mark kibort

actually, 500hp when you are going 60mph is pretty boring. remember, for any given acceleration rate, the power required to accelerate would go up with the cube of speed. Not to discount the fun of a 1000hp engine, but if things didnt break apart, to get the acceleration of a common 1st gear, at redline. (50mph or so for our cars) , you would need 8x the hp at 100mph to have that same rush! 300hp x 8 =2400hp! Or something like this

I dont know what would be best, but keep in mind that the HP curve determines your acceleration. I would suspect you want to trade torque levels for HP levels based on the fact that lower torque at higher rpm might save some stressed components. I dont know exactly what you are trying to do, but that might answer some concerns.

mk

dprantl

Haha, 60mph is where the real fun begins, at least in my case - i.e. when the wheel spin becomes manageable.

Dan
'91 928GT S/C 475hp/460lb.ft

RKD in OKC

Having owned and driven a 400 rwhp 944 Turbo and can understand what you are wanting to do with the gear based boost control. In my car the throttle was VERY sensitive in first, second, and in the middle of third. It was way easy to just spin the tires instead of go. AND the closer to red line it feels like you could put down more power as rpms increase without spinning.

I've seen boost controllers that allow you to set a max boost for each gear, (and wanted to put one of those on my turbo) but not a boost controller that allows you to dial in the torque curve for each gear as well. I kinda thought that was what tuning with cams, headers, etc was for, ie., matching the "power curve" to the available traction, ie. higher speed can put down more power.

I guess I just don't understand the whole hp and torque argument when hp is basically calculated based on torque*rpm/5252rpm. Torque is the acceleration at a given rpm. Given two cars with the same gearing the one with the higher rpm torque peak (typically seen as higher hp due to the hp calculation) will be faster. The higher the torque peak the better advantage with higher rpm shifts in each gear and stay in the peak torque range.

However, if tuning a car for a specific track you might find that average corner exit speed and gearing put you either above or below your torque "power band" and that there is not enough straight for you to get back into your power band effectively. Then it would be advantageous to lower your torque band. Most modern cars solve this by adding more gears.

RicerSchnitzzle

Case in study...
A 928 leaves San Fransisco at 9:15 amPST , heading due east with 8 gallons of gas, 295 rear tires, Sammy Hagar Cd in the radio and half a box of Krispy Kremes... mean while a 911 leaves the Hamptons at 8am EST heading due west with a fresh coat of carnuba, stp gas treatment in the tank, vivaldi on the CD player and a full can of Binaca...

Taking the Torque and HP curves, factoring in final gear ratios of the 5 speed transmissions, who will reach the great continental divide first?

The 928. Couple reasons.
1. 911 owners take at least 30 minutes to work thier way through every flashing red light. vroom, ert, vroom, ert, vroom, ert.
2. 911 owners would slow way down in NYC as they pointed "Pistol Fingers" at themselves in all of the highrise glass windows... "Who's sexy?, Yea, You're sexy!" "Who's your Daddy?"
3. 911 owners would have to stop frequently to replenish the Armor All wipes they blow their noses with.
4. 911 owners would fall behind checking out local playgrounds along the way...for dates.

Just saying..

ptuomov

[QUOTE=RKD in OKC;6286505]Having owned and driven a 400 rwhp 944 Turbo and can understand what you are wanting to do with the gear based boost control. In my car the throttle was VERY sensitive in first, second, and in the middle of third. It was way easy to just spin the tires instead of go. AND the closer to red line it feels like you could put down more power as rpms increase without spinning.

I've seen boost controllers that allow you to set a max boost for each gear, (and wanted to put one of those on my turbo) but not a boost controller that allows you to dial in the torque curve for each gear as well. I kinda thought that was what tuning with cams, headers, etc was for, ie., matching the "power curve" to the available traction, ie. higher speed can put down more power./QUOTE]

You probably can then appreciate the fact that making power is not the problem! Take 951, add a 4-valve heads, and multiply by two... ;-)

In my opinion, eboost2 is pretty good. I haven't used one yet, but according to the product documentation, one set a separate boost program for each gear and then, within each gear program, one can set up a simple linear compensation function to start from some rpm. This will imo be close enough for government work.

But eboost2 isn't perfect. I have been toying with the idea of building a boost controller from splatco's cc18 controller. Actually, more than toying with the idea, actually toying with the controller. I got one for the holidays and played with the controller with my father for a couple of days. It's pretty cool product for something that runs about a hundred bucks with the developer kit. Plus I am waay more comfortable with coding than with welding.

