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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
We should not be overly concerned w velocity through the primary and secondary tubes so much. There is not really any scavenging opportunity with a low overlap turbo cam and with the back pressure the turbo induces.

We are probably more interested in velocity at the turbo's turbine wheel. That is controlled by the wheel and housing sizes and design (split system?).

How fast we fill or pressurize the exhaust manifold leading to the turbo is more a function of the total "volume" of the manifold, including the pipe to the wast gate(s).

Then efficiency of the basic design be it equal / unequal length, un-necessary & or extreme bends, collector design, and or the ratio between the primary and secondary pipes then become important to effectiveness.

An equal length system is just by design going to have more volume. However it should be more efficient and have potential for a higher VE. Trying to reduce its volume by moderating the tubing sizes may not be the best course of action.

An un-equal length system by its nature has the potential to have less volume and the react or fill and pressurize faster. If boost onset is what is of utmost importance, an un-equal length would probably be the choice. Then if one wants to moderate the tubing size for even better low end response, so be it.

Old 06-22-2009, 07:45 PM
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