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Throttle Body Size Study
- Throttle Body Size Calculator - the calculated science behind the table below.
Throttle Body Selection Chart
-----------80mm ----------85mm ---------90mm
---------0.8-1.2"/Hg ----0.8-1.2"/Hg ----0.8-1.2"/Hg
345_____5190-6360_____5920-7250_____6700-8200
370_____4840-5930_____5520-6760_____6250-7650
392_____4570-5590_____5210-6380_____5900-7220
426_____4200-5150_____4790-5870_____5420-6640
440_____4070-4980_____4640-5680_____5250-6430
N/A hp____360-500_______440-580_______510-660
"Using the chart is simple. If peak power is higher than the rpm in the 1.2"/Hg column, or peak torque is higher than the rpm in the 0.8"/Hg column, then you should really consider an upgrade. If peak power is higher than the rpm in the 0.8"/Hg column, or your shift point is higher than the rpm in the 1.2"/Hg, an upgrade can be of benefit in "max-effort" application, but isn't absolutely necessary. I even included accompanying power outputs, so you can also make a selection based off of expected N/A power."
5.7l (345 cu/in displacement). Peak horsepower comes at 5,800 rpm and peak torque comes at 4,200 rpm. 4200 < 5190 (torque) and 5800 < 6360 (horsepower) so you should keep the stock 80mm throttle body. In a max effort application (e.g. at wide open throttle), 5800 > 5190 horsepower, but the shift point 5800 < 6360. You could upgrade but it's not necessary. Even so, to ensure airflow smoothness, the max you can go with the stock composite manifold is 85mm and you should not exceed 85mm.
6.1l (370 cu/in displacement). Peak horsepower comes at 6,200 rpm and peak torque comes at 4,800 rpm. 4800 < 4840 (torque) and 6200 > 5930 (horsepower) so you should consider an upgrade to an 85mm. If you decide to go higher, again, 4800 < 5520 and 6200 < 6720, so there really is no need for larger than 85mm. In a maximum effort application, 6200 > 5520 so you could go between 85-90mm throttle body but its not necessary. The stock 6.1L manifold port matches the stock throttle body at 80mm. If you decide to get a larger throttle body, what you should also consider is port matching your intake. Since the 6.1l has an aluminum manifold, you can get this done fairly easily. If you don't want to port match, you can go along the route of the Fastman 84mm throttle body or the Ported Modern Muscle 85mm throttle body.
6.4l (392 cu/in displacement). Peak horsepower comes at 6,000 rpm and peak torque comes at 4,200 rpm. 4200 < 4570 (torque) and 6,000 > 5590 (horsepower) so you should consider an upgrade to an 85mm. If you decide to go higher, again, 4200 < 5210 and 6200 < 6380, so there really is no need for larger than 85mm. In a maximum effort application 6000 > 5520 so you could go between 85-90mm but it isn't necessary. As the same with the composite manifold, you should measure to see what the actual interior diameter size is and port match the throttle body to ensure airflow smoothness.
