j9fd3s

iTrader: (3)

actually to understand the v8-rx7 thing you have to look at it from the other direction. there are plenty of guys with this nice stock 350hp v8, its got a low center of mass, makes great power, gets decent mileage, sounds good.

but the car that they put it in from the factory sucks so much, an 86 mazda is better =)

Nihilanthic

Yanno, GTO, its obvious to everyone that a bigger powerband (and the higher torque required to have one) to maintain the same amount of power for a longer period (in terms of rpms) results in better performance down the line. Your defence of rotary engines isnt backed up by their ability to perform better, but rather by your emotional commitment to them and inability to accept that they can be outperformed by a competing engine design that youve probably spent lots of time putting down on equally emotional terms.

Classic example of Cognitive Dissonance.

We all know what can do the job easier, cheaper, and be easier to drive - a motor with a bigger powerband and torque, and that comes from either more displacement, forced induction, or both. Theres a good reason that R10 won lemans, even with a big, heavy engine!

Yeah, bigger motors have an advantage against smaller motors... thats exactly the point. Appealing to emotions and the 'challenege' of making a smaller motor make the same power, but with all the tradeoffs involved, might sway someone who doesnt know better or actually cares about such considerations, but some people want something that goes fast, is streetable, doesnt guzzle gas, and just works at the end of the day.

jimlab

Nearly the same where? At ONE POINT in their rpm ranges?

You can play around with hypothetical gearing all you want, but the reality is that if you take two different engines, they will more than likely have significantly different power curves, especially in your example of the diesel vs. the rotary. You cannot compensate for that with gearing, which only amplifies the torque curve of the engine. Even if you gear the cars so that at each engine's peak output, they're producing the same thrust at the contact patch, you still have THE REST OF THE RPM RANGE to consider.

Because chances are good that thrust at the contact patch is NOT higher on the low torque, high horsepower car over much of the rpm range. For someone who keeps harping on that rpm factor, you certainly seem to toss it out the window the minute it suits your purpose.

I don't give a **** if they do produce identical wheel torque at one point in the rpm range. The engine with more torque is going to have a much WIDER and POWERFUL torque curve, and the car with a broader curve will accelerate harder, over a longer rpm range, than the one with a peaky curve. Acceleration takes place across the entire rpm range, not just at one peak point.

No.

No, only one of us is right.

Paul Yaw's example is fatally flawed because he's not using the actual torque curves of the two engines to produce his acceleration graphs. He's only using peak values and assuming a hell of a lot.

Even if gearing were equalized to put them both at redline at the same speed at the top of each gear, that does not mean they would accelerate at the same rate. One of them is going to reach terminal speed in each gear more quickly than the other, and given equal vehicle weights, that's going to be the one with MORE AREA UNDER THE TORQUE CURVE.

Sizzlenut

I'm drunk and feel like contributing.
High horsepower, low torque: the graph peaks out pretty quickly, drops off pretty quickly. High horsepower, high torque, the graph is not as peaked, it's more consistant. Whatever. You'd need to shift ten times to stay in the peaky power band of the high HP car to keep up to a high torque car that you'd have to shift 5 times to stay in the power.
We all know it takes time to shift.
http://vettenet.org/torquehp.html

Nihilanthic

Sizzle gets a cookie.

Also, as much as I dont get along with Jimlab, you cant argue with the facts when hes right.

Sizzlenut

Ditto.
BTW, Jim, I just broke my breaker. Haha. Water under the bridge I hope. My 150 amp fuse is doing just fine.

GtoRx7

iTrader: (5)

Ah, but in my example I used est. and I bet the Cat engine has the same flat lined torque from 900rpms to 2,000rpms, and a REW does have pretty flat torque from 2,500-6,500 rpms. Cat range of torque- 1,100rpms. Rew range of torque 4,000rpms. Now Divide the torque of each, 650/215 and the cat has 3.02 times the torque. But Divide the 4,000rpms by 1,100rpms and you get 3.63 times the Revs the REW has. Revs, or time, or horsepower do the work, and the REW wins in this example by having more area under the curve, and more torque at the wheels, or more usable HP at the wheels to provide the torque. Torque over time is needed, which is measured in RPM's to provide wheel HP.

