How to make torque at higher RPM...
05-21-2006, 11:39 AM
#61
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Originally Posted by DavidNJ
Let me provide a little different take. It isn't peak anything that matters (unless you have a CVT transmission), and it isn't the torque curve per se, it is the area under the horsepower curve.
Now this is related to the torque curve, since it is hp is a linear function of torque and engine speed. But not quite the same.
Let's used the Accord vs MB Diesel example earlier. I'd like to change it to the MB gas vs MB diesel, since I actually worked the numbers on this in '04. At the time the gas engine had 221 peak hp, the diesel 201. However, the diesel had a flat power curve and the gas engines was constantly rising. When accelerating at WOT, the diesel would average around 195hp, the gas engine in the high 180s.
Although the diesel had nearly 50% higher peak torque, it was largely irrelevant for maximum acceleration. It occurred at 1800rpm, and the engine was way beyond that right away and never would drop below the low 3000s after a shift.
How, here is a little math game. Take a car going any road speed; 60, 100, 120, 150mph...you decide. Pick any tire size. Any gear ratio. Any engine speed. Just as long as the ratio of vehicle speed to engine speed gives the desired road speed.
If you say the engine makes a specific horsepower it will always have the same force accelerating the car. 720hp @19000 rpm from an F1 engine would be the same as 720hp @2400rpm in a truck engine. Don't believe me; work the numbers for yourself.
Now this is related to the torque curve, since it is hp is a linear function of torque and engine speed. But not quite the same.
Let's used the Accord vs MB Diesel example earlier. I'd like to change it to the MB gas vs MB diesel, since I actually worked the numbers on this in '04. At the time the gas engine had 221 peak hp, the diesel 201. However, the diesel had a flat power curve and the gas engines was constantly rising. When accelerating at WOT, the diesel would average around 195hp, the gas engine in the high 180s.
Although the diesel had nearly 50% higher peak torque, it was largely irrelevant for maximum acceleration. It occurred at 1800rpm, and the engine was way beyond that right away and never would drop below the low 3000s after a shift.
How, here is a little math game. Take a car going any road speed; 60, 100, 120, 150mph...you decide. Pick any tire size. Any gear ratio. Any engine speed. Just as long as the ratio of vehicle speed to engine speed gives the desired road speed.
If you say the engine makes a specific horsepower it will always have the same force accelerating the car. 720hp @19000 rpm from an F1 engine would be the same as 720hp @2400rpm in a truck engine. Don't believe me; work the numbers for yourself.
I don't think it really matters if you compare area under the HP curve or between two engines or area under the TQ curve. Like you said, it's a linear relationship. More area, in either case, is better.
CVT is an interesting animal. In a regular tranny, peak acceleration in any gear occurs at peak TQ in the rpm.
In a CVT, peak acceleration occurs at peak HP, because at that point the gearing can be the greatest and still accelerate.
The math problem is kinda fun! (math is fun???)
It works because of the direct relationship between the RPM at which the HP is made and the final gearing ratio used to obtain a speed.
In other words, in a simpler example. A car that makes 100hp at 2000 rpm will have twice the gearing (overall, doesn't matter if it's tranny, tires, rear) as a car that makes 100hp at 1000rpm. And they'll be traveling the same speed at 100hp.
05-22-2006, 09:24 AM
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If you say the engine makes a specific horsepower it will always have the same force accelerating the car. 720hp @19000 rpm from an F1 engine would be the same as 720hp @2400rpm in a truck engine.
There would have to be an identical change in torque over RPM to maintain
the same force of acceleration. As you stated in your post, it's not the peak
values that will determine the acceleration.
Due to the transmimssion input shaft speed, can you imagine the gearing and
tire size to make these two vehicles acclerate at similar rates?
05-23-2006, 10:54 AM
#63
FormerVendor
And you'd be completely right as well! If someone double the rpm of an engine then twice the gearing must also be used if they have the same power. That also means now that this seemingly wide powerband has been cut in two in real time as well. People don't see that almost ever since they don't race cars themselves. There's a reason these high rpm short stroke cars need all those gears. The power bands are narrower not wider even though they span much more rpm on a dyno sheet.
Originally Posted by DavidNJ
Let me provide a little different take. It isn't peak anything that matters (unless you have a CVT transmission), and it isn't the torque curve per se, it is the area under the horsepower curve.
Now this is related to the torque curve, since it is hp is a linear function of torque and engine speed. But not quite the same.
