pzull

Hi Bill, that's what i meant by the stock cat merging the two banks: they go into a mixing chamber.
I have tested (on my ex 964) two designs using same lengths and pipe sizes. The one with x-pipe had more torque lower down and imperceptible loss at high revs. If the headers were true equal length and the secondaries leading to the x pipe were equal in length (my customs were, 993 stock isnt), i find that the x pipe acts as another tuning point (both wave and scavenging as the pulses from two banks never clash and actually high pressure pulse from one bank "fits" into the low pressure pulse from the other bank) and because it is further from the exhaust port, it tunes for lower rpms.

I have read quite a bit of literature on this and they all say that an x-pipe acts a little like megaphones in that it delays the tuning pulse returning to the exhaust port and also widens the pulse albeit with reduced intensity (but it means a broader tuned rpm range)

I am recommending it in this case as the car is street tuned. In a race tuned car where most of the power required is in the high rev range then no x pipe would be better as there is less resistance/turbulence and high revving race cars do not require a lower rpm tuning point. I think it's the same argument for 4 cylinder cars: 4 into 1 vs 4 into 2 into 1

Anyway it's just from reading and one experiment/experience with a 964. Your experience could be much broader/deeper

mark kibort

Bill,

A Kw-hr is a unit measure of work or energy, NOT power.

I was very careful to say "unit measure of work" . So, you might want to re-read the first chapter again (of your physics 101 book).

mk

Bill Verburg

You said hp-sec and kw-hr measure work, they do not, they both measure energy as does ft-lbs, when you say hp-sec that is precisely the same thing as saying ft-lb

SundayDriver

From a geeky Engineer, you are right on target.

There have been a lot of weird terms and ideas in this thread confusing power, work, energy, etc. Plus invented meanings of potential energy and other non-engineering/physics terms that have been standardized for many years.

Larry Herman

What happened to the horse on 3 legs lifting 180 lbs 3 feet in one second?

mark kibort

Here is my quote

"yes, hp-seconds, just like killowatt-hours, is a unit measure of work. "

I never said that hp-sec measure work. If i did, show me!

I have a little problem with your "Dimensionally equivalance" of KE, work and ft-lbs. I agree work and energy can be used somewhat interchangebly, but ft-lbs is not a measure of work, without a "s" attached to it (i.e. distance).
And, power is the time derivative of work.

Lets look at a drag race. He who uses the most Hp-seconds will win.
you could use ft-lb-seconds , I guess, as long as the tire diameters were equivilant. (or you could use Thurstforce -seconds) But, how does a Hp-second (a unit measure of work) equate to a "ft-lb" again?

mk




"

DrJupeman

Huh? Didn't you just show yourself?

Mark, I think you're starting to make up terms here or at least confusing them. My understanding is that a kilowatt-hour (one "l", btw) is a measure of energy (1 kilowatt is 1000 joules/sec).

mark kibort

He is not on target, if he didnt read the post correctly.

There is no confusion of power, work or energy in anything I have posted so far. (at least I dont think im confused ) If there is, please let me know.

The general confusion comes in the areas of Torque, but more specifically, engine torque values and shapes of curves. In the end, its really the torque at the rear wheels we care about (as long as the tire diameters are the same, otherwise, its thrust force) , and this can be much more easily compared by looking at HP values at any vehicle speed. Quite simply, you maximize hp at any speed, and you then maximize acceleration. Two cars at any same turn at any same HP level, will have the same accelerative forces, regardless of their engine torque values.

acceleration = power/(mass x velocity) showing that with this Newtonian identity, acceleration is directly proportionally to power at any vehicle speed.

