Why do the dyno curves always dip between 3k and 3.5k?

[TimberwolfZ28]

Seems the AFR dips, as well as the hp and TQ curves. Is there a turbulence issue? or something else?

I've seen this on a LOT of dyno charts out there

[SAMCRO]

Curves will always cross at 5252 if done in scale

[TimberwolfZ28]

Originally Posted by SAMCRO

Curves will always cross at 5252 if done in scale

I think you missed the point of my question?

[aharp]

depends a bit on the exhaust. With a good exhaust and the rest of the package matching my afr lines are flat as kansas. The hp/tq dip can be brought up in some areas with timing and fuel find tuning on each

[Bruce Woltz]

Originally Posted by TimberwolfZ28

Seems the AFR dips, as well as the hp and TQ curves. Is there a turbulence issue? or something else?

I've seen this on a LOT of dyno charts out there

It's a characteristic of bikes with 2 into 1 that are over exhausting.. Bruce

[Hillside]

Originally Posted by TimberwolfZ28

Seems the AFR dips, as well as the hp and TQ curves. Is there a turbulence issue? or something else?

I've seen this on a LOT of dyno charts out there

Not all do that, but what exhaust/engine size are you referencing??
Scott

[compressor#v]

Originally Posted by Bruce Woltz

It's a characteristic of bikes with 2 into 1 that are over exhausting.. Bruce

It's a charachteristic of D&D fatcats in many builds.

[TimberwolfZ28]

Originally Posted by Hillside

Not all do that, but what exhaust/engine size are you referencing??
Scott

I'm not referencing any particular build... it's just something I see on about 80% of twin cam dyno charts. Here, nightrider's website, hdforums, etc.

[mccycle]

The duration, amplitude,and phasing of the exhaust returning expansion or suction wave in correlation with the cams overlap triangle, mostly the evc timing and rate of closing speed. Sometimes late ivc reversion also plays an effect. This will drive you nuts trying to calculate this on the 45 degree common manifold v-twin.

[n7ki]

You also get that dip with straight pipes with no baffles/restrictors. Nightrider.com has an article on that called Making Drag Pipes work. This may be the info you are looking for.

[Mtclassic]

if you use andrews 21's or 26's and supertrapp 2.1 on a 95" you will not get a dip.

['05Train]

No dip on mine.