booger....how did you're angine blow with the Vortec Kit?

 

Superchargers are not load based I thought .... HP should build in a perfectly Linerar manner if the rpm's go up so does the boost??

 

9.5lb's of boost and only pulling 5 degree's of timing . Broke a ringland....#5 piston . Vortech pulls like 10 dergee's after 6000rpm . So its safe if you dont mess with it

 

Load shouldn't drop off as you accelerate. It should increase as long as you keep the pedal on. Load affects boost indirectly by requiring more gas to maintain speed. More gas = more boost because throttle plate opens wider. HP doesn't increase exactly linearly however. Just look at a dyno graph--it's a curve.

My original question related to 1/2 throttle--why boost initially goes up and then drops back down even though load increases with speed and the pedal is kept steady. As engine RPMs increase, engine-induced vacuum increases AND blower speed and boost going into the piping leading to the throttle body increases. It must be, if there's no leak in the system, that the engine vacuum is increasing faster than boost because the increased boost pressure from the blower is partially blocked by the half open throttle plate (which conversely increases the plenum vacuum). So, at some point boost drops off and actually turns negative thus opening the BOV and abruptly increasing vacuum even faster. At WOT, this doesn't happen because there's no restriction to the boost pressure entering the plenum--so boost keeps on coming. The fine balance between increasing blower output (with increasing RPM) versus increasing engine air consumption is slanted towards boost with WOT and vacuum with some point less than WOT.

 

My understanding of how the Vortech S/C operates. The VORTECH performance is MAF signal engine load based .The MAF signal (modified by the ss box) determines when the FMU and fuel pump turn on. When the vortech fuel pump comes on the engine rpm rises and the S/C pulley(s) rotate faster (compressing the air) putting out a denser slug (BOOST) of air fed into the intake. During the transition engine manifold vacuum decreases going from negative mm hg to psi. As long as the MAF signal is above a certain level the blower will make boost.

 

When cruising the vacuum keeps the BOV open . When you give it gas the vacuum goes down and the BOV closes and starts to build boost . Then as rpm's rise the boost will rise with rpm's . As soon as you let off the gas , the throttle plate closes and vacuum is back at the plenum and the BOV opens again releasing the boost built up on the other side of the throttle plate. The SS box controls the Aux fuel pump and is set to turn on at a set rpm and or boost level . The FMU raises the fuel preasure at a rate of 8 to 1 ...8lb's of fuel preasure for every 1lb of boost
Bill

 

Where I disagree with the above description is "the Aux fuel pump and is set to turn on at a set rpm and or boost level".. What comes first chicken or the egg? Only kidding. If the fuel pump comes on at a certain rpm level then it would always come on whenever it reached that level which is not the case. As far as coming on at boost, boost cannot occur unless the Aux fuel pump comes on.. I believe the trigger that starts the S/C to doing it's thing is the MAF signal which is an indication of engine load...MAF signal (voltage )is modified (increased) by the ss and sent to the ECU. ECU thinks it's a good MAF input and commands the injectors to provide more fuel.. Boost goes up RPM goes up and ss then controls to the fuel and timing maps stored in the ss software..

 

In the R4 software ..you can set the aux. pump to come on any time you want and at any boost level , or both . Your BOV is ran off of vacuum . Adjust it and find out . You can screw down the bolt on top to have it close under more vacuum or unscrew it to have it close at less or [ 0 ] vacuum . The SC it self is ran off a belt and will turn faster and push more air the faster it goes...no matter what . It all depends if the BOV is closed or open if it going to build boost or not

 

That's right. Boost is simply positive plenum pressure and it's a function of the difference between engine demand for air (vacuum) and blower supply of air through the throttle plate. The blower is "always on". When the BOV closes at 4" or less of vacuum, all the blower's pressure hits the thottle body and into the plenum. Greater than 4'" and the blower's pressure is shunted out, to some degree, through the BOV port to the outside world. When the BOV is closed, there's a shifting balance between engine-induced vacuum and blower-induced pressure that has nothing at all to do with the aux fuel pump. You can think of the aux fuel pump as maitaining the proper AFR but it doesn't change boost.

