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Little, if any. Open you mouth wide and breath through it. Doesn't change much in the volume of air you get in cause you got the same size wind pipe, diaphram, and lungs.

Put on better flowing heads, exhaust, and then the stock throttled body could be the restriction. It's not in stock form.
What is the stock dual Throttle Body size,?:popc1:
 

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The stock Bronco Throttle Body is 51mm.

The BBK #3501 is a 56mm Throttle Body.

The BBK #3503 is a 61mm Throttle Body is for high RPM applications and 460 engines. It also requires port matching to the intake manifold and a tune correction prior to installation.


Throttle Body Sizing and Horsepower Level
Dual 51mm = single 72mm = 470 HP
Dual 56mm = single 79mm = 570 HP
Dual 61mm = single 86mm = 670 HP


I may change to a BBK 61mm when I change my tune, as it is tunable and only affects performance at or above 3500 rpm, but the BBK 56mm is fine for now. Regardless of which Throttle Body I use, my low rpm torque will still be the same. And I am not sure why there is such a buzz about a single 90mm Lightning Throttle Body when the focus should be on low RPM torque, not high RPM Horsepower. This is a heavy truck, not a lightweight Mustang.

Heck, a MAF Sensor should not be too small becoming a restriction and should not too large which tends to loose resolution and accuracy. I am curently running a 75mm Pro-M Mass Air Meter that was factory calibrated to 19 lb injectors. The 42 lb/hr calibration was correctly done in my tune.


Mass Air Meter Sizing and Horsepower Level
55mm = 275 HP (Stock 88-93 Mustang)
70mm = 350 HP (Stock 94-95 Mustang)
75mm = 550 HP (75mm Pro-M Bullet)
80mm = 450 HP (Stock Ford)
85mm = 650 HP (85mm Pro-M Flanged)
95mm = 750 HP (95mm Pro-M Flanged)
80mm = 800 HP (Pro-M 80 mm )
92mm = 1500 HP (Pro-M 92mm)





With a 351W, look at an better flowing Intake and mandrel bent Y-pipe and 3" exhaust first. With a 302W, go for the Y-pipe and exhaust. That is after you have done a quality tune-up and ensured that your PCM was happy...
Thanks that was very enlightening. I knew that the Edelbrook Performer Truck intake offers the 56mm and 61mm as an option. I think it mentions that the 56 only give you about 7 additional HP. They also say that the intake needs to be ported to take full advantage of the 61mm, but I really haven't gone that deep into as yet. But, the intake and headers are my next big upgrades.
 
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