Strange moment curve

[harkes]

Hi

Had my car on the dyno the other day and got this rather "funny" moment curve. Any idea what is going on?

6250rpm = 8000rpm

[Ivan141]

I have read about incorrect tyre pressures causing this kind of effect, but I cant say for sure.

[jondee86]

Undulations or "waves" in the torque (moment) curve are often caused
by intake resonance affecting the VE of the engine. You can try and tune
them out by changing the fuel and ignition timing at the rpm's where the
torque is low.

Cheers... jondee86

[harkes]

Ivan141 Wrote:I have read about incorrect tyre pressures causing this kind of effect, but I cant say for sure.

Now that you mention it my tyre pressure was a bit low...

[rene]

is the red curve power and the other torque ?

because it all look strange but what is the set up off engine ?

[jondee86]

rene Wrote:is the red curve power and the other torque ?

Pretty sure the red line is just telling you to ignore the power trace
and look at the torque (moment ) trace.

The shape of the curve is influenced by a lot of factors, including the
amount of smoothing that is applied either mechanically or electronically.
Here is a curve from a stock engine on a hub dyno (no inertia smoothing
from a heavy roller).



The trace clearly shows the torque fluctuations. On an inertia dyno these
fluctuations would be largely smoothed out, and the curve would look a
lot nicer. Hey... everyone likes smooth curves :wink:

Cheers... jondee86

[NoHachi]

Non-smoothed curves are actually a bonus. They tell you where you need to put your rpm bins for best interpolation (if the omex does interpolation).

You want the rpm intersects to lie on the peaks and valleys of the VE (hp) curve so straight lines connecting those points follow the hp curve as good as possible.

How is this engine running on idle and just off idle? Very big VE swings there, which can lead to some weird oscillations.

[harkes]

Hey

Specs:
Inlet manifold - custom with 350mm funnels (from top of valve), silvertop ITB
Exhaust - Martelius R1
Redtop - with ported top and 11,5CR
Schrick 296 IN and 256 OUT
OMEX 500

Ill have the lift measured tomorrow

I am wondering if the rather special construction of the R1 can cause this? The joining of 1-2 and 3-4 exhaust ports is not common as I know.

[robokill]

I never seen such a great difference between in and out cams. Does that work well ?

[jondee86]

The exhaust will have harmonics that improve the scavenging at
certain rpm's. And the intake will have harmonics that improve the
cylinder filling at certain rpm's. Depending on where these "peaks"
occur in the rpm range, you will get better or worse torque.

Factory engineers will spend thousands of hours experimenting with
different designs on an engine dyno to balance the peaks and troughs.
When you design your own intake and exhaust, you take the chance
that you will have some different results (good or bad) from the
factory setup.

Cheers... jondee86