The dicey part comes with a half-open throttle. At some point, the partial blockage of the throttle plate reduces the full effect of the blower into the plenum but increases the vacuum effect of the engine on the plenum and the pressure/vacuum equation shifts towards engine vacuum as the RPMs go up. So, boost goes up initially but then drops back down at a steady 1/2 throttle as vacuum overcomes boost. It's only at or near WOT that the blower can continue to overcome increasing engine air consumption and lead to ever-increasing boost--up to the max of 8 lbs determined solely by redline and the size of the blower drive pulley.

Load comes into this because as load increases, the pedal is pushed down more to maintain acceleration. This opens the throttle plate and allows the P/V balance to shift towards boost. The aux fuel pump is the passive party--responding to the shifts in pressure/vacuum but not creating them.

Another way to think of all this is that boost is the equivalent of force feeding the engine. To force feed, you have to provide more air and fuel than the engine is consuming. To do this in a sustained, not just transient fashion, you've got to have WOT or something close to it.

 

GLAD you came up with it...I got tired of typing

 

Re-read my message because I edited it a bit after you responded.

Thanks!

 

This thread has left me with a confused undrestanding of how the S/C works. So how do you get unconfused , you call the folks that make the S/C as well as Split Second Co. since the Vortech guy didn't know how the SS worked.

And here is what I found out. The SS guy explained that the SS vacuum line senses manifold press and performs the following function within the box. Manifold press vs RPM look up table (approx 950 cells) determines a calibration value that is applied to the stock MAF sensor signal that is then sent to the ECU. This modified MAF signal along with other engine parameters i.e RPM, inlet temp. etc, establishes the injector pulse width to correspond with the pseudo engine load. Additionally the FMU/Aux Fuel pump is commanded on by the SS box to meet the load.The SS software maps are overlays to the stock ECU map's.

The BOV is the mechanical equivalent to a diode. It has no direct function in boost but you can't boost without it closing..

 

Great job!

 

I 2nd that! We have all become a lot smarter.

 

Just for completeness, the BOV doesn't exactly function like a diode which is strictly an on-off device. A BOV is a totally on-slightly on device. That is, when under vacuum and hence with a BOV shunting to the outside, there's still pressure going past the BOV. The BOV doesn't eliminate the blower entirely from the intake system. That's why a blown car feels way more responsive even under vacuum. The Vortech guys describe this as having a "more efficient" intake system with cooler and denser air via the combo of blower and intercooler even when the BOV is open.

 

Yes I realized that driving home last night that the BOV has several states where a diode properly biased is on or off. Often wondered why the car was so much faster when off boost. Appreciate the respopnse..One other thing I've read where people either like or dislike the BOV sound. Some resort to putting a filter. I hear nothing from mine..What does no sound indicate? Should it make a sound when venting?

 

The BOV should be heard during most vacuum states--a high-pitched whistle or a blowing sound. Venting, it makes a sudden whoosh that you may not hear very well inside your car with the windows up.
I'm certain your's is working normally but may be drowned out by your modded exhaust.

 

Now that you mentioned it I hear a sound (hard to describe) under boost. Sounds like whip, whip, whip,.. Could it be the BOV is venting when it shouldn't. I am able to get about 6 psi boost on the gauge..which frankly is fine with me from a engine reliability standpoint..and the car is as fast as I want it to be..But if the BOV needs to be adjusted how do you know when it's properly adjusted.. Vortech folks saw no problem with it being silent..

 

Under boost the BOV should be silent and you can immediate notice boost by this absence of whistle/blowing noise. Most folks adjust their Vortech BOV to have around 6 threads showing above the jamb nut. I'd be worried that someone adjusted your's too tight and you're getting surge--bad! Get your car up on ramps or jack stands. Pull off the splash shield. Have a friend rev it a few times up to around 4 in. of vac. You should feel the pressure coming out of the BOV port stop around there. If it stops at higher vac (7 or higher) the adjuster should be backed out. If it leaks pressure below 2 in. vacuum, you've got a bad BOV (like I did). Also, check all the piping joints for air tightness. A leak anywhere in the intake system will act like a leaky BOV.

 

jpc350z..... That sound your hearing.....Is it while you are boosting ....or is it when you first let off the gas ?
I would say..If its while you are boosting , you have a leak some where . If its when you let off the gas from from a boosted run ....I would say its compresor surge . And you need to adjust it . Since your only making 6lb's ...I would say you may have a leak