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Cantlin01 said:
Is the 78mm to much air for my 01 gt? I don't want it to bog down the horse power in m car
American muscle says anything over 70mm you lose some power (Dyno proven) , as far as bogging down I'm pretty sure you wouldn't bog down. But I would go with a 70mm since they recommend it and they say that size produces the most power.
 

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Is the 78mm to much air for my 01 gt? I don't want it to bog down the horse power in m car
Anything over 70MM is just to much air. Your Mass Air Flow can only adjust for so much so anything after that measurement wont be accounted for. You can run that big if you're running a supercharger, turbo or nitrous set up but for NA cars a throttle body that big can't be used to its full potential!

I hope this helps, let me know if you have any questions!

-Dan
 

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I agree that 70 mm is as big as a TB for the 2V needs to be, however it has nothing to do with the MAF's inability to measure the airflow.

Any engine running n/a can only ingest as much air as its displacement and volumetric efficiency allow. At an unattainable (running n/a) 100% VE and 6500 rpm that would be 528 cfm, or 2375 lb/h at STP¹--comfortably below the stock MAFs 2650 lb/m maximum. At a more realistic, yet still high for the 2V, 85% VE the most it could digest would be 2020 lb/h, well below the MAF's capacity.

The problem is, and why larger than 70 mm TBs can hurt performance, is to be found in the charge velocity; the speed of the air flowing into the plenum. At a point as the TB gets larger, when running at WOT, the charge velocity will fall to a level at which air flow into the cylinder is reduced--this causes reduced power at WOT and higher RPMs. Also reduced is the effect one intake pulse's mass has on pulling along the one behind it.

Chapter 7.6 of John Heywood's Internal Combustion Fundamentals explains this in great detail. It has nothing to do with the MAF's capacity.

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¹ - STP = Standard Temperature and Pressure. 0.0°C and 1 atmosphere, 32.0°F and 14.7 psia.
 

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cliffyk said:
I agree that 70 mm is as big as a TB for the 2V needs to be, however it has nothing to do with the MAF's inability to measure the airflow.

Any engine running n/a can only ingest as much air as its displacement and volumetric efficiency allow. At an unattainable (running n/a) 100% VE and 6500 rpm that would be 528 cfm, or 2375 lb/h at STP¹--comfortably below the stack MAFs 2650 lb/m maximum. At a more realistic, yet still high for the 2V, 85% VE the most it could digest would be 2020 lb/h, well below the MAF's capacity.

The problem is, and why larger than 70 mm TBs can hurt performance, is to be found in the charge velocity; the speed of the air flowing into the plenum. At a point as the TB gets larger, when running at WOT, the charge velocity will fall to a level at which air flow into the cylinder is reduced--this causes reduced power at WOT and higher RPMs. Also reduced is the effect one intake pulse's mass has on pulling along the one behind it.

Chapter 7.6 of John Heywood's Internal Combustion Fundamentals explains this in great detail. It has nothing to do with the MAF's capacity.

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¹ - STP = Standard Temperature and Pressure. 0.0°C and 1 atmosphere, 32.0°F and 14.7 psia.
That was a mind full lol great info man
 
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