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      10-25-2007, 08:10 PM   #45
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Quote:
Originally Posted by gbb357 View Post
Thank you for pointing that out. You got cars out there that makes tons of horsepower but cannot put it on the ground. BMW is one of the best out there in terms of putting it on the ground. The big advantage that Lexus has is it's torque figure. But to be honest, i think BMW's higher and faster rpm should equalized that, and that's probably why the numbers are so close between the IS-F and M3 when Car and Driver tested them.
You would think that the high rpm would equalize that, but in fact, it doesn't! The fact that the Lexus has more hp means that it has more torque at higher rpms. While the Lexus can't rev up to 8400 rpms like the M3, the Lexus has tons more torque up to its redline of 6700 or whatever it is and will be pulling the m3 HARD until it has to shift at 6700 rpms.
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      10-25-2007, 08:13 PM   #46
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Quote:
Originally Posted by Swamp2
The reasons/methods I have used to determine the car is under rated are scaling on power to weight. Power to weight ratio is one of the best indicators of acceleration performance (F=ma, more or less). The M3 has a substatntially better power to weight ratio and especially considering the additional power losses from an automatic transmission (meaning power delivered to the ground divided by weight, which is what really matters). The M3 has been dyno-ed at 373 rwhp(link). So we have:
  • M3 lb/rwhp = 3648lb/373 rwhp = 9.8 lb/rwhp
  • IS-F lb/rwhp = 3725lb/333 rwhp = 11.2 lb/rwhp
If the M3 has been dyno-ed at 373rwhp, then that does not equate to 414hp on crank. That equates to 466hp. Now that's under rated!
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      10-25-2007, 08:16 PM   #47
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Originally Posted by ChitownM3 View Post
the Lexus has tons more torque up to its redline of 6700 or whatever it is and will be pulling the m3 HARD until it has to shift at 6700 rpms.
Yes, but what happens after it shifts? The M3 will keep on accelerating at the lower gear whereas the Lexus will work to get on top of the next gear...

Torque delivered at higher rpm will be reflected in the max power rating of an engine. So, all you need to do is to compare the max power ratings in that regard as opposed to doing separate comparisons on max torque and redline. What do you know? They (reported max power at crank) are about the same.

