What to look for in a dyno chart
11-19-2003, 09:25 PM
#1
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What to look for in a dyno chart
Ok, we aren't talking strictly numbers here... JUST the shape of the charts... which is technically better?
1) Something like this graph with a continually rising HP figure and broad torque curve?
http://www.kokeln.com/r_d/flipper_gr...ipper_dyno.jpg
2) Something like this with a noticeable "max" in HP but carried out to redline and broad torque curve?
http://www.vitesseracing.com/Catalog...Stage2HPTQ.gif
3) Or something like this with a "max" HP figure carried out to redline and a peaky torque curve?
http://www.lindseyracing.com/pics/363dyno.jpg
Additional questions:
Is the torque curve very important if the HP is high and carried out to redline?
When upshifting, would you attempt to land on the RPM where the torque peak occurs for optimal power?
Thanks!
1) Something like this graph with a continually rising HP figure and broad torque curve?
http://www.kokeln.com/r_d/flipper_gr...ipper_dyno.jpg
2) Something like this with a noticeable "max" in HP but carried out to redline and broad torque curve?
http://www.vitesseracing.com/Catalog...Stage2HPTQ.gif
3) Or something like this with a "max" HP figure carried out to redline and a peaky torque curve?
http://www.lindseyracing.com/pics/363dyno.jpg
Additional questions:
Is the torque curve very important if the HP is high and carried out to redline?
When upshifting, would you attempt to land on the RPM where the torque peak occurs for optimal power?
Thanks!
11-19-2003, 11:44 PM
#2
RL Technical Advisor
Hi:
You've asked a great question.
A street engine and a race engine are operated at totally different RPM ranges and things tolerated in one would be horrible in the other.
Point 1:
A good race engine should have a good usable RPM range from 4500 to 8000. Best torque will be in the 5500 RPM range and best power will occur around 7500 to 7900. Variations in cams, head flow, exhaust system design, and compression will change these values a tad.
Point 2:
A good street engine should idle smoothly at 800-900 RPM, have good usable torque from 2000 to 6500 and best power around 6000. These figures change with displacement, cams, exhaust system design, and compression.
A good rule of thumb as a general predictor of overall performance is something called "area under the curve". The taller and wider the torque curve, the more usable power you will have and thusly, maximum acceleration provided that the car has the appropriate gear ratios.
Street engines require a smooth & stable idle, maximum usable torque, and good power. Race engines need a wide but higher RPM range and max usable power in a 2500 RPM spread.
Gears are CRITICAL in each application and I cannot overstate that,....
Shifting occurs at peak HP and the next gear should maintain the RPM at or slightly above peak torque.
Does this help?
You've asked a great question.
A street engine and a race engine are operated at totally different RPM ranges and things tolerated in one would be horrible in the other.
Point 1:
A good race engine should have a good usable RPM range from 4500 to 8000. Best torque will be in the 5500 RPM range and best power will occur around 7500 to 7900. Variations in cams, head flow, exhaust system design, and compression will change these values a tad.
Point 2:
A good street engine should idle smoothly at 800-900 RPM, have good usable torque from 2000 to 6500 and best power around 6000. These figures change with displacement, cams, exhaust system design, and compression.
A good rule of thumb as a general predictor of overall performance is something called "area under the curve". The taller and wider the torque curve, the more usable power you will have and thusly, maximum acceleration provided that the car has the appropriate gear ratios.
Street engines require a smooth & stable idle, maximum usable torque, and good power. Race engines need a wide but higher RPM range and max usable power in a 2500 RPM spread.
Gears are CRITICAL in each application and I cannot overstate that,....
Shifting occurs at peak HP and the next gear should maintain the RPM at or slightly above peak torque.
Does this help?
11-21-2003, 08:13 AM
#5
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Originally posted by Steve Weiner-Rennsport Systems
A good rule of thumb as a general predictor of overall performance is something called "area under the curve". The taller and wider the torque curve, the more usable power you will have and thusly, maximum acceleration provided that the car has the appropriate gear ratios.
A good rule of thumb as a general predictor of overall performance is something called "area under the curve". The taller and wider the torque curve, the more usable power you will have and thusly, maximum acceleration provided that the car has the appropriate gear ratios.
11-23-2003, 03:35 PM
#6
Banned
Also, you can think about it this way - a high HP peak at 6000rpm is all very good when you are at 6000rpm (which is only for a fraction of a second at a time usually) but the best performance will be achieved when the average HP is highest throughout the used range of the engine.
So out of a flat HP curve and a climbing curve with the same peak, the flatter curve will be faster in practice.
