scalbert

But once a few miles are on the car, and temps held in check, it will make in the 210 - 215 range. That is for a 6-Speed.

DIO 87 Prelude

zeroday
A-CL Veteran

Registered: Dec 2001
Location: Philly, PA
Posts: 3104

quote:
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Originally posted by DIO 87 Prelude
hey TypeR ever hear of gear ratios?
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um..ever hear of displacement?


What about it??? He was saying that because the CL has 1000 more rpm it is better and faster.

blackmagiCL_S

humble.

scalbert

No...

Take two cars which make nearly the same torque. Car A makes more peak torque at a lower rev and car B makes 5% lesser torque but makes its torque for 1k revs longer. Now assume equal gearing. Car B will be falling behind until the first shift. At which point the ability to hold the lower gear in Car B allows it to pull closer and then shift. Now the cars are in the same gear and car A is pulling ahead but has to quickly grab the next gear. Once this shift occurs car B has the advantage and pulls even, etc.

During the shifts a drop of 25% or more may occur. So if a car can hold a gear longer while producing less overall torque it might be able to win.

Now alter the gearing to favor the extra revs and the table may turn. Traction limitations excluded.

DIO 87 Prelude

not to discredit your statement.....but, when are cars going to have equal gear ratios, 99% of cars brought here to the US or made for the US market have shift points that accomodate 2nd gear up to 60 for the 0-60 test w/o a 2-3 shift(so as to not lose that extra little bit) and for the 1/4 mile to be done in either 3 or 4 gears. Therefore making your statement about one falling behind the other one invalid. ( Unless they would make the gear ratios equal, not likely)

Allout

A large Total area under the curve is really what makes a good motor. The larger the area under the curve means more usable HP/Torque. That's why you can have two cars with equal peak HP numbers and one will leave the other in the dust.

TypeR and the SC guys are a testimony to this. Their curves broadened in addition to higher peaks.

pimpscls

damn thats pretty good

power3dfx

i think he was trying to explain the concept about rev and hp/torque. when explaining a concept, you must avoid other factors or keep them consistent so that the expanation makes sense. i dont think he intended to apply this to real world.

scalbert

power3dfx was correct, it was conceptual and attempting to remove other variables.

But to apply it here and based on what you presented; the cars gearing would be set to give nearly the same road speeds. This would allude that the CL-S6 should have shorter gearing (when the wheel/tire combo is accounted for). This shorter over all gearing does help to make up some of the torque deficit.

I do have one instance for same gearing but different motor. In the C4 when they went from the L98 motor to the LT1. The transmissions were untouched for the automatics; the L98 motor actually made a little more torque at a lower revs. But the LT1 motor made its torque about 1k revs longer. This did allow it to stay in a lower gear longer and out accelerate the L98.

ferizzo

The torque curve does look tasty on those Gs!

J98CL

I have heard that the G35 is some what the american Skyline version. My buddy found a site saying that they are the same ride. Has anyone elese heard this?

gavriil

I stand by my statement.

As long as a vehicle is able to put the power on the ground, total HP is what matters in ultimate acceleration. Not where on the rev band that power it made.

gavriil

Scalbert, I dont think the above is true. If both cars ahve equal gearing, of the same weight and can equally put the power on the ground, torque and where it's made, is irrelevant.

gavriil

It's called the Skyline in Japan and Europe.

gavriil

Actually you give me a reason to restate. In a more acurate way.

Torque and where it's made on the rev band is irrelevant. Assuming gearing, weight are identical and the way the vehicles put all the power to the ground, what matters for ultimate acceleration, is the total area under the HP curve.

cusdaddy

BTW.. Redline of the VQ35 is 6600rpm, not 6250

scalbert

It is completely relevant unless the cars have CVT transmissions. Where the power is made and where the car is in the revs band during shifts is very important when accelerating. In addition, holding a gear longer while still making torque (not dropping off significantly) is also important.

