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I have followed Dean and Jeff’s MBC anticipator project (ref drs<underscore>anticipator) very closely, and decided to try a variation of their idea.
A quick re-cap is that one problem with an MBC is that when setting it to the upper limit, pressure spikes can cause fuel cuts. Dean’s idea was to install an air pressure regulator in parallel with the MBC to pre-load the waste gate, thus allowing the MBC to open the waste gate faster.
I wondered if it might not be more effective to mount an air pressure regulator at the MAP sensor to bleed off any pressure spikes. As the picture shows, I installed a “T” fitting at the MAP sensor, and tapped in an air pressure regulator. One quick note here. There are two styles of air pressure regulators. One limits the air pressure on the exhaust port, and the other limits the air pressure on the intake port. My regulator limits the pressure on the intake side. When the preset pressure is reached it bleeds any excess out the exhaust port.
My theory is that the MBC should be set to open at a slightly lower pressure than the air pressure regulator is set at. In this scenario, the MBC will start to open the waste gate, but if manifold pressure is rising faster than the waste gate can open, the APR will bleed any excess off, thereby eliminating fuel cuts.
The steps I used to set the MBC and APR were:
1)Before installing the APR I set the MBC so that I could get fuel cuts on a regular basis. Not all the time, but frequently. The idea here was to set the MBC “on the edge”
2)I installed the APR with a pre-set to about 10 PSI
3)Did a test run, and could not get much boost (as expected)
4)Continued test runs, each time adjusting the APR to a higher pressure. As expected I continued to get more boost.
5)I stopped adjusting the APR when I could consistently run the boost gage to ½ way in the red.
I’ve only run last night and this morning, but I am happy with the results, no fuel cuts, but high boost.
Now a couple of comments and questions,
-I suspect that the APR I have is expensive (it just happened to be in a pile of junk in my garage), but I am guessing that a second MBC could be used instead.
-I am concerned that if the relationship between the MBC and the APR is not correct, the waste gate will never open, causing the turbo to run hotter and longer than normal. I’m not too worried about this, as it’s not really possible to stay at full boost for very long J Comments anyone ??
-I generally only getting boost ½ way into the red in 3rd and 4th gear (not 1 & 2). I suspect this is because of the pressure loss across the intercooler. However, with this setup I would guess that I can move the MBC upstream of the intercooler, as the APR will take care of pressure spikes.
As always, any comments are welcome.
-Steve
posted by 67.98....
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