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  #76 (permalink)  
Old 05-14-2010, 08:37 AM
How fast is fast enough?
 
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Quote:
Originally Posted by PontiacPhil
Good luck to you too! Everybody tells me the application is harder than the actual test. Took me a week to fill it out the flippin' thing.

As far as TQ vs HP, my computer is sitting here crunching on an FEA, so I had some time to think about it. I would say that torque is a bigger factor in road races (which was Mr. Shelby's area of expertise, correct me if I'm wrong), where HP may be more important in drag racing. Here's why:

When you're going through chicanes and constantly accelerating/decelerating, F=ma tells me that torque to the rear wheels will get you up to speed quicker than the other guy. In a road race you are not granted the luxury of keeping the engine at peak power output all the time. Accelerating from one turn to the next will result in a lower lap time.

When it comes to drag racing, HP may be more important because more energy converted from fuel energy in the engine to kinetic energy of the car equals faster MPH and ET. I believe the area under the HP curve, NOT the torque curve, gives total energy output (since horsepower is energy per unit time, and integrating the HP curve multiplies energy/time by time. Integrating the torque curve would give units of lb-ft-s^2 ), integrating the HP curve gives total energy output during that period of time. The kinetic energy of your car is 1/2mv^2, so to maximize the velocity you would want to maximize kinetic energy, which we now know is done by maximizing the area under the HP curve. If I was a drag racer I would probably want to use a CVT, and I would set it up to keep the ratio such that the engine is constantly at peak power output, NOT peak torque.

You're half way there.

On the road race thing, you're correct, you do want maximum torque at the wheels for maximum acceleration. Now think about how having maximum horsepower combined with the proper gearing makes that happen...

And yea, my application was a PITA, I was trying to take it this past spring but one of my engineering recommendations came from a guy who has his doctorate but not his PE, I assumed he had his PE since he worked professionally for a while and has his PhD. - my mistake, and it cost me 6 months of waiting time.

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Old 05-14-2010, 09:56 AM
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I may not be real engine savvy but I have learned through the years that statistics can be twisted to imply just abut anything you want to imply. Now we have torque converter stall, gears, etc to make a point. Throw out auto trannys, gearing, make it a simple old John Deere tractor. Very few horsepower, lots of torque, lots of weight. It will pull over a mountain top but won't hit 15 mph on a good day. You couldn't put enough gears in a transmission to make this tractor do 100 mph. Torque gets it rolling, pulling, horsepower will not influence this engine because it simply wasn't built for H.P. A massive crankshaft, large bore, heavy flywheels and a camshaft designed for the application. I love the acronym K.I.S.S, keep it simple, stupid. or silly, if that offends any. There's way too many what ifs, this way, that way, just to make a point that there may be an exception to every rule, but basics are basics. It goes to show what lengths folks will go to win an argument, can't be wrong, take a step back, or humbly say, yes, you're right. But, but, but...it gets old, kind of like having a discussion with one of my ex-wives or a fence post.... Arguing for the sake of an argument, pissing people off, or just being disagreeable...lmao! Let's talk politics, another twisted topic.
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  #78 (permalink)  
Old 05-14-2010, 10:32 AM
How fast is fast enough?
 
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Originally Posted by dinger
I may not be real engine savvy but I have learned through the years that statistics can be twisted to imply just abut anything you want to imply. Now we have torque converter stall, gears, etc to make a point. Throw out auto trannys, gearing, make it a simple old John Deere tractor. Very few horsepower, lots of torque, lots of weight. It will pull over a mountain top but won't hit 15 mph on a good day. You couldn't put enough gears in a transmission to make this tractor do 100 mph. Torque gets it rolling, pulling, horsepower will not influence this engine because it simply wasn't built for H.P. A massive crankshaft, large bore, heavy flywheels and a camshaft designed for the application. I love the acronym K.I.S.S, keep it simple, stupid. or silly, if that offends any. There's way too many what ifs, this way, that way, just to make a point that there may be an exception to every rule, but basics are basics. It goes to show what lengths folks will go to win an argument, can't be wrong, take a step back, or humbly say, yes, you're right. But, but, but...it gets old, kind of like having a discussion with one of my ex-wives or a fence post.... Arguing for the sake of an argument, pissing people off, or just being disagreeable...lmao! Let's talk politics, another twisted topic.

