NEVER shift before redline for all out acceleratio

[umairhashmi]

Looked at some drag racers tonite and for some reason they NEVER upshifted until the bike hits redline (11k RPM),regardless of which gear the bike is in .Is this always the best thing to do for all out acceleration in a straight line???

 

[WuzzaCBXRider]

To absolutely know your shift points you have to know when your motor quits making horsepower. A factory redline is almost always NOT the correct shift point for the best acceleration. Unless you're in high gear going for an ultimate top speed run, you're not gaining speed any faster by going beyond the motor's horsepower output. If your bike dynoed its highest HP at say 10,600, you would want to shift then, and not wait till the tachometer's marked redline of 11,000.

 

[NightCrawler]

(CBXRider @ Nov. 05 2006,01:44) To absolutely know your shift points you have to know when your motor quits making horsepower.  A factory redline is almost always NOT the correct shift point for the best acceleration.  Unless you're in high gear going for an ultimate top speed run, you're not gaining speed any faster by going beyond the motor's horsepower output.  If your bike dynoed its highest HP at say 10,600, you would want to shift then, and not wait till the tachometer's marked redline of 11,000.

Yup.

I had this discussion with a co-worker a while back. He told me ALL bikes make the most power at the red-line.

I politely walked away ...

 

[reward69]

Well I havent even had my bike to the track, but I can tell you from my previous car drag racing experience that shift points are critical. I have always ran the 1/8th mile tracks locally and all my cars I've had you would be amazed at what 1 or 2 hundred rpms would do to et. My last car like to be shifted at 6800rpms, if it was shifted either below or above it would loose et. I had an air shifter and it was very accurate on shift points. It would fall off close to a tenth if you shifted +/- 6800 rpms. I never had the car dynoed, but the track is one of the best tools for testing there is.

 

[CAT3]

I disagree with shifting AT the peak hp rpm. I too drag raced cars for several years, and tested out different rpm shift ranges. Every combination is slightly different, however, the common among them is shifting just AFTER your peak power, this puts the engine into a higher power area upon shift completion, on most applications. True enough, shifting at the revlimiter may cost you on ET. But the sweet spot is normally b/w max hp rpm and rev limiter, so that the next gear is setup with more power available.

With nitrous applications, it may be beneficial to shift earlier than normal. This is due to the increased torque nitrous makes, and the lower the rpm the more torque produced. On my car for NA I would shift at 6700-6900rpm, depending on Density Altitude (DA) for lowest ET, and with N2O I would shift 5900-6050rpm for best ET based again on DA.

Experiment and find where your bike likes to be shifted. This is just my experience from the cager racing perspective.

 

[Revolution]

just yesterday some guy told me never hit redline or limiter in first. something about the valves can float cause they're moving faster than the engine speed [crank?]...

 

[Mr. Anderson]

smoking gunz, never listen to that guy again, the rev limiter is there for a reason and in most cases will not cause any problem by hitting the rev limiter all day long. the one exception to this is never down shift from a higher gear while racing (common mistake on some cars miss-shifting 2nd to 1st instead of 2nd to 3rd.) and yes then bad things will happen if the clutch is fully engaged after the missed shift as the revlimiter cannot stop the decceleration of what is going to happen .

as for the best shift on the rpm band, a dyno graph would have to be analyzed to see where and how hp is being made. the more flat the hp curve is the less important this is. also is the hp 1k rpm after the peak hp higher than 1k before pk hp? is so then shifting after peak hp would make more sense. this is just a very broad and basic statement but ultimately a dyno graph of your bike would have to analyzed to determine best shifting time.

 

[Professor]

(CBXRider @ Nov. 05 2006,00:44) To absolutely know your shift points you have to know when your motor quits making horsepower.  A factory redline is almost always NOT the correct shift point for the best acceleration.  Unless you're in high gear going for an ultimate top speed run, you're not gaining speed any faster by going beyond the motor's horsepower output.  If your bike dynoed its highest HP at say 10,600, you would want to shift then, and not wait till the tachometer's marked redline of 11,000.

There is another factor you need to look when determining the shift point….. What does the hp/torque curve look like in the rpm range after you make the shift? There might be cases where pulling slightly past the peak hp allows the rpm to fall in a better spot on the curve for the next higher gear.

This is one of the reasons some shift controllers can be programmed for different a different RPM for each gear.

 

[Red05]

The tach is sweeping so fast at that point, I've found that planning to shift at 10,200 actually ends up shifting at 10,450 or so...which works very well on my set-up. AS stated earlier, 100 or 200 RPM makes quite a difference.

