[venox22]

Just thinking away to myself yesterday........... and was just thinking about the varying designs in exhaust manifolds!! shape/pipe diameter/pipe configuration etc etc

I see the JCW manifold employs a 4-2-1 design, yet the GTT(janspeed) manifold employs a 4-1 design, what are the benefits of such contrasting designs???

[MINIMANIAUK]

manifold design is unbelievably complex,pipe lengths,collector points,pipe diameters,wave theory,pulses,heat,pressure, flow,noise all come into play but the short answer is 4 into one is better at high rpm ,and high flow rates, and less concerned with peak torque. 4-2-1 is better at mid range flow and torque more suited to road use . on a track the engine is always kept at very high rpm and seldom dropped to the mid range so 4-1 better. the stock/jcw manifold have very short primary pipes and keep the noise down but are not a great design, hence the popularity of the aftermarket manifolds and more free flowing exhausts

[Carlinho]

4-2-1 it´s a better choice if you don´t use it only in track...

[roland2003]

There are formulas available for exhaust manifold design which I used in designing the GT Tuning one to establish primary length & diameter and secondary length & diameter. You need to know valve overlap and other numbers to calculate. Ours isnt perfect (theres no space to get it 100%) but its a hell of a lot closer than any others Ive measured up and applied the same formula too.
Best Regards Roland GT Tuning