matching gearing to your power curve

[grumpyvette]

first thing to keep in mind is that theres no such "thing" as horsepower, horsepower is a mathmatical formula for the RATE at which TORQUE can be applied the formula for hp is (tq x rpm/5252=hp

example

450 ft lbs of torque at 3000rpm=257hp

450 ft lbs of torque at 6000rpm=514hp

because the torque at the higher rpm useing gearing can be applied faster

here read this

http://www.69mustang.com/hp_torque.htm

 

http://www.ubermensch.org/Cars/Technical/hp-tq/

 

http://vette.ohioracing.com/hp.html

 

where most guys go wrong is in not correctly matching the cars stall speed and gearing to the cars tq curve, if you mod the engine for increased high rpm performance but fail to also match the stall speed and gearing to that higher rpm tq curve much of the potential improvement is wasted.

example

in the close to stock engine above, the engine should be geared to stay in the 3500rpm-5000rpm range for max acceleration (lower in the rpm range if mileage is a big factor)

in the moded engine above the rpm range moved to 4000rpm-6500rpm requireing differant rear gears and slightly higher stall speeds to gain max acceleration in the same car,

you should readily see that a trans that shifts at 5000rpm will work in the first example but would waste most of the power curve in the second example,where shifting at 6500rpm under full power acelleration would make more sence.

a 3.08 rear gear and 700r4 trans matches the first example well but it would take a swap to a 3.73-4.11 gear to allow the engine in the second example to keep its most effective power band matching that second power curve well.

 

links youll need to figure out correct rear gear ratios

 

http://www.miata.net/garage/tirecalc.html

 

http://www.wallaceracing.com/reargear.htm

 

http://users.erols.com/srweiss/calcmph.htm

 

http://www.geocities.com/z_design_studio/transmission_300zx_tt.html

 

http://users.erols.com/srweiss/calcrpm.htm

 

http://users.erols.com/srweiss/calcrgr.htm

 

http://www.prestage.com/Car+Math/Ge...io/default.aspx

 

http://www.geocities.com/z28esser/speed.html

 

http://server3003.freeyellow.com/gparts/speedo.htm

 

http://www.pontiacracing.net/trannyratios.htm

 

http://www.tciauto.com/tech_info/gear_ratios.htm

[David K]

I always look foward to your reads, Grumpy. Lots and lots of info, thank you.

[grumpyvette]

glad to help out

[Pop N Wood]

first thing to keep in mind is that [b'] theres no such "thing" as horsepower, horsepower is a mathmatical formula for the RATE at which TORQUE can be applied the formula for hp is (tq x rpm/5252=hp

 

Oh, man. We aren't going to start that again? Horsepower is very real, just as real as torque. The ONLY reason car guys compute HP from torque is because that is the easiest way to do it. It is possible to measure an engine's power output directly then use the same equation to compute torque. I have seen it done. Would that then make torque "not real" but a "mathmatical formula"?

 

HP is a measure of power, the exact same thing as kilowatts. You can just as easily rate a lightbulb in terms of horsepower (a 100 watt bulb is really an eighth HP bulb). But it doesn't make a whole lot of sense to try and rate a light bulb in ft-lbs.

 

And I have said it before. Horsepower is what determines how quickly a car can accelerate, NOT torque. To go fast, the optimal gearing is whatever keeps your engine revs closest to the horsepower peak. A fat torque curve only relaxes the gearing requirements and makes the car more pleasant to drive.

[grumpyvette]

Jim Powers

 

"Horsepower is very real, just as real as torque"

.

I know what your saying makes sence in that you cam change the equation and get the tq from a hp level BUT...your not reading what IM saying correctly, ..look at it this way,

you can have TQ without hp but

ITS IMPOSSIABLE to have HP without BOTH tq and RPM and that power is only torque times a measurable rpm level at which the TORQUE IS MEASURED AT.

.

"HP is a measure of power, the exact same thing as kilowatts."

not strictly true, yes hp levels can be converted to kilowatts but thats torque measured at a set rpm level equals "power" (the rate at which that torque can be applied) which can mathimatically be related to "kilowatts" in that it takes (X) amount of power to supply a set size load (that 100 watt light bulb) ITS IMPOSSIABLE to have HP without BOTH tq and RPM and that power is only torque times a measurable rpm level at which the TORQUE IS MEASURED AT.

