Felix C

Considering a 5.7 with stock 241 heads(and LS6 intake) and typical street exhaust.

Notice the double hump in torque, first peak and then a trough and then the peak as the intake forces torque at 4800rpm. Good example was the TSP 224 cam comparo where the graphs have now disappeared.

Is this a result of tuning? exhaust type? wave harmonics? Or camshaft timing as in too much duration bleeding off compression?

What I am getting it that I would rather tradeoff a few upper end hp and not have the depression occuring after the first peak in torque.

S10xGN

iTrader: (11)

In for opinions!

Ethan[ws6]

iTrader: (13)

If I'm understanding what you are asking correctly, it's mostly in the cam grind. I have had cams that had an almost flat torque curve(texas speed torquer v2 being the one I'm running now). I have also done cams that, with the same heads and tuner, made that "double hump" you are talking about.

Wnts2Go10O

iTrader: (12)

from what ive gleaned, its harmonics.

Ethan[ws6]

iTrader: (13)

Explain?

409CISecondGen

iTrader: (2)

My stock cam/heads dyno had a double hump.

Some have said not to look at it as a drop, but as an extra bump early on.


The new BRZ/FR-S has it pretty bad and there is some speculation why:
http://www.ft86club.com/forums/showp...9&postcount=33

the "more scavenging going on" hypothesis fits with my experience as I have stepped headers with a merge collector and an X-pipe.

Felix C

Well, that would be a sight as I have not experienced that in an LS1/LS2/LS6.

Is that not a VVT motor in the dyno in the link? I would expect a different torque curve in a VVT motor.

I did think it was due to exhaust scavenging after viewing before/after results from closed/open exhaust.

409CISecondGen

iTrader: (2)

Dark Blue: Stock
Light Blue: +Intake, exhaust, tune
Red: +3.91s, Headers, Fast102, Ported TB, 180*T-stat,

Can anyone explain the dip/bump in the red torque curve?

http://www.flickr.com/photos/74632166@N04/7679148592/http://www.flickr.com/photos/74632166@N04/7679148592/ by http://www.flickr.com/people/74632166@N04/, on Flickr

http://www.flickr.com/photos/74632166@N04/7679155014/http://www.flickr.com/photos/74632166@N04/7679155014/ by http://www.flickr.com/people/74632166@N04/, on Flickr

Felix C

The blues are typical and no double hump. Steady or gradual upward incline to the 4800rpm peak.

I see what you mean regarding the red although it levels than gains and not show a decrease as is what I was referring to in the OP.

Wnts2Go10O

iTrader: (12)

each valve train has a spot where there is sort of resonance frequency. some of it comes from the springs used. the springs are moving or "vibrating" as the cam/lifter/pushrod/rocker combo compresses the springs then allow them to expand. the faster the engine is going, the higher the frequency at which the springs are moving or "vibrating." there is a point in all springs where the movement/vibration can be in sink with previous vibrations and it adds to them (think of swinging on a swing, you match your movements with it to go higher and higher). aka.. it resonates, it builds. when it reaches its peak at the 3000-3500 rpm range, it gives you that strange dip. after that point it dissipates and goes back to the normal curve.

timing chain sets can do this as well. pushrods CAN do it based on deflection but its not so much an issue in street motors i dont think.

you can hear an exhaust resonance around 2000-2500ish on most F-Body exhaust systems. the drone/sound builds and builds then after 2500 or so, it dissipates.

jimmyblue

iTrader: (11)

What you've done is add at least two pieces that are
meant to add some resonant airflow "upside" - the headers
for sure, the intake probably. When you overlay that onto
the natural breathing of the motor you'll see humps if the
natural and exhaust-extraction peaks are separated far
enough in RPM. If not then they'll appear to be one fat
one.