Have any of you guys a actually measured the pipes to see how equal length they are?
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I'm not quite sure what is meant to be equal about the downpipes as far as the design goes. Is each downpipe equal in length? Or does it mean that when a car is fitted with the equal length downpipes that the 'secondary' from each bank of the engine is equal?
A rear CF2 manifold has about 3" of secondary after the collector before the downpipe is bolted on, the front manifold has the flange immediately after the collector, is that taken into account in the design?
CF3 centre cats are staggered, the cat for the rear bank is further back than the cat for the front bank, is this taken into account in the design? If it is, does that mean when you fit a single sports cat to the centre you are effectively making your secondaries more unequal?
When we did CF2 manifold conversion downpipes for the 156 & 147 GTAs we measured up and found we were within 10% of being equal when the centre cats and the rear manifold's extra 3" is taken into account, and that was following the straightest smoothest route.
These downpipes are all certainly longer than the originals, and lengthening the secondaries will alter the engine's torque curve and sound properties without a doubt.
Other things to bear in mind:
- the primaries are not equal length
- If you were going for a tuned length exhaust system, longer primaries would be the goal to increase power & torque, but they would be seriously awkward to build & fit.