Notice the up, down, up, down that occurs between 4500 and 7000 rpm.

Motor is stock JDM ITR with BC3+ cams, velocity stack intake, SMSP long tube 4-2-1 header, and 2.5" exhaust. Hondata and cam gears were tuned for three hours by Steve Sakai and he could not get the torque curve to smooth out.

Any ideas on what might be causing the roller coaster?

 

What is the size of the primary tubes on that SMS header? I have seen big tube headers have a similar effect on a torque curve.

 

I have seen this on a few other dyno plots, and my personal opinion (which is prolly not worth beans...) is that the roller coaster/oscillating effect comes from the intake (and to some degree exhaust) resonance. Some rpm show a gain, others a decrease in power. As far as I understand resonance is ALWAYS going to be there. You maybe able to "tune" it to occur at different rpm, but there is always going to be a a speed that things work well, and others that don't. Is it beeter to have the peaks occur at the same time, or have the intake peak happen at a time when the exhaust is down, for a "smoother" curve (less rise and drop)?

Most of the roller coasters I have seen happen on about 700-800 rpm "periods", but yours seems to be on a shorter ~500 rpm period. Could that be because of the long duration BC3+ cams? Or is it more header resonance. I guess the dyno masters might chime in and gives noobs some input.

Do you have any other plots on the same motor, with some different parts, maybe without the header, etc...?

 

I have tried a different 4-1 header and saw the same up, down, up, down in the torque curve.


Modified by red civic standard at 6:45 AM 4/26/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DOHCsideracing &raquo;</TD></TR><TR><TD CLASS="quote">
Most of the roller coasters I have seen happen on about 700-800 rpm "periods", but yours seems to be on a shorter ~500 rpm period. Could that be because of the long duration BC3+ cams? Or is it more header resonance. I guess the dyno masters might chime in and gives noobs some input.

Do you have any other plots on the same motor, with some different parts, maybe without the header, etc...?</TD></TR></TABLE>

Here is the same motor with Skunk2 Stage1 cams, J's racing intake, and AN-r with street collector. Same tuner.

 

Here is another plot of an ITR motor with SMSP header:



Notice that the torque curve has slight peaks at 5000, 5500, and 6000 just as my motor does. I am starting to believe that it resonant frequency behavior (as DOHCsideracing has suggested). I think that my intake probably had resonant frequencies that matched those of the header and that is why we see this behavior.