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Thread: HP or Torque ? for lower lap time ?

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    Senior Member bellwilliam's Avatar
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    Default HP or Torque ? for lower lap time ?

    serious question, need help in my thought process of a car I am building.

    everything else being equal. which car will turn a lower lap time (at say BW, WSIR, Infineon or Thundrhill) ? and why ?

    car A - 150whp, 120ft/LB
    car B - 120whp, 150ft/LB

    not sure if I need to add other criteria. not even sure if this is a right question.
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    I don't know the answer but car b is nearly impossible.

    Edit* not.impossible, but highly improbable.

    I'm also curious though, I recently changed from my turbo Miata to rotrex, I lost a lot of torque, but gained a little HP. No track testing yet...
    Last edited by donutbob; 08-24-2011 at 11:39 PM.

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    Track Whore Pure EvoIX's Avatar
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    hp = top end speed. torque = acceleration. I say on a flat out track (ACS), you want more hp. On a track like SOW or BW, you want more torque. That is my understanding. Correct me if i overlooked something.
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    Pro Lurker GreyFocus's Avatar
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    Hp is the magic number a dyno spits out showing how high you carry tq in the rpm range. That's why a s2k makes 200+hp but only 140ish tq. Because it hold that tq value for 8500-9000 rpm. Torque is volumetric efficiency, basically how.much air is moved in a given time. Turbo cars and large displacement make torque because they aare moving alot of.volume at a given time. When more torque is made then hp, its because their is either a lack of rpm(think diesels) or a intake/exhaust breathing restriction at higher rpms(think turbo cars with high psi levels on a undersized turbo)

    Now with that said, i would want a good amount of both, with a slight bias toward Hp, like a V8 that can rev decent (LSx, new mustang 5.0), a honda 4 cylinder with a rotrex, or a turbo setup with good intake and exhaust flow( external gate, good tubular manifold, free flowing filter/ exhaust system). my current power band on the focus is the best ive had on the car compared ot the previous setups, its 313whp, 250wtq, so the torque is good without being wheel spin violent, but its not choked and flows well in higher rpm, thats why the hp to tq gap is large. the larger the gap between the hp and tq, the more efficient the setup is working. So the torque is still strong on the upper RPMs rather then falling off. my last setup only made 250whp with the same 250wtq and psi level, this is because i had a restricted turbo exhaust housing and exhaust system, plus the turbo itself was smaller and less efficient.
    Last edited by GreyFocus; 08-25-2011 at 01:26 AM.

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    Senior Member DocNrock's Avatar
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    I believe it was Richard Petty who said: "horsepower sells cars, raw torque wins races."

    That said, I think Clint's reply above is spot-on. One thing about torque that wasn't said, though. With high enough torque, you can probably exit corners one gear higher, and not have to lose time shifting into that gear once you get into the higher rev range.
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    Yah that statement gets twisted into total bull****. Look at a data log of your RPM down a straight away, any power value at RPM that your not in down that straight away is a second order effect (driver/tq modulation) at best.
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    BMW Master bawareca's Avatar
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    I have put a lot of thought in that and I can share some info.It is a little different from William's case because it is for higher hp/tq cars,but may be usefull.
    One of the things that has to be in the equation is the weight of the car.My understanding is that the lighter the car,less tq you need to make it driveable on the track.As an example you can imagine wheat will happen if you double the tq number of a S2000-it wont be anymore that great car to drive.A friend of mine has swapped 3.5 l 6 cylinder engine in his 1985 3 series BMW.It is more torquye engine with only 190 hp.He cannot exit the corners on full throttle and has to be very carefull on the throttle,but later on the straight goes out of RPM-that is not good setup for me.I have the same E30 with 2.7 l turbo with 360 tq/hp that tops at 6200 rpm,which is also not a good setup for that car.My next engine will be high compression/low boost with rev limiter just under 7 k rpm.Less peaky,more limear and it will allow me to use the bigger diff ratio possible.

    Quote Originally Posted by DocNrock View Post
    ... One thing about torque that wasn't said, though. With high enough torque, you can probably exit corners one gear higher, and not have to lose time shifting into that gear once you get into the higher rev range.
    It is actually the other way around.General rule is that for the maximum possible performance on the track you should be on the rev limiter on the highest gear at the end of the longest straight.Here comes the thing-more revs(more hp)you have,higher diff ratio you can run,and as we all know the diff ratio is torque multiplier.Example-S200 again.

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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by GreyFocus View Post
    When more torque is made then hp, its because their is either a lack of rpm(think diesels) or a intake/exhaust breathing restriction at higher rpms(think turbo cars with high psi levels on a undersized turbo)
    bingo. but with electronic wastegate that cut psi as rpm increase. to hold down the hp number.
    Last edited by bellwilliam; 08-25-2011 at 09:28 AM.
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    Quote Originally Posted by gixxer_drew View Post
    Yah that statement gets twisted into total bull****. Look at a data log of your RPM down a straight away, any power value at RPM that your not in down that straight away is a second order effect (driver/tq modulation) at best.
    Spoken like an engineer.

    IOW, huh?
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    Senior Member robburgoon's Avatar
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    William, the answer to your question is horsepower, horsepower horsepower.

    Horsepower is derived from torque. Torque at low rpm, low hp. Torque at high rpm, high hp.

    When most people describe "big torque" what they actually mean is "fat torque and hp curves". Making the same peak horsepower but with great big fat torque and hp curves instead of a skinny peaky one is how Richard Petty is winning his races.

