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[Gecko]

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.

[Twolanerider]

Short answer is they all don't.  Neither of mine do.  Some exhaust systems are noted for a torque dip early on.  Some tuners don't start tuning early in the curve.  If there's a real dip, however, there is either poor tuning or a choice of parts that could probably have been better selected.

[HOGMIKE]

Short answer is they all don't.  Neither of mine do.  Some exhaust systems are noted for a torque dip early on.  Some tuners don't start tuning early in the curve.  If there's a real dip, however, there is either poor tuning or a choice of parts that could probably have been better selected.

 

Ours don't either.....
 

[Gecko]

Okay, let me rephrase that.  When there is a dip...  why 2500 rpm?  It must have to do with cylinder scavenging, but what is significant about that particular spot?

[Twolanerider]

Okay, let me rephrase that.  When there is a dip...  why 2500 rpm?  It must have to do with cylinder scavenging, but what is significant about that particular spot?

Again, wouldn't be particularly there.  2500 is not a magic number for parts combination inefficiency or a lack of tuning competence.  I've seen dips all over a torque curve.  Whether they be for slipping clutches, bad parts choices or poor tuning 2500 isn't a one-RPM-fits-all location for things not working as they should.

[mrmagloo]

Means you're runnning a Thunderheader?   

 

[AXIL]

   no dip in my thunder header.  oh! i geuss i know how to tune.

[timo482]

ive looked at lots of dyno charts - i know what he is talking about - and it can be tuned out by using correct exh and correct tune.

its pretty easy to recognize a chart of a bike with true duals

least amount of torque and hp  between 2500 and 3500 rpm

but they usually show really high numbers up at 5k

so ride in third and you have lots of power

i just dont get it

to

[grc]

Funny thing is, most folks who have never read all these things on the 'net or in a motorcycle rag, and have never seen a dyno chart, probably don't have a clue that a dip or flat spot exists.  I see all sorts of folks who used to be satisfied with their car or bike become unhappy overnight, just because they read a bunch of crap somewhere telling them that there is something wrong with how their vehicle runs.  Untold gazzillions are spent to "fix" problems that most folks never knew they had.  One marketing genius sells you the pipes to make your bike loud and look "cool", thus reinforcing your manhood.  Of course, the pipes change the air flow through the engine, so another marketing genius sells you an add-on box to add more fuel and "fix" the lean condition caused by the pipes.  Then the bike owner reads some more stuff and determines that the little black box isn't good enough, he needs a more expensive device and a dyno tune by some guy who probably couldn't spell dynomometer dynamometer last week but now he is an expert dyno operator and tuner.  Yup, that's the ticket to solving the problem he didn't know he had in the first place.  Only, the "tuner" couldn't tune his way out of a wet paper bag, so now there is a big flat spot and pinging and popping on decel and the gas mileage sucks.  So off to the ads and the internet for the next idea, and we have the auto tuning devices for another $1k or so.  Yeah, let's try that.  And if we get lucky, the seller of such devices actually has a base map that matches our particular bike, and it actually works as advertised.  Or, we find that the base map does not match up well with our bike and the "auto tune" isn't so "auto".  Now we have to go back to the dyno guy to get the base map fixed, but of course he already proved he couldn't tune his way out of a wet paper bag, and there is no one else in the area.  

Where does it end?  Thousands spent so far on a "problem" the rider didn't even realize he had.  I have a much better idea and proposal:  Take all that money, put it in your PayPal account, then send it to me.  My PayPal account is OU812.


Jerry


edit:  good thing no one hired me to tune their bike, since I didn't spell dynamometer correctly either.

[DESERTBEAR54]

Jerry,
       Well Put!!!

[JCZ]

Thanks for the chuckle Jerry.  You're very entertaining while you make the point.

[Wild Card]

Jerry, you must be a hoot at all the family parties.   

[digga25]

Jerry,you hit the nail right on the effin head!!!!!!1

[petewerner]

Mine has a small dip in the 2500 range, but I think alot of that was the first couple of runs, 4th and 5th gears and changed plugs(type and gap) as well as a new HD K&N airfilter if memory serves...Plus some changes to AFR to get it running not so skinny!! Now I can't feel any softness there?? But I see what the OP is speaking of.

[willyB]

After originally loading a canned map from FuelMoto my 2500 RPM torque was 93.39 (44.46 HP) and after a good tune on my buddies dyno 2500 RPM torque was 97.66 (46.49 HP). Torque dip gone!

Peak torque and HP numbers only increased from 105.99 to 108.25 TQ and 88.19 to 89.52 HP but the curves are now much smoother.

I will say, the FuelMoto map ran "real" good. I would have never noticed any performance differences without actually looking at the dyno sheet.

I have V & H True Dual, Hi-Outputs slipons and PC-V.