Gary Lewis Posted February 16, 2018 Share Posted February 16, 2018 Yes, yes you do have secondary waves, and collisions, magnification due to interference, standing waves, reverberation, constantly changing temperatures affecting the local speed of sound, energy (heat *and* velocity) lost due to expansion, ect... This is why I say it is a very complex equation. That is beyond my abilities -or at least desire- to solve for. Link to comment Share on other sites More sharing options...
85lebaront2 Posted February 16, 2018 Share Posted February 16, 2018 That's for sure. There's a finite end to each tube, and the wave created when a pulse comes out of one tube goes back up the other three - on a V8 using equal-length headers. But, if we put a crossover in downstream of the collector does that cause another set of waves that add at some RPM's and subtract at others? The reason for a downstream from the collectors or manifolds crossover (H or X) is the unbalanced pressure pulses, the same thing that gives you the V8 "rumble". On an inline 6, or even a V6, you do not need it nor really want it, same for a flat plane crank V8. On these the pulses are evenly spaced and it is actually detrimental. I wish I could find the formulas Chrysler used in the 60s to calculate the runner length for intake ram tuning. I uses the same concept of pressure waves, but uses the pressure pulse generated when the intake closes to create a new pulse when it reverses at the end of the intake "tube" to arrive at the intake valve just as it opens. Newer engines with variable length intakes use this to help at low end, and again at higher rpms to produce more power efficiently. Link to comment Share on other sites More sharing options...
Pebcak Posted February 16, 2018 Author Share Posted February 16, 2018 The reason for a downstream from the collectors or manifolds crossover (H or X) is the unbalanced pressure pulses, the same thing that gives you the V8 "rumble". On an inline 6, or even a V6, you do not need it nor really want it, same for a flat plane crank V8. On these the pulses are evenly spaced and it is actually detrimental. I wish I could find the formulas Chrysler used in the 60s to calculate the runner length for intake ram tuning. I uses the same concept of pressure waves, but uses the pressure pulse generated when the intake closes to create a new pulse when it reverses at the end of the intake "tube" to arrive at the intake valve just as it opens. Newer engines with variable length intakes use this to help at low end, and again at higher rpms to produce more power efficiently.So is this going to be Common Core Math to figure this out? If it is then I'm not going to be any help. Honestly, I really appreciate all the input. I would have never dreamed that this much can go into exhaust on a vehicle. I've learned a lot this week so I'll see what I can come up with for a rough draft of what I might get. On Feb 16, 2018 8:32 AM, "85lebaront2 [via Bullnose Enthusiasts]" <redacted_email_address> wrote: Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 16, 2018 Share Posted February 16, 2018 The reason for a downstream from the collectors or manifolds crossover (H or X) is the unbalanced pressure pulses, the same thing that gives you the V8 "rumble". On an inline 6, or even a V6, you do not need it nor really want it, same for a flat plane crank V8. On these the pulses are evenly spaced and it is actually detrimental. I wish I could find the formulas Chrysler used in the 60s to calculate the runner length for intake ram tuning. I uses the same concept of pressure waves, but uses the pressure pulse generated when the intake closes to create a new pulse when it reverses at the end of the intake "tube" to arrive at the intake valve just as it opens. Newer engines with variable length intakes use this to help at low end, and again at higher rpms to produce more power efficiently. CFD modeling has come a *long* way from slide rules in the 1960's... (Yes, the A12/SR51 was designed in that era) There are so many different factors that influence the outcome I would wonder if we could get an *absolute* answer -even today. Plus manufacturing ability is always making new things possible. (Find a few YouTube videos of Nissin CNC tube benders) Wrt exhaust systems there a few basic principles. But even then one needs to account for combustion temperature, pressure when the valve opens, mass and heat coefficient of the material, whatever. Yeah it will make your head swim. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted February 16, 2018 Share Posted February 16, 2018 I'm sorry, I didn't directly address this. No. You don't have to do crazy mental gymnastics to get an exhaust system that suits your needs. This is not like the threads that start "I NEED a really lopey idle, but want a fuel efficient torque monster... and I want to do it for $150 with bolt on components" My advice is to keep the runner/head pipe volume down and use as large a volume muffler and tailpipe as you like. If you want a sound that is low and throaty go with a big muffler and tailpipe. If you want something that 'barks' then smaller volume and free flowing design. With a 351 -at 'normal' truck engine rpms- 1.75 head pipes and a 2.5 collector are verging on too big for best torque. (IMO) But if the engine is not stock, and you drive it like you stole it, you would be fine and might want more. Headers are always good... except for longevity, and serviceability. Not being able to change a spark plug or starter with the pipes on the engine is hugely frustrating. Link to comment Share on other sites More sharing options...
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