the vtec hit isn't what i'm talking about. When set up propertly vtec never does "hit" it feels like a smooth transition.
The motor is spinning faster it can do more work in a given time right? that means that one second of acceleration at 3k RPM does less work than one second of acceleration at 7k RMP.
Horsepower is afte all a measure of work that can be done.
No Replacement for Displacement
s13sr20chris wrote:ok here i take issue. i think long stroke engines are tuned to be torquey because they are unable to rev high. just like a pushrod motor is tuned that way for the same reason.
I think the problem is that each of us are using a different set of base assumptions, and we end up comparaing apples and oranges. Stroking a motor to me entails swapping in a crank with longer throws, which would increase displacement. Higher displacement = Greater torque. To hold displacement constant would require a change in bore, thus piston area.... the comparasion gets messy in a big hurry.
C-Kwik wrote:That is exactly what I am saying is NOT the case. In any given gear, If you make 150 lb-ft of torque at all RPM's, it will accelerate at the same rate in that gear at all RPMs.
Excellent point! Max acceleration occurs at the peak torque RPM in each gear. The relationship between the rear wheel torque output in each gear is the key in determining shift points for maximum acceleration.
This is interesting... I need to be thinking about this.
Awesome discussion!
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s13sr20chris
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MrFox wrote:I think the problem is that each of us are using a different set of base assumptions, and we end up comparaing apples and oranges. Stroking a motor to me entails swapping in a crank with longer throws, which would increase displacement. Higher displacement = Greater torque. To hold displacement constant would require a change in bore, thus piston area.... the comparasion gets messy in a big hurry.
yes, good of you to point it out. i had forgotten to mention the prerequisite disclaimer. all else being equal. that being said for the displacement to remain equal the bore must change. i agree. messy it is.
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s13sr20chris
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RobDET wrote:right... but acceleration is greater when torque is the same... that was my point... I'm speaking of the same motor in the same gear... the only variable in the S2k is RPM (torque changes but not mutch) Gearing is a factor but it doesn't have to be. If you ignore gearing the motor can still accelerate the car faster at 8K then it can at 5K even tho torque is pretty mutch the same... This is what you just said i think and what i ment by my previous post...
sorry bro. c quick is right. torque controls rate of accel. also the cam profile is the single biggest factor in power.
torque is an instantaneous measurement of force. horsepower is how mutch force is applied over time. Acceleration is a measure of the increase in kanetic energy of a body over time... c'mon guys... THAT is physics.
Did you guys miss out in calclus and physics class?
I'm giong to stay with the S2k because it is an extreme example of my point. Do not look at the lower cam section of the dyno chart. Only pay attention to after the cam change.
at 6k RPM the motor can convert a given volume of gasoline and oxygen into heat to create forward motion. at 9000 RPM the same motor with the same displacement and the same amout of torque can convert 30% more air and fuel into heat into motion.
so imagine the motor being able to fill a 100 gallon tank of air and fuel in one second at 6000 RPM and then igniting it.
that same motor would fill a 130 gallon tank in one second at 9000 RPM. Now ignite the bigger tank...
In one second you have made different amounts of energy.
Did you guys miss out in calclus and physics class?
I'm giong to stay with the S2k because it is an extreme example of my point. Do not look at the lower cam section of the dyno chart. Only pay attention to after the cam change.
at 6k RPM the motor can convert a given volume of gasoline and oxygen into heat to create forward motion. at 9000 RPM the same motor with the same displacement and the same amout of torque can convert 30% more air and fuel into heat into motion.
so imagine the motor being able to fill a 100 gallon tank of air and fuel in one second at 6000 RPM and then igniting it.
that same motor would fill a 130 gallon tank in one second at 9000 RPM. Now ignite the bigger tank...
In one second you have made different amounts of energy.
RobDET, the mechanical advantage of gearing does not increase with RPM. Although the engine will be generating greater power at higher RPM, the vehicle will be traveling at a corrosponding higher speed, when operating within the same gear.
Rather than looking at this issue from a work energy standpoint, you need to go back and refer to statics, dynamics, and simple Newtonian physics to understand.
Rather than looking at this issue from a work energy standpoint, you need to go back and refer to statics, dynamics, and simple Newtonian physics to understand.
it is all about work and energy mate... that is what horsepower and acceleration measures...
Statistics have to do with pure math. Dynamics: Of or relating to energy or to objects in motion. And newtonian physics is the exact reason why horsepower determines Acceleration.
