I do you not hit the rev limiter all the time?
10-05-2018, 03:56 PM
#31
Three Wheelin'
HP is one thing, torque is another
Torque is a rotating force produced by an engine’s crankshaft. The more torque an engine produces, the greater its ability to perform work. The measurement is the same as work, but slightly different. Since torque is a vector (acting in a certain direction), it’s quantified by the units pound-feet and newton-meters. When the torque curve falls off, the ability to perform work (move the car thru the air and tire friction loss) lessens.
Berra’s theorem, torque is the capacity to do work, while power is how quickly some strenuous task can be accomplished. In other words, power is the rate of completing work (or applying torque) in a given amount of time. Mathematically, horsepower equals torque multiplied by rpm. H = T x rpm/5252, where H is horsepower, T is pound-feet, rpm is how fast the engine is spinning, and 5252 is a constant that makes the units jibe. So, to make more power an engine needs to generate more torque, operate at higher rpm, or both. But even at higher RPM, if the torque drops off, the car is producing less power, and that lessens the work the engine is able to do. Go ahead...kill me now. The simple rule is "stay within the maximum torque curve for maximum power", i.e, the ability to do work (move the car forward).
Torque is a rotating force produced by an engine’s crankshaft. The more torque an engine produces, the greater its ability to perform work. The measurement is the same as work, but slightly different. Since torque is a vector (acting in a certain direction), it’s quantified by the units pound-feet and newton-meters. When the torque curve falls off, the ability to perform work (move the car thru the air and tire friction loss) lessens.
Berra’s theorem, torque is the capacity to do work, while power is how quickly some strenuous task can be accomplished. In other words, power is the rate of completing work (or applying torque) in a given amount of time. Mathematically, horsepower equals torque multiplied by rpm. H = T x rpm/5252, where H is horsepower, T is pound-feet, rpm is how fast the engine is spinning, and 5252 is a constant that makes the units jibe. So, to make more power an engine needs to generate more torque, operate at higher rpm, or both. But even at higher RPM, if the torque drops off, the car is producing less power, and that lessens the work the engine is able to do. Go ahead...kill me now. The simple rule is "stay within the maximum torque curve for maximum power", i.e, the ability to do work (move the car forward).
10-06-2018, 12:48 AM
#34
10-08-2018, 02:22 AM
#35
Rennlist Member
10-08-2018, 10:47 AM
#36
10-08-2018, 11:39 AM
#37
Rennlist Member
Regarding the above discussion on operating at max engine torque:
Don't forget the effect of the gear ratio. If you plot the torque available in each gear up to redline, you will find that even though the engine is not at peak torque, there is more torque available to the wheels at higher RPM and lower gear. For example, at 7000 RPM there is 1695 ft lbs in second gear going into the final drive. In third gear at 4500 RPM there is 1380 ft lbs going into the final drive. If you plot all the gear ratios, you will see that there is always more torque available to the wheels in the lower gears. That is why we shift at redline.
Regards,
Lang G
Don't forget the effect of the gear ratio. If you plot the torque available in each gear up to redline, you will find that even though the engine is not at peak torque, there is more torque available to the wheels at higher RPM and lower gear. For example, at 7000 RPM there is 1695 ft lbs in second gear going into the final drive. In third gear at 4500 RPM there is 1380 ft lbs going into the final drive. If you plot all the gear ratios, you will see that there is always more torque available to the wheels in the lower gears. That is why we shift at redline.
Regards,
Lang G
10-09-2018, 02:50 AM
#38
Rennlist Member
I need to get my 99 on a dyno. I could swear that on my drive earlier today that the torque swell starts just after 4000 and relatively short shifting it (which for me is anything less than redline) it gets down the road pretty quickly. I've built a custom x pipe exhaust, catless, and my goal was to maintain backpressure to keep the torque at a usable RPM, as well as a rip snorting wail at WOT. Hit on all regards.. now I just need the powerband proven on paper.
10-09-2018, 02:00 PM
#40
Race Car
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autocrossers really bang on the 2nd gear limiter a lot...miata dudes will just lay into it for seconds at a time. I have tapped the 2nd gear one many a time and even the 3rd gear one on occasion. The x51 engine with muffler bypass makes it even worse because it really moves all the power up high and 7k rpm will sneak up on you.
Personally...the limiter is there for a reason. Don't bang it with the car in neutral, but tapping it every now and then in gear isn't the end of the world
Personally...the limiter is there for a reason. Don't bang it with the car in neutral, but tapping it every now and then in gear isn't the end of the world
10-09-2018, 02:04 PM
#41
Drifting
Italian tune ups!
11-30-2018, 11:50 AM
#43
Three Wheelin'
Posting on an old thread because my son gave me the answer why it's faster to shift at or near redline despite the torque curve tapering off much earlier. This is common knowledge to those of you who track your cars, so I apologize for (the guy who was educated by his son) preaching to the choir, but since it was an open/unresolved question in this thread, it seems worthwhile to comment. The reason for revving beyond the torque peak is not for acceleration in the gear you are in, but so that the engine is set up to be in the meat of the torque curve after you shift into the next gear.
I still feel (quite possibly incorrectly) like acceleration gets stronger in the current gear as you rise above the torque peak to redline (at least in my 996), so that part of the question isn't answered by this, but there is no question it is faster to shift at or near redline if you are going to go through several gears (despite the power curve showing much earlier peak torque).
I still feel (quite possibly incorrectly) like acceleration gets stronger in the current gear as you rise above the torque peak to redline (at least in my 996), so that part of the question isn't answered by this, but there is no question it is faster to shift at or near redline if you are going to go through several gears (despite the power curve showing much earlier peak torque).
Last edited by peterp; 11-30-2018 at 12:56 PM.
11-30-2018, 08:42 PM
#44
Rennlist Member
The drop off in torque after the peak isn’t really that pronounced on these cars either, which I think makes it feel like the car pulls strong all the way to redline.
11-30-2018, 08:44 PM
#45
Rennlist Member
That’s a great point. However, technically, it’s not just for the next gear, it’s also for the gear you are in because even though torque has dropped off, you are still using a gear multiplier that offer greater resultant torque than if you shifted into the next gear. So it’s for both - the current gear, and the next gear.