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, Thu, 31 Oct 2002 10:47:29
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The MBC will improve the peak boost, and will increase the peak torque proportionately. The actual values will be affected by air temperature, amount of heat soak in the IC, external fans, grill out? and how the operator ran the vehicle on the rollers. And the results vary by air filter, air box mods, turbo compressor dishcharge silencer removed, stock or viggen IC, amount and quality of TBTC rework, and exhaust system mods.
Depending on what the MBC is set to, and where it gets its pressure from, the torque curve will stay steady up to the 5K rpm range, or will taper well before that. MBCs that get pressure from the compressor housing hose barb will suffer from severe boost taper.
So one sample of a MBC dyno run is only one of many results.
I had a dyno run in April 2001, a hot day, with the MBC tapped into the center of the stock IC's integral return pipe. The boost taper was improved, but still pronounced. I did get wheel HP that was equal to or better than some modified C900's. Today I have a Viggen IC and the MBC gets pressure from the TB, so it would hold torque well into the RPM's and would have a much better HP measurement. I had and still have the funnel mod.
Dyno's will always provide results for turbo vehicles which underestimate the power and torque on the road. When you are in 3rd or 4th gear on a dyno, doing 5500 RPM, the IC is seeing a lot of heat. On the road you would be moving very fast and the IC would be getting a very strong cross flow of air to cool it. Relative to that, the IC on a dyno is seeing almost no cross flow air. So on a dyno the intake air temps are way to high. So the charge air is less dense and the torque goes down. A T7 would not have so much of a problem with this, but you would not be using a MBC on it for more boost either.
Note as well that a MBC makes the turbo spool up much faster and provides strong boost in gears 1&2. This makes the vehicle much faster! Note that things happen fast on the street and slow on a dyno. A dyno will be mostly blind to boost lag. A vehicle with a large turbo could have lots of lag and have great HP readings on a dyno. But such a setup could be a dog on the street. Power is great, but not if you have to wait for it.
posted by 207.43.195...
, Thu, 31 Oct 2002 10:47:29
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