Glad your having fun! In your hypothetical example, you'd be right. Remember not all high hp, low torque cars are peaky in torque. But in my hypothetical example you would be wrong. In fact the Cat. motor would need slightly slower speeds in each gear to match the REW acceleration abilities. So the higher torque engine would need to shift more times, in a real world race.

As much as I dont get along with you, I cant argue with the facts, your dumbass.

Nihilanthic

Close, but no banana. Its powerband relative to the total rev range of the motor. If the motor only revs to 5K rpms and it starts at 3K, thats a bigger powerband than 4 to 6K, for example. One half vs a third, for example.

Besides, a 300 hp diesel woudl beat a 300 hp rotary assuming both were in cars of the same total weight with appropriate gearing and equal traction.



FLAT TORQUE still provides PEAKY power. Look at a Honda VTEC motor. A downsloping of torque provides FLAT POWER. You want FLAT POWER, not PEAKY power. You are however correct that a engine with flat torque woul have constant acceleration - however, if it had as much power as the torquier motor, than earlier in the powerband it would be out accelerating the peaky motor becuase it had more power and more torque at that rpm than the peakier motor did.

Furthermore, an ideal electrical motor conneted to the drive wheels making constant power would have a torque 'downslope' as it went asymptotically from max torque at zero rpms to min torque at higher rpms... with a engine with, say, a flat powerband constantly shifting its just a more 'steplike' curve, but its still a curve where wheel torque goes down as speed goes up.

In other words, the torquey motor would be out accelerating the flat torque motor more, the farther it is from its redline, meaning the rate of jerk goes down, but it will still out accelerate the peakier motor. Unless, of course, you think a RSX would somehow beat a car with equal weight, 200 hp, and 300 foot lbs of torque, assuming equivilant traction and gearing.


No, you cant. And its "you dumbass"... but then again I dont even know why you said that.

GtoRx7

iTrader: (5)

Show me how, and use real world dyno charts to prove it. Its possible either would win, depending on the exact engine we are comparing

Alright, now we are bringing in engines that have no values. If you take that same downsloping torque motor, enhance its breathing, and not loose ANY downlow torque (or horsepower actually) and pull its torque flat all the way to redline, you would have a better, faster engine!!!!!!!!! How is it slower or worse? The honda V-tec motor is faster than ANY old n/a 4 cly. due to the fact it has peak torque from 2500-7800 rpms, for its size, that is as fast as it gets, and your a total dumbass in thinking the way you do. Horsepower wins! Its what moves cars, more down low torque creates more down low HP! This is how it is!

This depends on the engines we are comparing, as a flat torque engine with 10,000rpms would possibly have more horsepower under the curve than the engine with high torque, and downward slope. I dont want to go through all this again. Even if the high torque one is has 300ft-lbs at 1,500rpms, it would only rev to 4000rpms to produce 200hp, then fall on its face. Baised on this, yes the honda engine would win, due to more hp under the curve, and have a wider powerband. I looked up the RS-X dyno results and it has peak torque from 2500-7800rpms, with 140ft-lbs or torque. If you do the correct math, it will have more Ft-lbs to the tire at the same rpms (within the powerband) than the big ol' 300ft-lb V8's powerband.

Sorry, I forgot the "a", as in - "your A dumbass".

Nihilanthic

Im too lazy to quote, so I wont.

1. Its a "DUH" thing that given equal power to weight, if one car has that peak power for longer than the other, the former car will out accelrate it. Its also a truism, I shouldnt have to explain it.

2. VTEC is faster than "any old na 4cyl" because it MAKES MORE POWER. What you fail to realize is that whle it makes 'peak torque' for a longer period, if another motor made PEAK POWER for half of its rev range, but not peak torque, it would still out accelerate it. Yeah, the vtec is making peak torque longer, but only makes its 200 hp for a brief period. A turbo 4 making 200 hp for a much longer period might not have peak torque for as long, but guess what? The turbo 200 hp car will OUT accelerate the 200 hp VTEC car during the start of the turbo's power band (with higher torque) and have inverse jerk (rate of acceleration slowly going down) and come down to matching the VTEC's rate of acceleration at the end of its power band, when its time to shift. The VTEC will have the same, slower, rate of acceleration throughout its powerband.