The idea boost controller would take two driver inputs, the gear position and the throttle position. Then, for each gear position and throttle position, it would set the boost such that the torque curve is perfectly flat at the desired level. Calibrating would require dyno time, one would just have to run a number of different dyno pulls with the old fashioned boost controller limiting the boost to varying levels. Then, one would estimate a function torque = f(boost, rpm) from the dyno data and invert the function to solve for the boost given the desired torque and the current operating rpm.

I am planning to start with eboost2 and then start working on that roll-my-own boost controller later. Again, I might fail but not for the lack of trying!

Sorry MK for the thread hijack. It's tangentially related to your topic though, so maybe there are mitigating circumstances.

Best, Tuomo

Daniel Dudley

I would say the 928 owner would win in most cases, but in some cases he would lose, being unable to get in the car with such a huge chip on his shoulder.

Sounds like you have a real interesting motor in your car. How much horsepower do you think you are making ? I'm guessing maybe 350 ?

dr bob

We all wonder why the back-motor crowd loves 928 owners. Sheesh!!!

turbochad

shamwow!

mark kibort

If we are talking about 2 928s, that is generally correct. But, the conversation is talking about two cars with identical HP but different torque values. This means the engines can be different. a greater torque value, doesnt nessarily provide greater acceration, as this would be determined by the rpm range the car us operated in. HP is not just "calculated" . Its the end all catch all for acceleration. engine torque is meaningless without rpm associated with it.
after all , hp is the rate of doing work. faster the rate, the faster the acceleration. Now, if you are talking torque at the rear wheels, which is calculated too, you are correct. However, torque at the rear wheels is determined by HP at any vehicle speed.
remember, the dyno outputs HP as a measured value. (rate of change of kinetic energy). Torque is actually derived. Both are calculated by the acceleration rate of the drums at any MPH. Torque is found by using an rpm signal from the engine. without that, the output is just HP vs MPH. (actual rear wheel torque could be output too, but it could be in the 1000s of ft-lbs of torque due to gear box mulitplication)

mk

RKD in OKC

This guy gives a good explanation with some very good examples...

Horsepower versus Torquel

"Dynos measure torque and then hp is calculated. Any given car, in any given gear will accelerate at a rate that exactly matches it's torque curve."

mark kibort

I blasted him about 15 years ago. very misleading and wrong in several spots.
I copied the blast on that other thread as someone wanted to see it. If you want me to PM you with the message I sent to bruce, let me know.


I just told you how a dyno measures output. it measures the rate of change of kinetic energy (if we are talking about rolling inertial dynos) . torque is calculated as well. (otherwise, it would only be able to produce rear wheel torque, as multiplied through the gear box.) without knowing engine speed (it has to know this to make a torque output) the results is just HP vs MPH.

The fact that even to know torque at the rear wheels ( as multplied through the gear box) says that it is measuring HP. because if you need to know the RPM, and you need to know the rate of change at that speed, you have just used HP factors to find torque. Its not that one is "better" than the other. power contains 2 times more information. remember:

acceleration = power/(mass x velocity)


ahhh, here it is anyway. sorry about the length. Lots of errors, lots of comments.

enjoy:

Torque and Horsepower - A Primer
From Bruce Augenstein, rba@augenstein.ultranet.com
________________________________________
There's been a certain amount of discussion, in this and other files, about the concepts of horsepower and torque, how they relate to each other, and how they apply in terms of automobile performance. I have observed that, although nearly everyone participating has a passion for automobiles, there is a huge variance in knowledge. It's clear that a bunch of folks have strong opinions (about this topic, and other things), but that has generally led to more heat than light, if you get my drift :-). I've posted a subset of this note in another string, but felt it deserved to be dealt with as a separate topic. This is meant to be a primer on the subject, which may lead to serious discussion that fleshes out this and other subtopics that will inevitably need to be addressed.
OK. Here's the deal, in moderately plain english.

>>>>>>>>>>>>>>>>>>>>may as well be in Swahili
Force, Work and Time
If you have a one pound weight bolted to the floor, and try to lift it with one pound of force (or 10, or 50 pounds), you will have applied force and exerted energy, but no work will have been done.
>>>>>>>>>>>>>>>>>>>>>>no energy is exerted if work isn’t done. If energy is exerted, it has to be stored or converted. Conservation of energy law, says energy can not be made or destroyed. If the weight is lifted, the energy goes up in kinetic energy until it stops where it is converted to potential energy.