Let's used the Accord vs MB Diesel example earlier. I'd like to change it to the MB gas vs MB diesel, since I actually worked the numbers on this in '04. At the time the gas engine had 221 peak hp, the diesel 201. However, the diesel had a flat power curve and the gas engines was constantly rising. When accelerating at WOT, the diesel would average around 195hp, the gas engine in the high 180s.
Although the diesel had nearly 50% higher peak torque, it was largely irrelevant for maximum acceleration. It occurred at 1800rpm, and the engine was way beyond that right away and never would drop below the low 3000s after a shift.
How, here is a little math game. Take a car going any road speed; 60, 100, 120, 150mph...you decide. Pick any tire size. Any gear ratio. Any engine speed. Just as long as the ratio of vehicle speed to engine speed gives the desired road speed.
If you say the engine makes a specific horsepower it will always have the same force accelerating the car. 720hp @19000 rpm from an F1 engine would be the same as 720hp @2400rpm in a truck engine. Don't believe me; work the numbers for yourself.
Now this is related to the torque curve, since it is hp is a linear function of torque and engine speed. But not quite the same.
Let's used the Accord vs MB Diesel example earlier. I'd like to change it to the MB gas vs MB diesel, since I actually worked the numbers on this in '04. At the time the gas engine had 221 peak hp, the diesel 201. However, the diesel had a flat power curve and the gas engines was constantly rising. When accelerating at WOT, the diesel would average around 195hp, the gas engine in the high 180s.
Although the diesel had nearly 50% higher peak torque, it was largely irrelevant for maximum acceleration. It occurred at 1800rpm, and the engine was way beyond that right away and never would drop below the low 3000s after a shift.
How, here is a little math game. Take a car going any road speed; 60, 100, 120, 150mph...you decide. Pick any tire size. Any gear ratio. Any engine speed. Just as long as the ratio of vehicle speed to engine speed gives the desired road speed.
If you say the engine makes a specific horsepower it will always have the same force accelerating the car. 720hp @19000 rpm from an F1 engine would be the same as 720hp @2400rpm in a truck engine. Don't believe me; work the numbers for yourself.
05-23-2006, 01:08 PM
#64
Adrenaline_Z, when you are finished with gearing and tire size, the same hp will always apply the same force. Always.
Erik, I usually look at rev range as % of the speed of the top of the range. As you said. with their flatter torque curves and positively sloped power curves, there is always a significant power drop after a shift. However, even with LS1 and Viper humpbacked power curves (power peak 10% or more below the maximum engine speed), tighter gearing will keep you toward peak power. However, in these cases, tighter gearing may even cause the desired rev limit to drop.
Erik, I usually look at rev range as % of the speed of the top of the range. As you said. with their flatter torque curves and positively sloped power curves, there is always a significant power drop after a shift. However, even with LS1 and Viper humpbacked power curves (power peak 10% or more below the maximum engine speed), tighter gearing will keep you toward peak power. However, in these cases, tighter gearing may even cause the desired rev limit to drop.
05-23-2006, 02:28 PM
#65
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Originally Posted by racer7088
And you'd be completely right as well! If someone double the rpm of an engine then twice the gearing must also be used if they have the same power. That also means now that this seemingly wide powerband has been cut in two in real time as well. People don't see that almost ever since they don't race cars themselves. There's a reason these high rpm short stroke cars need all those gears. The power bands are narrower not wider even though they span much more rpm on a dyno sheet.
F1 engines use about 50% of their 19000 rpm band, or at least they did with the 3L V10s. Once they get out of a corner they keep the revs in the upper 15% or so of the rev band, probably much like drag racers. Even a 'Glide with a high stall probably uses no more than 40% or so of it's rpm range. After 1st gear, a Pro Stock uses less than 20% of it's rpm range.
05-23-2006, 03:04 PM
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Adrenaline_Z, when you are finished with gearing and tire size, the same hp will always apply the same force. Always.
to peak values as opposed to power curves when speaking about acceleration
(change in velocity).
05-23-2006, 06:44 PM
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Originally Posted by racer7088
And you'd be completely right as well! If someone double the rpm of an engine then twice the gearing must also be used if they have the same power. That also means now that this seemingly wide powerband has been cut in two in real time as well. People don't see that almost ever since they don't race cars themselves. There's a reason these high rpm short stroke cars need all those gears. The power bands are narrower not wider even though they span much more rpm on a dyno sheet.
05-24-2006, 01:12 AM
#68
FormerVendor
Yes Jessica.
