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Ok, just have to ask, 518 or 516 heads? 518 are MW.
The 516 heads with larger valves and mild porting do well. The combination sounds like a winner for driving/cruising. Hopefully the available gas works OK.
Yup you did and then ridiculously suggested 3 inch.
Tubing is measured and identified by outside diameter. You have either 2" OD, or 2 1/4" OD. Factory 383's had 2 1/4" OD compression bent exhaust to the muffler. The tail pipes could be smaller. My Charger ran 12s at 109 mph. The Moroso calculator has it at about 450 hp. The car had 2 1/4" full body mufflers and compression bent exhaust.
Looking at all the posts on this thread I still say leave the 2'' pipes that you say look to be new and when you have the new head pipes made to connect to the HP manifolds have an "H" pipe installed if at all possible like @Don Frelier said to balance out the system. I think this would offset the fact that the pipes are 2'' diameter. If you are 330 h/p or less this should be fine for your car IMHO.
IMO....that the 2" O.D. tubes should perform better, depending on the runner lengths to the 4 into 1 collector and cam profile (longer exhaust duration) will support higher exit velocity and better scavenging of the cylinders. It has to deal with the resonant frequency of the exiting exhaust gases and the "tuning effect" similar to the Max Wedges' cross ram intake manifold, tuned to a specific RPM range. The same principle applies to the exhaust system. The reflected pressure wave actually reinforces the exiting exhaust pulse, pulling more spent gases from the cylinder, allowing more complete cylinder filling (more power developed). Larger diameter pipes or longer lengths or both will cause this effect to be diminished. BTW....pipe is measured by the O.D. in inches X Schedule....2" pipe measures 2-3/8" O.D. x Schedule (Sch 5 or 10 or 40). Tubing is measured by the I.D. X wall thickness.....1-1/2" tubing measures 1.900" O.D. x 0.109" wall for Sch 10. Both pipe or tubing can be EITHER welded or seamless construction. Just a little information.... BOB RENTON
This is true up until the pipe is ether to long or to short in which dyno testing is needed to know exactly where the best length per size pipe is. The effect of diameter change is t normally so drastic as to “Kill” the engine performance if the length is altered to suite the diameter. Be it exhaust manifolds or headers, the length of the exhaust pipe should end in a pressure wave cancellation box so the negitive wave can travel up the pipe to help draw in more air and fuel into the cylinder. The amount difference can be huge. You have this part slightly wrong; Once the exhaust valve opens, the spent gasses and pressure wave leave the cylinder out the head and down the pipe. This positive pressure wave, the way I see it, is assisting the gasses out to a point but not the reflective wave going back up the exhaust pipe. Going back up the pipe creating a negative pressure at the next timing event for the opening intake valve to a deeper depression to pull in more air and fuel. Just like the cross ram induction system your reference earlier. David Vizard has written about this. Engine masters did an episode on adding collector length. Both worth while to check out. But both, (IIRC) were in reference to header usage, not exhaust manifold use. With the headers, the effect was in the lower rpm range adding substantial torque.
Your 2 inch will be fine. I have a 512 Stroker that Dynode in the mid 500HP and close to 600FPT. I run a 2 1/2 in exhaust ( I do have headers though.) and have had zero problems. My headers are wrapped so I do have some improved flow with that, but they still feed 2 1/2 main pipes and magnaflow mufflers.
Rumble & RJ, have you guys actually tried varying the tube length on the primary and collector with headers on a car at the drag strip? I was lucky enough to get the Hooker adjustable headers with my '65 Coronet. I played with both the primary length, and separately with collector length. Didn't make enough difference to worry about. The stock style manifolds are a completely different deal. My bet is the pressure wave reflection has almost no effect at the exhaust valve due to the manifold design. IMHO.