However, yes, that doesn't say anything about the shape of the torque curve--the specifics of how torque is delivered over the rev band--which will surely affect average acceleration times.
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      10-25-2007, 08:17 PM   #48
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Originally Posted by gbb357 View Post
If the M3 has been dyno-ed at 373rwhp, then that does not equate to 414hp on crank. That equates to 466hp. Now that's under rated!
The M3 engine is most likely slightly underrated, but where did you get the 20% loss exactly? For a BMW, that should be more like 12%-15%.
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      10-25-2007, 08:20 PM   #49
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Originally Posted by lucid View Post
The M3 engine is most likely slightly underrated, but where did you get the 20% loss exactly? For a BMW, that should be more like 12%-15%.
That's not quite exact science, it's just a base equation or number that most people go by. It is usually around 15%-20%. The only real stat is when you actually dyno the car.
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      10-25-2007, 08:21 PM   #50
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Originally Posted by lucid View Post
Torque delivered at higher rpm will be reflected in the max power rating of an engine. So, all you need to do is to compare the max power ratings in that regard as opposed to doing seperate comparisons on max torque and redline. What do you know? They (reported max power at crank) are about the same.
Right, which is what I was trying to say, that the higher redline is meaningless cause thats what HP measures, and the Lexus has more hp.
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      10-25-2007, 08:25 PM   #51
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Originally Posted by ChitownM3 View Post
Right, which is what I was trying to say, that the higher redline is meaningless cause thats what HP measures, and the Lexus has more hp.
Well, M3 has 414 hp and Lexus has 416hp at crank (reported), right? So the higher redline of the M3 cancels out the torque advantage of the Lexus, and they come out even with regard to max power output (assuming these figures are accurate, which they probably aren't.)
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      10-25-2007, 08:27 PM   #52
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Originally Posted by gbb357 View Post
That's not quite exact science, it's just a base equation or number that most people go by. It is usually around 15%-20%. The only real stat is when you actually dyno the car.
True. One would have to dyno the engine AND the wheels to come up with an accurate loss figure. But my understanding is that BMW is especially good with minimizing losses.
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      10-25-2007, 08:28 PM   #53
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Originally Posted by lucid View Post
Well, M3 has 414 hp and Lexus has 416hp at crank (reported), right? So the higher redline of the M3 cancels out the torque advantage of the Lexus, and they come out even with regard to max power output.
True, so I guess it has to do with the torque curve. To me it seems like the Lexus has more torque available at lower rpms which cancels out the fact that it weighs a bit more. I can see the m3 running 12.7 at a drag strip by car and driver here in America, so in otherwords both cars will probably be very close in straight line performance.
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      10-25-2007, 08:30 PM   #54
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Originally Posted by lucid View Post
True. One would have to dyno the engine AND the wheels to come up with an accurate loss figure. But my understanding is that BMW is especially good with minimizing losses.
That might be very well true with BMW, but apparently not with Lexus.
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      10-25-2007, 08:30 PM   #55
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Originally Posted by lucid View Post
True. One would have to dyno the engine AND the wheels to come up with an accurate loss figure. But my understanding is that BMW is especially good with minimizing losses.
Even that isn't accurate. I've seen so many differences in dynos it just doesn't make sense. One dynojet at one shop will dyno 10 or so more hp than another on the same day. Dynos are only good in evaluating how effective a mod is.
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      10-25-2007, 08:31 PM   #56
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Originally Posted by gbb357 View Post
That might be very well true with BMW, but apparently not with Lexus.
Well we are talking about an automatic here. I'm just getting into the import scene, I've been an american car enthusiast for a few years now and it is general concensus that an automatic loses about 18% and a manual about 15%.
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      10-25-2007, 08:34 PM   #57
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Quote:
Originally Posted by ChitownM3 View Post
in otherwords both cars will probably be very close in straight line performance.
If I recall correctly, the C&D acceleration times for the M3 were rather preliminary--whatever they could pull off in Spain. They mentioned something about expecting better performance numbers when they do their full test in the US, which would put the two cars pretty close indeed (on a straight line). I didn't expect that.
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      10-25-2007, 08:36 PM   #58
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I think your right lucid. I remember reading somewhere about the 335i dyno test close to 300, maybe 290. Now in comparison to the IS350's dyno test that where around 266 to 275. Basically the 335i's engine where only losing around 15% or less.
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      10-25-2007, 08:39 PM   #59
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Originally Posted by lucid View Post
If I recall correctly, the C&D acceleration times for the M3 were rather preliminary--whatever they could pull off in Spain. They mentioned something about expecting better performance numbers when they do their full test in the US, which would put the two cars pretty close indeed (on a straight line). I didn't expect that.
I'm almost sure when they test these two together in a comparison test next time, it will be a lot closer if not the BMW getting the better results. I'm saying this for the fact that BMW has the better transmission, whether it'll be the SMG or conventional manual.
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      10-25-2007, 08:41 PM   #60
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Originally Posted by ChitownM3 View Post
Even that isn't accurate. I've seen so many differences in dynos it just doesn't make sense. One dynojet at one shop will dyno 10 or so more hp than another on the same day. Dynos are only good in evaluating how effective a mod is.
Well I guess that's an instrumentation issue. In the end, force is force. Manufacturers have access to high precision well-calibrated dynos, and have that data, but we don't see them...
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      10-25-2007, 08:42 PM   #61
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Originally Posted by lucid View Post
Well I guess that's an instrumentation issue. In the end, force is force. Manufacturers have access to high precision well-calibrated dynos, and have that data, but we don't see them...
Yup, its a shame that GM is currenlty the only company using SAE certified numbers. At least you know what ur getting when you buy a GM, like 505 hp in the z06!
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      10-25-2007, 08:51 PM   #62
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Originally Posted by ChitownM3 View Post
Yup, its a shame that GM is currenlty the only company using SAE certified numbers. At least you know what ur getting when you buy a GM, like 505 hp in the z06!
I hear ya bro. Now can we see a pic of your SS Camaro?
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      10-25-2007, 08:51 PM   #63
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  • 416hp (a shade more than the M3)
  • 371 ft lb torque (excellent)
  • Redline 6800 rpm (not so hot...)
  • Estimated curb weight 3800 lb (not so good)

    Does this weight include driver's and luggage's weight??
  • lb/hp IS-F: 9.1
  • lb/hp E92 M3: 8.8 (1655 kg, 414 hp)

    E92 M3'S weight include driver's and luggage's weight.
  • 0-60mph: 4.2s (4.4 from C&D test, admitted some traction problems)
  • 0-100mph: 9.8s (est. CarTest E92 M3 10.6s - anyone have an actual test number?)
  • 0-150mph: 24.7s (est. CarTest E92 M3 26.6s - anyone have an actual test number?)
  • 1/4 mi: 12.7s @ 114
  • Braking 70mph - 0: 159 ft
  • Skidpad (300ft): .92g (E92 M3 .94g)

I am suprised by how good the straight line performance is lugging around 3800 lb with only 416 hp and a 6800 rpm redline. The torque is fat though!

Other details:[list]


Original article here.