Funny thing is, given equal cars in equal conditions, there is NEVER an exception to the rule "the highest average horsepower put to the ground, down the track runs the quickest."
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  #79 (permalink)  
Old 05-14-2010, 10:32 AM
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Quote:
Originally Posted by ap72
Now think about how having maximum horsepower combined with the proper gearing makes that happen...
I think I have your answer. Bear with me on a little thought experiment:

Two guys are racing. They have identical cars, both set up with CVT's, 3:1 axle ratio in a 3000 lbm (93.17 slug) car, 30" tall tires. Guy #1 has his CVT set up to keep his engine at peak torque, Guy #2 set up at peak HP. Engine's peak torque is 500ft-lbf @ 5000 rpm, peak HP of 498hp @ 5500 rpm. Refer to chart below, threw it together really quick, totally hypothetical. Assume no friction.

RPM Tq HP
3000 375 214
3250 385 238
3500 400 267
3750 420 300
4000 440 335
4250 460 372
4500 480 411
4750 490 443
5000 500 476
5250 490 490
5500 475 498
5750 435 476
6000 400 457
6250 350 417
6500 300 371
6750 250 321

Guy #1 is therefore pushing a constant 1500 ft-lbf at the rear wheels. With 30" tires this is 1200lbf of thrust. So guy #1 is accelerating at a constant rate of [a=F/m=1200lbf / 93.17 slugs = 12.88 ft/s^2] which is 8.78 mph/s. After 10 seconds he is going 87.8 mph and he will have travelled (d=at^2/2= 12.88ft/s^2 * 10^2 s^2 / 2) 644 ft (darn near 1/8 mile).

Guy #2 is pushing a constant 1425 ft-lbf at the rear wheels, 1140-lbf thrust at the wheels. Results in acceleration of 12.24 ft/2^s, after 10 seconds he's going 86.04 mph and has covered only 612 ft. He has lost the race.

Here is where everybody has been mistaken with engine horsepower. Since there is a gear-train involved you cannot look at horsepower at the flywheel, you must look at horsepower delivered to the wheels. Since Guy #1 is putting more torque to the axle than the other guy, and they have the same rear gear ratio and tire size and hence the same axle RPM at any given vehicle speed, Guy #1 is actually delivering more HP to the tires. The way to deliver power is through torque. Power is a result of torque and rotational velocity, nothing more.

:edit:

WHOA HORSIE! Did anybody notice my major flaw in thinking there? With a CVT the two cars are using a different transmission ratio, hence the torque delivered to the rear axle pinion is not equal to engine torque. Guy #2 who's at higher RPM's will need a numerically larger CVT ratio than the Guy #1 given the same vehicle speed, meaning he will be DELIVERING more torque to the rear axle even though engine torque is lower. I think ap may be on to something here.

Last edited by PontiacPhil; 05-14-2010 at 11:13 AM.
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Old 05-14-2010, 10:33 AM
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Quote:
Originally Posted by ap72
"the highest average horsepower put to the ground, down the track runs the quickest."
Exactly. Key phrase "put to the ground".
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Old 05-14-2010, 11:10 AM
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Quote:
Originally Posted by PontiacPhil
WHOA HORSIE! Did anybody notice my major flaw in thinking there? With a CVT the two cars are using a different transmission ratio, hence the torque delivered to the rear axle pinion is not equal to engine torque. Guy #2 who's at higher RPM's will need a numerically larger CVT ratio than the Guy #1 given the same vehicle speed, meaning he will be DELIVERING more torque to the rear axle even though engine torque is lower. I think ap may be on to something here.
New example. At 50 mph, the guys' tires are spinning 560.5 rpm, meaning the driveshaft is turning 1681.5 rpm. Guy #1 is always at peak torque, so his engine is turning 5000 rpm which means his CVT is currently at 2.97:1. Guy #1 is therefore delivering 500 ft-lb x 2.97 = 1485 ft-lb to the rear axle.

Guy #2 is running at peak HP, so his engine is turning 5500rpm and putting out 498hp/475 tq. At 5500 engine rpm and 50 mph his CVT ratio is 3.27, so he is putting 475 ft-lb x 3.27 = 1553 ft-lb to the rear axle. Guy #1 just got SMOKED!

ap72 may have been right all along. It doesn't matter how much torque your engine makes because horsepower is conserved (it remains constant when going through a gear reduction, neglecting losses). By maximizing horsepower the end result is a maximization of torque at the rear wheels.

