When shifting a 5 speed...

[*K*night Rider]

Well, I used this calculator ( http://www.bgsoflex.com/shifter.html ) and got these results (I used the dynograph from the 205hp 3800)

<blockquote>quote:</font><hr>
Computation Results
Using the Criterion for Maintaining the Same Horsepower Before and After Shift:

Finding Best Shift Placement Points For Ratio 3.75 to 2.19:
Found optimum shift RPM at 6186, which achieves 157 horsepower and lowers the RPM To 3612 after shift

Finding Best Shift Placement Points For Ratio 2.19 to 1.41:
Found optimum shift RPM at 6077, which achieves 167 horsepower and lowers the RPM To 3912 after shift

Finding Best Shift Placement Points For Ratio 1.41 to 1.00:
Found optimum shift RPM at 5975, which achieves 177 horsepower and lowers the RPM To 4238 after shift


-----------------------------------------------------------

Maximizing the Area Under the Horsepower Curve:
Finding Best Shift Placement Points For Ratio 3.75 to 2.19:
Found optimum shift RPM at 6250, which achieves maximum area under horsepower curve, and lowers the RPM to 3650 after shift

Finding Best Shift Placement Points For Ratio 2.19 to 1.41:
Found optimum shift RPM at 6244, which achieves maximum area under horsepower curve, and lowers the RPM to 4020 after shift

Finding Best Shift Placement Points For Ratio 1.41 to 1.00:
Found optimum shift RPM at 6246, which achieves maximum area under horsepower curve, and lowers the RPM to 4430 after shift
<hr></blockquote>

So which do I want to do? Maintain the same horespower or maximize the area under the curve?

Ugh, too much calculas :(

[FuryCharger]

you want the first one, that gives you the shift point at the peak horsepower. if you look at a dyno chart after the peak horsepower, the line begins to drop right? thats what area under the curve means. it means at 6250 i think it was, horsepower will still be in effect but after the peak it will decline. sorry if thats confusing, but basically u want the first shift point.

[Seppo Kaitainen]

The second one. Not that we can spin up to 6250 with a stock pcm anyways.

[*K*night Rider]

lol, looks like the debate is on!

[zlexiss]

I'll weigh in with a guess that the second is the one you want.

Having the same horsepower before and after a shift is a good start. Your horspower in the current gear is declining, and shifting at that point means the next gear picks up at the same point. Earlier than this, and you're losing out.

However, the gear change also changes the torque at the wheels. The same horsepower now gets you less acceleration in the higher gear. So to me, waiting a little longer than the equal horsepower point would be the way to go. The max under the curve numbers seem to be closer.

What I want is a chart that shows the instantaneous acceleration at each point in the RPM range at each gear for the car. Shift up when the falling acceleration of the current gear is equal to the accel rate that the new gear would be at its lower RPM.

-Jeff

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by *K*night Rider:
lol, looks like the debate is on!<hr></blockquote>

There is no debate, only what is physically correct and which isn't. If you had a continuosly variable ratio transmission, you would want to stay at peak numbers. But you don't, and if you did you wouldn't have to shift anyway.

The first thing to note is that if what you posted is accurate, the first computation simply seeks to match horsepower at the end of one gear to the horespower at the beginning of the next. Essentially this is a meaningless calculation. It's one use is to compare to the second calculation. The difference between the two calculations gives you information about the shape of the horespower curve. If our curve was perfectly symmetrical, then the calculations would yield the same numbers. Other interpretations of this calculation are not valid. You are not going to get higher peak horespower numbers from shifting technique. I don't even know how anybody could believe that.

Secondly, your goal in accelerating down the drag strip is to minimize the elapsed time. This is accomplished by increasing the average acceleration, not instantaneous acceleration numbers. Therefore, you want to shift so that the average power throughout the rpm band swept by each gear is highest.

Somebody wanted a graph showing instantaneous acceleration in each gear. A graph of the torque curve is all you are asking for. The vehicle's instantaneous acceleration is always proportional to the torque curve. If you plot the torque/rpm and acceleration/rpm on the same graph, you will find that the shape is exactly the same.

Also, if you look at any dyno graph, you will se that torque hits it's peak before horsepower does. You will also note that while torque starts to decline, horespower is still rising, adn will continue to rise until torqe has decreasd drastically.

Remember, if we didn't have gearing to worry about, then maximizing the average torque would be nice. But unfortunately, each time you upshift, you lose torqe multiplication and significantly change your acceleration. Basically your torque curve (and therefore HP curve) better be falling off really fast before redline if you are going to shift early. Ignoring considerations about durability of the motor, shifting late would be "better" than shifting too early on a car with a remotely "sporty" powerband.

[gregmondro]

might be a stupid question, but isn't the 6.2k the rev limiter?

[MustangEater8251]

GUys the best way in my opinoin is go out and try different things, see what works and what doesn't, never ahd my car dynoed and I feel I shift jsut right and can tell when I do not. Every car is differnet, hell my own car is differnet depending on how I run it, will fugure how I shift.

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by MustangEater8251:
GUys the best way in my opinoin is go out and try different things, see what works and what doesn't, never ahd my car dynoed and I feel I shift jsut right and can tell when I do not. Every car is differnet, hell my own car is differnet depending on how I run it, will fugure how I shift.<hr></blockquote>

I agree, that is the best way.

[Bliggida]

<blockquote>quote:</font><hr>Originally posted by HAZ-Matt:
I agree, that is the best way.<hr></blockquote> Yeah but you are taking advice from a guy that blew up two transmissions, 4 gears, 3 clutches, four driveshafts, 9 rear ends...
:D I dunno how many of what he blew, but it's alot.

[OneQuickV6]

Throw it on the dyno and see where peak power is....Easiest way to know where YOUR car should be shifted.

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by Bliggida:
Yeah but you are taking advice from a guy that blew up two transmissions, 4 gears, 3 clutches, four driveshafts, 9 rear ends...
:D I dunno how many of what he blew, but it's alot.<hr></blockquote>

Haha, i think your numbers are too low.

[Dominic]

You want to shift after the peak power of a vehicle in a drag-race situation. Shifting later puts you in a higher RPM for the next gear, which makes up for the slight loss of power to take going past the peak horsepower rpm of the engine.

This is why for a 5200RPM peak power engine, you're best best is to shift right around 6K. It puts you in the band and maximizes the total horsepower made.

[HAZ-Matt]

<blockquote>quote:</font><hr>Originally posted by Dominic:
You want to shift after the peak power of a vehicle in a drag-race situation. Shifting later puts you in a higher RPM for the next gear, which makes up for the slight loss of power to take going past the peak horsepower rpm of the engine.

This is why for a 5200RPM peak power engine, you're best best is to shift right around 6K. It puts you in the band and maximizes the total horsepower made.<hr></blockquote>

good call
[img]graemlins/thumbsup.gif[/img]

[*K*night Rider]

And thats what I do anyway :D

And for all of you saying "Just go out and try it."

No shiz! I have, many times...I was just starting a conversation about the theory and math of when to shift.