    Having a wide/fat curve is great for a number of reasons.

    William, are you serious? You know this stuff.


    Finally peak numbers really don't mean ****. Area under the hp curve in the range of rpm that you use (and some of the rpm that you accidentally find yourself in) is what matters.
    Last edited by robburgoon; 08-25-2011 at 10:04 AM.

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    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by bellwilliam View Post
    serious question, need help in my thought process of a car I am building.

    everything else being equal. which car will turn a lower lap time (at say BW, WSIR, Infineon or Thundrhill) ? and why ?

    car A - 150whp, 120ft/LB
    car B - 120whp, 150ft/LB

    not sure if I need to add other criteria. not even sure if this is a right question.
    The car with more horsepower, period. Power is a measure of Work done; torque is just a measure of Force. You can have 1,000,000,000lb/ft of torque at 0 RPM and obviously no work is being done (no power being made).

    Work = Force x Distance. Power = Work / Time.

    So, you can have 2 motors that produce the same amount of torque (Force), but if one can produce that same Force at a higher RPM (i.e. over a longer distance), it does more Work (and therefore creates more power).

    Look at the BMW 3-series. They have a deisel model with like 400lb/ft of torque and (IIRC) ~270hp. It is much slower than the regular gas model with 300hp & 300lb/ft torque.

    PS - Remember, the torque number that the engine produces on the dyno is NOT the torque number that makes it to the tires. That engine torque force is run through several different gear ratios (gearbox gear, final drive ratio, tire size). Look at F1 - 800hp and like 300lb/ft of torque. All you need to do to increase/decrease the amount of torque at the tire is change the gear ratio. This is what F1 does - runs a really high RPM (more work/power done/produced) through a very short gear ratio.

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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by robburgoon View Post
    William, the answer to your question is horsepower, horsepower horsepower.

    Horsepower is derived from torque. Torque at low rpm, low hp. Torque at high rpm, high hp.

    When most people describe "big torque" what they actually mean is "fat torque and hp curves". Making the same peak horsepower but with great big fat torque and hp curves instead of a skinny peaky one is how Richard Petty is winning his races.

    Having a wide/fat curve is great for a number of reasons.

    William, are you serious? You know this stuff.
    my question is not 2 engines making same peak hp, of course I would take one with higher torque number (or flatter torque).

    okay, I didn't want to spill it. but reason for this has to do with HP/weight ratio. many race sanction use hp/weight number to class a car. they don't use torque/weight number.
    in theory, if you can throw a diesel engine (or a gas engine with similar hp/torque ratio, yes it is doable), you would gain a lot of advantage. say a 130whp, 180ft/LB engine in a Miata, you would still be classed to race a Spec Miata making 130whp, 100ft/LB. assume both engines able to rev to 7,000rpm, but the high torque engine only has higher torque at low rpm, it will have similar torque number (as low torque engine) at higher rpm.

    I am explaining this well. may be someone else can help me explain what I am looking for.
    Last edited by bellwilliam; 08-25-2011 at 10:21 AM.
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    Senior Member robburgoon's Avatar
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    William, do this:

    Make an engine that has a wide torque curve that tapers downward as RPM goes up. You'll want torque to go down fast enough that horsepower stays as level as possible. If you do some math, you should be able to figure out the proper torque curve shape to do that. Make the properly shaped portion of the hp curve as wide as possible so you don't need to shift much.

    That will exploit the rules as much as possible I think.


    Also, be prepared for Greg to look at your flat 200whp curve, whip out a calculator, and then charge you for 240whp peak anyway.

    People who exploit holes in the rules tend to end up having their cars get banned. Just ask Sharp and Hall.
    Last edited by robburgoon; 08-25-2011 at 10:25 AM.

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    Senior Member bellwilliam's Avatar
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    Rob:

    that's called a turbo engine with electronic wastegate. 50psi at 2,000rpm, 1 psi at 7,000rpm.
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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by bellwilliam View Post
    Rob:

    that's called a turbo engine with electronic wastegate. 50psi at 2,000rpm, 1 psi at 7,000rpm.
    Build it. Get it banned. I dare ya

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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by J. Tyler View Post
    Look at the BMW 3-series. They have a deisel model with like 400lb/ft of torque and (IIRC) ~270hp. It is much slower than the regular gas model with 300hp & 300lb/ft torque.
    that's an excellent example.
    I am puzzled why though. may be there are other reason. diesel engine are typically heavier, rev much lower. that might be why it is slower.
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    Senior Member robburgoon's Avatar
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    Electric motors have an interesting shape too. Huge torque at low rpm, low torque at high rpm. That's part of why some electric cars are 1 speeds and 2 speeds.

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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by robburgoon View Post
    Build it. Get it banned. I dare ya
    LOL.
    I am pretty sure this has been done before. many race sanction use/used hp/weight number. so it must of been done before. or may be not, because it isn't faster ?
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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by bellwilliam View Post
    LOL.
    I am pretty sure this has been done before. many race sanction use/used hp/weight number. so it must of been done before. or may be not, because it isn't faster ?
    Or because it's a pain and will just get it banned/nerfed.

    Ask Derek Gardner.

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    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by bellwilliam View Post
    that's an excellent example.
    I am puzzled why though. .
    Power = Work / Time

    What part of that are you having trouble with?

    *Edit: The gas engine performs more work per unit time, which is why it's HP number is higher. More work done = car goes further down the track (accelerates faster).

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