twincharging prototypes needing constructive critisism (SC14 + turbo)

[brett_celicacoupe]

im hoping that the air flowing from the turbo doesnt get dangerously hot (for the SC) until significant boost is being made. this way the bypass could allow potentially damaging hot air to slip pass the SC. this may need to be solved with a small W2A setup

i also see another flaw in my above diagram where under the circumstance of WOT the bypass will be open(TB.3), and the pre-SC TB will be open also (TB.1). whilst there is significant air flowing through the bypass (from the turbo), there may be some that will try flow through the disengaged SC.....so it will most likely spin a bit. but i guess this isnt really a problem unless SC begins to spin up around 8000rpm or more.

this could be another reason why an electronically controlled pre-SC TB (for TB.1) could be better (instead of running paralell to driver TB)......just more of a programming/setting up headache

[mic*]

Brett,

Looking at your diagram i know a lot of thought has gone into it. Well done.

I dont think WO-TB1&TB3 will worry the SC if its disengaged. The pressure will be the same across both sides so twould not induce much spinning, certainly not overspinning.

I am curious why you feel its necessary for two TB's in parallel (TB1 & 2)?

For example, i cannot flaw the setup with TB1 eliminated. TB3 would need to be open say 5% under vacuum, closed at ATM, then have a progressive opening programme under boost. Like MYNE's setup but with a post SC (driver controlled)TB rather than pre.

Conversly you could eliminate TB2. Then bring TB1 back to before the Y split in your pipework and you have the same thing as MYNE.

Different intercooling positions... Personally yours looks better on paper, but MYNE is saying with experience that its a laggy volume for an intake. However if you had the post SC TB2 setup you wouldn have this prob... But you still have warm/hot air heating the SC periodically...

It all comes down to cooling i reckon... Thats why i been playin with WI...

The other main problem i see is clutched operation of a SC14 on a 1G, whilst still achieving a nice pulley ratio, ie boost. The "good single turbo" school of thought is pretty convincing to me unless i can have my 1 bar from idle... Assuming the standard 124mm SC14 pulley and electro clutch is used, you would need a 220mm crank pulley to get the ratio, and then pray that a clutch engineered for half the load will still hold... Bit chunky eh?

[DeftAnesthetik]

very timely that you your link Deftanesthetik, Brett & I were just talking last night about how one might use megasquirt to drive his twin-charge engine.

Am curious about what kind of control is there on the 1-way valve? can you provide some more detail on it?

(btw: we seems to have used too much bandwidth from you geocities site).

cheers and well done!
Charles

actually it's not my site, i had gotten lucky to stumble across it. i am also planning to build a twincharged 4a.

[brett_celicacoupe]

I am curious why you feel its necessary for two TB's in parallel (TB1 & 2)?

For example, i cannot flaw the setup with TB1 eliminated. TB3 would need to be open say 5% under vacuum, closed at ATM, then have a progressive opening programme under boost. Like MYNE's setup but with a post SC (driver controlled)TB rather than pre.

i would say the whole purpose of TB.1 is to make things smoother and efficient. in the instance of the car 'putting' along at 1800rpm, if the SC was unrestricted at its inlet, it would be trying to force a whole lot of air through the engine when it really doesnt need it. cruising along at 1800rpm is about 6% of the full throttle available. it would be wise to have the TB.1 a little ahead of it so maybe at 9% while the TB2 is at 6%. now if the SC is only able to pump a small amount of air, the load it imposes on the engine should be VERY low.

but your probly wondering why you just wouldnt shut the SC after a stable RPM is reached for a second.... but then we need to think about gear changes.

say you are doing a 1/4 mile run, or even a leisurely street light acceleration .... could you imagin the SC switching on and then off in EVERY gear?? everytime it cuts in, a jolt is felt..... not so good for the smooth factor.

but wait..... under WOT acceleration, the pre-SC TB will be open and the SC on....so the only way to prevent overboosting is to switch the SC off.

so now i may be thinking that the solution is yet another electronically controlled TB in place TB.1 that mimics the movements of the driver controlled TB most of the time, but except under WOT and above ~3500rpm. under WOT and above 3500rpm, it would close....and so the SC would pump NO air and would freewheel in a vacum


so if there was a TB before the SC, we could have the SC on at all times unless
1. the turbo is making enough boost so the SC isnt needed
2. the engine RPM hasnt varied for ~ 2-3 seconds. ie highway cruising


so while the SC is going, there is only very minimal throttle open, the SC should theoretically 'freewheel' in a near-vacum and therefore not consume much of the engines power.


but now i am beginning to see another problem.....during the transition period, when the turbo begins to make a decent amount of boost, the SC will amplify this boost from the turbo even more....this may cause a problems in knowing when to open the bypass valve....cause theoretically you would want it to open when the pressure is close to equal on each side of the bypass.