>>>>>>>>>>then he goes on for a while on basic torque , hp formulas, for which he is correct. He ends up here and then starts to dig a hole.

. Therefore, the following formula applies for calculating horsepower from a torque measurement:

Torque * RPM

Horsepower = ------------

5252

This is not a debatable item. It's the way it's done. Period.
The Case For Torque
Now, what does all this mean in carland?
First of all, from a driver's perspective, torque, to use the vernacular, RULES :-). Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it.
>>>>>>>>>>>>>>>>>>>>>>>>Right, but he misses the point, and helps others to get confused. At the fastest rate of acceleration of a car is not at max torque at any given SPEED, its at as close as possible to max HP . Who cares if the fastest rate in any particular gear is at max torque. At max Torque, you are at a lower hp range, and HP = torque through the gears at any particular speed. So, in otherwords, downshift and increase torque to the wheels instead of torque max of the engine! Key key point!

Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Yes, but misleading again and also incorrect. First you would be at two totally different vehicle speeds. The torque (force) required as you go faster goes up due to aerodynamic forces going up with the square of speed, (and the power required goes up by the cube of speed) So, even though you had the same torque at 2000rpm as you did at 4000rpm, the acceleration rate would slightly lower. But, to a more important point, who cares about engine torque, as HP actually determines torque through the gears to the ground. So, what you want is the maximum torque through the gears to the rear wheels meeting the ground. This is reached at high hp ranges, not at peak torque ranges. All that is said by Bruce here is that at 2000rpm, you are using less of the available hp potential vs at 4000rpm of the engine . However, neather are you at 4000rpm, but if you down shifted a coupe of gears, getting closer to max HP , you would have the fastest rate of acceleration at that speed.

Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.
>>>>>>>>meaningless. Only a point of random intersection based on the units of RPMS and Torque units of FT-LBs


In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising. However, as I said, horsepower has nothing to do with what a driver *feels*.
>>>>>>>>>>>>>>>>>>>>>>again, wrong. HP is comparatively equivilant to the torque through the gears. You may not believe it, but its true. The max acceleration of your car will be at 6000rpm (if this is max HP) at 60mph, If you are in a gear that reaches 60mph at redline. (it could be any speed where you are in a gear at max HP) you could easily shift up a gear and go 60mph in the taller gear and be at max torque, but your acceleration rate would be a lot less!!

You don't believe all this?
Fine. Take your non turbo car (turbo lag muddles the results) to its torque peak in first gear, and punch it. Notice the belt in the back? Now take it to the power peak, and punch it. Notice that the belt in the back is a bit weaker? Fine. Can we go on, now? :-)
>>>>>>>>>>>>>>>>>>>>more of the same mistake. True for only 1st gear. But, take that same rate of acceleration in 1st gear power peak. Call it 50mph, note your g forces on your g tech. Now, shift down a gear and punch it at max torque. Watch your g meter go down in acceleration force report! Max acceleration will always be fastest for a car at the closest point possible to max HP at any speed!
Acceleration = power/ (mass x velocity).
The Case For Horsepower
OK. If torque is so all-fired important, why do we care about horsepower?
Because (to quote a friend), "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*.
>>>>>>>>>>>>>>>>>>>>>>i.e. this means more hp is better than less HP

>>>>>>>then he goes on with some truths about HP.
At The Dragstrip
OK. Back to carland, and some examples of how horsepower makes a major difference in how fast a car can accelerate, in spite of what torque on your backside tells you :-).
A very good example would be to compare the current LT1 Corvette with the last of the L98 Vettes, built in 1991. Figures as follows:

Engine Peak HP @ RPM Peak Torque @ RPM

------ ------------- -----------------

L98 250 @ 4000 340 @ 3200

LT1 300 @ 5000 340 @ 3600

The cars are geared identically, and car weights are within a few pounds, so it's a good comparison.
First, each car will push you back in the seat (the fun factor) with the same authority - at least at or near peak torque in each gear. One will tend to *feel* about as fast as the other to the driver, but the LT1 will actually be significantly faster than the L98, even though it won't pull any harder.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>clear as mud. NO wrong. No one will ever be at max torque after first gear, where his truth ends. So ,, both cars would accelerate fastest to max torque, THE higher HP car would have more engine torque above max torque all the way to redline. After that, in each gear after first, you would be above max torque anyway, and through the gears, the greater HP car would dominate (accelerate faster) in every gear at every speed past max torque in 1st!)

