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Discussion Starter · #1 ·
I know the redline is 7000 rpm, but when racing someone off the line what would be the best shifting point (rpm wise)(without powershifting) Cause i have been shiting @7000 everytime, but i just want to know if there is a quicker way. I know some people shift @ 7500 rpm and some at 6500, BUT what is the quickest!!!????

Thanks Keith
 

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far be it from me to speak from experience, I barely race anyone, but from what I've heard, WOT (wide open throttle) happens at 4250 rpm so whatever you shift at, your next gear shouldn't drop below that. Is that right guys? I've shifted around 6200 or 6500 depending on how I'm feeling, or if i'm heading up an incline.
As for normal driving, usually shift around 2300 just to avoid any hopping in the clutch.
 

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I can't tell you exactly because I don't think my stock tachometer is exact. The fact is that you shouldn't get near the rev limiter. If you know how to read dyno plots you will see why.

I've found that according to my tachometer shifting at 6,400-6,500 works the best. I've gon to around 7,500 and never hit the rev limiter, so if your tach is exact you should be shifting at or before 6,500rpm.
 

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my 4-cyl redded at 6.5K(stock) and i used to shift around there. also coming into play are quickness of shifts, clutch technique, and gear ratios. i used to chirp third on stock tires with a lift-throttle style shift. i just kept both hands on the wheel and when the time came, i reached down and hit, yes hit, my stick into the next gear while i yammed the clutch to the floor. never grinded it once! pasengers would trip out b/c i would only have my hand off the steering wheel for like a fration of a second. who says a machine is faster???
 

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Smot-Poker
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wo!

this is some highly intresting shit!

Ive been told that regardless of how fast your car is or your opponents, it comes right down to the shifting skills. I mean, racing a car that has say a second faster 1/4 mile, aint gonna do him shit if you gots the shifting power DOWN PAT! This is why i want a racing clutch and short shift for my next (most important) mods. Does anyone have any general tips as far as being able to harness the speed and power of this car in particular?

p.s. im kinda new to the manual tranni
 

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Smot-Poker
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also

i have also been told, that since this car is a sport/luxury vehicle. the stock clutch is designed for a comprimise of smoothness and performance. If this is true, wouldnt it make sense to want to replace the stock clutch as one of the first mods, in order to aquire the fast bite that is needed to kick some ass in a race. Pllease correct me if I am mistaken

Cheers
 

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Like you said ... when racing, the most important thing is the skill ... So what makes you think that a harder gripping clutch or a shortshifter is gona make you way faster??? (I'm assuming that your clutch isn't slippin)

The most important things are:
the way you launch - your 60ft time
your shiftpoints

If you know how to shift in the first place a shortshifter won't do anything for you. If you know how to launch properly a harder gripping clutch won't do you any good unless your original clutch is slipping.

I'm talking from experience here, not from my imagination. I ran high 14s in my NA mx6 with a regular clutch and no fricken shortshifter. :p
 

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Smot-Poker
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For starters, yes, my clutch slips like a muthafuka everytime I try to drive a little harder then normal run-o-the-mill cruisin, it just slipps right out. My RPM goes nice and high, but doesnt seem to take the car with it. ALSO, like i have stated in past posts, i am very new to this manual tranni thing anyway, so i believe having a short shifter to learn on would be easier for me.
 
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Discussion Starter · #10 ·
I wholeheartedly disagree with whoever says a different clutch won't make a difference. That is complete crap, and you should know it. A competition clutch (racing) is one of the most useful mods you can do to make you faster off the line, and have better shifts. Much more effective than many others that people do to "boost hp". Of course driver skill has a huge effect, but come on.
 

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Well, technically speaking, from a mathematical point of view, you want to maximize the area under the power curve during the total acceleration time. The integral of power is work and so, by maximizing the area (integral) under the power delivery curve, you maximize the work done (maximize the car's speed after a "race".)

Though it's hard to believe, the power delivered to the wheels is roughly the same in each gear, ignoring loss differences between the gears. For example, a stock KL03 will turn roughly 135 peak HP to the wheels in 1st, 2nd, 3rd, 4th or 5th (or even reverse) gear on the dyno. Most people run in 3rd or 4th but the results don't vary that much. So to analyse this, you need to know what the power curve of the engine (FS, KL...doesn't matter) looks like (especially either side of the power peak), where the power peak occurs and what the gear ratios are for the transmission.

At the risk of oversimplification, you want to shift at the point the power delivery in you current gear falls below what it would be in the next gear. As you climb the RPM scale from the power peak in a given gear, the power output is dropping. When you shift, you'll end up dropping the engine RPM again, likely below the power peak. What you want is, if possible, to ensure that the power at the next gear's RPM (which will be RPM * nextratio/currratio) will be equal to or greater than the power at the RPM you are at now.