I beleive this is one of the better write-ups on the subject, specifically mid way down when discussing the L98 and LT1 C4 Corvettes.

HP, Torque and Gearing

Zapata

gav,
must disagree power band is SO important.......

gavriil

Guys, in this case we assume that gear ratios and final drive are identical. As well as weight, aerodrag, other drag, etc.

What matters is the TOTAL area under the HP curve. If that total area is larger in quantity than another car's, then the first car wins. Peak torque and where it appears does not matter.

scalbert

Precisely, the area matters and by making torque at higher revs you significantly increase this area. But that isn't what was originally stated. Also, where the power occurs does matter.

I understand where you may have been going but it isn't what I gleaned from your statement. In addition, total area does not represent absolute results.

Take for instance the example (Hypothetical) torque plots below. Both cars have the same area under the curve. However, Car B would win in a drag race (with everything else equal) even though it has a lower peak torque output. It would win because it would be spending more time at a greater torque value; in the upper revs.

scalbert

BTW, just for fun I did a quick chart for comparison albeit sided towards the CL-S6 since, in this example, it has headers and intake.



The G35 has an obvious advantage below 5k revs assuming similar gearing (which they are close). But above 5500 revs the CL-S is the winner. When racing, most of the time would be spent above 5000 RPM. However, in a drag race the G35 should win if driven well as it is RWD and has better low end grunt. It should be able to have short times 0.2 - 0.3 seconds quicker. This means the CL-S6 has a lot of catching up to do.

Back to area under the curve and extending the torque curve. Guess which vehicle has the greater area here?? The CL-S by about 7.5% with a 20% advantage from 4500 RPM and up.

scalbert

I should add that the better low end torque makes the G35 easier to drive in traffic. That is one of the reasons I got the blower...

gavriil

Scalbert, you obviously missed this post of mine above:


"Actually you give me a reason to restate. In a more acurate way.

Torque and where it's made on the rev band is irrelevant. Assuming gearing, weight are identical and the way the vehicles put all the power to the ground, what matters for ultimate acceleration, is the total area under the HP curve."

gavriil

No Scalbert, here is where you get confused. I think.


In reality the above example may actually be correct, because eratic/sudden changes in torque cause cars to be slightly slower due to the fact that they dont put all that power on the ground as well as "flat torque" cars.

In theory though (and that is why I was so emphatic on the "able to put the power on the ground" issue), if the total area under the torque or HP curve (same thing) is equal, then the cars will accelerate equally, keeping everything else equal.

A good example of the above is evident in this thread of mine, with the SPI car. Look at the rediculous torque curve. Then look at the acceleration times as compared with the others.

gavriil

Scalbert, although correct the above is, it cannot be used as an example for my main point due to the numerous differences of the above 2 cars. As you said, RWD, etc.



Interesting.

How the hell does one find the TOTAL AREA under a curve? Excel does it but I cant remember the formula.

scalbert

This is incorrect when applied to drag racing, etc. It is true if only a single gear is used, gearing is set to allow the entire rev band to be used or a CVT transmission is used. However, a shift will occur and this will drop to revs some but not down to 1k. It may only drop to about 70% of its red line. This eliminates the use of anything below this 70%+ range. So the only real interest after 1st gear is the last 70% of the rev band.

So if a car make more of its power below where the revs drop to during a shift; much of its total area is removed.

Had you limited your statements to show only the total area where the engine revs will be in then I would agree. But that is not what was stated.

scalbert

My main point was to show how the area under the curve can be deceiving. After 1st gear, which would negate off the line traction issues, the CL-S is not at a deficit as many would assume.

Since we were just dealing with comparisons an absolute value was not needed. So the easiest way would be to take the values in equal steps, say 500 RPM increments, and sum them. The percentage difference would be the close when calculating total area. It is more accurate the more points, smaller increments, are used.

gavriil

I see it now. THanks. You are right, I was wrong. Or at least, not exactly right. That's what makes the difference, the area where the engine will operate AFTER the shift.

