I have searched the forums and have not found a solid answer, some people say with a MBC they hold boost to redline and others say tapering down is normal, I have a Buschur MBC and is set to 19.5psi, even in higher gears the boost goes to 19.5psi to 4krpm then tapers down to 17psi to redline, I have checked and tightened all the intercooler and stock bov clamps but still it is the same boost levels, could an aftermarket bov solve this if my stock bov is leaking at higher rpm's? I would like to do at least 19psi to redline, and if it is leaking why does it hold boost at lower rpm's, also my hoses from the boost solinoid is removed and caped.

I have k&n panel filter, ur turboback with highflow cat, dynoflash, mbc set at 19.5

 

that drop off is perfectly normal, my car does it too, its called "boost spike", yor not leaking

 

why are some people holding boost to redline? I do have a MBC and I thought the purpose of a MBC is to hold boost.

 

I don't believe it's the bov leaking, just like Renagade said, its more like a boost spike. I changed the bov to an APS unit and boost still tapered down, even with a Turbo XS HPMBC installed. When I changed from the Turbo XS unit to the Blitz SBC ID, now it holds steady to redline, and no spikes!

 

is there anyone with the Buscher MBC that hold steady boost?

 

crank bc to 21/22. it will taper to 19/20

 

I cranked it to 20.5 peak and what a diffrence now it goes to 18, do you think if I crank it to 21.5 then it tapers to 19 will it be safe at 21.5 at low rpms?

 

From what he describes it is not boost spike. Boost spike is a very short lived thing. It happens at or near WOT. As the compressed air surges through the lines it takes a short time for the pressure to get from the point it's tapped into to the wasegate. This spike typically lasts about one second.

What I think he's talking about is boost reaching the set point and holding that set point until the RPM's get into the upper portion of the powerband.

A leak could cause that. The way you have your MBC hooked up can also cause it. The amount of boost you are trying to push could also cause it, but I rather doubt this last one with a stock Evo if you haven’t blown up your engine.

Where did you tap your MBC into?

 

I taped it from the line between the bov and manifold. also in higher gears it holds 20psi until 4k rpm then drops again to 17-18psi.

 

Parden the newbie obvious question, but you disconnected/bypassed the solenoid, I assume?

 

I have a Hallman Evolution MBC and mine tapers as well. It stays solid at 20psi until around 5k RPMs. I am trying to get a video of my boost gauge in all gears.

 

Mine seemed to hold fine at 19psi (it would spike at 21 at times) untill I got rid of the test pipe and race muffler for a hi-flow and Magnaflow (all Buschur parts) Now it does the same as the above mentioned. I spike at about 21/22 psi and drop off to about 17 psi at 7K rpm

 

Problem solved, it seems like if you set the boost lower it tapers more, I took my car to an AWD dyno and ran the car, according to the dyno I was running 17psi tapering to 15psi but my gauge would show 19.5psi and drop to 17psi, when we crancked the boost up to 21.5psi according to my boost gauge it only droped to 20.5psi and holds almost all the way, according to the dyno I am at 19.5psi and drops to 18.5 at 6k rpm, so my boost gauge is not accurate and when I set at at low 17psi it drops at lower rpm to 15psi but when I set it to 19.5psi it only drops 18.5 at very high rpm, and my air/fuel was 10.7/1

hope this helps some of you.

oh and the car is pulling like a crazy ape on speed

 

What boost gauge are you running?

 

autometer gauge, also my friends 01 porsche 996tt with factory electronic boost gauge was showing about 1-1.5 psi wrong.