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Thread: The Mega Supercharger 4AGZE thread, using twinscrew charger

  1. #316
    how much is Too Much Toyota JustenGT8's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Whoa that's some complicated finessing, but admire your patience.

    A coupla comments. The bypass valve is more there to unload the SC and stop it trying to suck stuff all air thru a partially open throttle. In doing so it creates ridiculous heat. The bypass provides an alternative path for the intake and even though the pathway is small it's still plenty big enough to provide the engine with air for cruise and light throttle.

    RE BOV valves as bypass valves...well they do work but perhaps you need a setup that generates more vacuum? I have used them on both of my V8 SC setups and they work perfectly. With the vac line opening the vslve and airflow to the engine still very clearly in vac post SC aiding the valve to stay open they have worked really well. Better yet, they close quickly on boost and as you have noted they also seal better. I'm not sure why your setup didn't operate as expected? I can't see why you wouldn't have enough vac?
    Lily Simpson 6.7.2010
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  2. #317
    Junior Member Backyard Mechanic jondee86's Avatar
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    Lightbulb Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Yeah... it took me a long time to suss out why the GFB valve would not work. It wasn't until I started thinking in terms of absolute pressure rather than vacuum, that it became clear. The dischanrge of the s/c is connected to the intake manifold, and the GFB gets its signal from the discharge manifold. Being a belt driven positive displacement s/c, manifold pressure drops virtually instantaneously when the throttle snaps closed, so no residual pressure to blow a valve open.

    Thus the GFB has the same pressure under the piston from the manifold as it has on top of the piston from the manifold pressure signal line. The area on top of the piston is greater than the area under the piston (plus the spring) and there is no way that it can open. Doesn't matter what the manifold pressure is... that fucker will not open. The tech guy at GFB stopped talking to me when I pointed this out to him

    Its a closed system independent of atmospheric pressure. To make it work as expected, you need to have an actuator diaphragm open to atmosphere on one side. THEN, you have 15psi available to assist in opening the valve when there is less than atmospheric pressure on the other side of the diaphragm. If you used the butterfly type valve pictured higher in this thread, then that would have worked as you suggest.

    As far as the function of the bypass is concerned, it serves to equalise the pressure before and after the s/c. And since the s/c is always pumping, I'd say flow would be from the discharge side to the intake side. The ISCV admits air on the intake side. Car runs at about 60kPa(abs) at 100km/h, so I have changed the solenoid switching point to 80/75kPa and will see how that feels.

    Cheers... jondee86

  3. #318
    how much is Too Much Toyota JustenGT8's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Not in my experience? With the throttle shut or small (cruise openings) there's plenty of vac post SC. SC discharge is stuff all and definitely not creating positive pressure in the intake manifold....the flow to the engine is via the bypass valve, around the SC. this is with a pretty big 2.7litre twinscrew ....it's sitting on 6.8 litres of engine though.

    The vac required for a butterfly valve is less but clearly you still need vac....in my experience it's also enough to drive the BOV style valve as well.
    Lily Simpson 6.7.2010
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  4. #319
    Junior Member Backyard Mechanic jondee86's Avatar
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    Arrow Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Interesting. You can see from the graph I posted in #203 above, that the MAP reading drops instantly when the throttle snaps closed. I don't have an intercooler so no left over pressure to pop a valve open.

    And of course, the MAP is less than atmospheric at cruise, so there will be a pressure differential capable of holding open a valve actuator that has atmospheric pressure acting on one side of a diaphragm. This is fundamental to the operation of the "mini cooper" type bypass valve that takes a MAP pressure reference from right beside the butterfly.

    As to the direction of flow in the bypass ? I don't have any means of measuring the pressure in the duct between the throttle and the s/c. I have seen it suggested that the pressure in the intake may actually be lower than at the s/c discharge. Given that the s/c is "sucking" on the intake side and "blowing" on the discharge side, this does not seem like an unreasonable suggestion.