[Pop N Wood]

First off let me start by saying that when I grow up I hope to know as much about cars and engines as you.

 

But..

 

I look at it from a basic physics point of view. Power is a measure of the ability to do work. Horsepower and kilowatts are simply different units for measuring the same thing. They have exactly the same relationship as meters and feet. And just like something doesn't get longer just because you measure it in feet instead of meters, power doesn't change by expressing it in different units.

 

In a way we are arguing wording. You are saying HP is derived from torque. I am saying yeah, you could look at it that way but you could just as well say that torque is derived from HP. Taking it a step further I am also saying you are actually better off thinking about torque as being a function of power and not the other way around.

 

What I really think is important is that power is very real, and more importantly, it is power that determines how fast a car can go.

 

For example, given an engine running at a constant speed I can generate virtually any level of torque I want (either up or down) by selecting the appropriate gear ratio. However there is nothing a transmission can do to increase power. The "power" out of the transmission can never be higher than the power going into the transmission. This is the first law of thermodynamics. The same is obviously not true for torque. In this case you are better off thinking of torque as a function of engine power and gearing.

 

You said

 

ITS IMPOSSIABLE to have HP without BOTH tq and RPM and that power is only torque times a measurable rpm level at which the TORQUE IS MEASURED AT.

 

If you follow the equation that HP is torque times RPM, then that statement makes sense. However if you take a physical interpretation of power then the statement is misleading.

 

If you have a car with an automatic transmission sitting at the line with the engine reved up but the brakes on so the car isn't moving, is any power being generated? Yes. The engine is generating HP but it is all being dissipated as heat inside the transmission torque converter. The power has to go somewhere, it can't disappear. Now release the brakes and the car starts to move. The engine's mechanical power is now allowed to "do work" on the car by accelerating it down the track rather then just heating up the tranny fluid.

 

Take a car spinning it's tires. Is the engine producing any less power just because the tires are spinning? No. The engine may be producing the same power, it is just that only part of the energy is being used to accelerate the car while the rest is being used to heat up the tires and convert them to smoke. If you look at this from a conservation of power outlook then everything is simple. I can't go fast because all my power is being used to vaporize the tires. But if you try and look at what spinning tires do to RPM and torque measurements, then things get too complicated too quickly.

[Guest Your Car is Slow]

I think the point of his comment was where the measurement is taken.

 

If the car isnt moving....for all intents and purposes its making 0hp and 0tq (because the point of measurement is at the tires..not at the crank).

 

while you can measure crank HP on certain dynos....its pretty useless as by the time it is applied to the wheels...all sorts of factors have reduced that amount to what is actually measured and what moves the car forward.

[Guest Anonymous]

DELETE

[grumpyvette]

"why is there no need for further spark advance? How is it possible for accelleration to continue? "

 

 

the chevys spark plug is located much more towards the exhaust side of the cylinder dia. than would be ideal.

it takes approximately 40 thousands of a second for the flame from the ignition to cross a 4"-4.25" bore,at low rpms and still takes about 15 milliseconds at high RPM due to the much faster movement of the compressed fuel air mix in the cylinders, lets look at what that means

if the chevy plug is located 4/5ths of the way to one side thats a time of about 32 thousands for the pressure to build as the flame travels 3.4" in the chevy this of course speeds up as the swirl and turbulance increase with increased engine RPMs and piston speed and the increase in the speed fuel air mix trapped in the quench area is increaseingly thrown from the sides of the cylinder into the center cylinder area, increaseing the burn speed b] this results in more useable energy WORKING on the piston AFTER IT PASSES TOP DEAD CENTER ON THE POWER STROKE. BUT MODERN WEDGE combustion chambers use increased QUENCH to speed the flame front and lower the burn time combined with a smaller combustion chamber and a more centrally located spark plug to get even better results than the older designs, even CHRYSLERS new (HEMI) is really a very shallow combustion chamber like a modified wedge to better use QUENCH and swirl to speed burn times

 

http://naca.larc.nasa.gov/reports/1939/naca-tm-914/

 

http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf

 

http://www.combustion-net.com/library/articles/PDFs/0210-spark-ignition-engine-cycle.pdf

 

http://www.nedians.8m.com/Comp_IC.html

 

http://mb-soft.com/public2/engine.html

 

 

http://hpp.primediaautomotive.com/archives/tech/0209hpp_fire.shtml

 

 

