Why a power dip between 4-5500rpm makes sens

Speedo007

Speedo007

New member
I'm subscribed to tons of motorcycle websites and forums, and this morning I fell on a post that as obvious as it may be, I never thought of before.

Now why are manufacturers putting torque/power dips at certain places in the RPM range when they could easily eliminate them through the injection mapping, exhaust design, etc..

2 good reasons: First one is to allow them to meet certain pollution standards that are evaluated at certain rpms. (Just like for exhaust sound, as long as they meet the standards at a certain RPM, it can become way louder past that)

Second reason is to improve mpg at certain RPM...oh interesting...the FZ8 cruises at about what, 5200rpm on the highway?....and looking at the dyno chart, thats in the bulleyes to improve mpg...



Doesn't me it's perfect to be that way or that it can't be improved, but it does now suddenly make way more sens to me now...
 
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Deleted member 438

Guest
Speedo007 said:
I'm subscribed to tons of motorcycle websites and forums, and this morning I fell on a post that as obvious as it may be, I never thought of before.

Now why are manufacturers putting torque/power dips at certain places in the RPM range when they could easily eliminate them through the injection mapping, exhaust design, etc..

2 good reasons: First one is to allow them to meet certain pollution standards that are evaluated at certain rpms. (Just like for exhaust sound, as long as they meet the standards at a certain RPM, it can become way louder past that)

Second reason is to improve mpg at certain RPM...oh interesting...the FZ8 cruises at about what, 5200rpm on the highway?....and looking at the dyno chart, thats in the bulleyes to improve mpg...



Doesn't me it's perfect to be that way or that it can't be improved, but it does now suddenly make way more sens to me now...
Click to expand...

I've never really given the dips much thought, but your theory makes a lot of sense.
 
H

Hoover

Guest
Makes sense.
I doubt they would ever coroborate your theory though.
 
Speedo007

Speedo007

New member
And all I can say is since my sprocket conversion engine now runs at 6200-6500rpm on the highway and mpg has dropped by about 25% overall.
 
K

K-Gr.

New member
Hoover said:
Makes sense.
I doubt they would ever coroborate your theory though.
Click to expand...

Why? This is nothing to be ashamed of. Honda with their new VFR said in press release that exhaust has 2 valves and that the second one stays closed until certain RPMs, so that the bike is quiet enough to meet regulations.
 
Speedo007

Speedo007

New member
Yep it's just constraints they have no choice but to work around. Better mpg, less pollution, less noise at rpms where bike would be used in "normal" conditions. And once in a while when you just want fun without consideration for the planet, you just twist the throttle, and get lower mpg, more pollution, more noise, and more fun haha
 
FZER

FZER

Avid Rider
Very believable I think 65mph is right in that range and on long trips I do get 50mpg.
 
Speedo007

Speedo007

New member
To increase torque in lower RPM, which it does quite nicely. I was sharing the info so those interested in the mod, know exactly by how much it affects mpg.
 
R

rysyndrome

New member
Speedo007 said:
To increase torque in lower RPM, which it does quite nicely. I was sharing the info so those interested in the mod, know exactly by how much it affects mpg.
Click to expand...

oh ok, so do you think the extra low end power is worth 25% loss in mpg? Any idea how much more torque is gained by this mod? Thx
 
Speedo007

Speedo007

New member
By the seat of my pants it felt like maybe a 15% increase in torque...the big difference is with the sprocket change you're basically always above that power dip...so even on the highway it feels like you're in 5th gear, so always power on the tap. Is it worth it? depends on your wallet I guess, cause it did make the bike noticeably more enjoyable. If you do mostly touring, then I wouldnt recommend it, cause you'll basically be cruising at same speed all the time and just burn more fuel. If city, twisties and secondary roads is on the menu, it is well worth it yes. I must say that part of that 25% mpg decrease is that after sprocket change I was riding even more aggressively cause the accelerations were so entertaining :)
 
R

rysyndrome

New member
Nice to know there is a good option for increasing the torque if I get bored of the stock setup. Being this is my first bike I am extremely happy with the power thus far. Still this would be a decent way to change it up down the road. Thanks
 
Speedo007

Speedo007

New member
Just keep in mind that the desire for more power can be endless, we always end up getting used to whatever power is available. I had a Speed Triple and after a few months I was shopping for sprocket conversion cause the bike simply wasnt intimidating anymore, the bike was already a beast stock...but just like drugs, it takes more and more to get the same kick...unless you start looking at bikes that are more fun to ride at slower speeds hehe
 
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ausfz8

New member
Changing Sprockets has been proven on a dyno with back to back results that you actually lose power. the affect it has though does lower your top speed but gains you better acceleration. this power dip does look like it is an affect that Yamaha have put into place for better emissions, noise and safety in mind.
I have been doing a lot of research lately on this matter and have found different dyno charts with different air/fuel ratios and finally more recently this morning come across something else that will contribute.
It seems that the Stock Exhaust with the muffler and Cat converter are way too restrictive. this also goes in hand with the emissions factor of around the closed loop area which is trying to get a 14.6-14.7 A/F Ratio instead of more optimum power of anything around 12.8 to 13.6 AFR.
last contributing factor that I have just come across this morning is the fact that these bikes have Secondary Butterflies that dont open up aggressively enough to allow the air and fuel in like the primary butterflies do when the throttle is opened up at lower rpm.
It seems like these bikes have plenty more left in them to have a lot more fun with but are restricted in so many ways to pass emissions and safety.
 
Marthy

Marthy

Member
Stock exhaust sucks! Even decat with your choice of slip-on too. Been there... You need a full exhaust swap (Apakrovic... no sure?) Or my midship exhaust fixed the dip at mid range too.

Sent from my SAMSUNG-SGH-I337 using Tapatalk
 
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ausfz8

New member
Thats exactly the path im looking at heading down Marthy. thought of doing it for some time now for better sound and look but didn't realise just how good of torque and power gain you would get from it. I have a custom motorcycle exhaust shop around by which i'll get them to cut off and insert a mid pipe that i can put my short Scorpion slip-on onto.
 
toothycardus

toothycardus

New member
Speedo007 said:
Just keep in mind that the desire for more power can be endless, we always end up getting used to whatever power is available. I had a Speed Triple and after a few months I was shopping for sprocket conversion cause the bike simply wasnt intimidating anymore, the bike was already a beast stock...but just like drugs, it takes more and more to get the same kick...unless you start looking at bikes that are more fun to ride at slower speeds hehe
Click to expand...

I just ride my Honda XR250R for about a week (off road as well) them come back to the FZ8 = :eek::dropjaw::D
 
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decooney

New member
I see that graph provided back in 2012 on the first post is from Graves.

Interesting graph and explanation. A flat spot is one thing, but that dip shown in the graph is horrible. It sure explains what I noticed with my stock bike. Wish I had seen this before.

Now with exhaust changes and Power Commander I installed, the flat spot and dip is gone. The midrange pulls harder and it seems as if the bike just takes less effort to cruise steady at highway speeds.
 
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