3. YOU'RE as in "you are". Learn some grammar.

jimlab

Look, it's really pretty simple. You don't have to compare diesel engines to F1 engines or play games with gearing. In fact, you don't even have to look any farther than some of the posts on this forum where people have asked about installing a Renesis 13B in an FD.

Would it be more reliable? More than likely, since it's naturally aspirated. Would it be faster? HELL NO.

Why? Take a look at the real-world Dynojet results below...



Look at the Renesis' torque curve compared to the torque curve for the 13B-REW. Which engine do you think would make the car faster?

A. The Renesis, because it turns 9,000 rpm and that's 1,000 rpm "better" than 8,000 rpm. (I kid you not, there are people on this forum who actually believe that)

B. The Renesis, because its horsepower peak comes at higher rpm, and therefore it's doing more work.

C. The 13B-REW, because it has far more area under the torque curve.

The answer is C. Even if both engines produced the same peak horsepower, at any given rpm, the 13B-REW will accelerate faster and harder than the Renesis. Period.

jimlab

Ever wonder why your car doesn't accelerate as hard in higher gears as it does in lower gears? Let's use the 3rd gen. RX-7 as an example and find out why.

1st gear ratio - 3.48:1
2nd gear ratio - 2.02:1
3rd gear ratio - 1.39:1
4th gear ratio - 1.00:1
5th gear ratio - 0.72:1
Differential ratio - 4.10:1

According to Mazda, torque peak for the 13B-REW is 217 lb-ft. @ 5,000 rpm, so let's calculate maximum torque at the axles for each gear.

Torque at the axles = engine torque * transmission gear ratio * differential gear ratio - frictional losses (est. 15%)

1st gear = 2,632 lb-ft.
2nd gear = 1,528 lb-ft.
3rd gear = 1,051 lb-ft.
4th gear = 756 lb-ft.
5th gear = 545 lb-ft.

OK, so already it's obvious that force at the axles is falling off as gear multiplication is reduced in higher gears. Maybe we've already got our answer. But what about horsepower at the axles? What's it doing?

First, let's calculate axle speed in each gear at the same rpm (5,000) used to calculate maximum torque at the axles.

Axle speed = engine rpm / transmission gear ratio / differential gear ratio

1st gear = 350 rpm
2nd gear = 604 rpm
3rd gear = 877 rpm
4th gear = 1,220 rpm
5th gear = 1,694 rpm

Now, since we know that horsepower = torque * rpm / 5,252, let's calculate horsepower at the axles using the torque and rpm at the axles we've already calculated.

1st gear = 175 horsepower
2nd gear = 176 horsepower
3rd gear = 176 horsepower
4th gear = 176 horsepower
5th gear = 176 horsepower

Wow. Now isn't that interesting?

Horsepower at the axles for a given rpm is the same regardless of which gear the transmission is in, and yet we know that 4th gear doesn't accelerate as hard as 3rd gear, let alone 1st gear. The same amount of work is obviously being done, but we're accelerating slower in each higher gear. What's the deal?

Torque at the axles falls off as gearing multiplication is reduced. The higher the gear, the lower the multiplication, and therefore the less force at the contact patch, causing the car to accelerate slower in each subsequent gear. This is absolute fact and easily observed in any vehicle on the road.

Now... if acceleration really followed the horsepower curve instead of the torque curve, wouldn't it stand to reason that the car would accelerate just as hard in any gear? So what went wrong?

mycarisolderthanme

Can't we all just get along?

I admit I haven't done all that much research on the topic, but performance per dollar wise, the V8 fellas seem to have the rotary beat. I can definitely respect that. Can't the V8 guys respect the nostalgia involved with the rotary? Forget about the ignorant fanboys trying to argue that V8's destroy the handling of sevens. At least respect the time/money Mazda put into R&D to create a factory motor COMPLETELY different from every other motor out there. No, it wasn't the greatest motor ever produced, but I'd say it was a damn good effort in engineering. It's a piece of history to me, I guess.

