Um even without a true cold air intake the straight pipe and cone work wonders on our bonnevilles. Our bonnevilles have trouble with the restrictive air box and turbulent air. Doing this removes nearly all the previously stated trouble. It helps performance a lot.
And you dont need one bigger than 3". The bigger size is only useful if you are using ram air, and then its only useful at higher speeds. Also with a size larger than 3" you also have to worry about how the ends are smaller and the turbulent air this causes.
The open cone with less turbulent air will improve performance but the warmer charge will negate the benefit.
You need a cold air charge.
1% hp loss for every 10 deg F rise in inlet temp.
Check out your under temp. It'* around 140 F...and a lot warmer if those 600 F headers heat up that inlet pipe thru radiant heat.
Even the stock box takes in fender air that is around 80 F.
So that'* a 60 F temp difference which = 6% hp loss. Can you calculate 6% of 200 hp. Yep, that'* right, 12 hp lost. Not to mention the additional loss when your computer retards your timing when the resistance from your IAT sensor detects the hotter charge.
The diameter of your throttle body is about 3 3/4". So the 3" pipe is an actual reduction in size = increased pressure drop due to increased air velocities.
It all adds up.
Bigger and colder is better.
Ty is working on a cold air box set-up for our Bonne'*.
My homemade one is working well for now but it won't stand up in the long run....like my PVC 4" pipe.
This set-up gave me a 1/2 sec improvement in 0-60 time over the stock box with a flat K&N filter.