Last edited by PontiacPhil; 05-14-2010 at 11:21 AM.
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Old 05-14-2010, 11:39 AM
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"In theory"

Theory is a wonderful thing unfortunately we don't race text books and besides that race cars can't read. It's important to remember that in the racing world that we don't race dyno's or flowbenches. It's ALL about the combination. I'm not sure you've noticed but generally all top notch engine builders aren't young guys. There's a reason for that. When I was in my early twenties I too built some pretty stout engines. It wasn't until I started hanging out with the old-timers that I really began to understand how to build consistently winning combinations. That requires years on the starting line at all sorts of sh** hole race tracks. Years of trying different combinations. Breaking stuff, trying things that make no sense at all. While the phrase "no replacement for displacement" might be true. No replacement for experience rings even truer. While injecting new technologies into the craft is important you can't turn your back on what's been successful in the past. I got my BSME a long time ago and while it's been helpful I find that most of what I use today is tacid knowledge picked up over time and not something that's found in a textbook.
To put me in my place I still go visit my friend who is nearing 70 and listen to him like a sponge. I pick up something every time I go to his shop. His NHRA Wally that he won in Pro Stock was won without his never having gone to college.

I'm still trying to figure out why this thread was even started.
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  #83 (permalink)  
Old 05-14-2010, 12:08 PM
How fast is fast enough?
 
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Quote:
Originally Posted by PontiacPhil
I think I have your answer. Bear with me on a little thought experiment:

Two guys are racing. They have identical cars, both set up with CVT's, 3:1 axle ratio in a 3000 lbm (93.17 slug) car, 30" tall tires. Guy #1 has his CVT set up to keep his engine at peak torque, Guy #2 set up at peak HP. Engine's peak torque is 500ft-lbf @ 5000 rpm, peak HP of 498hp @ 5500 rpm. Refer to chart below, threw it together really quick, totally hypothetical. Assume no friction.

RPM Tq HP
3000 375 214
3250 385 238
3500 400 267
3750 420 300
4000 440 335
4250 460 372
4500 480 411
4750 490 443
5000 500 476
5250 490 490
5500 475 498
5750 435 476
6000 400 457
6250 350 417
6500 300 371
6750 250 321

Guy #1 is therefore pushing a constant 1500 ft-lbf at the rear wheels. With 30" tires this is 1200lbf of thrust. So guy #1 is accelerating at a constant rate of [a=F/m=1200lbf / 93.17 slugs = 12.88 ft/s^2] which is 8.78 mph/s. After 10 seconds he is going 87.8 mph and he will have travelled (d=at^2/2= 12.88ft/s^2 * 10^2 s^2 / 2) 644 ft (darn near 1/8 mile).

Guy #2 is pushing a constant 1425 ft-lbf at the rear wheels, 1140-lbf thrust at the wheels. Results in acceleration of 12.24 ft/2^s, after 10 seconds he's going 86.04 mph and has covered only 612 ft. He has lost the race.

Here is where everybody has been mistaken with engine horsepower. Since there is a gear-train involved you cannot look at horsepower at the flywheel, you must look at horsepower delivered to the wheels. Since Guy #1 is putting more torque to the axle than the other guy, and they have the same rear gear ratio and tire size and hence the same axle RPM at any given vehicle speed, Guy #1 is actually delivering more HP to the tires. The way to deliver power is through torque. Power is a result of torque and rotational velocity, nothing more.

:edit:

WHOA HORSIE! Did anybody notice my major flaw in thinking there? With a CVT the two cars are using a different transmission ratio, hence the torque delivered to the rear axle pinion is not equal to engine torque. Guy #2 who's at higher RPM's will need a numerically larger CVT ratio than the Guy #1 given the same vehicle speed, meaning he will be DELIVERING more torque to the rear axle even though engine torque is lower. I think ap may be on to something here.

Holy Metal Batman, you had an epiphany!

For a given wheel speed if you gear your engine to be at the hp peak rather than the torque peak you will in fact have more torque applied to the tires!

Which is why running the track at the highest average power wins. And why you need to gear and stall your car for highest average power, not torque. And why you shift not based on a torque curve but a hp one.

Now explain that to someone without a masters in mechanical engineering- apparently I can't.
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Old 05-14-2010, 12:13 PM
How fast is fast enough?
 
