Recommended Pipe Max Power (Kw) Diameter (inches) 75 2 120 2.5 165 3 230 3.5 375 4 550 5 635 6 The recommended MAXIMUM power for optimal performance with a 3.5" pipe is 230kw ie approx 310hp X 2 =620hp. Multiply by two because there are two pipes. The current configuration (2 1/4") is optimal for say 100kw ie approx 134hp X 2= 268hp
Stephen as im sure you understand these theories are a basis to start a system. How the vehicle actually reacts to it is a different story and further R@D must take place on the street and dyno. When we developed our 360 headers it started all as math. Then when we actually built it, the system wouldnt even fit into the car. Sure, 3.5" would be great to use but you would never be able to fit it into the 550 and drive it on the street. Exhaust design is all trail and error and these books do carry information that is outdated. On a street car we cant simple cut away parts of the car to fit the headers or exhaust in there, and we need power that we can use in everyday drive. Keep in mind a race car will operate almost at all times in its peak powerband.......a street car does not. In modern day street cars space is very limited, and its very hard to tune them. Its not a simple adjustment of the carbs. The point is books and theories are a basis to aid you in a perfect world where everything would fit. We have to adapt these theories for street conditions, longevity, fitment, and to work with the factory computer.
Dan My comments weren't directed at you, rather generally I know you have had great success with the 360 headers and look forward to seeing what you come up with for the 550. In response to what you just posted, my first reaction was to chuckle as I know exactly what you mean. Why did I use 3" instead of 3.5"? Unfortunately the realities of the real world, get in the way of the theoretical. That said, my car has significant power gains at every single point of the power curve over standard, because I have not changed the diameter of the tuned portion of the exhaust system. What I think is being misunderstood by many is the different components of the exhaust system. There is only one that is important in terms of gas velocites etc, the tuned portion. ie the headers. This is where all the compromises have to be made, do you want a wider or narrower power band, where do you want it etc. backpressure and reversion here do have a role to play. After the tuned length the ideal system is none at all. Due to the fact that the need to route the noxious gases away from the occupants as well as muffle the car, reduce emmissions etc, we are stuck with this portion of the exhaust system.
This is 100% true. People dont understand how important headers are the car and how beneficial they are. You can fully change the cars power band, etc just by changing the header design. It really is a black art few understand. I think it was ground breaking when we gained 17whp on a highly tuned 360. I cant think of any other bolt on upgrades for the 360 that give similar gains.
Firstly, thanks Dan and Stephen for all the explanations. I do believe that 3" throughout is what is need for my goal of 600hp with my 550M. I am already using 3" on my Mustang Cobra V8 with modified headers. So I agree headers are the place to start. Also no argument abut removing any flow restrictions downstream of the headers. Couple of points needing clarification: I was surprised to learn that "The current 550 configuration (2 1/4") is optimal for say 100kw ie approx 134hp X 2= 268hp" , yet we are already flowing and measuring more than that arent we? E.g. Stephens X-pipe/BMC dyno results. I guess you mean there is a resistance effect so you dont get the full benefit of an upstream change or engine improvement. We are talking rear wheel hp, right? Just removing the pre-cat restrictors in the headers are surely giving half of the gain? V12 exhaust pulses are different to V8 so the scavenging and flow peak effects are different and the theoretical calculations need adjustment, but by how much? Anyway, as Dan points out, we need to see the practical effect of the whole system - real measurements. Ron
Ron The numbers are crank, not rear wheel. It does not mean that a car must have a twin 3.5" system to flow 600hp, it just means that a 3.5" twin system with properly designed mufflersall designed to createless than 2psi backpressure will not cause any performance restriction. I'm really not sure about the precat issue, my car is an Oct 2000 build Aust/US/CDN spec and it doesn't have pre-cats. To achieve the power outputs, my headers were reworked, to remove some performance restrictions, cats removed and a 3" full system added. My numbers come from back to back dyno testing, not seat of the pants. In addition, as you are aware, I am running the BMC CDA airboxes. There is more power available from a well designed set of headers IMO, so I look forward to seeing what Harmony comes up with.
For those who have been glued to this thread, there is a nice visual article on exhaust pulses and effect of pipe diameter sizes: http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=47 Enjoy, Ron
Thanks for sharing Ron.i'm not sure about the analogies the author has used, but the principles seem sound, so far as they relate to the tuned component of the exhaust system. The exhaust gas velocity half way down the exhaust pipe has no effect on pulsing and charge dilution at the exhaust port. Whilst not an expert in the subject myself, I know enough to believe that the author of the article hasn't really understood the principals involved. A bit like me actually, knowing enough to be dangerous!
Right, and the whole situation, is a complex dynamic one and the ideal pipe size only works over a small rpm range, so much for the theory, now back to the dyno, Ron
This is an old thread however for me it is current. I have tried another thread with no response. My 2004 575 has pre-cats. I have removed the large rear cats (I will call them post-cats) and plan to replace them with a 2 into 1 post-cat delete 3in pipe each side. There is a sensor at the rear of the post cats called a thermocouple by Ricambi. Does anyone know if I have to extend the fitting for these or something else to avoid a CEL? Thanks in advance for any help.