Conversly you could eliminate TB2. Then bring TB1 back to before the Y split in your pipework and you have the same thing as MYNE.

i see a small problem with this. when the pre Y-pipe TB is 100% open and the SC on, there will be air doing 'loops' around the Y-pipe and through the SC because the engine is restrictive. this system wont actaully put any pressure on the engine becuase it will try to flow back out the TB....but it will blend with the incoming air until a steady state sort of system is reached


anyway...... thats my latest thoughts

[jonra23]

The Lancia Delta S4s ran a twincharger in Group B rally cars until group B was banned.

pic and quote from "Forced induction performance tuning" by A. Graham Bell.




"basically, the air flow path is as follows: the air flows from a high mounted air filter down through the turbo compressor and on throught the first of two air to air intercoolers. From there the flow path can take two routes, or even both routes, depending on the turbo and blower outputs. Before the turbo begins to provide boost, the flow path continues on from the first intercooler (via the supercharger)through the second and the inlet manifold into the engine.
However as engine speed increases and turbo boost begins to rise, a bypass valve at the blower progressively opens, bypassing some flow into the engine. The bypass opens further as boost rises, thereby progessivley reducing flow through the blower. Finaly, when fully open, all the output from the turbo compressor bypasses the blower. With the blower now merely freewheeling, power loss to it is minimal at higher engine revs."

[thechuckster]

don't forget that like most rally cars, the Lancia wasn't designed for cruising and smooth idle - that setup was all about smooth (but still gut wrenching) power delivery across a wider rpm band than a turbo-only setup could provide.

Am curious as to where the lancia had the throttle(s)?

And interesting to note that it had the blow-off valve (sensibly feeding back into the intake) but no air-injection or other anti-lag hardware (like the audi had). Or is that simply missing from the diagram?

[mic*]

Brett first of all just think about this, which is a statement based on my experience with the SC; Load on the SC, and therefore crank power loss, is proportional to the pressure ratio (PR) across the unit. Eg, if you restrict the inlet or outlet, the SC will be creating a HIGH PR. This is your enemy.

i would say the whole purpose of TB.1 is to make things smoother and efficient. in the instance of the car 'putting' along at 1800rpm, if the SC was unrestricted at its inlet, it would be trying to force a whole lot of air through the engine when it really doesnt need it.What would happen is the air would recirculate thru TB3 (open say 5% - see my post above - mimicing a factory ABV) keeping the all important PR low. On a "SC only" setup you would close this TB/ABV when you reach ATM manifold pressure. This is so you dont bleed boost. On a twin charge setup you could possibly leave it open as the turbo will quickly create its own pressure? cruising along at 1800rpm is about 6% of the full throttle available. it would be wise to have the TB.1 a little ahead of it so maybe at 9% while the TB2 is at 6%. now if the SC is only able to pump a small amount of air, the load it imposes on the engine should be VERY low.

but your probly wondering why you just wouldnt shut the SC after a stable RPM is reached for a second.... but then we need to think about gear changes.

say you are doing a 1/4 mile run, or even a leisurely street light acceleration .... could you imagin the SC switching on and then off in EVERY gear?? everytime it cuts in, a jolt is felt..... not so good for the smooth factor.

but wait..... under WOT acceleration, the pre-SC TB will be open and the SC on....so the only way to prevent overboosting is to switch the SC off. PR is the factor. There is a clear path for air from the SC inlet to outlet with TB3 open so the SC will not "overboost" anything. It can only recirculate at a higher pressure.

so now i may be thinking that the solution is yet another electronically controlled TB in place TB.1 that mimics the movements of the driver controlled TB most of the time, but except under WOT and above ~3500rpm. under WOT and above 3500rpm, it would close....and so the SC would pump NO air and would freewheel in a vacum Again PR. If you restrict that SC inlet it wont freewheel. It'll have a HUGE VAC at the inlet, and all the boosted glory of the turbo at the outlet. Bad bad bad.

so if there was a TB before the SC, we could have the SC on at all times unless
1. the turbo is making enough boost so the SC isnt needed
2. the engine RPM hasnt varied for ~ 2-3 seconds& greater than ~-8psi VAC
Sounds good



but now i am beginning to see another problem.....during the transition period, when the turbo begins to make a decent amount of boost, the SC will amplify this boost from the turbo even more....this may cause a problems in knowing when to open the bypass valve....cause theoretically you would want it to open when the pressure is close to equal on each side of the bypass.

