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Thread: HP or Torque ? for lower lap time ?

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    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by olitho View Post
    the first one is mostly correct. Hp does determine how fast you are going when you hit the wall.

    The second one is not right at all. Torque is measured by how bent out of shape burgoon gets when he does not get the humor.
    lol.

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    Senior Member DocNrock's Avatar
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    The follwing is not an attempt at humor. My statement on the first page was somewhat overly simplified as most on this board are sophisticated enough at this stuff that I didn't feel I needed to spell it out. Unfortunately, it got dissected and misconstrued. So I feel somewhat of a need to save face while trying to get this thread back on track so that some will be unable to make me appear like a complete idiot.

    Quote Originally Posted by bawareca View Post
    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.
    While I agree the final drive ratio is the torque multiplier and can compensate for lower torque, I was not talking about where you want to be in the rev range at the end of the straight, I was talking about corner exit before the straight. It is obvious that you want to be in the upper rev range when you get to the end of the straight. My comment was aimed at corner exit, where if you have high enough torque, or a final ratio that compensates for lack of torque, you can exit the corner one gear higher and still be accelerating well out of the corner, then shift at your usual shift point for the following gear. You'll save the time to shift one gear if you can exit one gear higher. This is particularly relevant to manual transmission turbocharged cars, in which you have to come off boost to shift, then allow for the turbos to spool again when mashing it after shifting. This is not so important in DCT turbo cars where shifts are flat-footed and you do not come off boost and the shift takes about 0.2 seconds (ie, GT-R).

    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.
    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.
    Torque is what is measured by a dyno, and horsepower is calculated from the torque measured versus rpm. I thought it was completely obvious to everyone on this board as sophisticated as they are with this basic topic that everyone would know that peak numbers don't mean anything and that it is ALL about the area under the curve and that the magic number of horsepower is a calculated from measured torque.

    Quote Originally Posted by robburgoon View Post
    Back to William's original question, the other reason why Richard Petty is winning with his big torque (wide horsepower curve) is when racing wheel to wheel in traffic, often times something strange will happen like you'll run down a slow ass E36 bmw, have to brake, and you'll find yourself in the wrong gear. In my miata, I curse and slam it down into 3rd. In a corvette, you say "wrong gear? what's that?" and give the slow prickster the finger as you rumble past quickly back into the powerband.
    Bingo! This is similar to what I meant by being able to exit a corner one gear higher if your torque is higher (meaning a high value and broad torque curve = AUC), or is well-compensated by gearing. But to clarify lest I get misunderstood again is that it has zero to do with where you want to be in the rev range at the end of a straight.

    Quote Originally Posted by robburgoon View Post
    Now that's a load of horse****. The F1 engine can launch the corvette, the trick is having a clutch that can suffer a little to get the corvette rolling. Then the corvette will have a fun time trying to get the power down without spinning tires.

    The corvette engine will do everything the F1 car needs it to do with no problems. It will just be half as fast and weigh too much and probably need a lot of fabrication since aren't F1 engines part of the frame?
    Here is something that has not been discussed, probably because it is so difficult to modify from a production car. Rob says earlier in the thread that torque really doesn't matter, because you can compensate for the lack of it with the final drive ratio. The drive ratio and gearing are torque multipliers, I completely agree. But it has been implied that horsepower is absolute. I would disagree. Similar to the ability to compensate for lack of torque with the drive ratio, you can compensate for lack of horsepower by lightening the car. Thus it is not just horsepower, but it is acutually the power to weight ratio that is most important since we seem to be splitting hairs in this thread. But for most production cars, signficant weight loss is much more difficult (and expensive) than changing the final drive for torque compensation, which may explain why hp is being portrayed as more absolute than torque. And, to prevent being misunderstood again, I am not talking peak horsepower, but again the area under the curve.

