In general, the mono-blade throttle bodies can net more horsepower simply because they allow more air to enter the engine. But, there are several other factors to consider as well. Does the engine have power adders (big cam/supercharger/turbo)? Does the engine have headers and free flowing aftermarket exhaust? Also, the tune can make a big difference. Many tuners prefer dual blade throttle bodies as opposed to a mono-blade "big mouth" design because mono-blade are more difficult to tune correctly. However, all things being equal, a mono-blade design such as Venomous 1 Racing's Big Mouth throttle body can net an additional 8 to 10 wheel horsepower on a dyno *IF* you your engine has a big cam, supercharger, or turbo. You will not see a noticeable gain on stock engine (maybe 2-3hp). I hope that helps.
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