This chart may come in handy for anyone looking to add long tube headers to their Challengers. It matches up horsepower to primary tube diameter. https://www.rpmoutlet.com/how-to-size-headers.htm Primary tubes of 1-3/4" to 1-7/8" are for big block engines. If you installed them on a 5.7 Hemi, for example, you will lose a considerable amount of low end torque. Smaller diameter pipes would be better. While they flow less volume than larger ones, the exhaust in smaller pipes flow faster. Until you reach the RPM where the sheer volume of exhaust gases require bigger primary tube diameters, smaller tubes will scavenge the cylinders more efficiently. If you are using the engine in the 1,500 to 3,500 RPM range, which is typical for a street-driven car, you definitely want 1-1/2" to 1-5/8" primary tubes for any small block. Generally, small tube headers do not lose their edge in horsepower and torque until you exceed 5,500 RPM.
Can't swap out the headers on my 3.6. There seems to be a lot of bad information out there regarding what size exhaust to run on the 3.6. I believe the header diameter is 2.25, and many people think you can't run a larger exhaust tube than that. Some disagree.
Based on the following header chart, a small block putting out between 450-525 crank hp. would require header tubes between 1-5/8" stepped to 1-3/4. Anything larger and you would lose some low end torque. Choosing Header Tube Size (rpmoutlet.com)
Many people think I can't do a lot of things that I do. I was lucky enough to find a "Near New" set of Borlo CAT Back Exhaust I put on the 3.5 V6 in the 300 for $150 Had my Friend at Midas install without any problems. Left off the Big @ss Resonator tips and used turn downs. Have not seen any advantage, but have the peace of mind they are true Duals with X-Pipe rather than the Single with a Big @ss Muffler.
I was going to let this go, but it really bugs me when supposed Muscle Car Sites do such a stupid mistake: Small Block Engines (Engines up to 400 Cubic Inches / 6.5 Liters) Big Block Engines (Engines over 400 cubic inches / 6.5 Liters) Cubic Inches has NOTHING to do with Block Size 361, 383, 400, 413 & 440 were all BIG BLOCK Chryslers Cubic Inches=bore x stroke Also: I ran 2" tube Headers on all my 383-440's and had plenty of LOW END Torque
I agree with you. A big block in the old days (77yo) Could be less then a 396 or a 383. for that matter... They calll my challenger 1320 a small block - All I can say is about 500 HP, Call it what ya want it hauls ass...bmac