    As an example, below is the dyno plot from my GT-R with street and track maps overlayed. The plot was taken from SP Engineering's website: SP Engineering



    There are two points that I believe this graph illustrates. One is that even though my car has nice peak numbers, we all know peak numbers in and of themselves are meaningless unless they are associated with broad curves, ie., the area under the curve. The second point goes back to Clint's posting on the first page regarding smallish turbos. The GT-R turbos are quite small. The benefit, even though this is obvious, is that they typically spool more quickly. The downside, when tuning a car to make more boost than OEM tuning, is that as the revs go up, the wastegates must be tuned to allow them to push a lower psi to keep them in their effficiency range so they're not just blowing hot air, risking engine damage. My street tune peaks at 18 psi in the midrange and drops to 16 psi at redline. The track tune peaks at 17 psi and drops to 14 psi at redline, so as to incorporate a safetly margin when running hard for 20 to 25 minutes at a time. But even though I have one psi less in the midrange and 2 psi less at redline, the torque and hp differentials are relatively small. This illustrates how closely these turbos are to the outer envelope of their efficiency range. Also, if you look at how early in the rev range the torque band is reached (about 2900 rpm), you can see how quickly these smallish turbos spool. But this comes with the tradeoff of a rather flat hp curve near redline, as the boost is lower. The only way to improve upon this is slightly larger ball bearing turbos, which spool similar to the stockers, but can push more air closer to redline and still be within their efficiency range. So, while less than ideal, both the torque and hp curves are a great improvement over stock, and the car makes plenty of power for a road course. I wouldn't even consider a turbo upgrade at this point.
    Last edited by DocNrock; 08-30-2011 at 02:55 AM.
    2009 Nissan GT-R -- nicely modded

  3. #83
    BMW Master bawareca's Avatar
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    Your torques are more than more track cars will ever dream of.That is why I am converting my somewhat peaky low compression mid-boost motor to high compression low-boost.
    You are correct that exiting on higher gear will give you advantage,but then again,this can be solved mostly with gearing.It will be easier than moving the powerband to the left.As an example,with my last setup I was lost in a few corners at SOW.If I exit on 3rd the RPM <3000 and it takes a day for the turbo to spool.If i exit on 2nd,the RPM >6000 and I have to be very carefull with the gas and have to upshift almost immediately.Moving the powerband to the left would require huge sacrifice at the top end,which may be Ok on that track.My opinion is that higher diff ratio and/or close ratio transmission would be the better solution.

  4. #84
    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by bawareca View Post
    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.
    Negative, ghostrider.

    See gixxerdrew's post about calculating gear ratios for maximizing area-under-the-curve usage.

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    BMW Master bawareca's Avatar
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    Quote Originally Posted by J. Tyler View Post
    Negative, ghostrider.

    See gixxerdrew's post about calculating gear ratios for maximizing area-under-the-curve usage.
    That is how it is in F1,but they probably dont know much about gear ratios
    You probably can explain why one would want it different way.Saving some gas on the straights?Less engine wear?
    Last edited by bawareca; 08-30-2011 at 08:59 AM.

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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by bawareca View Post
    That is how it is in F1,but they probably dont know much about gear ratios
    It's true for many engines, but not all. An old dodge slant six has a redline at 5,000, but IRRC even trying to go fast you shift below 4K because there is no freaking torque up there at ALL. The engine can't breathe that high. The F1 cars are tuned to make the most area under the horsepower curve possible and with the rev limit being the biggest problem, they put all their torque as high as possible. Also, when tuning gear ratios don't forget to leave some room for tailwinds and drafts.

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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by DocNrock View Post
    Similar to the ability to compensate for lack of torque with the drive ratio, you can compensate for lack of horsepower by lightening the car.
    Now you're just being difficult! And I think you're getting lost on a tangent. Leave weight loss completely out of it. It has almost nothing to do with comparing a torquey engine and a horsepower engine.


    You don't compensate with gear ratios much for a horsepower engine, what you describe brings to mind putting two transfer cases in series for rock crawling. Most of the time without getting too crazy with gearing you can get all the torque you can handle at the lowest speeds that we see (20mph? and how often do we use 1st gear?). Horsepower just lets you stay in the shorter gear longer (higher output torque to rear wheels) before shifting to the taller gear. And like you say, a fatty hp curve engine means if you decide you need to short shift, you don't get kicked in the balls as hard for it.

    I think you might be too focused on the engine torque curve when even though horsepower isn't something you measure directly, it's the best way to compare what real torque you can manage to produce at the rear wheels at a given car velocity.

    Also, I think many of us know that area under the horsepower curve is what matters, but William was worrying me when he wasn't coughing up curves for comparisons.