BTW most people dont realize that almost all USEFULL cylinder pressure is providing pressure on the piston only about 24-30 degrees past TDC on the power stroke of the whole 720 degree repetitive cycle

look at this chart

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

notice the piston has only moved less than 1/3" inch down the bore by that time, thats one of the reasons longer rods with their better rod angle can help at high rpms, at 7000 rpm that piston only has .0007 secounds to allow that cylinder pressure to exert useable pressure on the piston, note that the burn time and the cylinder filling efficiency falls off fast after about 4500rpm so power PER stroke starts to fall off also,yet the number of power strokes per minute increases so over all power will continue to increase at least for awhile above that point

[grumpyvette]

"First off let me start by saying that when I grow up I hope to know as much about cars and engines as you."

I HAVE NEVER EVEN HINTED THAT I WAS SMARTER THAN ANY OTHER PERSON ON THIS OR ANY OTHER SITE, YOUR OPINION IS EVERY BIT AS VALUABLE AS MINE, WE ARE BOTH HERE TO EXHANGE IDEAS,I TRY TO SUPPORT MY POSITION WITH FACTS AT ALL TIMES,IM ONLY SAYING THAT I LEARN FROM MY OWN MISTAKES,AND HAVE A GOOD CAPACITY TO LEARN FROM OTHER PEOPLES MISTAKES , and RETAIN ALMOST ALL DATA,AND RESEARCH ANSWERS, BEFORE WORKING ON ANYTHING, PLUS I ENJOY TEACHING

 

 

look at it from a basic physics point of view. Power is a measure of the ability to do work. Horsepower and kilowatts are simply different units for measuring the same thing. They have exactly the same relationship as meters and feet. there the basic flaw in your logic, torque can do work without rpm, example, if you used a large lever about 8 feet long you could move a car thru a 1/4 mile in 1320 one foot long shoves on the bumper with the tip wedged behind the bumper and the ground

 

TORQUE= the tangential force F? times the lever arm r.

 

In a way we are arguing wording. TRUEYou are saying HP is derived from torque. I am saying yeah, you could look at it that way there is no other way but you could just as well say that torque is derived from HP.false, (torque x rpm/5252 = hp) "torque is force over distance" Taking it a step further I am also saying you are actually better off thinking about torque as being a function of power and not the other way around. wrong , only because you can,t have hp without TQ, but you CAN HAVE TQ without HP

 

What I really think is important is that power is very real, and more importantly, it is power that determines how fast a car can go. true

 

For example, given an engine running there you go adding RPM and TQat a constant speed I can generate virtually any level of torque I want (either up or down) by selecting the appropriate gear ratio. However there is nothing a transmission can do to increase power. true The "power" out of the transmission can never be higher than the power going into the transmission. This is the first law of thermodynamics. trueThe same is obviously not true for torque. In this case you are better off thinking of torque as a function of engine power and gearing. only if your willing to realize that both tq and rpm are required to measure hp but only tq (force x leverage plus distance) is nessasary to do work

 

You said

 

Quote:

ITS IMPOSSIABLE to have HP without BOTH tq and RPM and that power is only torque times a measurable rpm level at which the TORQUE IS MEASURED AT.

 

 

If you follow the equation that HP is torque times RPM, then that statement makes sense. However if you take a physical interpretation of power then the statement is misleading.

[Phantom]

Grumpy,

I noticed on my dyno results that my torque curve is above 300 from about 3,200 rpm to about 5,200 rpm - max 326 at around 4,200. The HP curve is nearly a straight line climbing from 100 at 1,750 to 300 at 5,000. the climb then tapers and tops out at 311 at 5,500 and is back down to 300 at 6,000 where the rev limiter kicks in. At 4,000 rpm it's about 280. With the T-56 and a 3.7:1 LSD and shifting at 5,800 the rpm ranges are:

2nd: 3,880-5,800 ~ 65 mph

3rd: 4,236-5,800 ~ 95 mph

4th: 4,462-5,800 ~ 115 mph

5th: 4,292-5,800 ~ 155 mph

6th: 3,867-5,800 ~ ??

Basically it keeps me at the peak of the torque curve and at 88% plus hp at all times. Looks pretty good to me. Now if I just had some tires that could hook it all up in 1st and 2nd.