 

[heavybusa]

good discussion, thanks for posting.

 

[Mr Brown]

I shift when the tach hits about 10,7. I bought a shift light that I will set about 10,5 by the time I hit the button it will be where it needs to be.
Gunz, like Mr Anderson said, that guy has no idea what he's talking about, ignore him. You can run into the limiter in any gear and not tear anything up, unless you're spraying, in which case VERY bad things can happen!

 

[Revolution]

tanks

 

[bitabur]

You can calculate mathematically when the best time to shift is.

We know that the gearing change when shifting to the next gear is going to reduce the torque output because you are shifting to a higher gear, meaning a higher torque divider. We also know that the torque output of the engine is going to fall near the top of the powerband.

Lets set some variables:

Tc = torque in current gear
Tn = torque in next gear at same (wheel) speed

Gc = current gear's gear ratio
Gn = next gear's gear ratio

The time to shift is when:

Tc = Tn * (Gn/Gc)


I believe if you take your dyno'd torque graph, multiply the vertical scale by (Gn/Gc) and multiply the RMP scale by (Gc/Gn), the proper shift point from one gear to the next is where the two cross.


This makes the assumption that your (actual) speed will not change while shifting, which is not exactly true. I believe pushing the actual shift point a little higher will tend to compensate for this.

Does this make sense? I'll make some pictures of what I'm talking about later if it doesn't.

 

[CAT3]

(bitabur @ Nov. 05 2006,18:23) You can calculate mathematically when the best time to shift is.

We know that the gearing change when shifting to the next gear is going to reduce the torque output because you are shifting to a higher gear, meaning a higher torque divider. We also know that the torque output of the engine is going to fall near the top of the powerband.

Lets set some variables:

Tc = torque in current gear
Tn = torque in next gear at same (wheel) speed

Gc = current gear's gear ratio
Gn = next gear's gear ratio

The time to shift is when:

Tc = Tn * (Gn/Gc)


I believe if you take your dyno'd torque graph, multiply the vertical scale by (Gn/Gc) and multiply the RMP scale by (Gc/Gn), the proper shift point from one gear to the next is where the two cross.


This makes the assumption that your (actual) speed will not change while shifting, which is not exactly true. I believe pushing the actual shift point a little higher will tend to compensate for this.

Does this make sense? I'll make some pictures of what I'm talking about later if it doesn't.

It makes sense yes, same thing a few of us have said, but if you had a chart to show those not tracking it might help.


Question on the limiter, is the factory limiter cutting spark or fuel? If I had my guess it would be spark, which out of the two I prefer, less *KABOOM* happens that way.

 

[umairhashmi]

I understand that the most accurate way would be to dyno it but for someone who is not a drag racer i dont wanna spend my money on it.I have 06 busa with 3k miles on it so i was wondering where the top of the powerband is in general

 

[Mr Brown]

Do you have a shifter?

 

[umairhashmi]

(Mr Brown @ Nov. 05 2006,19:43) Do you have a shifter?

Bike is stock except for yoshi RS3 bolt ons and an undertail

I just wanted to know for those bike night drag races at red lights J/K

 

[Mr Brown]

(umairhashmi @ Nov. 05 2006,21:45)

(Mr Brown @ Nov. 05 2006,19:43) Do you have a shifter?

Bike is stock except for yoshi RS3 bolt ons and an undertail

I just wanted to know for those bike night drag races at red lights J/K

When you see the tach hit 10,5 shift. Do you clutch it when shifting?

 

[umairhashmi]

(Mr Brown @ Nov. 05 2006,19:47)

(umairhashmi @ Nov. 05 2006,21:45)

(Mr Brown @ Nov. 05 2006,19:43) Do you have a shifter?

Bike is stock except for yoshi RS3 bolt ons and an undertail

I just wanted to know for those bike night drag races at red lights J/K

When you see the tach hit 10,5 shift. Do you clutch it when shifting?

Yes i always use the clutch but i have read you dont have to if you know how to do it right.At 10.5 the front wheel is barely on the ground though.Ill try it on a empty road one of these days for fun. I guess it goes without saying to keep all my 205 lbs on the tank to keep the thing from looping on me

 

[Mr Brown]

Preload the shifter. When you see the tach go thru 10,5, let off the throttle just a little, and it will go into 2nd. As soon as you lt off the throttle, hammer it again and reload the shifter. Repeat as needed. The front wheel doesn't need to be on the ground as long as you're going straight.........