  8. #88
    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by bawareca View Post
    That is how it is in F1,but they probably dont know much about gear ratios
    You probably can explain why one would want it different way.Saving some gas on the straights?Less engine wear?
    No, it isn't. If what you are saying is true, please explain what they do when they need to slipstream or use DRS? The engines are rev-limited to 18,000rpm. According to you they set 7th gear to hit 18,000rpm at the end of the longest straight. So what happens when they are slipstreaming and going 20kph faster on that straight than a normal lap? There is no rev-limiter-override button on those fancy steering wheels, FYI.

    In addition to the above reason, like both myself and Drew have said, race engineers will calculate & set the gear ratios to maximize the usage of HP curve area. I'm not sure where an F1 engine makes max HP, but I doubt it is right at redline. I would guess it is somewhere around 17-17,500. Usually they will set 7th gear such that maxHP is achieved at maxSpeed at the end of the longest straight, thus leaving a few hundred RPM left to be used for slipstreaming/DRS.

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    Smack-Talkin' Member J. Tyler's Avatar
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    Take the 335i I drove last year as another example. Redline was 7,000rpm, max HP was ~5,800rpm. I shifted at ~6,000-6,200rpm. You would never set that car up to hit 7,000rpm on the longest straight.

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    Senior Member psychoazn's Avatar
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    Quote Originally Posted by J. Tyler View Post
    Take the 335i I drove last year as another example. Redline was 7,000rpm, max HP was ~5,800rpm. I shifted at ~6,000-6,200rpm. You would never set that car up to hit 7,000rpm on the longest straight.
    The only way to determine this is to look at a graph. In the case of the AP1/F20C, peak power is typically at ~8300RPM. Would you shift at 8500RPM or at redline to go fastest? The obvious answer is Redline.

    Same with a (older) stock STI. 4000RPM for peak torque, 6000RPM for peak power. Do you shift at 6500 or redline?

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    BMW Master bawareca's Avatar
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    On most high performance engines the rev limiter is within 200-300 of the max power.That means that on a regular basis lalp by lap you are at the RPM where the max power is,and when you are slipsteraming(or using DRS,since 10 races) you can go up to the rev limit.300 RPM extra is probably ~15MPH for F1 at 7th gear.
    DRS was introduced this year.I dont see why you wont take it into consideration when calculating the gears.
    Last edited by bawareca; 08-30-2011 at 11:56 AM.

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    BMW Master bawareca's Avatar
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    Quote Originally Posted by J. Tyler View Post
    Take the 335i I drove last year as another example. Redline was 7,000rpm, max HP was ~5,800rpm. I shifted at ~6,000-6,200rpm. You would never set that car up to hit 7,000rpm on the longest straight.
    I have no idea why a car would have the peak power at 5800 rpm and rev limiter at 7000.You can make the limiter at 8000,but it doesnt make sense.On my engine the peak power is also at 5700 rpm,and I always short shift before 6500,there is no reason to try to go any higher.As the example with the S2000,"real" limiter is supposed to be 200-300 over the peak power revolutions.
    Last edited by bawareca; 08-30-2011 at 11:58 AM.

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    Senior Member psychoazn's Avatar
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    Quote Originally Posted by bawareca View Post
    I have no idea why a car would have the peak power at 5800 rpm and rev limiter at 7000.You can make the limiter at 8000,but it doesnt make sense.On my engine the peak power is also at 5700 rpm,and I always short shift before 6500,there is no reason to try to go any higher.As the example with the S2000,"real" limiter is supposed to be 200-300 over the peak power revolutions.
    Because the engine itself can handle the higher RPMs; why not give the driver the option to rev? Additionally, in the case of the turbo cars, they simply get choked up top by tapering boost (or some other mechanism) which results in a severe torque dropoff....

    In the case of the F22C, peak power is AT redline...

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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by bawareca View Post
    I have no idea why a car would have the peak power at 5800 rpm and rev limiter at 7000.You can make the limiter at 8000,but it doesnt make sense.On my engine the peak power is also at 5700 rpm,and I always short shift before 6500,there is no reason to try to go any higher.As the example with the S2000,"real" limiter is supposed to be 200-300 over the peak power revolutions.
    And you guys wonder why I rip on BMW drivers.... All kidding aside, there are lots of reasons to rev an engine well past the hp peak. To determine shift points, you usually shift when the rwtorque of your current gear at your current rpm is inferior to the next gear at its rpm, OR you've smacked into the rev limiter, whichever comes first. Exceptions would be when you would have to downshift almost right after the upshift.

