SC bypass valve...

[barryogen]

I have an idea for an bypass to use for my project... but just need another head(or a few) to look at my ideas, and poke holes if holes need to be poked.

Basically, because of where I want the throttle body(after the blower, and as close to the stock position as possible to keep throttle response), I will need to unload the SC completely at idle and light throttle openings, or bend/break throttle bodies, which I'm none too keen on.

I was thinking of using an external turbo wastegate sitting between the blower and throttle body.

A wastegate has 2 fittings, one on either side of a diaphragm which "see" different pressures.
The "cold side" is connected to the plenum and "sees" the pressure changes AFTER the throttle body.
The "hot side" is connected to the intake piping between the blower and the throttle body.

So basically the the wastegate sees the pressure drop across each side the throttle body.

Now at idle, vacuum sucks against the diaphragm and pulls the valve open, allowing air to go out the open gate, the blower runs cooler and causes much less load. As the throttle opens, pressure changes become much less, so the gate closes.


Can anyone see anything wrong with this setup?

edited to re-word some of it a but better.

[Rick]

I think what you are needing is a blow off vavle instead of a wastage, and that would get plumed in between the supercharger and the throttle body, and is operated when there is vacume, ie suddenly backing off the throttle.

In the factory 4agze setup the throttle body is before the supercharger so there is no need for a blow of valve as such, because the supercharger is switched on via the computer and clutch, there is a bypass valve to allow the motor to breathe when the super charger is not operating.

But a blow off valve acting as a bypass valve at idle may cause problems, as I read somewhere you wanted to have the supercharger consistantly running which is proberally not wise, might give you idle problems, ruff take off etc... its a pitty as my car has a similar setup (still not running) and I am not to sure what to use, I think for me its going to be a bit of trial and error once I get it going to find the best option.

Send "ZAK" a PM on how well his car performs as he has a supercharged AE86 with the t/b after the supercharger and is running a blow off valve.

[ChaosAD]

How about a blowoff valve or two? Just plumb them exactly as you would a turbo car, just use plumb-back ones and plumb them back to between the afm and blower.

Dont see why they wont work as its the same principle as a turbo engine

[Rick]

Dont see why they wont work as its the same principle as a turbo engine

It would work as long as it allows air to be sucked through the BOV, when the supercharger is disengaged and/or no boost. Thats the part I am not sure of, as in a turbo setup air can still pass the turbo when off boost, idle etc.. but if the supercharger is not spinning there is non or very little air able to pass through it, and I thought the springs in the blow off valve maybe too strong to open the valve at idle/no boost???

[ChaosAD]

How does the air get past the s/c on the gze when its idling? could use that + a b.o.v. maybe?

[Mr Revhead]

i thought about using the bypass valve off a 3sgte.

[Zak]

Don't worry about sucking air through the supercharger, you can stop it from spinning and the engine will still idle and cruise fine. I even disconnected it to see what difference it made, and it's stuff all, so don't bother with bypass valves.

But, you have to run a blow off valve or some thing to realase the pressure, other eise as you say, you'll brake some thing. It won't work as a by pass valve at idle as they have a spring keeping tension on them so they don't leak at idle. You get the same problem with a waste gate too.

You can't run the charger constantly on if you have the throtal body after it as you can't cruise as such, it's all or nothing, so run a switch or sensor or some thing with the electro clutch.

[barryogen]

My reasoning for using a wastegate rather than a BOV is that BOV are too harsh, very on/off rather than gradual like a wastegate.

Both can be made to operate in the same way(in this situation), so my thoughts tended towards using a wastegate for smoother operation.

If it doesn't work, I'll ditch it and use a BOV, but my preference is for smoother operation, not on/off.

[Zak]

The blow off valve will be identical to a waste gate, just one was made for high exhaust temps. Having your boost venting like you want will make one hell of a noise, mine is bad enough in 10sec spurts let alone any time your not on boost.

If you weren't so far away I'd show you what it's like, but it's bloody loud.

[sergei]

How about just use TVIS canister and solenoid valve to activate the waste gate in first place, plumb it in such way so it will bypass the supercharger but it would be plumbed back in (basically it will be plumbed in parallel to SC). The plumb back will make sure that it will not sound like Zero on kamikaze attack. Use IDL signal from TPS (through a op-amp buffer and relay/transistor) to activate bypass.

[barryogen]

The blow off valve will be identical to a waste gate, just one was made for high exhaust temps. Having your boost venting like you want will make one hell of a noise, mine is bad enough in 10sec spurts let alone any time your not on boost.

If you weren't so far away I'd show you what it's like, but it's bloody loud.

hmmm, ok then, might have to re-think it.

Would having multiple ones a bit better noise wise? I mean then they would be moving the air at a much lower rate, so less noise would be made?

[Zak]

That might work, plumbed back in it will be quiter, but you'll still hear it thats for sure.

To give you an idea of how loud it is, if it goes off beside you, it does hurt your ears, and thats only 2000 or so rpm worth.


It's the only think I don't like about it, is that it's on or off, you can't make a small amount of boost like on a turbo. At least with a toyota charger.

[sergei]

what about using scooter gear to drive it crazy idea but modified CVT from a scooter will be perfect for supercharger (no drive at idle, and max rpm of supercharger independent from engine) sound good....
That is just having crazy ideas because I am fiddling with a scooter right now...

[Zak]

Thats a pretty damn good idea, but I'm not sure it could take the drive, there is alot of power used to spin it, more than a scooter would dream of making thats for sure.

It's a good idea though, I might do some more looking into.

[sergei]

It depends how much power is needed for a supercharger.
if say 30hp it is possible for that gear to work. but if it is say 75hp then it is a bit difficult.
But judging on the belt size on the pulley it should be around 10-20hp to run that supercharger which is possible with scooter gear.

[barryogen]

That might work, plumbed back in it will be quiter, but you'll still hear it thats for sure.

I had assumed that you would have it plumbed back... I mean otherwise it would woosh like a banshee all the time, and that'd be enough to drive most people crazy.

It's the only think I don't like about it, is that it's on or off, you can't make a small amount of boost like on a turbo. At least with a toyota charger.

Thats precisely what I like about them, gives you that "big engine" feel all the time.

what about using scooter gear to drive it ;) crazy idea but modified CVT from a scooter will be perfect for supercharger (no drive at idle, and max rpm of supercharger independent from engine) sound good....

Have looked at using a setup like this, but most seem to top out at fairly low RPM, so unless you severely under drive them on the input(engine) side, and overdrive the output(SC) side, it would just run out of go.

[Zak]

Mines not plumbed back in caus there isn't any pipe off the intake on the charger, just a small pipe (about two inches long) with the filter on the end.

I did think about a small muffler or some thing on the end of the blow off valve, but I'm not sure if it would really work.