Shifting at RPM or horsepower

[Mandi Engineering]

I am still new to LSR and have been curious what is the best way to go about shifting to reach my desired MPH. I will be using a motorcycle engine and wondering if I should shift closer to the RPM limit of 14,000 or where the horsepower peaks at 12,500. Reason I am confused is because I'm not sure if the extra rpm will help increase speed with % of tire slippage or if it just boils down to keeping the engine at peak horsepower to move through the air.

[RidgeRunner]

      A lot depends on the shape of the horsepower curve and how fast the shift can be completed.  A flatter curve around peak HP as opposed to a radical spike and a quicker shift completion allows more leeway in shift points.  If the rpm's drop too low on the final shift they won't recover for max speed against the vehicles aero wall.

           Ed

[SPARKY]

for max accel try not to fall back below peak TQ after shifts

[Sumner]

for max accel try not to fall back below peak TQ after shifts

I have some spreadsheets on my site that will help with that....



... above is a partial screen shot of one.  The part that is of interest to determine if you are staying around the peak torque Sparky is talking about is in the lower part of the sheet. Let's say you shifted from 1st to 2nd at 60 mph.  Your rpm there in first is 10715,  you loose 2806 rpm on the shift, and then in second you are turning 7909 rpm.  If you know the torque curve of your motor then you can see what it is at 7909.

As you can see you can pick any shift point and see what the rpm drop is and what the rpm will be in the next gear.  Here is an another example for using the 4 speed car spreadsheet...



... that shows the 1-2, 2-3, and 3-4 shift points at different rpms.  You can find the car and motorcycle ones here...

http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html

Good luck,

Sum

 

[kiwi belly tank]

If you're running a bike engine in a car you'll need to ring it's neck to make it work so run it like you stole it. I've driven a bike engine lakester & that was the only way to get results.
  Sid.

[Stainless1]

You will need to keep it up in the power after the shift so if it will run near the red line in a gear run it there in that gear.... it will get to a spot that is will not, that may be the point that you are at the aero/power wall... then try a different set of sprockets. 
I would gear it for target speed about 500 RPM below peak HP to start. 
Small motors make their power with RPM... if you are feeding it air it will make power beyond what the dyno says.

[ETM]

In theory:

If your HP rises all the way to redline then just shift at redline.

If your HP is a curve:  Determine your RPM drops between each gear.  When the HP value on the right side of the curve falls below the HP value the next gear will land on it’s time to shift.

Don’t go out of your way to find peak engine torque. Peak engine torque will tell you at what RPM a given gear will accelerate hardest, but it does not take into account the torque multiplication effect of gearing.  It is probable, even likely, that a lower gear delivers more torque to the rear wheels due to torque multiplication. The torque curve does not take this effect into account while HP does.

In practice:

The salt is about traction and managing wheel spin.  In the lower gears you will be short shifting in an effort to better match torque delivery to the traction available. I like logging longitudinal G to get a good feel for how much wheel spin to allow. Long-G * 21.94 = MPH per second the vehicle is accelerating.

[RansomT]

What engine are you using?   Mods to the engine?

[SPARKY]

but it does not take into account the torque multiplication effect of gearing.  It is

TQ X FDR= TE tractive effort   FDR= TR X RA X TC 

TR=trans ratio
RA=rear axle ratio
TC=tire correction

run your dyno sheet torque # through this formula will tell you how to maximize

[ETM]

but it does not take into account the torque multiplication effect of gearing.  It is

TQ X FDR= TE tractive effort   FDR= TR X RA X TC 

TR=trans ratio
RA=rear axle ratio
TC=tire correction

run your dyno sheet torque # through this formula will tell you how to maximize

Torque alone does not tell the story.  As your formula shows, torque has to be supplemented with RPM and FDR.  Yes, you can build a chart using said formula and create a chart with trace for every gear with MPH on the X axis and RPM on the Y a axis. It gets involved.  Or, you can simply use the HP table and apply the RPM drops to it as I described above.  Both will give the exact same result, only one is easier.

The purpose for my torque comment is not to say that torque is meaningless, it is to reduce the common misconception that peak torque is the end all when discussing acceleration.  If asked: What accelerates a car faster, 400 ft-lb at 4000 RPM or 300 ft-lb at 6000 RPM most people answer 400/4000.  That would be incorrect. There is a 13% difference on the HP numbers the values create in favor of 300/6000.  This means that there will also be a 13% advantage at the rear wheel torque after the FDRs are added using the long calculation and chart.
.

[SPARKY]

       RPM x TQ
HP= -----------
           5252

RPM  has equal value to torque   
which leads to the old saying you can multiply TQ but not HP
If you can do the R's you can get the TE by changing the FDR or the tire size   we are almost saying the same thing  I am just providing the metric on how you can get the max TE for a given speed---I got my  red hat with 28" tires at 7850 rpm with a FDR of 2.14

I got my Blue hat with 24.5 tires in od with 1.66 FDR with 15# more TE at 6850 rpm

[Mandi Engineering]

I will be using a stock 2006 Kawasaki 636 engine for a motorcycle chassis at first to ensure the chassis is true and no problems going straight. After testing I will then add a turbo and go from there to tune. The gearing i will be using on the bike predicts a top speed of 210mph although I know this is for tarmac conditions with a tail wind. My target speed is 175mph.

I forgot that I would be short shifting the first few gears to minimize slippage and only coming close to redline in the last few gears. I will analyze the dyno graph once performed to see which is best in theory and then make adjustments while actually testing. Thank you for clearing my mind.

[tauruck]

I got lost at TE.

I have much to learn.

[RansomT]

I will be using a stock 2006 Kawasaki 636 engine for a motorcycle chassis at first to ensure the chassis is true and no problems going straight. After testing I will then add a turbo and go from there to tune. The gearing i will be using on the bike predicts a top speed of 210mph although I know this is for tarmac conditions with a tail wind. My target speed is 175mph.

I forgot that I would be short shifting the first few gears to minimize slippage and only coming close to redline in the last few gears. I will analyze the dyno graph once performed to see which is best in theory and then make adjustments while actually testing. Thank you for clearing my mind.

IIRC, the "power under the curve" of that year 636 is pretty strong above the peak HP.  I would shift high in the RPMs (in the upper gears) probably 13,500 or so.  Also, I wouldn't "plan" on short shifting in the lower gears until I got her on the salt just to see how much spin ou are getting. Shifting much below peak TQ may get you into a bog situation.  The tune will be tricky in the lower RPMs range, because the load will be much higher pushing that vehicle than the orginal bike.

[SPARKY]

I got lost at TE.

Mike all of the multipliers change with each rear gear change, Trans gear change, by shifting the trans, or changing the tire diam.

what one is trying to is bring the biggest TE number to the speed on is trying to achieve---

I was able to bring 15 more ft. lbs. by gearing up, tiring down and going back toward peak torque of my engs TQ curve---using this on an excel spread sheet I was able to go almost 6 mph faster  most  likely due to the old LSR saying:

  " It is easier to pull the gear than the tire".

TE is what is put to the ground  as the old add used to say it is where---(POWER TO)  the rubber meets the road---

 the driving force-- so to speak---

does not deal with tire slip or capability