Ok, I'm embarrassed to ask this since I have a supercharger and should presumably know the answer...

My supercharger increases boost as a function of RPMs, obviously. But am I right in assuming that the boost only persists if the throttle is kept wide open? In other words, if I mash the pedal to the floor until I reach 5000 rpms but then lift off the pedal just enough to keep the rpms at 5000 does the level of boost stay constant while keep the car at 5000 rpms?

I just installed a boost gauge and based on the gauge boost only builds and/or holds during WOT. I don't have a boost leak do I?

I have made no changes to the car since my most recent dyno which showed boost readings that I expected (i.e. increasing as a function of RPMs up to between 7 and 8 psi)--but of course the dyno was done at WOT.

--Steve

 

You are correct about the boost dropping after letting off the gas. At that point the motor should drop into a vaccum state. That means your bypass valve is working properly.
Mike

 

My assumption would be that since you have effectively almost closed the throttle body blade with your throttle, much less air is rushing past the air valve (blow off valve) and it is releasing some of the boost. That is what is supposed to happen right?

edit: too fast, mprowe350. Too fast.

 

I concur with all of the above findings and have a boost guage.

It doesn't matter if I am WOT at 100 mph when I release the peddle negative number on the guage like 15-20 below 0 boost on my guage.

So what PSI did you make at 5k? Inquiring minds want to know?

I have had to do runs with a second person to dial in my boost because I am going too fast to watch all my guages, the rpm and the road. So I invite a friend over to ride with me.

Last time we hit 10 pounds neither one of us recall much about the guages etc we were pinned to the seat .

After I stopped I said, "well what did it do?"

He said "I'm not sure what rpm were you at?"

I said, " not sure but we were flying."

LOL!

Luckily it did trigger the EGT warning and he caught that and it was recorded in memory thus the reduction to 9 lbs. Have Fun!

 

OK, so you guys are only seeing boost at WOT??? At partial throttle, what does the boost gauge show??

 

Some partial amount of boost at the given RPM compared to what it would be at full throttle.

 

My guage goes negative of zero, the default is 15 but it raises slowly upwards towards zero.

I have done this so often I can raise up to just before boost and stay at dead zero, hehe, not the best way to drive your car though.

It will fluctuate between -20 and 0 as MPH said. I can make boost while not at WOT though, it's not like N20, I can make boost on 3/4 throttle depends on how I drive really. ATI says not to "feather" I think this type of driving is what they may mean by that?

 

Ok, sounds like I might not be crazy then.

To recap... If I'm accelerating--even not WOT--I see some amount of boost. The boost is much greater, obviously, if I'm at WOT. Next time I dyno I'll scan a boost-per-RPM plot.

As soon as acceleration becomes negative (i.e. I'm no longer speeding up--just maintaining RPMs--but still going fast) boost begins to drop until it gets back to vacuum state.

It's my understanding that in an unboosted, non-WOT state, the car should show a vacuum of around 15 psi (i.e. minus 15 psi on the gauge).

--Steve

 

Zimbo your car sounds perfect and is acting exactly as mine is. The common denonimator between our cars is the lack of the Aeromotive DFMU which might act differently. In fact it did on my car, kicked in boost at 4k rpm's never under that. I have made between 2-5 lbs of boost at 3200 rpm's and zero or negative at 3200 rpm's depending on how I got to that rpm.

Your car is acting perfectly and sounds like you did real good. Congrats. Nice to have that guage eh? Strangely enough it's often the last guage purchased!

 

Totally.. after installing fuel pressure/boost/EGT greddy gauges I learned even more about my supercharger and how it works... amazing stuff


max - you gotta get a greddy boost w/ memory for those max boosts! I love it on mine... I drive it like hell and hit that button and I can see what the highest boost i hit..