Originally Posted by Jessica
Narrower power band even though there is a wider rpm span???? There is a wider range of piston speed though, and I think that's what you mean about the powerband. A six inch stroke engine from 3.000 to 6,000 actually has more powerband than a three inch stroke from 6,000 to 11,000. (and the six inch stroke will more more power and go faster)
05-24-2006, 10:42 AM
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Hmmm..... I've never thought about the powerband vs. rpm span thing before.
That means that a car making 200 lb/ft of tq from 3-6k rpm would be faster than a car making 100 lb/ft from 9-12k. The second car would have to make that power over a span of 6k-12k to keep up with the lower rpm car.
Probably why those big single turbo cars have slow 1/4 mile times. They make power from 6k-8k. But at those high rpms, that's REALLY narrow of a power band.
I just saw a 1400hp supra dyno sheet. at 4k rpm, it makes only 200 lb/ft of tq. And like 250 at 5k rpm. But, 750 at 8000 rpm.
That means that a car making 200 lb/ft of tq from 3-6k rpm would be faster than a car making 100 lb/ft from 9-12k. The second car would have to make that power over a span of 6k-12k to keep up with the lower rpm car.
Probably why those big single turbo cars have slow 1/4 mile times. They make power from 6k-8k. But at those high rpms, that's REALLY narrow of a power band.
I just saw a 1400hp supra dyno sheet. at 4k rpm, it makes only 200 lb/ft of tq. And like 250 at 5k rpm. But, 750 at 8000 rpm.
05-24-2006, 02:02 PM
#70
Actually 200lbf-ft from 3k-6k would be the same as 100lbf-ft from 6k to 12k.
The need is to look at the rev range for the application. For example, an oval track car typically doesn't shift (frequently outlawed by the rules) and needs one gear from the middle of the corner to the end of the straight. Whether running alone or in traffic. And including the start of the race and the frequent yellow flag restarts.
That could easily require a range of 4500-7000 for an intake restricted late model on a short track. And maybe even more. That is around 35-40% of the rev range.
A road racing car may be able to shift, but still want a little breadth to have be able to stretch a gear in traffic or when a downshift occurs at a place that might unsettle the car or driver. It would also depend on the gearbox. A stock Corvette T-56 has around a 30% drop in revs on a shift. However, the racing T-56 has only 25% drop on most gears and a 30% drop in first, allowing a smaller rev range.
A drag racing engine, like the Supra, which can be ensured a narrow rev range by always shifting at the redline and never downshifting, can have a relatively tight rev range.
A street/strip engine, which needs to work at 1500rpm in traffic, 2200rpm on the highway, and 7000rpm needs a broader range, or two distinct ranges, both being functional. That is, 4500-7000 is adequate for the track, however 1500-4000 still needs to be functional for the street.
The need is to look at the rev range for the application. For example, an oval track car typically doesn't shift (frequently outlawed by the rules) and needs one gear from the middle of the corner to the end of the straight. Whether running alone or in traffic. And including the start of the race and the frequent yellow flag restarts.
That could easily require a range of 4500-7000 for an intake restricted late model on a short track. And maybe even more. That is around 35-40% of the rev range.
A road racing car may be able to shift, but still want a little breadth to have be able to stretch a gear in traffic or when a downshift occurs at a place that might unsettle the car or driver. It would also depend on the gearbox. A stock Corvette T-56 has around a 30% drop in revs on a shift. However, the racing T-56 has only 25% drop on most gears and a 30% drop in first, allowing a smaller rev range.
A drag racing engine, like the Supra, which can be ensured a narrow rev range by always shifting at the redline and never downshifting, can have a relatively tight rev range.
A street/strip engine, which needs to work at 1500rpm in traffic, 2200rpm on the highway, and 7000rpm needs a broader range, or two distinct ranges, both being functional. That is, 4500-7000 is adequate for the track, however 1500-4000 still needs to be functional for the street.
05-24-2006, 03:30 PM
#71
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The Engine Masters Challenge has used 2500-6500 wide open throttle testing, or 4000/6500 or about 61% of the max revs. That's one of the things that mades it a "Challenge".
Unfortunately the EMC became a "live with detonation" contest until this year when SCR was limited to 10.5. Detonation shouldn't be the problem now.
Unfortunately the EMC became a "live with detonation" contest until this year when SCR was limited to 10.5. Detonation shouldn't be the problem now.