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    BMW Master bawareca's Avatar
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    Quote Originally Posted by psychoazn View Post
    Because the engine itself can handle the higher RPMs; why not give the driver the option to rev? Additionally, in the case of the turbo cars, they simply get choked up top by tapering boost (or some other mechanism) which results in a severe torque dropoff....
    You can gain some advantage by going 1000 rpm over the peak power in 2-3 gears,but at 4-5 you are wasting time doing that.J.Tyler is shortshifting,I am short shifting at ~300-400 after the peak power.When the turbo engine with smaller size turbo chokes,it chokes badly.Some call it fall off the cliff,other call it to fall flat on its face.

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    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by psychoazn View Post
    The only way to determine this is to look at a graph. In the case of the AP1/F20C, peak power is typically at ~8300RPM. Would you shift at 8500RPM or at redline to go fastest? The obvious answer is Redline.

    Same with a (older) stock STI. 4000RPM for peak torque, 6000RPM for peak power. Do you shift at 6500 or redline?
    No, the obvious answer is not redline. Again, you should shift at whatever RPM maximizes the used HP curve area for the gear you are in. Maybe that works out to you shifting at redline, maybe it doesn't; different engines have different HP curves and gear spreads. You have to look at a dyno graph and what the individual gear spreads are, and then calculate the ideal shift points from that information. If you have a racecar with adjustable gear ratios like F1, you can calculate the ideal individual gear ratios for a particular track/car setup/engine map.

    Quote Originally Posted by robburgoon View Post
    And you guys wonder why I rip on BMW drivers.... All kidding aside, there are lots of reasons to rev an engine well past the hp peak. To determine shift points, you usually shift when the rwtorque of your current gear at your current rpm is inferior to the next gear at its rpm, OR you've smacked into the rev limiter, whichever comes first. Exceptions would be when you would have to downshift almost right after the upshift.
    Well.... Again, it's about maximizing HP curve area usage for each gear, not rwtorque. (Of course, rwtorque is related to HP...but I think you get the basic idea )

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    BMW Master bawareca's Avatar
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    Quote Originally Posted by robburgoon View Post
    And you guys wonder why I rip on BMW drivers.... All kidding aside, there are lots of reasons to rev an engine well past the hp peak. To determine shift points, you usually shift when the rwtorque of your current gear at your current rpm is inferior to the next gear at its rpm, OR you've smacked into the rev limiter, whichever comes first. Exceptions would be when you would have to downshift almost right after the upshift.
    dyno.jpg
    You can tell me what exactly would I gain going past 6300-6400 RPM on 4-5-6th.The car has also a heavy and uneficient aero.

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    Senior Member psychoazn's Avatar
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    Quote Originally Posted by J. Tyler View Post
    No, the obvious answer is not redline. Again, you should shift at whatever RPM maximizes the used HP curve area for the gear you are in. Maybe that works out to you shifting at redline, maybe it doesn't; different engines have different HP curves and gear spreads. You have to look at a dyno graph and what the individual gear spreads are, and then calculate the ideal shift points from that information. If you have a racecar with adjustable gear ratios like F1, you can calculate the ideal individual gear ratios for a particular track/car setup/engine map.



    Well.... Again, it's about maximizing HP curve area usage for each gear, not rwtorque. (Of course, rwtorque is related to HP...but I think you get the basic idea )
    You need to read my previous posts. We've already done the graphing and mapping for the different s2k engines and transmissions.

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    Smack-Talkin' Member J. Tyler's Avatar
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    Quote Originally Posted by psychoazn View Post
    You need to read my previous posts. We've already done the graphing and mapping for the different s2k engines and transmissions.
    Ah OK, I'll read them later today when I get home. I thought you were speaking in generalities, not specifically about the S2000/gearbox.

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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by robburgoon View Post
    To determine shift points, you usually shift when the rwtorque of your current gear at your current rpm is inferior to the next gear at its rpm, OR you've smacked into the rev limiter, whichever comes first.

    Bingo!
    To the right of The Sheriff. Isn't everyone?

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