The reason we get into HP-seconds, is that there is an effect of the different shape of HP or torque curves on the level of those accelerative forces over the time period for which they are applied. So, when folks start talking about flatter torque curves, or losing midrange torque, they sometimes forget that its all about maximizing utilized HP , and this will happen at the upper end of the RPM / HP / Torque curves. a flat torque curve means that HP is rising. a GT3RS has a very flat 275rear wheel torque curve. a viper has a falling torque curve with near 500rw torque. However, the Viper has a flat HP curve which has an advantage over a GTRS's peaky HP curve, which is equalilzed by using close ratio gears to equalize the hp-seconds applied, area under the curves, or average HP applied over a given vehicle speed range. (depending on how you want to look at it)



Mk

mark kibort

Open up any physics book an it will probably use this same term. Its not made up, its a basic fact. A kw-hr is a "Unit measure of work" or energy.
One Killowatt is the work done in one hour by an something working at the constant rate of one Killowatt. Since this is 1000J of work each second, the work done in one hour is 3600 x 1000 = 3,600,000 J

Power is energy or work per unit time. The units of power may be used to define new units of work or energy. a common one is the " Killowatt-hour".

so, below, you just forgot to mention the time factor in your definition of a kilowatt-hour.



mk

mark kibort

So, yes in the British system, where work is expressed in ft-lbs and time in seconds, the unit of power is one foot-pound second. a larger unit would be the "HP".
So, KW is a unit measure of power, while the HP-second, or KW-hour would be units of work or energy not power.

Your first quote is correct, but the second one leaves out a key component, time! (i.e. Kw can be measured in ft-lb-seconds, hp, etc.) . So yes, Hp-seconds would be the same as saying ft-lb-seconds.
hp-seconds
kw-hours
or
(ft-lb-seconds)-hours

Is that more clear?

mk


Bill said:
You said hp-sec and kw-hr measure work, they do not, they both measure energy as does ft-lbs, when you say hp-sec that is precisely the same thing as saying ft-lb



Quote:
kW is a unit of power as is hp

Quote:
kw-hr a unit that measures the amount of energy used and can equivalently be measured in ft-lbs, joules, newton-meters, dyne-cm, ergs etc.

__________________
Bill Verburg
'76 Carrera 3.6RS(silber hotrod), 993RS brakes, SC/RS trans, Ruf aero, Bilstein sport, Kinesis 8 & 9.5 x17, 235/45 & 275/40,
'95 993(Blau track car), 3.8RS engine, RS brakes, G50/30 Cup trans, RS aero, 8 & 10 x18/9 & 10 x18, JIC comps
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FlyingDog

Although the deleted pic was an accurate depiction of this topic, it was probably inappropriate.

DaveM993

See quote.

TX996

It is really a suckers question. I mean that is a suportive nurturing way.

Fun for forums but the point is this.

It depends on the car and the tracks you run on and against whom and how you drive etc...

Ask how the Porsche Spyders run with the Audi's, Turbo VS N.A. high revers like the S2000.

Many different ways to a similar result.

What I would want on an autocross course is WAY different than what I would want at the Nurburgring.

If you are getting run down on straight-aways.... getting pulled out of corners.... it all is something different....

Me personnaly, I am a toruqe guy. If you want a chance in a race where I run it is short and tight... if someone slips after following them for 15 minutes and you do not have the grunt to capitalize on it coming out of the corner (where I feel most mistakes are made) it is tough.

Teams that can change...change a LOT, gearing, tuning, tons based on track, wet or dry, day or night.... it all is detail and what you like need IMHO.

Bill Verburg

One more try, probably won't do any good but what the hey, I've got nothing better to do right now

Sorry it's so long but it really is necessary to understand the basics before discussing the really important things like hp vs torque

dimensional analysis is a fundamental way to check on the validity of a process and check methods of solution against each other and to check on the agreement or relationship of apparently different quantities. IFF(that's not a typo) the dimensions validate each other can two ways of describing something or of calculating a result be considered correct. Forget the units for a few minutes, look at the dimensions. as long as the dimensions match there is always a conversion factor available to change the units to suit.

a little refresher math
^ exponent
^-1 reciprocal meaning it's in the bottom of a division
^-2 reciprocal multiplied by itself meaning both are in the bottom of a division



the fundamental quantities
s - displacement, the dimension L, it's metric is feet, yards, miles, cm, m km etc
t - time, the dimension T, it's metric is second, minutes, hours etc
m - mass, the dimension M it's metric is slugs, grams, kg, etc.

