[robbiec]

OK, so I've been waiting for 3 1/2 years for someone to reliably tune the 325/328 valve lift and cam timing. Sounds like OE Tuning can do it, but who other than e90pilot has their tune? What can Active Autowerke do? Fuel and spark, or the timing and lift as well?

With the same compression ratio and displacement as the 330, the 325 should be able to make the same, or at least close to the same torque, regardless of the intake manifold. Can anyone unlock the potential of this motor? 3 liters and 10.7:1 compression should be able to yield much more than 185 ft-lb! I can live without the top end power of the 330, but how about another 30 ft-lb at 2,700 RPM? Should be possible without the manifold swap.

[e90pilot]

The manifold is mostly responsible for the large increase in torque.

[BudVlad]

Originally Posted by e90pilot

The manifold is mostly responsible for the large increase in torque.

+1 I had my car on dyno after I installed the manifold without the tune. There was an increase in torque but no power increase.

[robbiec]

Originally Posted by e90pilot

The manifold is mostly responsible for the large increase in torque.

There's no way the 325 manifold is responsible for a 35 ft-lb reduction compared to the 330. Not at such a low RPM. The 325 engine would run out of breath and fall on its face at 5k if that were the case. An intake manifold can provide a tq increase at higher RPM, where a larger volume of air is required, but not at the low rpm where both these engines see their tq peak.

Do either of you manifold swappers know if the inside diameter of the two intake manifolds are the same or does the 330 have larger diameter runners?

[BudVlad]

Inside diameters of the two manifolds are same. Maximum torque with the 3 stage manifold is at 2000 RPM.

[e90pilot]

It's a three stage manifold which causes resonance at three different points: low, mid, and high rpm. The resonance will increase the pressure at the intake valve causing an increase in torque at the resonance peaks. That's where you get the increase in low rpm torque without the decrease in power at high rpm. That and there's tuning to optimize the airflow properties of the manifold.