I will admit, if I did decide to build a budget racecar, it would probably involve an LS. =p

Nihilanthic

Some people want performance more than history, snobbery, or gimmicks. Because Ive yet to hear any reason to use a rotary for performance or bang/buck reasons, I dont care. The chassis is awesome, but the engine isnt, and its expensive to modify. And, BECAUSE its so rare, service and parts are more expensive and hard to find.

OTOH, I can get a motor that isnt held on nearly as high a pedistal that can make more power, cheaper, with more reliability, from a variety of sources (2.3T) and even an advanced one that is up on a pedistal (like the LS1) or is simply iconic and THE benchmark and has a rich racing history all of its own (SBC) if such things actually mattered anyway.

88IntegraLS

No one owes you any explanation. If you can't figure out the physics behind available horsepower vs. peak horsepower, get an education.

GtoRx7

iTrader: (5)

Thanks for all your smart input on the subject at hand.


As for everyone else, the fact a Rx-8 isnt is as fast is due to having less Horsepower under the curve. I understand all you said Jimlab, I understand all Nihantic said as well. You guys are great, whatever, just shrug off what I have been saying, and act as if I am a idiot, and use "well the rotary isnt as good" I WASNT EVEN WANTING A V8 vs. Rotary debate. I am just saying the gobs of torque isnt the ultimate player, as RPMS is needed to make it happen. So everyone calm down, I just dont care at this point. The ultimate engine in the world would have a few thousand Ft-lbs, FLAT from 800rpms to 20,000 rpms and have perfect VE at each rpm, making it have thousands of hp. This is why Variable valve timing, and valve-tronic, and varible compression is making better engines than ever before. So get out of the stone age.

jimlab

And you're still wrong...

A torque curve is plotted vs. RPM...

When you don't have enough displacement to get by with a couple huge valves, sure.

The same Physics applies to all them new fangled engines too, genius...

Nihilanthic

RPMS are a means, not an end. Youve bought into marketing about how higher revs = better, and need to get over it!

Again Audi's R10 DIESEL RACE CAR could NOT have possibly gone much over 5200 rpms.. 5500 MAX. why? Diesel engines by their design cant burn fuel fast enough to rev higher. Yet, it still managed to cream the competition with its wide powerband, which was easy on the driver, and better fuel consumption meaning less pitstops.

Anyway, powers a good way to quantify the work you can do, but something youre missing out on here is that for the 'perfect motor' there would be no transmission, just an engine that makes the same power from .000000001 rpms to infinity (or whenever it cant overpower wind resistance) rpms. And guess what that would look like?

It would basically look like an asymptotic curve that Im sure youve heard in math before. Assuming power is constant, and y as wheel torque and x as speed in rpms, Theres obviously nothing meaningful at zero rpms, or at infinity rpms, but really close to zero there should be superhigh torque, and really close to infinity there should be superLOW torque.

But regardless, that kind of model shows what a perfect CVT, or an ideal electric engine, would do - perfectly smooth acceleration near that asymptotic curve as it slopes down to less and less torque as rpms go up, and eventual drag forces make it max out its speed.

Now, a engine with flat torque might be more controllable, but it wont be as fast as one with flat power. A engine with flat torque would instead have a step-like graph of wheel torque through the gears - not matching the asymptote through the MIDRANGE, and only catching up to it at the end of its rpm range. However, it would FEEL faster because jerk would be effectively zero.

Now, a 'torquey' motor with a broad powerband, for example, would be a STi. As well as a v8 or whatever. I happen to have a graph left over from a VERY useful applet I've lost that helps demonstrate this:



Im sure you can already figure out where to shift- where the lines intersect.

Now, obviously, thats not PERFECT, but in the midrange it would be outperforming a flat torque car. A flat torque car would be a 'curve' of straight horizontal line segments of y = whatever wheel torque in the same place as each gears curve above, and would not have the same amount of acceleration from the higher torque at the same hp at lower rpms as the torquier motor right there.

Do you get it now? The best you could hope for is to match the asymptote as close as possible. Flat torque feels faster, but if a flat torque motor making any arbitrary amount of horsepower had a 'torquey' motor with the same amount, the torquey one would beat it, and thats because at the midrange it WILL out accelerate it becuase it already is making its max power, and continues to do so - the flat torque hasnt yet reached it.