In general, what I said was not incorrect, but as you said, I did not limit it to the "after the shift rev band area" point. And that made it incorect.

Bottom line, the total area WHERE THE ENGINE WILL OPERATE DURING THE ACCELERATION RUNS is what matters for all-out acceleration runs, keeping everything else equal. BUT! For that area where the runs happen, torque fluctuations of the 2 different engines dont matter. The TOTAL AREA is what matters.

gavriil

So Scalbert, I also now see why you brought the G35 vs CLS graph as an example. So if the CLS makes more power (total area under curve - by the way there must be a scientific term for that measure), at high rpm, where the acceleration competition takes place, shouldnt it be faster (everything else equal)?

Is it the RWD factor that important in this case to make the difference for the G35? Polar Moment of Interia. So much better for RWD cars...

scalbert

Remember, I did the plots based on a stock G35 and a CL-S6 with H/I so it is biased. However, as most would agree, in a fictional race between these two cars, the modded CL-S6 would pull some at speed but not out of the hole.

typeR

acctually if you care to read what i said was ...

i dont see anything about better and i only see where i said the g was faster....hum....

F23A4

checkout www.nissan.co.jp and click on Skyline.

Aegean_Blue6

Wouldn't this be energy? Power is energy/time, so integrating over time by taking the area under the curve gives you energy.

This actually brings up another interesting point as I'm typing - I was assuming that for the used portion of the band, an equal time would be spent in any given range. However, you actually will end up spending more time in the sections of the curve with less torque. Needs more thought, but it seems like this fact would somehow favor a car with a flatter torque curve vs. a car with equal area under the curve but a peakier torque curve.

gavriil

I dont think so. Because time is irrelevant here. It's RPM what's on the other axis. I think the term is..."work". Does that make sense for those that took physics and still remember?

gavriil

Totally makes sense. Many times I thought of the above and tried to make sense of it. In simple terms, your thought above is correct though. But the difference in acceleration, I am guessing, will be very small. Still though. It is certainly a factor.

gavriil

The other issue that many times has me thinking is how passengers feel torque, IN RELATION to rpm changes. Obviously torque is felt due to intertia reasons but how will that feeling be affected when:

1. A car that makes tons of torque at mid rpm (e.g. WRX)

2. A car that makes more torque at higher rpm (e.g. S2000)

Assuming they both make equal PEAK HP:

I believe the feeling in the WRX is so much more intense because the torque fluctuations are so much more severe than those in the S2000.

But let's take a car that has a completely flat torque curve. But tons of it in absolute terms. Will the feeling be affected more by the absolute value of torque, or will it be more affected by the severity of torque flactuations?

Scalbert?

gavriil

Here is what I found:

Work. The amount of energy transferred to or from a body or system as a result of forces acting upon the body, causing displacement of the body or parts of it. More specifically the work done by a particular force is the product of the displacement of the body and the component of the force in the direction of the displacement. A force acting perpendicular to the body's displacement does no work on the body. A force acting upon a body which undergoes no displacement does no work on that body. Also, it follows that if there's no motion of a body or any part of the body, nothing did work on the body. See: kinetic energy.

scalbert

Turbo cars have a rush of torque which makes it easier to feel. But for the WRX and S2000 analogy, the WRX does make noticeably more torque and torque is what you feel. I would speculate that at the peak torque values the WRX is pulling harder; whereas the S2000 may not pull as hard, but it will pull well for longer.

A car will accelerate it fastest; you feel it the most, at the peak torque.

Generally a car with a flat torque curve doesn't feel as fast as one with a greater peak but not flat at all. The consistent pull of a flat torque curve tends to feel less exciting when actually you are doing very well.

I remember something I read years ago when there weren't forums, just BBS or listserv, for doing this very thing. One of the premier GN tuners of the time mentioned that he made a few changes to the car and it felt slower at the track. But when he picked up his time slip he was two tenths quicker than ever before. When back on the dyno he saw that the peak torque had dropped but the curve was flatter and extended out further.