The ST170 INLET manifold has the same port centres and stud/bolt spacing as the standard and RS manifold. However, the runner is much deeper by being higher at the top. The head needs porting to match, particularly for good injector performance. I'm can't remember if there is a problem with alternator clearance. The mounting is lower on the ST170, mainly because of RHS engine mount and clearance needed by the auxilary belt.

As said, the reason for the ST170 manifold is the dual length inlet runner. The change over (also reported as 6000 rpm) is the cross over point of the ST170 engine's torque curves with each different tract length. So as such, the manifold does not necessarily give more power, but widen the useful torque and power band.

Without using the long tract length (its spring default is short) you might move the torque curve higher in the rev range, so a bit more power, but less flexiblity in driving. Also, with the standard management, the rev limiter might inhibit this.

Martin