You saying a flat torque motor would be faster would only be if it made more power overall - such as if the flat torque motor, instead of having torque go down, held flat - it would make more power overall. Nobody is doubting that a more powerful motor can beat a less powerful motor, given the same weight - we're talking about of equivilant hp/weight, one having more torque than the other.

It may not feel as fast (the STi) but it will be faster than a flat-torque 300 hp car, because it matches truer to that asymptote. If you want constant acceleration, you need to bust out a jet, or go build yourself a little red Space-RX7 where drag doesnt apply, and constant thrust is constant acceleration. Unfortunately, on earth, there are certain laws of physics you have to adhere to.

Mazsport

.

GtoRx7

iTrader: (5)

YES!!! Someone actually reads what I was trying to say!! And I was starting to think guys just stuff words (and examples) in my mouth and ignore what I was TRYING to say. I just dont know how to say it perfectly at all times to let everyone make sense of it.

jimlab

Maybe it was because you kept insisting on shoving the word horsepower into every sentence and making incorrect statements about torque...

Nihilanthic

GTO - no offence, but this is pretty advanced math/physics for the majority. Its also very tricky to explain this concisely without having the requesite vocabulary and comprehension, so while you probably have an idea of what is being said, putting it all together was the sticking point.

Now, Im sure you can see how the STis torque curve matches the downslope of the theoretical curve of constant power, right? A flat torque 300 hp motor (supercharged S2K, or whatever...) would basically be flat line segments with the very right tip of them touching that asymptotic curve.

That wont be as fast, the STi would be outaccelerating it in the midrange, given the same power/weight ratio. Thats our entire point - acceleration is dependant on the whole powerband in each gear, and because we go by power, not peak wheel torque or peak acceleration in a given gear assuming 100% traction, to weight, you want torque! It also means you can have longer gears, or less gears, and still match the curve.

Now, all the other **** about power/displacement ratio, or engine rpms, ultimately dont mean a damn thing, see why? Its nothing but power, weight, traction, # of shifts and driver skill.

88IntegraLS

What! Integral calculus (the obvious field of mathematics behind calculating available power) is considered "early transcendentals" according to textbook authors. You mean they lied?

GtoRx7

iTrader: (5)

Well, because we have calmed down, I keep talking about horsepower for one reason. To bake a cake, you need to have ingredents. You need A and B, which would make C the cake. This is how I look at a engines performance, you guys are always speaking of torque, which is good, dont get me wrong on that. Dont think I am for or against any engine! But the fact remains, is this one question-

Does Torque on its own move a car?

No, that just A part, you also, no matter how little, need RPM, B. If a motor produces Heaps of torque, if its going to move a damn thing, the shaft on the engine needs to rotate. The second it does, its sheer definition is Horsepower. If we went around all day rating motors by only torque, it wouldnt really tell you everything. That is ALL I was trying to say. So belittle me all you want, I understand it all just fine. So lets just leave it at that, and pretend I didnt even bring it up, and keep all the personal, non-professional comments aside.

None taken

jimlab

Well, that explains a lot...

Yes. The twisting force that turns the drivetrain and wheels is called TORQUE.

Horsepower is nothing more than a MARKETING TOOL. It's a holdover from the days when people still used HORSES for transportation and work and had to be convinced that new-fangled auto-mobiles would out-perform what they were used to, expressed in terms they could relate to.

If you'd never heard of horsepower, internal combustion engines would still function and cars would still accelerate at a rate based on the torque curve of their engines.

While the engine is running, usable TORQUE is present at the flywheel or flexplate. CONTINUOUSLY. Until the engine is shut off.

Connect the output of the engine to a transmission and TORQUE is transfered through the drivetrain and differential to turn the axles, making the tires rotate.

The amount of thrust at the contact patch between the tire and the road surface is what determines the rate of acceleration and is calculated from TORQUE at the axles.

TORQUE at the axles is directly calculated by multiplying TORQUE at the flywheel by gearing, and then subtracting frictional losses.

Notice that at no time did I have to resort to mentioning horsepower or cake.