This is directly from howstuffworks.com
You can see from the horsepower equation that high RPM values favor horsepower. If you take an engine with a certain torque and run it at very high revs, it can generate lots of horsepower even though its torque hasn't changed at all. A racing engine can produce relatively low torque, but because it can rev so high it gets a great horsepower rating. A big diesel has huge torque, but "gets no respect" in terms of horsepower because it cannot ever get above 2,000 RPM. This "makes sense" -- if two engines produce the same torque, the one that can do it more times per minute does more work and therefore has more power.
Statistics have to do with pure math. Dynamics: Of or relating to energy or to objects in motion. And newtonian physics is the exact reason why horsepower determines Acceleration.
This is directly from howstuffworks.com
You can see from the horsepower equation that high RPM values favor horsepower. If you take an engine with a certain torque and run it at very high revs, it can generate lots of horsepower even though its torque hasn't changed at all. A racing engine can produce relatively low torque, but because it can rev so high it gets a great horsepower rating. A big diesel has huge torque, but "gets no respect" in terms of horsepower because it cannot ever get above 2,000 RPM. This "makes sense" -- if two engines produce the same torque, the one that can do it more times per minute does more work and therefore has more power.
more howstuffworks:
Another thing you can see from a car's horsepower curve is the place where the engine has maximum power. When you are trying to accelerate quickly, you want to try to keep the engine close to its maximum horsepower point on the curve.
Also consider...
power to weight ratio. It can and is used to make a very educated guess at acceleration. Not torque to weight.
notice that power and weight are the most important components to acceleration. You can get a very good guess from those. that is becuase those are the numbers that have the right units to compare... pounds, distance, and most importantly the KEY to it all TIME.
Another thing you can see from a car's horsepower curve is the place where the engine has maximum power. When you are trying to accelerate quickly, you want to try to keep the engine close to its maximum horsepower point on the curve.
Also consider...
power to weight ratio. It can and is used to make a very educated guess at acceleration. Not torque to weight.
notice that power and weight are the most important components to acceleration. You can get a very good guess from those. that is becuase those are the numbers that have the right units to compare... pounds, distance, and most importantly the KEY to it all TIME.
We are getting nowhere by shadowboxing the issue. It doesn't look like you can be convince without some #s.
Lets use the S2000's F20C as example.
240hp@8300rpm153ftb@7500rpm
So does the S2000 accelerate better at 7500rpm (peak torque), or at 8300rpm (peak power)?
At 7500rpm, the engine generates 153ftlbs of torque.First gear ratio is 3.133. Final drive is 4.10. Overall ratio: 3.133 x 4.10 = 12.84Thus, rear wheel torque: 153 ftlb x 12.84 = 1965 ftlb
Factoring in the leverage provided by the radius of the wheel will give us the amount of force that actually accelerates the vehicle.
The wheel/tire of the S2000: 225/50R16Rolling radius: (16/2) + (0.5*225/25.4) = 12.43 in = 1.036 ft
Thus, rear wheel thrust: 1965ftlb / 1.036ft = 1896lb
Repeating the exercise for 8300rpm gives us 1882lb
Basic Newtonian physics tells us F = ma. So which is going to give us more acceleration?
Lets use the S2000's F20C as example.
240hp@8300rpm153ftb@7500rpm
So does the S2000 accelerate better at 7500rpm (peak torque), or at 8300rpm (peak power)?
At 7500rpm, the engine generates 153ftlbs of torque.First gear ratio is 3.133. Final drive is 4.10. Overall ratio: 3.133 x 4.10 = 12.84Thus, rear wheel torque: 153 ftlb x 12.84 = 1965 ftlb
Factoring in the leverage provided by the radius of the wheel will give us the amount of force that actually accelerates the vehicle.
The wheel/tire of the S2000: 225/50R16Rolling radius: (16/2) + (0.5*225/25.4) = 12.43 in = 1.036 ft
Thus, rear wheel thrust: 1965ftlb / 1.036ft = 1896lb
Repeating the exercise for 8300rpm gives us 1882lb
Basic Newtonian physics tells us F = ma. So which is going to give us more acceleration?
I don't have a lot of time this morning... I'm not trying to be a **** either... i just still think that is in acurate. you ahve not calculated "thrust" like a jet makes. You have calculated another instantaneous quantity.
force = mass * change in velocity over time.
That is not what you have calculated with your "Thus, rear wheel "thrust": 1965ftlb / 1.036ft = 1896lb" There is no time. That is the key to what is wrong with your assumption.
because that set of numbers does not represent a FORCE you cannot use the F=MA formula.
"So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second." "
THAT is a value that you can use for "F"
force = mass * change in velocity over time.
That is not what you have calculated with your "Thus, rear wheel "thrust": 1965ftlb / 1.036ft = 1896lb" There is no time. That is the key to what is wrong with your assumption.
because that set of numbers does not represent a FORCE you cannot use the F=MA formula.
