Are 458 exhaust headers 4-2-1 or just 4-1 please
Good question. I always wanted to know. 4-2-1 more towards torque and low-mid range RPM, and 4-1 more towards free flowing and better for higher end power
Given a 4-1 header designed for top end power, and given a 4-2-1 header designed for top end power, and both headers designed to "sign off" at the same top end RPM, there is virtually no difference in the power production over the upper mid-range through fuel cutoff at high RPMs. What happens is that the 4-long-2-short-into-1 will have and extended power range of 250-300 RPMs down near 3000-3200 and "sign on" a little earlier than the 4-1 header. Now, the old conventional 4-medium-2-medium-1 headers using the same pipe diameters for primary and secondary tubes will have the mid-range-header characteristic as described. But Ferrari is smart enough not to use such headers. My assertion is that is is not the 4-2-1-ness of the header that maters, but all the pipe diameters and lengths (including the expansion chamber). When properly designed/tuned the 4-2-1 gives up nothing* to the 4-1 header over the powerband used when runningthe car hard. The 4-2-1 gives slightly better fuel milage and slightly better power in the 60-80 MPH range** than the equivalent 4-1 header. And the key word here is 'slightly'. (*) except for the added cost of the 2 additional merge collectors and a little more welding (**) data from F355 header
Mitch, pardon me. But you mentioned 4-2-1 header and 4-1 header being designed for top end power for both. From what I understand, 4-2-1 contribute more towards torque and mid range RPM; and 4-1 is more of free flowing header, less restrictive, top end power. Do correct me if I'm wrong. However, I do agree with you on your 3 para. Well explained.
See the following graph: http://www.freeimagehosting.net/c5034 In this grpah, there are 3 different header designs that have been fully optimized for the F355 engine. And by fully optimized, there are over 100 different combinations tried for each header. Not 100 random tries, but a sequence of experimental sets that feed the next experimental sets until the best responce is found. The graph expresses only the change in HP due to the headers themselves. Intake system performance was removed, and all other parameters held constant. This data was computed using (thousands of hours of) the Lotus Engineering engine simulation software. 40-50-60 is the conventional (i.e. old) style 4-2-1 header 42-50-60 is the modern style 4-2-1 header 42-65 is the 4-1 header All headers were simulated with properly architected merge collectors The actual F355 headers are not as good as these being shown, but somewhat different. The F355 header has a TQ bump right where these headers have a dip at 3000 RPMs. Then the F355 headers have a low performing mid-range from 3200 RPM to 5200 RPMs and up top are a few ponies down on these shown. The flat-ish blue line is the performance of the F355 representative engine without a header where the cylinders exhaust directly to the atmosphere. The graph shows that the old style 4-2-1 header (green) is essentially indistinguishable from the 4-1 header (violet) when both are designed for the same purpose. The graph shows that the modern 4-2-1 header (red) extends the header powerband down the RPM scale with no losses up top (when both headers are being designed for the same top end.) And a bit of a tradeoff is going on in the 3000-4500 range. Extremely careful selection of pipe diameters and lengths (including that of the expansion chamber) allows this kind of header to cancel out the cruise hole (flat spot). The careful observer will notice that the old style 4-2-1 header (green) uses different pipe diameters to be optimal than the modern 4-2-1 header (red). I seriously doubt that any driver could feel the performance different by the seat of his pants. All three of these headers have about 12 HP advantage over the factory headers. For now, the lengths must remain proprietary. {With great thanks to Lotus Engineering.}
Figure 6:: http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm Although the length of the secondary is longer than the one I found optimal for the F355, making it probably about1/2 way between the original 4-2-1 style and the ones I looked at.
fYI The Ferrari California, 458, 430, 360 headers are all 4 into 1 designs. In our dyno development the most power was 4 into 1 design while simultaneously adjusting primary header tubing size , primary tube lengths while maintaining equal length and utilizing high velocity merge collectors. By varying these criteria more power and torque is released from these engines. On the California we welded in Formula 1 style merge collector spikes to the stock headers and the car was tested on the dyno before and after and the resulting gain was significant. Making special headers for the California despite being a great car was deemed unnecessary.
Can someone compare and contrast the various header designs that are commonly advertised and sold for the 458 by various manufacturers? I've heard of, at least: Novitec Fabspeed IPE Agency Power Capristro
The stock manifold are not "headers". They are just basic "log" style manifolds. Not very efficient, but cheap to manufacture and easy to keep from cracking.