AND... having more gears closer together means you can keep the engine in the narrower part of the curve, and tune that narrow range for peak HP. (It is easier to build an engine with a high peak over a small range then over a wide range of RPMs.)
So out of a flat HP curve and a climbing curve with the same peak, the flatter curve will be faster in practice.
AND... having more gears closer together means you can keep the engine in the narrower part of the curve, and tune that narrow range for peak HP. (It is easier to build an engine with a high peak over a small range then over a wide range of RPMs.)
11-23-2003, 08:11 PM
#7
While others are correctly pointing out why a broad, flat hp curve (for area under the hp curve) is usually great from a driver’s point of view, one can almost say that the opposite is true from an engineer’s perspective- an engineer’s ideal would be more like a broad, flat torque curve with steadily increasing hp.
How do engineers and drivers get on somewhat opposing sides of something like this? Torque.
Torque is a double edged sword. On the one hand more torque makes more power, which is a good thing- pretty obvious. On the other hand, though, more torque breaks things; the driveline has to be rated to carry the peak torque, so if this goes up you need stronger (and usually heavier) components. Up-rate the power and you need more cooling ability, but not really stronger components.
Torque also breaks things inside the motor, mostly by way of detonation:
For any engine the torque peak is close to the V.E. peak, and thus the point of greatest risk of detonation. The detonation limit usually pretty much defines a turbo engine’s max power output: if you have a big enough turbo you can turn the boost up until a certain peak torque is reached, but not beyond due to detonation.
What’s the practical effect of this? Take your dyno curve #3 as an example- a high boost 944 turbo by the looks of it. Boost has likely been turned up to the detonation limit (about 380 ft/lbs), and with this engine architecture you’re making 360 hp. Nice flat power curve, good area under the curve if you can stay on boost…
Now take the same motor and improve the breathing by doing cams, intake and exhaust runner mods, headwork, etc. The detonation limit hasn’t really changed, so peak torque is still 380, but it doesn’t fall off nearly as quickly with higher rpms. Say by 6500 your torque is still 355 ft/lbs; you’re now making 430 hp, up a good 20%, and you haven’t really stressed most of the components significantly more (other than thermally). Alternately you can turn the boost down to make the same area under the curve with less stress on the engine and driveline.
Curve #1 looks somewhat close to what I’ve described above (a 911 turbo, I assume), and clearly it’s making more of its potential power. Thus an engineer might consider it “technically better”. Take this type of thinking to the extreme and you get very low torque 900 hp 19000 rpm F1 motors that can be extremely light (motor, gearbox, etc) largely because they don’t make torque. Of course the drivability issues of this type of setup, pointed out already in the other posts, are very real. It’s always a compromise, but I like the “technical elegance” of graph #1.
How do engineers and drivers get on somewhat opposing sides of something like this? Torque.
Torque is a double edged sword. On the one hand more torque makes more power, which is a good thing- pretty obvious. On the other hand, though, more torque breaks things; the driveline has to be rated to carry the peak torque, so if this goes up you need stronger (and usually heavier) components. Up-rate the power and you need more cooling ability, but not really stronger components.
Torque also breaks things inside the motor, mostly by way of detonation:
For any engine the torque peak is close to the V.E. peak, and thus the point of greatest risk of detonation. The detonation limit usually pretty much defines a turbo engine’s max power output: if you have a big enough turbo you can turn the boost up until a certain peak torque is reached, but not beyond due to detonation.
What’s the practical effect of this? Take your dyno curve #3 as an example- a high boost 944 turbo by the looks of it. Boost has likely been turned up to the detonation limit (about 380 ft/lbs), and with this engine architecture you’re making 360 hp. Nice flat power curve, good area under the curve if you can stay on boost…
Now take the same motor and improve the breathing by doing cams, intake and exhaust runner mods, headwork, etc. The detonation limit hasn’t really changed, so peak torque is still 380, but it doesn’t fall off nearly as quickly with higher rpms. Say by 6500 your torque is still 355 ft/lbs; you’re now making 430 hp, up a good 20%, and you haven’t really stressed most of the components significantly more (other than thermally). Alternately you can turn the boost down to make the same area under the curve with less stress on the engine and driveline.
Curve #1 looks somewhat close to what I’ve described above (a 911 turbo, I assume), and clearly it’s making more of its potential power. Thus an engineer might consider it “technically better”. Take this type of thinking to the extreme and you get very low torque 900 hp 19000 rpm F1 motors that can be extremely light (motor, gearbox, etc) largely because they don’t make torque. Of course the drivability issues of this type of setup, pointed out already in the other posts, are very real. It’s always a compromise, but I like the “technical elegance” of graph #1.
