this would leave the other TB 15% open which would let a lot of air escape

Yes, that is why you use a small TB with proper throttle cam setup. You would arrange it so that its adjustable. Ideally it would be possible to tune it to fully close the BPTB at what ever main TB position you want. That way you could fully tune throttle response exactly how you wanted it.

However, I think if you find a fairly small TB it will work just fine if both TB's move together exactly. When the main TB is open only 85% that means you dont want full power. My bet is if there was nothing in place to reduce boost from the SC 85% throttle would make the same amount of boost at the inlet as 100% anyway. Look at most turbo cars. They make full boost at anything past 2/3 throttle which makes driving them quite difficult. My 2JZ's throttle is like an on an off switch once the engine is in the boosting range..

[RAd28]

forgive me for not reading the 4 pages of good stuff just now, it's too late, but i have a few q's... does anyone know of a volumetic flow rate for the super charger? and for the turbo your planning on using? what ever this maybe...

[brett_celicacoupe]

SC14 is 1.4 litres of air displaced per revolution
SC12 is 1.2 liters of air displaced per revolution

[RAd28]

lol... yeah, it was late and i wasn't thinking... haha... what about the turbo? any ideas there?

[brett_celicacoupe]

something around the 350-400hp size....

it should behave similar to a 250hp turbo on the same engine without a SC

[Nim]

Okay, I got thinking about this. I'm sorry I didn't read everything here, but I got inspired by the 'heart valve' idea and drew up a diagram. I dunno how well this would work but yeah, it's quite simple compared to some of the other stuff on here.



This system would allow the SC to run all the time, boost up and press the other body closed (against a soft spring holding it open?). As the turbo builds boost it will start to press the body open further untill the turbo is making more boost than the SC, then the SC valve will close. This will cause boost to build up behind that SC body, and the blow off valve would open, dumping the extra boost in front of the turbo, adding extra boost to the turbo.

Or here's another idea. Have the SC before the turbo, then have a seperate intake that goes streight to the turbo. Have something on the turbo wastegate that sends a signal to open up a throttle body on the direct intake pipe. As long as the SC isn't providing more boost than the turbo, you shouldn't get too much compressed air escaping along the direct pipe from the SC.

[brett_celicacoupe]

only problem is the supercharger will hold the turbo valve closed completely while the turbo is not spooling enough to make pressure. seeing as a turbo is a non-positive displacement type fluid pump, blocking the outlet will mean the turbo will never make any pressure and so the valve wont open....ever.


the other thing is that the valve in front of the SC will never close and so the pressure difference on each side of the SC will be very high if the turbo was to make significant pressure. the problem with this is that greater the pressure difference either side of the SC, the greater the load the SC puts on the engine.




think about twincharging long enough and you can flaw any setup


least it got you thinking!