Ronin RX-LS swap headers... We're finally offering the long tube headers we've always wanted ourselves.
Note on the quasi-merge collectors. From a flow perspective these are effectively identical to slip-on merge collectors. The difference is that we wanted to avoid the slip as it offers potential for leakage which can make tuning a PITA (ask us how we know). These will use a full merge spike with a deep drawn stamped exterior, that lets us weld the spike first then burn them in all the way around so they can't leak.
The design is simple and clean with a focus on packaging and overall length.
A little background for those who might be wondering why long tube headers are such a big deal: when it comes to header theory there are two factors at play. The first is particulate motion where we're concerned with the flow of molecules. We're using 3' radius bends for a much smoother flow off the head vs. the 2" many of our competitors run. Smooth flow also is part of the reason why we wanted a quality merge.
The second factor is reflected pulse wave tuning. When the exhause valve opens the dramatic difference in pressure results in a shockwave that travels down the primary at the speed of sound. Fluid dynamics tells us that when a shockwave hits a signicant change in cross sections area, a negative pressure wave is reflected and travels back upstream. If we can time it so that this negative pressure wave arrives at the exhaust valve before it's closed (and ideally while the intake valve is starting to open) we can both scavenge the remaining exhaust and get the intake charge started back into the chamber.
How big is this influence? David Vizard ("How to Build Horsepower") references a 6-7 psi delta in the reflected shockwave, which is huge given the motion of piston into the chamber only gives a 1 psi difference since the valves are so big. If you have more than 1/2 psi pressure drop in a race engine you need more head. So long tube headers can get air moving with about a order of magnitude more force than the motion of the piston alone. Vizard's body of work is worth a read but here's an article to get you started if you're into this kind of thing. http://www.superchevy.com/how-to/exhaust/0505phr-exh
The trick is that this shockwave timing is near constant for a given length, meaning it's only optimized for one engine RPM. The influence of the shockwave is in play for a wider range but it's only mathematically perfect at one rpm. Equal length headers are nice but we choose to prioritize packaging since it's fine if one tube works at 5,500 rpm and the next one over is better at 6,000. Both cases influence the power band in productive ways. Conversely we've seen plenty of equal length headers that were built too short for any of the primaries to work out. Case in point, "3/4 length" and/or shorty headers are pretty much worthless regarding pulse length tuning. You can get smooth flow but the path is too short to for pulse wave scavenging to work out at any achieveable RPM and you might as well just run nice manifolds.
We've fought for length with these (should be 3+" longer than a few existing options). This will shift the "tuned" RPM somewhat below redline and broaden the sweet spot for HP at the top of the RPM band. 1 7/8" primaries are sized to be perfect for those needing to move some air in bigger engines. We've seen enough evidence to expect this to be great for 5.7L and larger engines but it really depends on the airflow demands of your engine. I would expect a healthy heads cam 5.3L to flow as much air as a stock-ish 5.7L. The headers will still mount and work correctly with a 4.8L but the primaries are probably larger than optimal.
A note on fit. 1 7/8" is a big bundle of tube to package. We've tucked these up for maximum ground clearance on the test cars we fit on. The collectors are clocked to ground (details we never understood why others didn't address). There may be some very slight clearancing required but it should be less than folks have experienced prior if you've run headers by others. The minimum clearance on an FD Samberg subframe is likely to be the aft inner corners of the subframe. It cleared on our test car but if it was mine I might have profiled the corners a bit to let things move under load. Note, our pending FD subframe should be PERFECT as will the FC kit but we wanted users to be aware when running mounting by others.
We're failry confident long tube headers are not possible with the Sikky kit (everything crashes given the high/aft engine placement), we have not tried with Hinson or Granny so caveat emptor in that regard.
We plan to offer a gasket option in the future but don't want to delay launching these. We like MLS gaskets (Mahle, Cometic and others) and anything with a 1.75" port size (tube ID) will work well. V-band clamps and hardware included.