The one thing I noticed though is that my torque drops like a rock after about 5,200 rpm. It goes from about 300 lb-ft to about 250 lb-ft by 5,800 rpm. Could that be caused by a restrictive exhaust or is it something else?

[grumpyvette]

"The one thing I noticed though is that my torque drops like a rock after about 5,200 rpm. It goes from about 300 lb-ft to about 250 lb-ft by 5,800 rpm. Could that be caused by a restrictive exhaust or is it something else?"

 

Id look at restrictive exhaust, but Id also look at carb air flow retrictions,intake and cylinder head restrictions, cam timing,ignition timing curve, and most likely of all, valve train harmonics, or weak valve springs without damper springs entering valve float or the lifters pumping up if your useing hydrolic lifters and the valves are adjusted on the tight side of the preload range ,(one of the reasons I prefer only 1/4 turn preload after the click stops at idle when the valves are adjusted on a hot engine)

 

look here

http://www.airflowresearch.com/

(Hydraulic Roller Rev Kits)

 

[Guest Anonymous]

DELETE

[Pop N Wood]

First off let me start by saying that when I grow up I hope to know as much about cars and engines as you.

 

Boy, that came out wrong. Wasn't flaming you or whining, just some self humbling humor to tell you the same thing you told me. Believe me, I have learned more from your posts then I have from any Hot Rod mag.

 

As for for the definition of torque vs. HP, I guess just different ways of looking at it.

 

In physics, they define work as force times distance. Thus no matter how hard you push on something, if it doesn't move then technically you have done no "work" on that object. The classic example is if you were to hold a 40 pound weight out at arms length. Are you doing any work? No, the weight is being held without moving. Are you expending energy holding the wieght? Of course. The rate of energy expendeture is, by one definition, a measure of power.

 

I would just be careful interpreting the equation HP = torque X RPM they way you are. That is not so much a definition of HP but an artifact of the realtionship between force and power. I still maintain you are better off tracing the power through a system and computing the torque from that, but I am not being very sucessful in articulating why.

 

The important thing is when you expain to someone whether they should build for "torque" or "power", then I shut up and listen. Your years of experience are spot on. But if you want to get into technical definitions of power, work and energy, well then things get a little more technical.

[Phantom]

Grumpy,

Engine is a stock 99 Camaro LS1 with a K&N intake right in front of the MAF, just behind the radiator. Engine has about 4,000 miles total on it now. Obviously a total computer controlled engine here with coil-on-plug electronic ignition. Reason I asked about exhaust is that I run 2.5" off headers to a Y connector to single 2.5" the last 4' throught the muffler. Thought it might be killing my top end?

[grumpyvette]

I run 2.5" off headers to a Y connector to single 2.5" the last 4' throught the muffler. Thought it might be killing my top end?

I think youll find that you will have some improvement by routeing the two 2.5" in pipes to a 3" muffler in and out for the last 4'

look at it this way, a single 2.5" pipe has aproximatly 4.5 sq inches of internal cross section so your feeding about 9 sq inches of flow into 4.5" of flow for the last 4'. a 3" pipe would have about 7 sq inches of area or about 57% less restriction a 3.5" pipe has about 9.6 sq inches and would in effect have little or no restriction compared to the two 2.5" pipes

here this might interest you

 

http://www.racerpartswholesale.com/flomstr1e.htm

 

http://www.victorylibrary.com/mopar/header-tech-c.htm

 

http://www.pagerealm.com/fbody/pipe.html

[Guest Anonymous]

DELETE

[Kevin Shasteen]

.., As for for the definition of torque vs. HP, I guess just different ways of looking at it..., In physics, they define work as force times distance. Thus no matter how hard you push on something, if it doesn't move then technically you have done no "work" on that object. The classic example is if you were to hold a 40 pound weight out at arms length. Are you doing any work? No, the weight is being held without moving. Are you expending energy holding the wieght? Of course. The rate of energy expendeture is, by one definition, a measure of power..,

 

FWIW,

 

When we speak of Tq & HP, are we not simply talking about Force? As to the 40# lbs weight held in someone's arms...since the weight doesnt move then are we doing any work(?)...the person holding the weight is working AKA: Expending Energy but the weight has not moved (accelerated). So we must first define our objective of what we will be using when we choose the word "Work". What is our objective-is it to merely expend energy, move a vehicle, or to move the vehicle as quickly as possible? What is our objective????

