I concur 100%

I like the E BOOST 2 and TXs DTEC also

The problem of course is that one you reach a point of dimishing returns forcing more boost will actaullt start to reduce the top end power

As the compressor is forced out of its efficency range it makes more and more of the hair dryer effect

Also - closing the wastgate at some point limits exhuast flow through the turbine and creates excessive back pressure

 

I have the stock turbo VIII - Buschur stage III with Buschur's manual boost controller - tuned by Al. Car hits 23 psi till 7k and tapers to 21 psi at 7800 (still running rich). 15 psi sounds low, even with restrictive exhaust. I don't think the cat back does a whole lot for you, except maybe save some weight...you still have the restrictions before the cat back. Sounds to me like your MBC isn't plumbed correctly, or is faulty. Have you checked those lines for leaks? Pressure check that system and let us know what you find.

 

There is no hope for you

 

FYI - from my experince the MIVEC actuation is what is aggeivating the boost taper with MBC's on IX's

With proper MIVEC and IGN timing the car can make a very good power band and plenty of power with the MBC taper you are seeing

 

Lines aren't leaky, will pressure test to 30psi to verify.
When I say dump back, I mean what most people call a turbo back, but the stock O2 is still there, as is a high flow catalyst. Its an Australlian made exhuast, a TaipanXP.



Thanks for the advice! Mivec is very new to me. I understand the idea of advancing in the midrange and retarding a bit up top, as I ran cam gears before. Sucks those were static, but the beauty of the IX is that the intake is almost infinitely variable, within reason of course.

Even though the power is a little low, the powerband is nice and fat compared to my VIII when it had the TME.

 

There are 2 ways to reduce the tapering on a MBC:

1 - drill out the little hole on the MBC wastegate nipple.....

2 - "T" in one of these TurboXS Aux Boost Controller to the WG line - basically a adjustable bleed valve. I used it on my VIII and was able to reduce the tapering effect seen in the hallman

 

the spring and ball valve in the MBC controls/limits the peak boost and the TXS ABC controls the slope of the taper - more bleed off, less taper

 

The backpressure that is causing the problem is cause by backpressure in the turbine housing. Unless you go to a larger higher flowing turbine housing and wheel, the backpressure will not be reduced enough to make a difference. Any backpressure changes after the turbine housing helps some, but has a very small effect in lessening the taper. The turbine housing backpressure before the turbine wheel is MUCH higher than after the turbine wheel. Hince the problem. The additional turbine housing backpressure causes the wastegate to crack open slightly IF you keep the same signal pressure going to the wastegate actuator. By reducing the signal to the actuator as the RPMs and (resulting tubine housing backpressure) climb, you can help this problem dramatically. This is how we were able to hold 27 psi solid on a WR-9 Turbo (read NO TAPER AT ALL).

Brian

 

The only way a MBC will work like this is if you can vary the bleed hole size as RPM's and backpressure increase. Nobody makes on like that. But if you did, then it wouldnt be a MBC anymore it would be an EBC.

 

Thanks Brian. Too many miles with a GT30 with nonexistant taper (on pump gas). Time to start saving those pennies! Who wants dibs on my Forge UNOS for really cheap?

 

Can you please post a boost plot?

I saw a thread started by Al, awhile back comparing a MBC and AVC-R - but the thread vanished....

 

I'd really like to see this too.

 

It was my thread that got deleted, because I was not a vendor. I was selling installation services and setup of an HKS EVC 6 to eliminate boost taper. I wrote a 6 page manual that explains how to set it up to eliminate taper along with telephone support.

I had some videos on the thread that showed on car holding 23 psi solid from 3500 RPM to 8700 RPM, with no taper at all. The only way to do this is with an RPM correcting boost controller, or a closed loop boost controller (expensive).

I never got the video of the one guys car running 27 psi solid up to 7700 RPM with his WR-9 Turbo. That car on a 40 degree night hit 45.5 lbs/min on a WR-9 (20G-9-5 with TME internals). We were setting up a pressure sensor to the Logworks, but are having trouble getting the sensor setup to read in Logworks. If we ever get that fixed. I can show the datalog of the pull. This is the maximum boost that we can hold at 7700 RPM with that combo. So we dialed the boost controller down to hit 27 psi and setup the unit to hold that to 7700 RPM.

We can turn the RPM correction off and it will spike 33 psi and hold 27 psi. Or we can turn the RPM boost correction on and turn the boost down and it will hold the 27 psi solid. It is a really neat setup.

I sold one setup manual to a guy out in CA. He said it worked great for him. Evo Ippo was his screen name, I believe and have setup 3 units including my own out in NC.

Brian

 

That's really sweet. With XEDE boost control, there was a load based map on one axis and an RPM based map on the other axis. The percentage input is variable from 0%-100%, and identifies BCS or boost/wg duty cycle, set up operator intuitively so higher number = higher boost and lower number = less boost.

The typical shape of the map curve involved lower numbers where the turbo was efficient and substantially higher numbers as the RPM increased.

My low end torque is right where it should be, my knock counts are pretty much nonexistant (except the rev limiter of course), but the top end power is soft due to violent boost taper.

In XEDE world, some VIIIs just wouldn't hold boost as well as others, and we'd put a bleeder tube in the line, so we could lower the numbers during low rpm, but still have more headroom for higher RPM.

Another issue I'm having is just acclimating to a 16G car all over again. Even if it was a ***** to the wall tune on race gas, it would still be making a lot less power from 5500rpm to the rev limiter than the GT30. Revving fourth gear is where this is the absolute worst, because the car just feels so darn slow as drag becomes more prevalent.

Drivability is so much better on this turbo with the shorter fifth and Mivec, it almost feels like an STi. Boosting and passing in top gear from 60mph is absolutely effortless. I'd like a crack at the old GT30 with Mivec, but I want to keep this one more stock. Maybe one of those Buschur/FP green variant turbo upgrades on stock cams later on. We'll see.