I personally talked to nick at american racing headers, they sell both. he recommended 3/4 to me for up and over 500 hp. these are some bad *** headers. Im glad i paid the extra money for them...

 

i have the ARH 1-7/8 stainless steel headers on a 383 and make almost 500rwhp on motor the car picked up alot when i had those put on and got it tuned and can't be more happy with the looks, quality and durability. i can't wait to see what it does on the juice!!!!!

 

i appreciate your testing and everything, but by what your saying is . if i was to use these exact headers on my 2002 ss m6 camaro, i would see similar results as far as the horsepower and torque numbers. and if not please explain why? arent these 2 diff engines with diff internal components? and external? im not trying to be an ***, but i always thought there was a reason for making a certain power output from a particular engine. diff components mattered like the cam or the intake exhaust size and how many bends in the pipe. whether you used an x or h design, true dual compared to y pipe. i guess what im trying to get out is, the limits of a particular engine depend on bore size, stroke, cam design, cfm rating, and no 2 engines are exactly the same. again im not trying to cause any more bull over this, but it just dont seem to jive with what ive learned and done. i also know things have changed with designs and quality

 

i would say the 1 3/4. depends on what exaust u are running too