Clifton

Dell,
While I can see your logic in the rpm range you've selected, it seems that the gear ratios of the car are not being factored in for the true "optimum" shift points.

To check your numbers, you may want to use some of the various shift point calculators that use mathematical formulas that factor gear ratio and hp at various RPMs.

I would expect you will find that you are shifting too early and that you would actually need to hold each gear a little longer to get the maximum benefit.

ROK

yup. shift at redline. don't short shift. it's not just engine power, but gears are obviously involved as well (multiplier)

shifting anything below 3k RPM during street driving is kinda weird. it's almost like lugging the engine. I typically hit 4-5K RPM because it not only feels best, but also sounds best.

Dave!

It really depends on the engine and gearing. Some engines will run out 1500rpm past their peak power so it only makes sense to redline the first few gears, then you'll want to keep the shifts focused around the peak as the ratios tighten up for the higher gears.

I'm bored and was just looking at some different power curves and it was the Audi 1.8T that peaked a little over 5000 but steadily dropped to redline at 7k. An engine like that you'd shift somewhere around 5500 to 4500 going from 5th to 6th (numbers from memory, saw it about half an hour ago). That's a bizarre engine, you figure they'd tune it for a little more power at the high end if they were going to have the redline that high.

I'm a mechanical engineer working on a job doing scheduling. This is such a bottled-up energy outlet for me I apologize if I've been a little overzealous.

LVDell

As I said, this is NOT exact and I have tried to purposely not go into mind numbing detail. Those exact numbers you are looking for have been figured out based on the hp/tq curve and gearing and are programmed into my AIM system in the race car for optimal shift points for each and every gear. For obvious reasons I am not posting those values here.

Sure, gears factored into the calculation would be nice as well but this is the 996 forum not the racing forum. That is a discussion I have no desire to get into. Just search the racing forum and you'll see why I don't participate in those discussions.

If y'all want to shift at redline, be my guess. I'll shift where it's optimal.


*********
Dave, I'm sorry you don't seem to understand fully the relationship between torque and horsepower. That's ok. I'm done with this conversation. No offense, I have to get to work though.

Please do some more reading on the relationship.

ivangene

I though Dell's points showed incredible thought and backed with data and real life track experience...any of you think you can pass him at the track, feel free to try... he knows what he is doing and works on these things to tweak out parts of seconds/lap times...I for one am impressed at how deep he gets into these things and its not just on shifting... you can ask him about nearly any subject from alignment to braking zones and tail pipes to iPod setting... Dell is a NO BS Get it done kind os P-Car owner!!

Dave!

I really don't appreciate the forced condescension. Edit: I'll retract that because it's nasty. Just know that I completely and fully understand torque, work, power, acceleration and their relationships.

Edit:
I know, that's why I was trying to see why he planned shifts the way he does. Having seen how much he knows it bothered me to see something he said disagree with what I know.

Clifton

So then I think it is fair to say that when you say optimal, you mean optimal for you but not scientifically optimal.

Run the specs of 996 or 996 GT3 through four or five shift calculators and that might optimize the thinking here.

LVDell

Don't be so damn sensitive. Geez. There was no condescension. I guess a smiley would have helped? I literally meant that I wish you knew more about the discussion so I didn't have to keep explaining it. That's all. I would have explained further but I am out of time. Heck, I'm typing this is the middle of giving a test. Gotta love lecture halls with internet terminals

Like I said, read up on it. That's how I learned about this stuff. My example that I was talking about was for the 2.5L boxster but the same concept applies to all the cars (normally aspirated).

Back to the topic, red heads

GNR996

someone say red heads?

like this?

Barn996

Did she drop something...?

LVDell

Now we're back on track!

Pac996

Proper cam. lifters, rods and pistons and she'll be good.

Dave!

Okay fair enough it came across as condescension, but I think it comes across like that because you're assuming I don't know what I'm talking about when it comes to torque and power--I do, very well, from school, work and engine specific reading. And I think you're mistaken when it comes to the torque, power and acceleration relation.

You're thinking torque is proportional to acceleration but it's power--it's easiest to think of it like this (I dunno what you've done with kinetics but I'll make it quick in case you haven't dealt with it): Power is the amount of work you do per an amount of time (work is energy) so you get power = energy / second. The kinetic energy of an object is based on the mass and velocity (1/2mv^2).

So you have power, which is rate of change of energy, and velocity, which is energy. Simply put, power is the rate of change of velocity, which is acceleration.

That's why it's throwing me off when you say you want to keep it in the meaty torque band and not the meaty power band.

Now, for the torque-power relation. Torque is the torsion force the engine applies at any given speed, work is force times the distance that force is applied (rotational work in this case), and power is how fast you can do that work. Power is 100% dependent on the torque the engine produces (P=T*rpm/5252 like you said), yes, but power is really the value you want to think about when it comes to acceleration; torque is for pulling stumps.

This is longer than I wanted and probably confused but I'm bored and tend to ramble. I found this, which does a much better explanation of what's going on than I did that you can read later if you like: http://www.fjr1300.info/misc/torque-power.html (Myths 3 and 4)

Of note is this bit in there:
What he's saying there is that the wheel torque is higher in the lower gear at the same speed in the higher gear even though the engine torque is lower.

Edit: Again Dell I'm not knocking your setup and don't mean to be since I bet it's setup just right for the track, it's just that there's a lot of weird information on torque/power and I like clearing it up since it's such a confusing topic.

Pac996

Here is my take. I am sure everybody will appreciate my insight ha ha.
You can have torque and hp whoopy. What you need is a good engine to start with right. I don't think some know whats going on at higher rpms. I wont exactly say Dell is right....because you'll quit reading

First point is hydrolic lifters. I don't know if Dell has been in a life of radical rpm cams or not but hydrolic lifters start dropping out at higher rpms specificly around 6-7k. They are not a contender at 8k for sure. Roller cams and non hydrolic lifters are needed for real responses at higher rpms. In laymen term shiza just starts floating in the high rpms with hydrolic lifters even with stronger valve spring.

Secondly numbers my foot Figure torque as how hard the power can pull you from what ever speed to higher and HP as staying power.

Turdly when applying power and setting up the suspension you want availability of working space to keep yourself so that there is HOPEFULLY (for a novice) always more higher rpms available in which ever gear you are in during a turn to keep the suspension settled. When things get squirly in a turn it IS NOT the time to change gears, brake or let off the gas. That is unless you are not snatching gears correctly and at the highest possible speed of the turn.

So change gears when ever wanted and race Dell as much as you like and my bets on Dell whopping your tails
Dell races and knows while some of us are thinking straight line and numbers.

LVDell

Pheh! I have a break between classes so I can play for a bit

Dave, It sounds like there is a little bit of truth in both angles we are attacking this. While I agree that hp is what I want on the straights (high speed sections) it's torque that I value in the mid speed sections. For a street car that is relatively heavy with a stock box we need all that torque we can get to put that hp down.

If I had a high revving lightweight car, no question would I want hp.

My brain hurts right now....are we getting closer together?