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[Gecko]

Yeah, yeah, we're correcting things we didn't know about, whatever.  Doesn't answer the question - why 2500 rpm?  I've heard people say it's because the run starts around 2000 and it takes a little while for things to stablize, the change in air flow from closed to open throttle, slow moving air to accelerating air, blah blah (sounds like arm-waving to me) - would there be a similar dip at 3500 if the run was started at 3000?  I don't think so. 

[Twolanerider]

Yeah, yeah, we're correcting things we didn't know about, whatever.  Doesn't answer the question - why 2500 rpm?  I've heard people say it's because the run starts around 2000 and it takes a little while for things to stablize, the change in air flow from closed to open throttle, slow moving air to accelerating air, blah blah (sounds like arm-waving to me) - would there be a similar dip at 3500 if the run was started at 3000?  I don't think so.  

Actually what's been said, repeatedly, is that there is no dip that must be there at 2500.  If you're seeing one something in the tune, the tune methodology or the parts combination isn't as good as it could be.  But there is no predetermined nor required 2500 rpm dip.

[HOGMIKE]

Dip? What dip?
 

[willyB]

Yeah, yeah, we're correcting things we didn't know about, whatever.  Doesn't answer the question - why 2500 rpm?  I've heard people say it's because the run starts around 2000 and it takes a little while for things to stablize, the change in air flow from closed to open throttle, slow moving air to accelerating air, blah blah (sounds like arm-waving to me) - would there be a similar dip at 3500 if the run was started at 3000?  I don't think so. 

My local tuner and former HD mechanic says that the stock configuration and TQ dip is the result of lean tuning to meet EPA. He says that tuning HD engines after better intake of air and out gassing of exhaust will virtually eliminate the TQ dip in this range. He also says that certain configurations of parts make the tuning balance tougher in many cases and that a qualified tuner who takes the time can eliminate those issues as well.

Best answer I got for ya.

Any HD qualified tuners out there who can confirm?

[timo482]

when my 2007 was new it had a minor issue, puked oil all over and ran terrible - new rings & hone & oil pump o rings etc ran several heat cycles on the dyno - i have the dyno sheet - no dip at all - nice and smooth stone stock - 10 runs - and no oil usage or leakage at all since, its dry - hence i have not changed a thing - i do oil changes and put in gas and ride it. so at least my stone stock hd has no dip in the dyno sheet. ive seen many dyno sheets of stock bikes that used to be posted to the net and stock curves were very nice and smooth, no dips.

to

[strokerjlk]

all dips are not created equal.
some exhaust have dips. take a d&d fatcat (touring model) for instance,they will dip somewhat at 3000-3300 rpms. but the dip might still might be better (more hp/tq) than say a 2-2 exhaust in that same rpm.
and yes some combos.motor,exhaust, cams etc will have trouble spooling the heavy drum at low rpms on a WOT run in high gear 1:1 ratio.
then there is clutch slip, most all modified motors will show some slip down low,even with clutch upgrades. this will be reflected on the wot dyno sheet.
then there is tuning dips. fuel,timing. so it is part of what you pay for when you get a dyno tune.
 we look at the whole picture and determine what is going on.
that said...what you see on a dyno sheet is WOT in high gear (most tuners) 1:1 ratio. so 5th gear on a 5 sp and 6 th gear on a 6 speed.
so just because you see a dip @ 2500 WOT in high gear,dosent mean it dips there in a lower gear,or that you are down on hp/tq @ 2500 rpm when cruising @ part throttle.
how many times do you wack the throttle to WOT @ 2200 rpms in high gear on the street? I know some do  but why?

FWIW you will never feel (SOP) a 3-5 hp/tq WOT dip @2200-2500rpms. when you are running through the gears.
and if you are cruising there,you are only making 15-20 hp anyway. (whatever it take to maintain your speed)

[Ed Ramberger - One_Screamin_Eagle]

Why is the dip in dyno curves always at 2500 rpm?  I know it can be tuned out, at least mostly, but there always seems to be a an actual drop in torque or a decrease in the rate of climb.  Why at that specific rpm?  It doesn't appear to matter what cam is in it (which it should), or what exhaust - some are just worse.

Never say always and never...

[HILLSIDECYCLE.COM]

Why is the dip in dyno curves always at 2500 rpm?  I know it can be tuned out, at least mostly, but there always seems to be a an actual drop in torque or a decrease in the rate of climb.  Why at that specific rpm?  It doesn't appear to matter what cam is in it (which it should), or what exhaust - some are just worse.

Engine combination/exhaust system.
Scott