Hi Guys,
I found some interesting stuff on Hooker's web site:
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What tube size do I need and is bigger better?
Header primary tube sizes vary on many factors: engine combination, transmission type, gear ratio and intended use of the vehicle. For example a truck header will be designed using longer length and smaller diameter primary tubes to enhance low to mid-range performance, where a header for a Pro Stock race car will have larger primary tubes and large collectors for the highest flow available.
Bigger generally is not better when it comes to street driven cars. when you put too large of a header or exhaust on a street driven vehicle, you usually notice a severe drop in low to mid-range performance due to a lack of backpressure. To combat this issue, Hooker sometimes builds 3 or 4 different headers for a particular application with varying tube and collector sizes.
Should I use exhaust wrap on my Hooker Headers? If your vehicle is being run on the street or for extended periods of time, you should never wrap headers. Exhaust wraps insulate the exhaust too much and the exhaust temperature is raised to a level that fatigues the header material causing cracks.
If under hood temperatures are an issue, we recommend using Hooker's Metallic Ceramic Thermal Barrier Coating. Our coating is applied inside and out. It is corrosion and heat resistant up to 1600°F. It also reduces underhood temperatures and has a polished high luster finish. Holding exhaust temperatures inside the header increases the exhaust gas velocity producing more horsepower.