Supercharged Propane 3.4

[ssdurango]

The reference line IS hooked up to the manifold after the throttle. If you slowly open the throttle with no load on the engine there will still be a vacuum in the manifold. - this will allow the BOV to open. The supercharger is moving more and more air as I rev the engine up - even at low speeds (unlike a turbo) All that air needs to go somewhere because the engine can't use it without a load on . I actually need it blow off in this manner.

Now, the next step is to see if the BOV seals tight during hard acceleration. I may have to adjust the spring tension.

[3400-95-Modified]

That can't be hooked up right, when you are building boost with the throttle plate open your BOV is opening and letting out the air, and it shouldn't be open at idle either... It should only open when the throttle plate slams shut and a LARGE vacuum is introduced to the post TB area,

Something isn't right there.

[hookdonspeed]

what is the valve rated for?
my friend had a high-boost DSM with a crappy BOV, when he would get upto higher boost, the pressure would push the valve open, even with no vac being created.
he had a stutterbox and it would blow the valve compleatly open everytime, fixed it when he put a better valve on made for the higher boost, not saying this is the issue, because i dont know what kind of valve your using, etc.. just a possible guess.

[hookdonspeed]

i just showed him your setup, he said also makesure you dont have a checkvalve in the line going to the BOV, the pressure your building under boost will help keep it shut until you pull vac again.

[ssdurango]

It's plumed right into the intake manifold, no check valves installed. I haven't driven the truck yet to see what happens under a load. It's working the way i wanted it to so far, I just wanted to show you guys. Remember, it's not a turbo, it's a eaton M90 roots blower - It will out flow 5 litre engine at any RPM. see 'Postive displacement pump'.

The vavle is rated for 10-25psi

[ForcedFirebird]

It just seemed like it was opening most when you had had more throttle. It should be closed as long as your guage shows boost. The boost in the manifold should help it stay closed.

S/C's will show more boost under load, so maybe it's just not loaded enough in neutral?

[TurboProject]

Can you tell us the manufacturer of that blow off valve? Is it actually a blow off valve? Or more of a pop-off-valve(just bleeds off excess pressure).

If it is a true blow off valve, then with the throttle closed there will be high vacumm(15-19 inHg) and that should cause the valve to open by pulling up on the valve(pressure on top of the valve is lower than on the bottom so it moves up). If it were opening because of high boost pressure build-up in the M90 discharge pipe then that would mean the pressure in the discharge pipe would have to be higher than that in the manifold so it would be pushing the valve open from the bottom(M90 pressure greater than manifold pressure). Maybe the latter is what you're saying is happening at a no load condition...M90 makes boost based on RPM and if the engine doesn't need it/can't ingest it, then that could cause a larger build-up in boost but I would think this pressure would also be present in the manifold so the pressures across the valve would be equal?

Here's a crazy idea: if you're wanting the blow-off-valve to bleed off pressure to keep things from over-pressurizing then you could possibly get a HOBBs switch, set it for the threashold of when you want the blow-off-valve(BOV) to crack and releave pressure and have that switch powering a solenoid valve that is connected to the vac line on the BOV. Get a solenoid valve that will vent to atmosphere when activated but be connected to the manifold when the solenoid is off. This way it will sure to open with that threashold is reached but then it should stay closed below that threashold when under load and you don't want it under load because then the two pressures will be equal. Actually I don't think this would work...lol. Or if it would you would need to adjust the spring in the BOV until it works like you want.

If this actually is a BOV then I still don't think it's working right....with the engine at idle and the throttle totally closed it should be wide open. Do you have a boost gauge hooked up? What does it show at idle?
I think all you really want is a pop-off-valve. It will just open up when it sees a certain pressure behind it and will vent the excess pressure and won't open otherwise. These would be slower to respond than a BOV but we're not talking about protecting a delicate centrifugal compressor blade anymore from pressure spikes...you've got that nice roots blower.

Ok...I've babbled on enough...

[ForcedFirebird]

Lol, Wayne, you just said what I did, only the long version

[ssdurango]

Well I don't know where to begin to answer all of that! lol First off, thanks for the input and second, what you are both forgeting is that if I really had boost in my manifold while the truck was in neutral the engine would over-speed into oblivion!

I'm using the ford bypass valve that is on the inlet of the S/C. But it's only a 1.25" diameter valve. As you can see in one of my videos, lightly reving the engine caused the hose to blows off in my face.

Then I ADDED a TurboXS type H BOV.

I don't want a pop off valve - any pressure building in the boost pipes during idle or cruise will be a drag on the engine and will heat up the intercooler. (blowers make more heat then turbos, in general)


What's a HOBBS switch? I Think I understand what you are proposing. Funny thing is though, It sounds like a complicated way of selecting the right BOV spring tension...

[TurboProject]

A HOBBS switch is just a simple mechanical switch that is adjustable for the pressure at which is closes a set of electrical contacts. I thought I had a picture of one somewhere but I guess I don't. I used to have one on my car for a simple electronic boost control. The switch sensed manifold pressure and was connected to a solenoid valve which was on the turbo wastegate line. When the max boost pressure was reached it would open the solenoid valve and allow the wastegate to open.

[ssdurango]

Here's a video of the first test drive this year, This is opening the throttle about 1/4 of the way:

http://www.youtube.com/watch?v=bsmUvdgol_k

The first time I lightly blipped the throttle the truck started fishtailing for the trees! I quickly stuffed in the clutch but the engine stayed revved right out. ( Good thing i've got a rev limiter ) The boost was blowing the throttle plate open. I put 2 helper springs on to pull the throttle closed and that's now fixed. It was quite the exciting and kinda scary day.

[3400-95-Modified]

So wait, before you blew you intake off, and now the pressure is holding open the butterfly???

That's odd....

[ForcedFirebird]

So wait, before you blew you intake off, and now the pressure is holding open the butterfly???

That's odd....

Remember he's using propane TB.

[3400-95-Modified]

Yeah but it snapped closed enough last time to blow off the pipe, and now its holding it open... thats whats weird, even with the BOV, which I still think is not working properly.

[ssdurango]

When I reved it by hand before I could feel it the spring getting overpowered slighly. I didn't think much of it at the time. It's kinda cool because even with the helper springs it feels like the truck is trying pull away from me all the time. It's like riding a wild horse!