the derived quantities
v - velocity derived by dividing s by t, v = s/t, it's metric is ft/s, m/s, mi/hr, km/hr, km/s, in./day etc, dimension LT^-1
a - acceleration derived by dividing v by t, a =v/t dimension LT^-2
f - force derived by multiplying m by a, F =ma, it's metric is pound, newton, dyne, ton, poundal etc., dimension MLT^-2
KE - kinetic energy, K= (mvv)/2, it's metric is BTU, joule, erg, hp-hr, hp-sec, ft-lb, calorie, kw-hr, ev, Mev etc, dimension ML^2T^-2
*note that all energy will have the same dimension as K, doesn't matter whether it's called potential energy, electric energy, chemical energy, atomic energy, it doesn't matter what the units or how it's measured the dimension is always ML^2T^-2, this is useful to know
t - torque derived by multiplying a force times a distance, it's metric is ft-lb, in-lb, N-m, dyne-cm etc., dimensionally ML^2T^-2
*note the dimensional equivalence of torque and energy, that means that they are essentially the same thing described differently or seen in different situations, but never the less fundamentally the same thing
P -power(as Tim Allen would say ruf ruf ruf) - derived by multiplying distance times force and dividing the result by time, P = sF/t, it's metric is hp, watt, kW, BTU/hr, ft-lb/min, cal/sec etc. dimensionally ML^2T^-3
*note not the same dimensionally as energy or torque

So to sum up power is not the same as energy
energy and torque are in some fundemental way the same thing, just looked at differently

In any event what I said was that the concept of torque that I outlined in responce to the first Marks question, fundementally agrees w/ Mark's concept of hp-sec. But I think that my thoughts are more straight forward and easier to understand, but that's just my opinion, your of course may differ.

mark kibort

I already got Dorsey S. on the Speed Channnel, to stop using the "look at all that torque of the Audi" and start refering to its HP or POWER. go back and watch the Porsche 550hp spider and the 650hp audi R10 Diesel in the last Laguna race. the audi had the porsche out of the turn, and down the straight. what the porsche did have, is better braking (lighter car) and better cornering(lighter car). For a while, the HUGE torque was given unfair credit for the audis performance. Now, I think the announcers as well as many others, have a better appriciation for power and power to weight ratios. the power of the audi is north of 650, as it has been for that class car in the past. It produces the same rear wheel torque as its high reving low torque predicessors at any same speed, EVEN coming off a corner. (see previous posts as to why)

I doesn't depend on driver, tracks, etc. the audi has a power advantage at any speed. gearing optimizes the utilization of HP for different tracks, and the close ratio gear boxes of the high reving lower engine torque value competitors, equalize this almost perfectly. The reason that the porsche does so well, is because of its handling and braking as mentioned. want proof, just watch the last few laps of the audi battle with the porsche .

you mention mistakes, i have never seen or participated in a gear mistake in quite a few years. If you dont have the smarts to pick the right gear at any speed, then you need a few more laps in that car or on that track! Probably more of an issue with a cup car, given that you have more gears to choose from, but in a 928 or most 911s, we go around tracks like laguna seca and sears with mostly 2 gears, and occassionally 3, if you count those 2 slow corners More proof of this, is that i follow LOTs of the high reving types. 7700rpm to 9000 rpms. (BMWs , S2000s, civics, vws with turbos, etc) I have NEVER seen any weakness in any of these cars coming off ANY turn on any race track ive been to! If the driver is keeping the car in the sweet spot of power, why would I???

you like Tight tracks, think a high torque engine pays dividends? trust me, it doesnt. if the HP peak is the same and the curve is near the same shape, the acceleration will be the same at most any curve exit speed. If it isnt, its possible the curve is so peaky, and the gear box gears are not close enough to keep the average power, power under the curve, or HP-seconds, the same. (but find me a peaky hp car that doesnt have a closer ratio gear box than my 928 and Ill show you a car that hasnt raced with us!)


mk