hp18racer

For those of you with data logging capability for your manifold pressure using a black **** MBC, I am curious how much variation you see in boost pressure?

Here's a snippet of data from my datalogs during a tune and test track session:

rpm manifold pressure (psig)
5021 16.5425306028
5106 17.2569820734
5188 17.4356674595
5290 19.9365376806
5324 13.8629749956
5428 14.5774264663
5524 16.0066194813
5608 17.6142078088
5664 16.721070952
5733 17.7928931949
5826 18.8647154377
5909 14.220200731
5968 21.0083599234
6045 18.8647154377
6117 14.220200731
6174 15.1133375877
6254 14.7561118524
6319 17.6142078088
6393 21.0083599234
6424 16.5425306028

I did not feel any surge, the boost gauge was steady at about 17psi. I have pressure tested the intake system starting at turbo in and found no leaks in a static test. Waste gate operates smoothly when removed from the car and tested using the black **** still in the car and regulated compressed air as a control signal.

eman930

what type of wastegate do you have

Ben951S

I'd say the logging is more suspect (maybe some interference, or sampling rate issue, who knows). You'd feel a 21PSI spike, or see twitches in your gauges. Go ahead and set 21psi and see if you notice the difference!

eman930

I agree, Youd def notice those spikes, Whats your A/f showing at the same RPM's, Or somthing is wrong with your wastgate not sealing off, Also check you hook ups and grounds

MM951

In my experience flucations in boost at WOT have had to do with pre turbo exhaust leaks..

Tom M'Guinn

What are you logging with (sensor and logger)? I'd start by confirming the log reading as others have suggested -- did the boost really climb 7psi in the course of climbing 59 rpms?

5909 14.220200731
5968 21.0083599234

I've never used a black **** but if the boost is boucing that much, you'd surely see it in other parts of the log (AFR, MAF, seat-o-pants, etc.)...

hp18racer

The data is from Chris White's techgt engine management system. I am not sure of the details of the particular map sensor.
The waste gate is a 38mm Tial. It is a Vitesse Stage 3 turbo. The car has a giant aftermarket intercooler.
AFR's are steady at just under 12:1 on boost. Injector duty cycle tracks the boost spikes.
I certainly couldn't feel a boost surge, my but says it isn't real.
If it is real it would have to be higher frequency than the samples from the data log.
When I apply regulated pressure to the MAP sensor the readings displayed by the techgt are stable.
The MAP measurements logged by the tecght off boost are steady which makes me inclined to think the problem is not electrical noise.
I have turned the boost up, makes more boost but not more power.
The behavior has been the same for two different motors that seem to be operating nominally (good compression).
I have not found any exhaust leaks pre turbo. I looked inside the crossover with a borescope to make sure it wasn't collapsed. I have had headers and crossover pipes break before so I am familiar with the symptoms. Also inspected all the blades on the turbo, all looks to be normal.
To date I can't seem to get more than about 280hp (per traqmate) out of the setup.

I am trying to figure out a good set of tests to run so I don't rely on guesswork and parts swapping to figure out why the boost is erratic and the power low.

I am putting in new intercooler pipes that will include a bung for a temperature sensor just downstream of the turbo. I am thinking I will hook up a boost gauge at turbo out and another that reads crossover pressure.

First test will be use a timing light and make sure I am measuring the same spark advance commanded by the techgt.

I'd like to see if the pressure drop or turbo out temperatures are reasonable, if the backpressure is reasonable.

I am thinking I could just run the gate on the spring (no black ****) to rule out a problem with the MBC making the boost erratic.

I am considering putting a factory gate back in temporarily to rule out a problem with the Tial gate.

eman930

Im assuming you dont have a cat on this setup right?

hp18racer

No Cat, No Muffler, 3" pipe.

eman930

Hmm this is weird.... Like noted youd feel a 21psi spike, and its really weird that in 61 rpm you go from 14psi to 21psi... I dont even think thats possable.... Id try swapping your wastegate first. Its also weird that with a stage 3 your not getting into the 300hp+ range

Thom

Are you logging with your laptop or with the ECU's internal datalogger?

Where is the MAP sensor located and which vacuum line feeds it?

hp18racer

The log is with the ECU's internal logger.
The MAP sensor is located where the HVAC blower normally sits. The pressure tap is a line with no T's to other systems off one of the factory fittings from the manifold b/t runners for cylinders 3 & 4.

Paulyy

normal i'd say.
Heres a graph, EBC vs MBC with Dualport waste gate.
Red: EBC
Blue MBC:

I couldn't feel the spikes either. so i think it's interference

Thom

I would try logging with the laptop at different logging rates. If you can find a logging rate low enough to hide this phenomenon then try afterwards another level of peak boost to check if you get consistent results.

Adker

Mine changes a couple of pounds at most.