*Sonic*

Just curious as to what could be the cause

did a RR day a few weeks back, and got 255bhp 240lb/ft, two weeks later I got 265bhp 230lb/ft with a big dip around 5k rpm

I had a problem with a broken up-pipe on the first RR, and I had replaced it for the 2nd RR

Car is UK MY00 PPP, with ported headers, ported up-pipe (headers end only) & Full Decat

One thing I did notice (but not till too late) was that on the 2nd RR they had pointed the fans at my Rad, and not at the Scoop (they must have thought I had a FMIC)

I did have some (-2.5 degrees) knock correction, and the ignition timing was pulled way back, at around the 4.5k/5k range, which you can see from the power curve the big dip before the rise again

The other thing that was different, was that I had replaced the larger bore restrictor (1.25mm) back to the standard one (1.1mm) so i did have a bit of boost spike on the 2nd RR


Any ideas for the drop in torque ?

Steve

NotoriousREV

equals

ergo

et voila, mystery solved

vulnax999

iTrader: (7)

Was the new up-pipe of a larger diameter? If so, lower gas velocity to turbo could have meant less torque, slower spool up yet still allow higher power as all the energy was being lost not leaked to atmos.

*Sonic*

LOL Rev, quite observant

I knew thats why the power curve dropped, but the torque was sort of sustained at 230 before & after the dip

Neil, the new up-pipe is another OE one, except it has been ported at the Headers end only, to match the header bore

then its back to normal for the turbo side

NotoriousREV

Can you scan the graphs and post 'em up?

What rpm were your figures at, before and after?

*Sonic*

here is the first run (with broken up-pipe)



And this was the 2nd run a few weeks later, with replaced up-pipe




S

NotoriousREV

There's something funny going on with the scaling. Your first run shows peak power at 8000rpm, yet the power curve only runs to 7000 and peak power is clearly made at ~6250.

Interestingly, pre-dip your torque is down on the previous run, however, post-dip you're making more.

Maybe the ported up pipe isn't good for torque but good for high-end power (maybe gas speed is dropping due to increased volume affecting the boost profile?)

Do you have the Delta dash logs for both runs? May be worth looking at ignition and fuelling values for both, just to see whats going on. I would personally suspect that the ECU is doing somthing funny wither due to temp or not coping well with up-pipe.