"So if you multiply torque (in pound-feet) by engine speed (in RPM) and divide the product by 5,252, RPM is converted to "radians per second" and you can get from torque to horsepower -- from "pound-feet" to "foot-pounds per second." "
THAT is a value that you can use for "F"
hold on hold on... I still don't think a force called thrust can be derived from torque... however... There is a mutch more basic problem than i had originally thought about... and you guys are probibly trying to say this??
at the torque peak the "twisting" push is greatest at the crank.
It follows that because all the other parts of the drive line are constnats (i'm also assuming we are staying in one gear) that at the torque peak the maximum "twisting" "force" is pushing on the wheels.
*something* else is going on however because to accelerate you have to do work and HP is a measure of work... i'll post agan when i have more time...
Don't give up anyone!
at the torque peak the "twisting" push is greatest at the crank.
It follows that because all the other parts of the drive line are constnats (i'm also assuming we are staying in one gear) that at the torque peak the maximum "twisting" "force" is pushing on the wheels.
*something* else is going on however because to accelerate you have to do work and HP is a measure of work... i'll post agan when i have more time...
Don't give up anyone!
i'm getting there... and going to be late for work as i think...
seems like torque is the right thing... but the bug in my head is that if you have a motor that makes 120 LBft at 4k and 120 lbft at 8K your acceleration will be greater in the 8k rpm motor becaue you have more area under the hp or torque curve. There is a bit more to that... humm
seems like torque is the right thing... but the bug in my head is that if you have a motor that makes 120 LBft at 4k and 120 lbft at 8K your acceleration will be greater in the 8k rpm motor becaue you have more area under the hp or torque curve. There is a bit more to that... humm
I'm at work but i have what i was thinking of... A car that has more "horsepower" can do more work in the same amount of time. That means that when you cram all that work into the same amout of space "0-30 in first" for example the HP is why the car can do more work during that interval right? I agree that at some point there will be a torque peak and that will be where acceleration is greatest. BUT another car making the same torque at less HP will not beable to do as mutch work in that time so the gears must be different to make it to 30 so the car is slower.
Does that sound about right. That is more like what i was getting at. Cramming more torque intervals into the same amout of time...
Does that sound about right. That is more like what i was getting at. Cramming more torque intervals into the same amout of time...
Right on... you are getting it! Your brain is resisting because this stuff goes against alot of common pre-conceptions.
For your last post, rather than 0-30 acceleration, think distance and time. Remember the definition of work.
Also re-read C-Kwiks response at the bottom of page 6. It'll make alot more sense this time around.http://www.nissaninfiniticlub....ber=6
For your last post, rather than 0-30 acceleration, think distance and time. Remember the definition of work.
Also re-read C-Kwiks response at the bottom of page 6. It'll make alot more sense this time around.http://www.nissaninfiniticlub....ber=6
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Jeff Williams
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The last time I checked, the Viper had 2 more cylinders than the Corvette.
Displacement is not the same as number of cylinders. I have a V6 in my old truck, that has 305 cubic inches(5.0 liters). My Q45 has 8 cylinders, but it is only 4.5 liters(275 cubic inches), whick is less than 305 cubic incles (1 cubic inch=0.016387 Liters).
So, to beat this dead horse some more, Technology IS the replacement for displacement. My 1962 GMC makes 151 HP, with 157 ft/lb of torque. My 1994 Q45 makes 279 HP, and 292 ft/lb of torque. If I am not mistaken, the 2003 Q45 hakes about 340 HP, and 300 ft/lb torque.
What makes the difference? Technology!
Displacement is not the same as number of cylinders. I have a V6 in my old truck, that has 305 cubic inches(5.0 liters). My Q45 has 8 cylinders, but it is only 4.5 liters(275 cubic inches), whick is less than 305 cubic incles (1 cubic inch=0.016387 Liters).
So, to beat this dead horse some more, Technology IS the replacement for displacement. My 1962 GMC makes 151 HP, with 157 ft/lb of torque. My 1994 Q45 makes 279 HP, and 292 ft/lb of torque. If I am not mistaken, the 2003 Q45 hakes about 340 HP, and 300 ft/lb torque.
What makes the difference? Technology!
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C-Kwik
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RobDET wrote:the vtec hit isn't what i'm talking about. When set up propertly vtec never does "hit" it feels like a smooth transition.
The motor is spinning faster it can do more work in a given time right? that means that one second of acceleration at 3k RPM does less work than one second of acceleration at 7k RMP.
Horsepower is afte all a measure of work that can be done.
Earlier VTEC motors had a sharp jump in torque. Newer ones tend to use a staged intake runner system to help smooth out some of it. But that is not what I was talking about.
The motor spinning faster can do more work IF switching to the next gear yields a lower torque value at the wheels than staying in gear.
