How much boost am I making? (Log Screenshot inside)

[pittzy23]

using air load and atmospheric pressure, as a guestimate, ~11 psi.

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[raptor17GT]

This is correct. The cool intake air is probably the wrong sensor since MCT and IAT are the same number. If HPTuners is up to date and this is the Whipple tune, then the proper sensor to log is IAT2. The latest versions of HPTuners stopped using MCT for some reason... at least in my case (gen2 2.9L with Whipple tune).

raptor17GT, MAP is not an actual sensor, it is inferred from MAF and the speed density tables. Looking at any inferred or calculated value could be completely wrong depending on how detailed the tuner was with adjusting tables. Even air load could be rescaled. On my Whipple tune, barometric pressure is set to a static value since the car doesn't have a sensor. So even the baro is wrong.

The logged MAF value in this case is hitting the maximum limit for the PID being used, so it is not even the right airflow, but the ECU uses the right airflow internally for its calculations.

Ah right MAP is inferred not measured. Appreciate the explanation

 

[Angrey]

so the stock kit was advertised as 10-11 psi (stock headers, 3.75 pulley)... I've gone down 2 pulley sizes to 3.5 + LTs. I feel like I am missing something

This is a difficult concept for some enthusiasts to understand. On a pulley size (say 3.75") on a stock motor, it makes say 11 psi. If you improve the intake side flow and the exhaust side flow, now the engine breaths easier and flows better so the blower has a more difficult time building pressure. You INCREASE power and yet the boost level can go down slightly. (even though you're making less pressure, you're flowing more volume and so the result is more air, which converted at stoich means more power).

There's so many variables involved that it's usually folly to compare cars using boost levels. How high the car rev limit is (particularly with a centrifugal which climbs exponentially with rpm), how many flow improvements on each side of the combustion chamber, what altitude/DA, (there's no SAE correction factor to apply to boost when you're at elevation).

The only real time boost for boost is generally apples/apples is when a turbo is wasting exhaust out of a wastegate (set to a desired boost pressure).

This is particularly applicable to certain commercial equipment (like construction equipment) that can create boost at sea level or at elevation (because at sea level it's wasting exhaust to prevent it from making too much). Therefore you get the work/output of the vehicle the same at sea level as you do at say 6,000 feet.

 

[Grimreaper]

I saw no change in boost on an 85mm pulley roush tvs when the cats were removed. Logged external map sensor.

Exhaust was 3 inch from stock connection back. Then went to full 3 inch from stock headers back. So piping and cat removal in the mid section which should have been a good chunk of reduction.

Murfie posted a spreadsheet that takes ait into account for airload to boost on here a while back if you search. Few good threads on the topic too.

I'm crossing into positive boost right around 0.7 to 0.8 airload. The tune thinks so and external sensor confirms it's all within a few Kpa. Kind of crazy how accurate roush SD is when logging against external sensor.

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