    However, in my case the ISCV is letting air into the suction side, so that will do something to raise pressure on the inlet side. So I can't be sure which way the bypass air flows, and it is not really important so long as the engine inlet air temps drop... and they do now

    What kind of valve are you using/did you use on your setup ?

    Cheers... jondee86
    Last edited by jondee86; 05-02-2018 at 08:13 PM. Reason: Clarification...

  5. #320
    how much is Too Much Toyota JustenGT8's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Both setups were simple valve style BOVs. You run then in reverse though as you want the intake airflow pre SC passing thru them to the post SC portion. The vac line actuator opens the valve just as it would as in a turbo BOV application, but it's the engine air intake requirement that also helps keep the valve open. As you go to full throttle you A) lose vac and B) the SC starts working as it has some air to work with and the valve closes sealing the system again..

    Next time I'm on the dyno I'll log intake temps with the valve working as plumbed....with the valve closed....and with the vac held open by a stronger external vac source
    Lily Simpson 6.7.2010
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  6. #321
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    This is how most of the big mutha blow off/diverter valves are built..



    They have what I call "double chamber" actuators, where there is an intake manifold signal on one side of the diaphragm and the other side is vented to atmosphere. Works fine with just manifold pressure to open and close, and the opening point can be adjusted with the spring pre-load. You possibly have this type of valve.

    And for sure I would use one (small one) if I was prepared to make some fairly major modifications to my ducting. But for the moment, I'll stick with my DIY solution, unless it gives me problems further down the line.

    Cheers... jondee86

  7. #322
    Junior Member Backyard Mechanic jondee86's Avatar
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    Exclamation Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    By comparison, the GFB 9301 valve is built like this...



    The piston (yellow bit) slides up and down within the bore contained in the cap. When installed in my application the top of the piston gets intake manifold pressure from the sensor line and the bottom of the piston gets manifold pressure from the s/c discharge duct. The system is closed... atmospheric pressure plays no part in operation of the valve, nor is it affected by pressure in the side discharge spigot.

    The area of the top of the piston is effectively slightly larger than the area of the bottom of the piston due the margin lost to the piston seat. With the same pressure top and bottom giving a small force differential in favour of holding the valve closed, plus the spring pressure, the valve cannot/will not/does not open... EVER

    It's designed for a turbo setup with the throttle plate after the turbo.

    Cheers... jondee86

  8. #323
    how much is Too Much Toyota JustenGT8's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Yeah gotcha. I have the piston valve as you have posted. Works well.
    Lily Simpson 6.7.2010
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  9. #324
    Junior Member Backyard Mechanic jondee86's Avatar
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    Question Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Piston type... like the GFB valve ? Well I'd love to be able to figure out why yours works and mine doesn't. What kind of s/c are you running, and do you have an intercooler ? This thing was driving me nuts for a couple of months and if I am missing something, I'd like to get straight in my head

    EDIT: Been out for a walk and got to thinking about what you said about the direction of flow thru the bypass. Then it came to me that if the air does flow from the intake to the discharge side of the s/c, then you may have the valve installed in the reverse direction to the way I have it installed.

    That is, intake connected to under the piston and discharge to the side outlet. And if the pressure on the inlet side of the s/c was higher than the pressure on the outlet side... it could work GFB say it takes a 2.5psi differential to open the valve.

    Have to admit that I was never able to find any reliable information on the direction of airflow in the bypass, so just assumed (yeah, I know) that it went from discharge to intake. Tomorrow I'll tap the intake side of my ducting and check the pressure during idle. If it is higher than the manifold pressure then that will confirm the direction of flow.

    Cheers... jondee86
    Last edited by jondee86; 08-02-2018 at 07:25 PM.

  10. #325
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Nah sorry the one above ...the valve valve Lol dunno why I typed piston?

    But having said that I can't see why the piston style of vslve wouldn't work as well....just reverse it and give it a whirl? Can't hurt
    Last edited by JustenGT8; 08-02-2018 at 09:36 PM.
    Lily Simpson 6.7.2010
    R.I.P.