Imagine a dyno plot showing the HP at the wheels. Now imagine overlaying that with a "window" that can slide along the RPM scale. This window will vary in width for each pair of gears (1-2, 2-3, 3-4, 4-5) and will be this wide:

Width (RPM) = StartRPM * gear_a/gear_b

where gear_a is the lower of the gear pair (1, 2, 3, 4) and gear_b is the higher of the gear pair (2, 3, 4, 5). StartRPM describes where, RPM-wise, the window starts on the curve and indicates where the engine will land, RPM-wise, when you shift. The other end of the window, which is StartRPM + Width wide, represents the current RPM in the current gear.

So... Let's take the 1-2 shift. 1st is about 3.35:1, 2nd is about 1.85:1 (I'm guessing here...can't recall the specs off the top of my head here at work.) So:

Width = StartRPM * 3.35/1.85 = StartRPM * 1.81

If you shift into 2nd gear and the RPM lands at, say, 3500, then you shifted from 1st at 1.81*3500 or 6335RPM. Does this shift maximize the area under the power curve? Probably not, because the power above 6335 is around 140HP and down at 3500, it's all the way down to 92HP (I'm using my dyno run as the model for this example.) This is shifting too early since more power was available to scoot the car in the remaining RPM till redline in 1st then there is now in 2nd.

In cases like this, the RPM you shift at should be redline - or whatever you feel comfortable with up to the fuel cutoff. 1st-2nd is tough to idealize because the ratios are quite far apart. 2-3 and 3-4 are easier to get realistic numbers for since those ratios are quite close.

Having said all this, I think for the first two gears, redline or higher shifts are best for outright acceleration. For the higher gears, something just less than redline is best.

Corrections welcome :D
 

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Smot-Poker
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all I have to say is

holy crap..
I understand
 

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Having said all this, I think for the first two gears, redline or higher shifts are best for outright acceleration. For the higher gears, something just less than redline is best.


Think this sums it up for me and in total agreement.
 
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Discussion Starter · #15 ·
One other comment to ponder

About the only thing Mike 94PGT didn't mention is that HP and torque are always equal at 5,280 RPM's...no matter the engine or vehicle. There's a lot that can be said as to how this comes into play too-- maybe somebody else has something more to add on this. One thing to remember (in addition to the many comments Mike made) is that the stock 2.5L is rated at its maximum 164HP output at 6600 RPM's. Beyond this, the HP will begin decreasing, although then you may be in a better position for the next gear (as Mike mentions in detail). Hmmmmmm...
 

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Re: One other comment to ponder

tlk said:
About the only thing Mike 94PGT didn't mention is that HP and torque are always equal at 5,280 RPM's...no matter the engine or vehicle. There's a lot that can be said as to how this comes into play too-- maybe somebody else has something more to add on this. One thing to remember (in addition to the many comments Mike made) is that the stock 2.5L is rated at its maximum 164HP output at 6600 RPM's. Beyond this, the HP will begin decreasing, although then you may be in a better position for the next gear (as Mike mentions in detail). Hmmmmmm...
Actually, I believe that HP/TQ cross-over point is about 5252.113RPM. This comes about purely because of the comparatively arbitrary way that "HP" is defined and the relation of PI (3.14159...) and the circumference of a circle. For more information about this, check out my Horsepower page to see how the well-known HP equation (HP = NT/5252) is derived mathematically.

Also, IIRC, the 1993 model KL03 produced max power at 6000RPM and for 1994 on-ward, the HP peak was lowered to 5600RPM.


[Edited by Mike 94PGT on 12-13-2000 at 12:39 PM]
 
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Discussion Starter · #17 ·
So we still havn't figured out what is the best shifting point when racing off the line, is it 6500 or 7000rpms?? What is it!!!!
 

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I guess you'll find out if you get your car dynoed. As it was mentioned before, it may vary from car to car depending on the mods. When I raced the 1/4 mile, I shifted on all gears between 6100 prm and 6300 rpms. Hopefully this summer, after I install the RT cat and get headers, I'll get my car dynoed in order to find the specifics.

(After all the basics bolt ons are done......get ready for a turbo...)
 
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Discussion Starter · #19 ·
Re: Re: One other comment to ponder

Mike 94PGT said:
Actually, I believe that HP/TQ cross-over point is about 5252.113RPM. This comes about purely because of the comparatively arbitrary way that "HP" is defined and the relation of PI (3.14159...) and the circumference of a circle. For more information about this, check out my Horsepower page to see how the well known HP equation (HP = NT/5252) is derived mathematically.

Also, IIRC, the 1993 model KL03 produced max power at 6000RPM and for 1994 on-ward, the HP peak was lowered to 5600RPM.
[/B]
WOW-- thanks for the HP link on your page! I'm still reading it. I'm sure glad I like math! As for the [email protected] I mentioned, this is how a couple of mags have printed it in the past...I guess they typo'd and it should really be [email protected] Oh, also, your link is actually at my Horsepower page (you had the extension as .html rather than .htm) :)
 

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Oops...

tlk said:
WOW-- thanks for the HP link on your page! I'm still reading it. I'm sure glad I like math! As for the [email protected] I mentioned, this is how a couple of mags have printed it in the past...I guess they typo'd and it should really be [email protected] Oh, also, your link is actually at my Horsepower page (you had the extension as .html rather than .htm) :) [/B]
Oops. Hehe...thanks for the correction.
 
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