MY 350 is getting slower now :(
04-08-07, 10:29 AM
#46
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04-08-07, 12:57 PM
#47
04-08-07, 02:18 PM
#48
No I wouldn't agree with that at all. The CVT would need to keep the engine at peak hp, not peak torque. Covering distance is work, not force. But again, I don't believe it would be MUCH higher. However, I have no doubt it would be the quickest possible set up.
Wait - next you're going to tell me you shift at hp peak... Please don't go there...
Wait - next you're going to tell me you shift at hp peak... Please don't go there...
Regarding shift points, I don't believe in shifting at peak HP at all. I believe in staying in the lowest gear I can until fuel cut.
04-08-07, 02:22 PM
#49
The only reason why I would consider resetting the ECU is to clear out anything that the ECU "remembers" that might be causing it to pull timing or run unnecessarily rich. For instance, if you got a marginal batch of gas that caused a bit of detonation while sitting in stop and go traffic, the ECU will adjust it's timing and fuel maps even more conservatively to prevent damage. Who knows how long it would take for that condition to clear on its own? I would expect the ECU to recover from that VERY slowly.
04-08-07, 06:55 PM
#50
I'm hesitant to post this since it is a bit off topic, but peak accelleration absolutely happens at peak torque, not HP. I didn't realize this until I plotted my own rate of accelleration chart using speed, distance, and time data that I captured in my car at full throttle from 3K rpms to redline. I was amazed to see that the accelleration plot looks exactly like my torque plot. After thinking about the Physics of it for a bit (F=MA), it made sence. Mass is constant, torque is the force, so the higher the torque, the greater the accelleration.
Regarding shift points, I don't believe in shifting at peak HP at all. I believe in staying in the lowest gear I can until fuel cut.
Regarding shift points, I don't believe in shifting at peak HP at all. I believe in staying in the lowest gear I can until fuel cut.
"Horsepower sells cars but torque wins races"
- Carroll Shelby
basically you are right on-
04-08-07, 07:24 PM
#51
Tech Info Resource
iTrader: (2)
Sure. That's undoubtedly why F1 cars accelerate so hard. Lots of torque.
You might want to read this to get why engine HP is more important than engine torque.
You might want to read this to get why engine HP is more important than engine torque.
04-08-07, 09:41 PM
#52
Sure. That's undoubtedly why F1 cars accelerate so hard. Lots of torque.
You might want to read this to get why engine HP is more important than engine torque.
You might want to read this to get why engine HP is more important than engine torque.
From the article you posted ...
First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.
Last edited by Gernby; 04-08-07 at 09:47 PM.
04-08-07, 10:17 PM
#53
Tech Info Resource
iTrader: (2)
Right. Which would you rather do, cover ground, or feel pushed back in the seat? I'll take covering ground every time, even if it doesn't feel as good.
IOW, the driver loves to feel the push back in the seat from torque providing acceleration, but I need the engine to do work, not feel good. Doing work is what the whole game is about. If it were not so, we'd build engines to make peak torque at the highest possible rpm, but we don't. We build for best torque over the operating range. Ideally this means the force the driver feels remains the same from the lowest usable rpm to the highest, but it isn't always so.
Click here for more.
IOW, the driver loves to feel the push back in the seat from torque providing acceleration, but I need the engine to do work, not feel good. Doing work is what the whole game is about. If it were not so, we'd build engines to make peak torque at the highest possible rpm, but we don't. We build for best torque over the operating range. Ideally this means the force the driver feels remains the same from the lowest usable rpm to the highest, but it isn't always so.
Click here for more.
Last edited by lobuxracer; 04-08-07 at 10:25 PM.
04-09-07, 08:14 AM
#55
I must humbly conceed that lobuxracer is correct about a CVT needing to maintain the engine RPM at peak HP instead of peak torque for maximum accelleration ... 
It wasn't until I plotted an accelleration chart comparing the stock IS350 to an ideal CVT that I could see that the benefit of higher RPMs outweighed the benefit of higher torque due to the gearing advantage (higher resulting thrust).
I still believe that a well implemented CVT would make a big difference in trap speed and time due to the significant increase in area under the curve.
It wasn't until I plotted an accelleration chart comparing the stock IS350 to an ideal CVT that I could see that the benefit of higher RPMs outweighed the benefit of higher torque due to the gearing advantage (higher resulting thrust).
I still believe that a well implemented CVT would make a big difference in trap speed and time due to the significant increase in area under the curve.
Last edited by Gernby; 04-09-07 at 08:17 AM.
04-09-07, 08:53 AM
#57
Back in my E36 M3 days we had a similar discussion about shift points. Always shift to maximize transmission output torque. Never shift at torque peak. You will lose the overall higher torque of the current gear and it will also put you in a worse spot in the next gear. Alot of lower tq/higher hp cars get their best times by shifting at redline, but not true for every car. Basically it's best to look at a dyno graphs and take the data like Gernby did and see where the best point is. Luckily for us the Auto tranny takes care of this as best as it can without it being a CVT type, which would be optimum. Just wish current CVT technology could hold the power the IS350 produces. Then again, doesn't the new Maxima have a CVT?
04-09-07, 12:37 PM
#58
Tech Info Resource
iTrader: (2)
I must humbly conceed that lobuxracer is correct about a CVT needing to maintain the engine RPM at peak HP instead of peak torque for maximum accelleration ...
It wasn't until I plotted an accelleration chart comparing the stock IS350 to an ideal CVT that I could see that the benefit of higher RPMs outweighed the benefit of higher torque due to the gearing advantage (higher resulting thrust).
I still believe that a well implemented CVT would make a big difference in trap speed and time due to the significant increase in area under the curve.
It wasn't until I plotted an accelleration chart comparing the stock IS350 to an ideal CVT that I could see that the benefit of higher RPMs outweighed the benefit of higher torque due to the gearing advantage (higher resulting thrust).
I still believe that a well implemented CVT would make a big difference in trap speed and time due to the significant increase in area under the curve.
The only reason I maintain the speed doesn't change is because I haven't seen it happen in the real world. Your CVT gearbox would completely overwhelm any streetable tire with the force it could apply at low speed. This might be the real world reason why lower gears make better ET but not better trap speeds. The mathematical model sure looks like the CVT would win hands down.
A lot of this stuff is counterintuitive. I only know it because I've had these same discussions with people before and had it proved to me (sometimes painfully) in clear, unambiguous terms. I get into lots of "discussions" about airflow where people want me to believe things I know are not true only because they're quite counterintuitive.
04-09-07, 07:05 PM
#59
Trap Speed and Density Altitude
Just put together a journal of type to compare a few runs I made. Sure enough I found a predicted trend. Higher trap speeds correlate directly with higher Density Altitudes.
I used the following to calculate Density Altitude:
http://wahiduddin.net/calc/calc_da.htm
This site to get weather history information:
http://www.wunderground.com/
I used the following to calculate Density Altitude:
http://wahiduddin.net/calc/calc_da.htm
This site to get weather history information:
http://www.wunderground.com/
Last edited by caymandive; 04-09-07 at 07:40 PM.
