Login


10252007, 09:10 PM  #45  
Lieutenant
15
Rep 488
Posts 
Quote:


Appreciate
0

10252007, 09:13 PM  #46  
Captain
45
Rep 706
Posts 
Quote:


Appreciate
0

10252007, 09:16 PM  #47  
Major General
177
Rep 8,034
Posts 
Quote:
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 curvethe specifics of how torque is delivered over the rev bandwhich will surely affect average acceleration times. 

Appreciate
0

10252007, 09:17 PM  #48 
Major General
177
Rep 8,034
Posts 
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%.

Appreciate
0

10252007, 09:20 PM  #49 
Captain
45
Rep 706
Posts 
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.

Appreciate
0

10252007, 09:21 PM  #50  
Lieutenant
15
Rep 488
Posts 
Quote:


Appreciate
0

10252007, 09:25 PM  #51 
Major General
177
Rep 8,034
Posts 
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.)

Appreciate
0

10252007, 09:27 PM  #52 
Major General
177
Rep 8,034
Posts 
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.

Appreciate
0

10252007, 09:28 PM  #53 
Lieutenant
15
Rep 488
Posts 
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.

Appreciate
0

10252007, 09:30 PM  #54 
Captain
45
Rep 706
Posts 

Appreciate
0

10252007, 09:30 PM  #55 
Lieutenant
15
Rep 488
Posts 
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.

Appreciate
0

10252007, 09:31 PM  #56 
Lieutenant
15
Rep 488
Posts 
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%.

Appreciate
0

10252007, 09:34 PM  #57 
Major General
177
Rep 8,034
Posts 
If I recall correctly, the C&D acceleration times for the M3 were rather preliminarywhatever 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.

Appreciate
0

10252007, 09:36 PM  #58 
Captain
45
Rep 706
Posts 
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.

Appreciate
0

10252007, 09:39 PM  #59  
Captain
45
Rep 706
Posts 
Quote:


Appreciate
0

10252007, 09:41 PM  #60 
Major General
177
Rep 8,034
Posts 
Well I guess that's an instrumentation issue. In the end, force is force. Manufacturers have access to high precision wellcalibrated dynos, and have that data, but we don't see them...

Appreciate
0

10252007, 09:42 PM  #61 
Lieutenant
15
Rep 488
Posts 
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!

Appreciate
0

10252007, 09:51 PM  #62 
Captain
45
Rep 706
Posts 

Appreciate
0

10252007, 09:51 PM  #63 
New Member
0
Rep 7
Posts 
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] 
Appreciate
0

10252007, 09:54 PM  #64 
Lieutenant
15
Rep 488
Posts 

Appreciate
0

10252007, 09:57 PM  #65  
Lieutenant General
358
Rep 10,367
Posts 
Easy
Quote:
Quote:
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? ISF 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 ISF 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 ISF. I even looked at the ISF 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 ISF number at around 2.2k rpm for the numbers quoted just above). Furthermore even though the ISF 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 ISF 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 ISF 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 ISF in actual accelerating force in all gears. For example peak force in 1st is about 3500lb vs. 2700 for the ISF. In third gear the M3 almost never falls below 1000 lb whereas the ISF 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. 

Appreciate
0

10252007, 10:04 PM  #66 
Lieutenant
15
Rep 488
Posts 
*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.

Appreciate
0

Post Reply 
Bookmarks 
Thread Tools  Search this Thread 

