Pornstar* IS right.
The correct US Patent to read is 4,766,853.
This patent shows torque curves and explains when to switch things open and closed.
[Yamaha has no fewer than 15 patents on this manifold all in the 1986 to 1989 timeframe and some of them are even more wicked than the resulting manifold.]
********************************************
However, something, in page/column 7, strikes me as unusual.
1. Yamaha states to CLOSE the valve at low rpm (like the SVT is currently with no crossover).
2. Yamaha then states to OPEN the valve at mid rpm (unlike the SVT but like the SHO....this is where they suggest the gain is possible).
3. Yamaha then states to then LEAVE the VALVE open and open the secondary runners (again unlike the SVT and like the SHO). This differs last piece differs from theory a bit but may be because of the effect the secondary runners have on tuning. There should be a positive effect of eventually CLOSING the valve again at high rpm, but possibly for the SHO this occurs out of the usable power range or to close to the redline to make it worthwhile.
If someone tries this on an SVT, they should really do the following on the dyno from 1000-redline:
1) Crossover open, secondaries propped open
2) Crossover open, secondaries deactivated
3) Crossover plugged/off, secondaries open
4) Crossover plugged/off, socondaries closed
Why? Because it is possible that you might find that the best torque curve is developed by creatively timing the secondary and crossover valve opening. That is truly the only way to determine the full benefit of such a modification.
Bottom line, if you read this paper, and make the assumption that the SHO and SVT manifolds will react similiarly, then the SVT MIGHT have the opportunity to boost both mid and high end power with the crossover as it reportedly did on the SHO.
The tough thing is figuring out the level of the gain. To do that, someone has to be the guinea pig.
Good luck. At your own risk.
defector
