I have tested enough to know that the goof balls at Hooker didn’t even know their own products.
Like calling Holley to get their “expert” advice on what size of THEIR a carb you should buy (which was too small every time and that has been proven wrong so many times now it’s not even up for discussion among people who actually have to make this **** run) calling Hooker was the same.
I have tested header sizing on every brand of engine and I can say with confidence IF you don’t cripple the engine with stupid cam timing a bigger tube header (correctly designed) will beat the hell out of the smaller recommended headers.
Compression matters too. Get the cam timing wrong and then cripple the engine with compression that doesn’t match your cam timing and header size won’t matter.
The lower your compression the BIGGER the tube can be. Counterintuitive but true.
So there is more to header sizing than just picking the biggest or smallest tube.
And sadly, the two best Chrysler headers Hooker ever made they no longer make.
If you didn’t have power steering your basic street/strip 318-340-360 should use the 5204 header and for more serious stuff the 5303 was the ****.
Of course, if you called Hooker they would tell you to buy their 1 5/8 garbage because everything else was way too big. And they were WRONG.
If you have power steering then you are stuck and IMO you’re just a street car.