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C-Kwik
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RobDET wrote:oah and by the way i have felt a BIG increase in torque... I drive a turbo car...
Actually, I should back myself up to clarify what I meant and talk about what a motor that has a torque curve that continually climbs feels like. It feels much different than the effects of having a flat torque curve. Imagine it more like the difference between riding a sleigh down a hill(flat torque curve) and a slingshot(Climbing torque curve).
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C-Kwik
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RobDET wrote:horsepower = 550lbs., 1 ft. in 1 secacceleration can be measured in ft/sec/sec and weight is constant. Therefore as the numerical value of HP increases no matter what torque is the car will take less tim OR less distance to accelerate at the same amount.
In terms of a car though, HP really only gives you an idea of the average acceleration over the set distance or set time. HP in that of itself tells you nothing about the acceleration at each moment in time though.
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C-Kwik
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Maybe I should have read all the new posts before responding 3 times. Rob, I think you are catching on to what we have been trying to say. We are talking about acceleration at a particular moment in the engine's rev band. The G-forces created by acceleration will be highest at the point of peak torque, for a given gear. The reason why a motor makes more HP at a higher RPM, even with less torque is because you can stay in a lower gear longer and through torque multiplication, make more torque at the ground. But if you are making less torque at the higher RPM, you will be producing less G-forces than you would at the torque peak in the same gear. I hope this is making sense.
Wow I thought GM only msde a 4.3 liter v6 engine. I never heard of a 5.0 v6 engine. That is awfully big. big block v6 big. Jeez even a stroked 4.3 only comes out to 4.6 liters. And with that 4.6 they were able to get 360 hp the wheels in an S-10. You had to have a 305ci v8 in your truck. With 151 hp from 1962 you must've had a single barrel carb and that special roll of quarters cam profile. Man that is hardly even comparable to a KA let alone a Q45. At least match or come close to engine years!!
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Jeff Williams
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GMC also prduced a 351 cu. inch V-6, and there was another over 400 cubes. The same platform produced a V12 702 cu. inch motor.D-UNIT wrote:Wow I thought GM only msde a 4.3 liter v6 engine. I never heard of a 5.0 v6 engine. That is awfully big. big block v6 big. Jeez even a stroked 4.3 only comes out to 4.6 liters. And with that 4.6 they were able to get 360 hp the wheels in an S-10. You had to have a 305ci v8 in your truck. With 151 hp from 1962 you must've had a single barrel carb and that special roll of quarters cam profile. Man that is hardly even comparable to a KA let alone a Q45. At least match or come close to engine years!!
The truck acutally has a Stromberg 97 flowing about 175 CFM.
Not wanting to propel a 42 year old truck with manual drum brakes and manual steering, I think I will pass on installing a 409.
My point was, over the last 40 years, "displacement has been replaced with technology", for better efficiency, torque, and horsepower. I thought that is what the thread was about.
Although, I still want a 2004 GMC HD truck with the fuel injected 494 engine.
Take the rap song, and change butts to cubes....
" I like BIG Cubes..."
yah... it's far simpler than i thought...
Oah and what i ment about vtec engagement... i had an early B16. the idea is that if vtec hits with a gib jump in acceleration you should lower it's engagement point becuase the big cams have a steeper torque curve. If you loose power right at the vtec switch than you should raise the engagement point... that way you can stay on the Low RPM cams longer.
In dyno charts it pretty mutch always shows a big blip at vtec engagement but hopefully you can see what i mean that moving the engagement points up or down in the RPM range will change where the 2 separate power curves meet.
Oah and what i ment about vtec engagement... i had an early B16. the idea is that if vtec hits with a gib jump in acceleration you should lower it's engagement point becuase the big cams have a steeper torque curve. If you loose power right at the vtec switch than you should raise the engagement point... that way you can stay on the Low RPM cams longer.
In dyno charts it pretty mutch always shows a big blip at vtec engagement but hopefully you can see what i mean that moving the engagement points up or down in the RPM range will change where the 2 separate power curves meet.
you people do realize what your argueing about right?
your trying to justify one parameter as better than another, when in reality they go hand in hand.
yes, technology is better than displacement when the object with more displacement lacks technology.
yes, displacement is better when both objects contain the same level of technology or the object with more displacement is also more technologically advanced.
ok, so some people like big displacement. some people like technology. to be truly superior, you need both.
your trying to justify one parameter as better than another, when in reality they go hand in hand.
yes, technology is better than displacement when the object with more displacement lacks technology.
yes, displacement is better when both objects contain the same level of technology or the object with more displacement is also more technologically advanced.
ok, so some people like big displacement. some people like technology. to be truly superior, you need both.