OK I know most folks think the car is hideous. Let's try to focus the replies on how much of a threat you think this car will be to the M3 strip/track/street. I think I may have to begin "back pedaling" a bit as I thought there would be no way they would get this car as fast as them seem to.[/quote]
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      10-25-2007, 08:54 PM   #64
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Originally Posted by gbb357 View Post
I hear ya bro. Now can we see a pic of your SS Camaro?


Only difference is now I have c5 chrome z06 wheels on it, car will be for sale next year once I get the m3. Car was a blast back in highschool, fastest thing on the road.
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      10-25-2007, 08:57 PM   #65
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Easy

Quote:
Originally Posted by ChitownM3 View Post
Swamp, ur little program is flawed. Anybody who does a lot of drag racing, or straightline performance knows that Max numbers mean absolutely NOTHING. You must take into consideration the whole torque curve. Plotting max numbers into your little calculator does nothing. What if the lexus makes that much torque throughout the rpm band? The car most likely is not underrated. If you look at the torque graph, the car makes a lot of power starting at 2k rpms, something the new m3 does not do.
Quote:
Originally Posted by ChitownM3 View Post
Oh, and by the way, you keep talking about power to the ground, and then refering to horsepower. Horsepower does not equate power to the ground, it is an easy calculation that allows simple minds to understand torque at higher rpms. You can figure out real power to the ground by looking at the torque numbers and gear ratio, something I don't feel like doing right now.
Easy there champ, you have no idea what you are talking about.

This is not my "little program" I have simply validated it and appreciate its breadth and depth. Have you ever even see it or used it (I know the answer to that so stop embarrasing yourself). This program constructs a full splined hp and tq curve from the given inputs. If you don't like the constructed curves, which ususally work out fine and accurately, you can over ride the entire curve with one of your construction based on a crank dyno curve or manufacturers data.

I have written a spreadsheet myself as well as a numerical integrator that does a small fraction of the things that CarTest does with some much simplified parasitic loss models. So I can go from a cars specs and full torque curve to acceleration through the full calculation. I suppose you can do this as well since you know all of the subtleties? Once I got tired of "playing" with my spreadsheets I stepped up to the plate and started using a real tool like CarTest. You do know the OEMs use such tools as well, right?

IS-F vs. M3 torqe at low rpms: Well you really "screwed the pooch" on this one as well. It makes me wonder if you have actually looked at M3s torque curve. You might try getting your basic terminology straight as well "look at the torque graph" to see the car "makes a lot of power"? Ugh.

The M3 develops 85% of its peak torque at 2k rpm, whereas the IS-F only about 73%, sure the Lexus has a lot more peak torque but in the end those numbers only come out about 25 ft lb in favor of the IS-F. I even looked at the IS-F numbers very liberally here to make sure the strong drop off at 2k (probably just a dyno effect and not reality) does not affect these calculations (I basically used the IS-F number at around 2.2k rpm for the numbers quoted just above). Furthermore even though the IS-F does have a lot more peak torque, its torque curve is quite a bit more peaky than the M3. So the advantage is really only really strong at a fairly small rpm range. See attached results based on the torque dyno curve in this thread, converted to crank torque.

The ratio of delivered hp to the ground to weight (or the inverse) is still one of the most important scaling parameters for acceleration. Torque to the wheels divided by weight is just about as important. Using the hp metric instead of torque just gives a bit more bias to being able to rev high where hp gets high. I'm sure I do not need to explain the benefits of a high reving design...

Which brings me back to CarTest. Have a look as the second attached image. Don't worry that the scales look different, I simply could not get the somewhat arbitrary factor of 10 in the scale and data removed in one plot. You will also have to try to ignore the what appears to be a HUGE total power loss for the IS-F this is simply becuase CarTest scales the x axis at the theoretical in vacuo top speed, which in 8th gear is darn fast in the IS-F and air drag losses start to get gigantic at 400 mph! Just on the aesthetics and ease of use side the software could use a few improvements here (just making it more like MS Excel). Notice that you get actual thrust in lb, at the wheel, across the full speed range is every gear. This takes into account the full torque curve, a myriad of drive train losses and all gearing factors (+ more). Notice the severe whooping the M3 gives the IS-F in actual accelerating force in all gears. For example peak force in 1st is about 3500lb vs. 2700 for the IS-F. In third gear the M3 almost never falls below 1000 lb whereas the IS-F barely gets above 1000. Combine this with the weight advantage of the M3 and you may, if you try real hard, start to see my point.

Your self described laziness to really dive into these numbers is your downfall here.
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      10-25-2007, 09:04 PM   #66
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*EDIT* OK, I see your point, curious, though. I'm guessing you put in the drive ratios and all, but how is it possible for the M3 to have more thrust through the gears and still shift at a higher mph??? I know about the higher rpms, but it shouldn't have that large of an advantage with power to the ground.
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