If we mess about with the formula, we can begin to discover exactly *why* the LT1 is faster. Here's another slice at that formula:

Horsepower * 5252

Torque = -----------------

RPM

If we plug some numbers in, we can see that the L98 is making 328 foot pounds of torque at its power peak (250 hp @ 4000), and we can infer that it cannot be making any more than 263 pound feet of torque at 5000 rpm, or it would be making more than 250 hp at that engine speed, and would be so rated. In actuality, the L98 is probably making no more than around 210 pound feet or so at 5000 rpm, and anybody who owns one would shift it at around 46-4700 rpm, because more torque is available at the drive wheels in the next gear at that point.
>>>>>>>>>>>>>>>>>>so wong, I wouldn’t know where to start and correct this.
Max hp (power peak) is not at 4000rpm, the greater HP would provide MUCH greater torque through the gear boxes and to the rear wheels at any speed other than 1st gear up to max torque. The shifting at 4600rpm logic is beyond help as well.


On the other hand, the LT1 is fairly happy making 315 pound feet at 5000 rpm, and is happy right up to its mid 5s redline.
So, in a drag race, the cars would launch more or less together. The L98 might have a slight advantage due to its peak torque occuring a little earlier in the rev range, but that is debatable, since the LT1 has a wider, flatter curve
>>>>>>>>>>>>>>>>>>>and then he goes on with some confusing example.

A final example of this requires your imagination. Figure that we can tweak an LT1 engine so that it still makes peak torque of 340 foot pounds at 3600 rpm, but, instead of the curve dropping off to 315 pound feet at 5000, we extend the torque curve so much that it doesn't fall off to 315 pound feet until 15000 rpm. OK, so we'd need to have virtually all the moving parts made out of unobtanium :-), and some sort of turbocharging on demand that would make enough high-rpm boost to keep the curve from falling, but hey, bear with me.
>>>>>>>>>>>>>>>>>so in otherwords, he has over 1000 hp and the example is missing the target!


If you raced a stock LT1 with this car, they would launch together, but, somewhere around the 60 foot point, the stocker would begin to fade, and would have to grab second gear shortly thereafter. Not long after that, you'd see in your mirror that the stocker has grabbed third, and not too long after that, it would get fourth, but you'd wouldn't be able to see that due to the distance between you as you crossed the line, *still in first gear*, and pulling like crazy.
I've got a computer simulation that models an LT1 Vette in a quarter mile pass, and it predicts a 13.38 second ET, at 104.5 mph. That's pretty close (actually a tiny bit conservative) to what a stock LT1 can do at 100% air density at a high traction drag strip, being powershifted. However, our modified car, while belting the driver in the back no harder than the stocker (at peak torque) does an 11.96, at 135.1 mph, all in first gear, of course. It doesn't pull any harder, but it sure as hell pulls longer :-). It's also making *900* hp, at 15,000 rpm.
>>>>>>>>>>>>this is because the average hp to the wheels over the operational range of the 1/4mile, would be slightly better than the stock car. Its first gear would keep the mechanically higher advantage and the rear wheel torque would be close to the same average along the pass, because the HP used along the way would be close to the same too. Even though the magic car would have 1000hp, up to 130mph in 1st gear and 15000rpm it would be way way down on hp along the way, making up big ground toward the end of the run.
A very very convoluted point.


Of course, folks who are knowledgeable about drag racing are now openly snickering, because they've read the preceeding paragraph, and it occurs to them that any self respecting car that can get to 135 mph
>>>>>>and more information about this crazy comparison
At The Bonneville Salt Flats
Looking at top speed, horsepower wins again, in the sense that making more torque at high rpm means you can use a stiffer gear for any given car speed, and thus have more effective torque *at the drive wheels*.
>>>>>>>>>He finally is making some sense !