05-24-2006, 04:10 PM
#72
FormerVendor
Yes 1000-2000 rpm is MUCH larger in powerband width that say 9000-12000 rpm even though one sweeps 1000 rpm and one sweeps 3000 rpm.
The one that sweeps 3000 rpm is only half the powerband width of the one that sweeps only 1000 rpm.
This is why small stroke engines always appear to "stack the numbers" and yet still need all those gears.
Valvetrain limitations usually prevent the high rpm engine from really acheiving the same true powerband length most often.
Basically if you go too small on the stroke you are short changing your heads.
If your heads suck though, destroking won't do much to hurt you since you couldn't of made much power anyway.
The one that sweeps 3000 rpm is only half the powerband width of the one that sweeps only 1000 rpm.
This is why small stroke engines always appear to "stack the numbers" and yet still need all those gears.
Valvetrain limitations usually prevent the high rpm engine from really acheiving the same true powerband length most often.
Basically if you go too small on the stroke you are short changing your heads.
If your heads suck though, destroking won't do much to hurt you since you couldn't of made much power anyway.
Originally Posted by silverTA2002
Hmmm..... I've never thought about the powerband vs. rpm span thing before.
That means that a car making 200 lb/ft of tq from 3-6k rpm would be faster than a car making 100 lb/ft from 9-12k. The second car would have to make that power over a span of 6k-12k to keep up with the lower rpm car.
That means that a car making 200 lb/ft of tq from 3-6k rpm would be faster than a car making 100 lb/ft from 9-12k. The second car would have to make that power over a span of 6k-12k to keep up with the lower rpm car.
05-24-2006, 05:15 PM
#73
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Originally Posted by racer7088
This is why small stroke engines always appear to "stack the numbers" and yet still need all those gears.
Valvetrain limitations usually prevent the high rpm engine from really acheiving the same true powerband length most often.
Basically if you go too small on the stroke you are short changing your heads.
If your heads suck though, destroking won't do much to hurt you since you couldn't of made much power anyway.
Valvetrain limitations usually prevent the high rpm engine from really acheiving the same true powerband length most often.
Basically if you go too small on the stroke you are short changing your heads.
If your heads suck though, destroking won't do much to hurt you since you couldn't of made much power anyway.
I'm just observing what's happening with the fast folks. How you or I explain "why" doesn't change what's happening.
But we've had this discussion before, haven't we?
05-24-2006, 07:10 PM
#74
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Originally Posted by Old SStroker
ProStockers make pretty good power with short strokes. All have Bore/Stroke ratios over 1.28:1 (F1 is over 2.2:1 !) None are really valvetrain limited, but some are rpm limited by rules.
05-24-2006, 08:27 PM
#75
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Originally Posted by Ben R
Pro-Stock isn't valvetrain limited? What is the current limitation for a Pro-Stock engine in terms of RPM?
I don't think it's necessarily a "limitation". Of course getting those very large valves to lift an inch or so at those speeds is "challenging" to say the least. From what I've heard, springs last a few runs, but have a "sweet spot" after a certain number of cycles. What have you heard?
05-24-2006, 11:11 PM
#76
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Originally Posted by Old SStroker
I'm just observing what's happening with the fast folks. How you or I explain "why" doesn't change what's happening.
But we've had this discussion before, haven't we?
But we've had this discussion before, haven't we?
05-25-2006, 12:00 AM
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How to make torque at higher rpms? How to make torque at higher rpms?
Very simple answer to the question of this thread. Build a forged 346/7 LS6 Motor, slap on a D1SC or Novi 2000 cent. supercharger, run up to 14 lbs of boost, and make 600+rwtq from 5000 to 6500 rpms!!!
Very simple answer to the question of this thread. Build a forged 346/7 LS6 Motor, slap on a D1SC or Novi 2000 cent. supercharger, run up to 14 lbs of boost, and make 600+rwtq from 5000 to 6500 rpms!!!
05-25-2006, 01:47 AM
#78
FormerVendor
Originally Posted by MTI 427 C5 Roadster
How to make torque at higher rpms?
Very simple answer to the question of this thread. Build a forged 346/7 LS6 Motor, slap on a D1SC or Novi 2000 cent. supercharger, run up to 14 lbs of boost, and make 600+rwtq from 5000 to 6500 rpms!!!
Very simple answer to the question of this thread. Build a forged 346/7 LS6 Motor, slap on a D1SC or Novi 2000 cent. supercharger, run up to 14 lbs of boost, and make 600+rwtq from 5000 to 6500 rpms!!!