 

I believe the HP rating is a significant anomoly. I look at it in similar fashion to our Dynamic Compression Ratio -vs- Static Compression Ratio discussions. Just because the engine doesnt see compression until the IVC occurs doesnt mean that the Static Compression Ratio is an immaterial one: it just means the end user must have a basic understanding in how the Static Comp.Ratio affects the engine.

 

HP to me does exist. It exhists in that it is a different measurement of Force: thus my agreement in that HP is a function of TQ...yet TQ is a function of Force. However, just because it is a function of Tq doesnt make Tq an island unto itself. Just because it is a different measurement of Tq doesnt mean that HP does not exhist nor does that mean that the process for HP is a misrepresentation of an engine's ability to do work.

 

IMO the process for calculating HP and the HP rating itself is very real and a DIRECT SIGNATURE of the engine's potential in its abilty to work in the realm of time. Say you had a Catapillar Diesel engine straight out of a Semi-Tractor -vs- a BBC dragster engine: you had to chose between one of these two engine's for your 1/4 mile dragster, and all you went by was the HP rating: which one would your prefer? They both put out gobbs of Tq-but obviously the BBC dragster engine has a HP foot print that is more dragster friendly for the 1/4 mile. So, once again we are dancing all around "The Intent of the Engine" and the "Engine's Ability To Work" coupled w/the required gearing to appropriately meet our needs.

 

So, in the example above, do I want a dragster whose engine puts out gobb's of Tq and one where I would have to shift thru 9 gears with a splitter on my shifter for each gear or do I want an engine where I can get away with a trans that merely shifts two to three times at the most? This is IMHO where the HP signature of an engine is best utlizied.

 

IMHO, the HP rating-once understood, is a perfect process for calculating an engine's ability to work: as in how fast will that engine work -vs- how slowly does that engine work. The HP process is a measurement in the engine's ability to rev.

 

In other words, what HP intensity do I want my engine to have & will that intensity fit in with the intent of the car?

 

Take two individuals and their ability to do work. One person is 9 feet tall 360 lbs rock solid while the other person is 5'10" 180 lbs. Both people are given tasks for an obsticle course. In the beginning a 200 lbs boulder must be picked up & moved 20 feet down the path...from there they both will come upon an apple tree & are told to pick one bushel of apples. From there they move to the agility part of the course which makes up for 2/3's of the course.

 

With this in mind-which person will be victorious? Obviously the 9 foot person will have no problem w/the 200 lbs rock nor the picking of apples from an apple tree due to their height. Yet, the shorter person will make up for the loss in "Power" once he makes it to the agility course due to their spryness & nimbleness. Now if the course were merely built to determine power then the 9 ft man would win yet if the course were built solely for quickness & nimbleness then obviously the shorter man would win.

 

Both men are capable of "work" yet their abilities to do work differ: the same force is being measured on each man-yet their output would be different: one would be quicker and efficient in one field while not so quick nor efficient in the other. So, once you have established that a distinction between smaller men & larger men does exhist-would you not classify this distinction so that when a task exists and must be accomplished by someone-would you not use your newly classified list of choosing the "Right Man" for the job so that time (efficiency) is not wasted? Is this not what the HP rating does for us?

 

HP is merely another tool for determining how quickly -vs- slowly an engine can work...and to what extent that quickness -vs- slowness affects your objective.

 

My .02c's worth-HP is just another way of classifying an engine's ability to work and I would not say it doesnt exist simply because HP is a functioin of Tq.

 

I may be wrong here but I enjoy the discussions nontheless: when we discuss we learn & that is very cool 8)

 

Kevin,

(Yea,Still an Inliner)

[A. G. Olphart]

Grumpy-

 

I'd like to thank you for your technical posts and their related links. I generally copy or bookmark them for reference. Nice to have available.

 

Kevin- I don't beleive either Hp or torque measures the quickness with which power may be applied. (I think mathematically that would be some sort of derivative). Physically it is dependent on torque and the (rotational) inertia of all the bits involved. A 200 Hp diesel the size of a small house won't accelerate nearly as quickly as a 2 liter producing the same power.

[Phantom]

Grumpy.

Thanks again for your feedback. I originaly wanted to go with the 3" but now I'm seriously thinking about going up to a 3 1/2". I'd hate to screw the car with something as simple as a too small exhaust.

Anything else in mind on a stock LS1 that could be tweaked to help that torque curve? Do I need to get into the ECM?