The big puzzle ... Thats basically what i said at the start, & is why i started thinkin my first attempt would be simpler, ie no turbo bypas. But there will still be the phenomenon of how the SC responds

i see a small problem with this. when the pre Y-pipe TB is 100% open and the SC on, there will be air doing 'loops' around the Y-pipe and through the SC because the engine is restrictive. this system wont actaully put any pressure on the engine becuase it will try to flow back out the TB....but it will blend with the incoming air until a steady state sort of system is reached Imagine there is no turbo for a second, and this is exactly how my car runs The "TB3" or ABV in my case closes at ATM manifold pressure


anyway...... thats my latest thoughts

[brett_celicacoupe]

okay ive decided to rethink the setup (again)

this time having no TB before the SC and only 2 TB's overall. also considering having the SC very close to the TB for the purpose of throttle response (less time to fill piping/IC etc)

ive also bought one of these suckers;


so with the new design, a piece of pipe would be joined to the above housing (between the 2 butterflys)

also with this design, the SC would be mounted on the inlet side.

it is likely this setup would need something to cool the air coming from the SC.....this could possibly be water injection.





however there is one small concern i have....the outcome might not be bad though. just wondering how the engine will react to reasonably hot air coming in, and then a sudden burst of colder air? id expect that the timing would advance majorly nearly instantly?


thoughts/comments/etc ??

[mic*]

[IMG][/IMG]

Ok, im a bit intoximacated, but this looks good. ...With the key to it being the tuning of the butterfly that the grey arrow points to. Would take some playin with to get right...

I think the coloured arrows & key are pretty straight forward. This is what i reckon would happenn on a permanent drive SC. Note that the blue arrow goes backwards in the "bypass pipe" for efficient VAC opperation of the SC. If the SC were clutched off under VAC, the blue arrow in the bypass pipe would point the opposite way & the blue arrow to the SC inlet would not exist (personally i think this defeats the merits of a charger & also creates "jolt"). If the SC were clutched off under high boost, the red arrow to the SC inlet would not exist. The green arrow in the bypass pipe is really just a prediction. I am not really sure what will happen as the turbo spools against the SC, ie. SC is pumping > than ATM pressure air...

WI at this point cools the SC lobes & the charge air...

BOV (not drawn) i think should go close to the turbo compressor outlet - plumback of course.

[brett_celicacoupe]

well i picked up this 1JZ TB the other week....

the steps of the stepper motor are VERY small...somewhere in the vicinty of half a degree i estimate.


the operation of this stepper motor seems to be identical to stepper motors found on the 7m/1g etc.

2 wires feed constant +ve power and the other 4 recieve grounded pulses in a predefined order and for a predefined time. so if i can setup a system to control the movement of this butterfly it will be very versatile.

one problem however is that i will have to incorporate a system to ensures it closes fully. currently the spring ensures the butterfly is at WOT at all times(with no power applied)...which makes sense seeing that the traction control may only be used 0.1% of the engines running time.


so the problem is this, for my application the TB may have to be held open for prolonged periods of time (ie under highway cruising). i assume the motor will not like current flowing through it for a long time and may get hot, burn out even.


writing this post has given me an idea though. instead of having a spring i could introduce some rotational friction . this should allow the butterfly to hold it's position without power being applied to the stepper motor. use no spring though


anyway this project will be on the backburner for another uni semester until the next holidays! plenty of time for more planning

[thechuckster]

go electro-pneumatic control of the valve? you've got a handy vacuum source (intake manifold)?

[mic*]

Wouldn this motor be very simmilar to those used in "drive by wire" TB setups, such as the VZ commonwhore.

Being such a commmon animal, perhaps worth looking into. Just given that i think every driver would be on the throttle in some way 90% of the time... The drive motor would have to cope.

[ViPeR_NiPPleX]

could you reverse the way the spring pushes on the throttle body, so its normally closed an the stepper motor opens it?.. probably difficult, but i love this thread

[2JZR31]

The best system would be one where the SC turns off once the turbo is going. The SC would just be used down low where the turbo is not making boost and SC would bring it onto boost quickly. I have seen a proposed method which I think would work very well. I think this will work best because there is no need to even tune the operation of valves etc because its works automatically. Automation is the key for smooth operation.

The SC sits before the turbo with a one way valve T'ed in-between. When the turbo starts spinning hard it will want to suck in more air then the SC can deliver. This air will be drawn in through the one way valve. A micro switch or similar on the valve will detect when this occurs and disengage the clutch to the SC. There will be no strange power dip as this is the exact point where the turbo starts to outperform the SC. There will be a slight power gain when the SC turns off due to the parasitic loss. This system should work very well as its operation is very simple and automatic.

Instead of a one way valve you could use the trac control setup to operate whenever the pressure inbetween the turbo and SC falls below atmospheric. (when the pressure between the SC and turbo begins to fall below atmospheric it means the turbo is starting to suck more air than the SC. This is the exact point at which the turbo starts to out perform the SC)

This setup is kickass. I am not sure if it has been tried out yet, but is promises the best SC low down response and turbo top end power of anything I have heard of and should have seamless operation. I'll make a diagram up tonight.

[c2888]

http://page7.auctions.yahoo.co.jp/jp/auction/g42983494

hks system on the japanese yahoo auctions

dunno if its the whole motor, or just the kit, but by crikey its $$$

/me has dreams of 300 lag free ps

Dan