Cause for torque drop at 5000 rpm?

[goldNSX]

On my dynos I've noticed a drop in torque around 5k rpm several times. What is the cause of this or otherwise: what is the cause of the locational peak at 4500 rpm? Vtec is around 6k rpm. How to get wrid of it?
I noticed also that the more freeflowing the exhaust (here CT) the more obvious the drop. Does this has to do with backpressure?

Regards,
Thomas

I've Taitec header and OEM cats in.

 

[goldNSX]

Here's another Dyno from last year, same Dyno station, all else the same except for the larger tires 265/35/18 than 245/40/17 and Remus (very silent sport exhaust). I believe that the header contributes to the peak at 4500 rpm compared to OEM NSX's. But why is there a drop at 5000 rpm?

 

[RC000E]

Well, first of all does the wideband show any fluctuation in the air/fuel? The issue is not an issue of a lack of backpressure (read: urban myth from old school hot rodders) but may indicate a resonance point for the exhaust/headers. The result could be superior scavenging resulting in a air/fuel "anomoly" which needs addressed through EMS.

I saw in another thread you got your ecu socketed, so if you were able to extract the program from your stock eprom get a hex editor and start figuring it out=cheap EMS.

 

[goldNSX]

We've dynoed 10 NSX's last year and all showed a little torque drop at 5000 rpm.

 

[RC000E]

Well, once again....what does the wideband indicate? What type of datalogging is being done. That rpm range could have a slight dip in the fuel map for fuel mileage reasons or could be excessively rich as a protective measure in the event the owner uses low octance fuel. This is common in my experience with OEM Honda tuning in performance engines. The new RSX's and Type R's have the same type of issue, huge gains can be found by simply leaning the fuel map out. High compression and a factory warranty often leads to necessary safeguards.

 

[Larry Bastanza]

That is about the cross over RPM for the shorting of the fuel pump resistor. When this relay shunts the fuel pump resistor, fuel pressure/volume increases, it take some finite time for the ECU to adjust. Standard operation for the NSX fuel system.

HTH,
LarryB