Finally, operating at the power peak means you are doing the absolute best you can at any given car speed, measuring torque at the drive wheels. I know I said that acceleration follows the torque curve in any given gear, but if you factor in gearing vs car speed, the power peak is *it*. An example, yet again, of the LT1 Vette will illustrate this. If you take it up to its torque peak (3600 rpm) in a gear, it will generate some level of torque (340 foot pounds times whatever overall gearing) at the drive wheels, which is the best it will do in that gear (meaning, that's where it is pulling hardest in that gear).
However, if you re-gear the car so it is operating at the power peak (5000 rpm) *at the same car speed*, it will deliver more torque to the drive wheels, because you'll need to gear it up by nearly 39% (5000/3600), while engine torque has only dropped by a little over 7% (315/340). You'll net a 29% gain in drive wheel torque at the power peak vs the torque peak, at a given car speed.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>This is the reason for the acceleration in at any speed being greatest at max HP. Contradicting all of this website information article points until now.
Any other rpm (other than the power peak) at a given car speed will net you a lower torque value at the drive wheels. This would be true of any car on the planet, so, theoretical "best" top speed will always occur when a given vehicle is operating at its power peak.
>>>>>>>>>>>>>>>>>>>>>>>>And he may not get this yet, but this is true for any vehicle speed. The closer you get to max HP, the fastest you will accelerate at any speed. The more you have your car at max HP , the more torque you will have at the wheels through the gear box. This is why close ratio gear boxes are so popular with race cars. The allow you to spend more time in the max hp range and less near max torque of the engine!! In the end, ironically, you end up with more torque to the driven wheels.
Ill give a clear example of this. Two cars both having 500hp come around turn 11 side by side, at Laguna at 50mph and near the top of their 1st gear. One has 250flbs of torque and the other 500ftlbs of torque. (they have the same gear spacing) they floor their cars to their respective redlines. Both cars will accelerate at the exact same rate (if they weigh the same too) they both will be get through their gear boxes, the exact same torque at the rear wheels, even though one has twice the engine torque as the other. Why, because HP determines torque through the gears at any given speed!!!!
Acceleration =Power/(mass x velocity --- a basic newtonian identity!
This means acceleration is proportional to power at any speed!
"Modernizing" The 18th Century
OK. For the final-final point (Really. I Promise.), what if we ditched that water wheel, and bolted an LT1 in its place? Now, no LT1 is going to be making over 2600 foot pounds of torque (except possibly for a single, glorious instant, running on nitromethane), but, assuming we needed 12 rpm for an input to the mill, we could run the LT1 at 5000 rpm (where it's making 315 foot pounds of torque), and gear it down to a 12 rpm output. Result? We'd have over *131,000* foot pounds of torque to play with. We could probably twist the whole flour mill around the input shaft, if we needed to :-).
The Only Thing You Really Need to Know
Repeat after me. "It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*." :-)
>>>>>>>>>>>>>>>>>>>>>>>repeat after to me. This all means its better to have more hp than less hp!!!! (and more average HP than less average HP!!)

Thanks for your time.
Bruce
>>>>>>>>>>>>>>>Bruce, thanks for taking my time to explain your confusing article that some take to be gospel. Please revise when you get a chance!!!



mk

RicerSchnitzzle

I kid, I kid. Just having fun with the 911 owner, or Porsche owner in general, stereotypes.

As for HP not sure, hoping for 330-340RWHP / 575RWHP on the juice, when I dyno in a few weeks. Just not sure how much the new cams will add and if she'll hold together north of 6700rpms.

SeanR

hehe

RKD in OKC

I've owned, driven, and raced a 89 944 Turbo S, 01 BoxsterS. The max speed for 1st thru 3rd the same and same rev limit. The cars weigh the same. 0-60 specs are the same on both cars. Same rated top speed 168mph. The torque curve on the Turbo was much different than the boxster. The boxster's torque curve peaked much lower and fell off were the turbo had almost no torque or hp until above 3000 rpm then remained almost flat to red line. The boxster felt much slower 0-60 and ran out of umph much above 60. 60-100 the turbo would run off and leave the boxster. These two cars have the same peak hp.

I've also owned and raced a 90 928 GT with guess what...the same 0-60 and 1st thru 3rd max mph/rpm as the other two cars. The 928 was heavier but had more hp and torque. The torque curve was the flattest of the three and it also felt the slowest. 60-100 the 944 Turbo was still faster, above 120 (4th gear) the 928 would run off and leave the other two cars.

To tell the difference in the way these cars perform with the hp curve would be very difficult where the torque curve is much easier. Why is that if hp so accurately represents the rate of acceleration? The rate of acceleration difference I felt driving the cars was obviously following their torque curves.

The differences in what we think makes things fast is why there is racing.

dprantl

Uh oh ...

Dan
'91 928GT S/C 475hp/460lb.ft