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Originally Posted by engineczar
"In theory"

Theory is a wonderful thing unfortunately we don't race text books and besides that race cars can't read. It's important to remember that in the racing world that we don't race dyno's or flowbenches. It's ALL about the combination. I'm not sure you've noticed but generally all top notch engine builders aren't young guys. There's a reason for that. When I was in my early twenties I too built some pretty stout engines. It wasn't until I started hanging out with the old-timers that I really began to understand how to build consistently winning combinations. That requires years on the starting line at all sorts of sh** hole race tracks. Years of trying different combinations. Breaking stuff, trying things that make no sense at all. While the phrase "no replacement for displacement" might be true. No replacement for experience rings even truer. While injecting new technologies into the craft is important you can't turn your back on what's been successful in the past. I got my BSME a long time ago and while it's been helpful I find that most of what I use today is tacid knowledge picked up over time and not something that's found in a textbook.
To put me in my place I still go visit my friend who is nearing 70 and listen to him like a sponge. I pick up something every time I go to his shop. His NHRA Wally that he won in Pro Stock was won without his never having gone to college.

I'm still trying to figure out why this thread was even started.
Its kind of a shame it took him 50+ years to learn what some guys pick up by their junior year isn't it? Imagine what more he could have done if he would have knew then what he knows now...

This thread was started so people don't have to sit on a track for half their life to figure it out. Apparently only one guy has learned anything so far though, and I'm fairly sure he could have gotten it without this thread... Maybe someone gained some understanding.
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Old 05-14-2010, 12:15 PM
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Quote:
Originally Posted by engineczar
...what I use today is tacid knowledge picked up over time and not something that's found in a textbook.
engineczar,

No argument from me on that point.

Quote:
Originally Posted by engineczar
I'm still trying to figure out why this thread was even started.
ap72 was asking what seemed like a straightforward question: Is it better to base shift points on the horsepower curve or the torque curve, and why?

I found the topic interesting so I put some thought into it.

Quote:
Originally Posted by ap72
Now explain that to someone without a masters in mechanical engineering- apparently I can't.
And comments like that are why the experienced engine builders on this site who don't have engineering backgrounds are quickly dismissing this discussion as a big d*ck waving contest.
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Old 05-14-2010, 12:21 PM
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Originally Posted by ap72
Its kind of a shame it took him 50+ years to learn what some guys pick up by their junior year isn't it?
50+ years? Why how many NHRA Pro Stock trophies do you have?
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Old 05-14-2010, 12:21 PM
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Originally Posted by ap72
Its kind of a shame it took him 50+ years to learn what some guys pick up by their junior year isn't it? Imagine what more he could have done if he would have knew then what he knows now...

This thread was started so people don't have to sit on a track for half their life to figure it out. Apparently only one guy has learned anything so far though, and I'm fairly sure he could have gotten it without this thread... Maybe someone gained some understanding.
This will be my last post in the thread, I promise. ap72 has officially taken it to WANKVILLE.

I in no way have the same attitude as ap72, I just want everyone to know that right now. I came to this site to be educated because like I said, degrees are just expensive pieces of paper without any experience to back it up. I was taught everything I know about cars at a young age by a guy who barely graduated high school. He was an excellent teacher and is the reason I am doing what I am today. I respect everybody's opinion and appreciate the help I have received on my project.

Thanks

Phil
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Old 05-14-2010, 12:24 PM
How fast is fast enough?
 
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Quote:
Originally Posted by PontiacPhil

And comments like that are why the experienced engine builders on this site who don't have engineering backgrounds are quickly dismissing this discussion as a big d*ck waving contest.
you're the only one with that degree...







FWIW, there are a LOT of good engine builders under 45, probably more under than over. They just don't mess around with 60 year old American V8's... Probably a wise choice.
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Old 05-14-2010, 12:28 PM
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Goooooooo Bobcat
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Old 05-14-2010, 12:29 PM
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I was beginning to believe that pontiac phil was indeed AP72...I owe you an apology sir! AP72 has indeed taken it to "WANKVILLE". I would be willing to bet this self-centered kid has never even built an engine. The initial post that started this thread was insulting and almost every other post is insulting and written in such a way that make me believe this kid thinks he's Christ. I have no degrees at all. High school educated. I have been turning wrenchs and messin around with hotrods since I was 16. I do not even attempt to understand all the physics BS past a certain point...I listen to the "blind old dudes" that have wasted 50 years of their lives figuring out stuff that jesus"AP72" had figured out when he was 16. I have learned some by my own expierience also. I am a professional mechanic.

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