  11. #326
    broken down ex guru Chief Engine Builder feral4mr2's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    i use a external wastegate on my twincharger (eaton m45). but it's more so because the TB is post supercharger that i use it than to bypass the supercharger, even though it does do this on idle and mild cruise.

    (picture taken before i made the pipe to return to the sc inlet pipe).


  12. #327
    Junior Member Backyard Mechanic jondee86's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    Yes... as I am discovering, there are better/simpler ways of controlling a bypass if you have the space (and foresight) to incorporate them at the design stage

    Today I made a couple of tests to see if I could get a better understanding of what is happening with my setup. I tapped a fitting into the side outlet of the Bosch valve and installed it in the same orientation as I have the GFB in my above pic. I hooked a industrial vacuum gauge up to the tapping on the Bosch valve to read the pressure in the duct pre-s/c and used my laptop to monitor MAP. Then I applied a Mityvac to the Bosch sinal input fitting so that I could manipulate the valve with pressure or vacuum.

    Ran the engine up to operating temp at idle (1150rpm) and took readings...
    MAP = 33kPa and intake = 21kPa. Manipulating the valve made no difference.

    Ran the engine at a high idle (1800rpm) and took readings...
    MAP = 32kPa and intake = 18kPa. Manipulating the valve made no difference.

    Swapped in the GFB valve in same orientation as before and took readings...
    MAP = 32kPa. Manipulating the valve made no difference.

    Hooked up the vacuum tank and took reading at idle... MAP = 29.5kPa. Not sure why it read lower... maybe I didn't apply as much vacuum as the tank does to open the valve ? So possible that I never got either of the valves to open when manipulating them with the Mityvac.

    Rather inconclusive GFB say that their valve needs 2.5psi (17kPa) differential to open, so it is not clear if the valve is open at idle. The fact that the MAP signal is marginally lower tends to indicate that it could be. The fact that I can feel the bump in acceleration when the valve closes means that it is definitely doing something when MAP is below around 85kPa.

    I'm running open loop idle control so there is no compensation being applied for any extra air coming from the post s/c ducting. I think that the low pressures involved may contribute to the apparent lack of any pressure variations between open and closed bypass.

    The only thing that does seem clear is that on my setup with my s/c, MAP is higher than pre s/c pressure, and I suspect that this would be true at all throttle openings. It is also possible that a larger bypass valve might help in getting my engine IAT's down.

    Cheers... jondee86

  13. #328
    broken down ex guru Chief Engine Builder feral4mr2's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    have you tried different rate springs? i used about 4 different rate springs until i got 1 to work how/where i wanted.


    plus the benifit of the wastegate is the is the port on either side of the diaphram. that alows for far greater control of it from either side of the TB.

  14. #329
    Junior Member Backyard Mechanic jondee86's Avatar
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    Post Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    The problem in applying the GFB valve is not with the spring. I ran the valve after taking the spring out, and it still doesn't open

    As I confirmed today, with a manifold pressure applied to the top of the piston, there is always a net force in favour of holding the valve closed. I have overcome that by isolating the manifold pressure signal from the valve when MAP drops below around 85kPa, and applying a lower kPa signal from the vacuum tank to pull the valve wide open.

    Ideally, I'd like to use a simple double chamber diaphragm actuator valve, and further down the line I will look at how it might be possible to fit one into my setup. I would prefer the valve to close progressively with the rise in MAP to give a smooth transition into boost. instead of the bump I get now when the valve closes abruptly.

    Cheers... jondee86

  15. #330
    Toymods Events Secretary Too Much Toyota trdee's Avatar
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    Default Re: The Mega Supercharger 4AGZE thread, using twinscrew charger

    god damn there's a lot happening in that engine bay johnny
    1988 AW11 9A-GTE - project #1 | 1980 KP60 4K - project #2 | 1994 UZZ31 Soarer 1UZ-FZE - Cruise missile
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    .....and the within first laps everything that made the AW11 great hit Rex as if the 'Gods of driving fun' had all Jizzed on his face.....
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    Mono blocs mate....as close to yours as a Ferrari is to a Fiesta

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