12-12-2010, 02:56 AM | #23 |
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I also can answer the second question about an additional gear. Using the gearing from the 135i DCT and it's FD does not appear to add as much to the performance as just the shift time reduction. Of course this assumes that these gear ratios were fully optimized. Since the 135i and 1M have the same redline, and probably will have similar shaped torque curves, it is fairly safe to assume that a gear set optimized for one would also be very close to optimal for the other. Basic reasoning and experience also informs us that higher redline vehicles will typically benefit more from the extra gear compared to lower redline ones (i.e. M3 "needs" 7 gears more than the 1M).
#1 is 6MT #2 is with 7 DCT and FD from 135i #3 is with hypothetical 6 speed DCT Keeping the turbos spooled is indeed an important effect. I'm not entirely sure if CarTest fully captures this effect fully. My guess is that is probably does. The "switch" in the software GUI for NA vs. turbo unfortunately appears to do nothing whatsoever. That being said CarTest does use a fully transient simulation and does obviously drop the rpm at shifts and then uses the new engine operating point for calculations just after the shift. Since the input dyno curves are always gathered under WOT and under load (i.e. no matter what boost is doing you'll never get more torque than the dyno curve) the torque available after a shift should be calculated assuming a best case scenario. With that understanding it might be the case that the negative effects of long MT shifts would not be captured in the simulation. However, for the short DCT shifts I think the sim should be matching the engine both before and after shifts pretty accurately. Also you can clearly watch the virtual tach in the sim dropping to a higher post shift rpm in the 7 speed DCT compared to the 6MT, so that effect is again absolutely included. Whether the sim captures the effect we know that in the real world, in the twisties and while driving at 8-9 10ths, this benefit of the DCT would be easily felt, noticed and could be measured. Maybe someone else can comment about the ability of a single gear dyno curve to capture the transient nature of a turbo engines output (power or torque) just before vs. just after a shift. On a very loosely related side note these sims provide my estimate for the top speed of a delimited 1M, it will be between 165-170. DCT or not the car is definitely drag limited in top gear.
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12-12-2010, 03:10 AM | #24 | |||
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Now about your simulations. Garbage in, garbage out. What gearing are you using for the 1M that has you at 215 mph in 6th? Your gearing looks off across the board. The power curves for the 1M and M3 also don't look accurate... What power and weight are you using for the cars? I listed the power and weights I used in my initial post. Quote:
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Clearly a full simulation is the way to go running these numbers. If it's not set up right, however, it's pretty worthless. You've also given the M3 a lot more area under the power curve than the dynos show. What peak torque was that run at? Way too high. You come off as defending the M3's honor. I'm simply trying to run some valid comparisons between the two. As I said, based on the dyno data to date the 35is motors look 15hp under-rated, so I used 350 hp, a fairly accurate torque curve based on the 1M and M3 and the published weights we have. Maybe try plugging that into the sim with the corrected gearing, both cars running manuals, get the torque right and let's see what it looks like. I have no doubt that the M3 is faster up top, but I think you'll be surprised how close it is.
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12-12-2010, 03:20 AM | #25 |
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Swamp, thanks for your efforts. I am surprised that the differences between MT and DCT are not a little more pronounced.
I was fairly disappointed a few months ago to hear the DCT option had been nixed for the 1M. Although your calculations suggest marginal improvement with DCT, I still wonder if one's subjective impression of N54 power delivery would not be substantially better with a dual clutch setup given the seamless shifts affording fairly constant boost levels. The N54 with the 6MT sometimes produces very noticeable 3rd-4th bog as you wait for boost to spool. Perhaps I am missing the optimal shift point, but it would be nice to avoid it altogether. I haven't had the opportunity to drive a 335is with DCT, and that would probably provide the closest approximation of what a DCT 1M would have been like. |
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12-12-2010, 03:59 AM | #26 | |||
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My power and weight figures are accurate, guaranteed. I used quoted figures for the 1M and I already covered the case of possible underrating which very well might be the case. If you really want a list of inputs I can provide that. Although power and weight are keys, there are literally dozens of inputs to these sims including some pretty small and subtle effects. Anyway I did not post "power curves". These are thrust curves and take into account much more than just the torque curves and gearing. Losses are the key thing you are missing. CarTest includes rpm and speed dependent losses for: transmission, axles, diff, tires and aero losses. Tire losses are very significant above about 75 mph. I agree a per weight way of looking at calculations is important. If you want a thrust per weight just look at the acceleration curves, that is essentially what those are and I posted them (the very last set of results). Quote:
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12-12-2010, 04:06 AM | #27 | |||
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Would be pretty similar. You haven't driven mine yet either. You definitely need to!
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12-12-2010, 04:32 AM | #28 |
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12-12-2010, 04:50 AM | #29 | |
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The issue I'm having beyond the speed in gears is that your "force at wheels" graphs show the 1M making 3500 lbs of force in 1st, while the M3 is 3800. From this and speed you can back out relative torque assuming similar losses- if the M3 is putting out the published 295 at the crank the 1M is putting out ~330. Meanwhile the 1M is rated at 370, and is dynos show that as quite under-rated. Yes, I think posting the numbers you're using would be a good idea to clear up the confusion.
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12-12-2010, 05:16 AM | #30 |
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Let me explain how force at the wheels is calculated, so you understand where I'm coming from.
Engine Torque (ft lbs) x Gear Ratio x Final Drive Ratio / Tire Radius (ft) * Drivetrain Efficiency For the 1M: 370 (ft lbs) x 4.11 (1st gear ratio) x 3.154 (Final Drive) / 1.06 ft x 85% = 3846 lbs For the M3 DCT: 295 (ft lbs) x 4.78 (DCT 1st gear) x 3.154 (Final Drive) / 1.06 x 85% = 3566 lbs So unless one of the numbers above is wrong or the losses for the two cars are much different, the 1M should have 8% more "Force At Wheels" in 1st gear. Your graphs show 9% less, or an 18% difference. Hence my questions.
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12-12-2010, 04:38 PM | #31 | |
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Note: My numbers do use a theoretical calculation of the tire diameter based on the nominal series values. You can get a slightly more accurate figure from the manufacturer based on rotations per mile figures. These are exact and always differ from the nominal calculated values just a bit.
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12-12-2010, 05:06 PM | #32 | |
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Why? Because one needs to examine power delivery over time, not at an instant. These are peak/instantaneous values matter much less than the observation that the average acceleration values at the same time and across time are higher in the M3. Also note that having so much torque to the wheels often simply overwhelms the available grip (in 1st gear) and thus you have wheelspin. The metric that with a single number best captures the dynamics of acceleration across a given time and through multiple gears is power, to be more specific indeed power to the grounds per weight. Assuming losses are pretty roughly constant across different models and that gear ratios are pretty well optimized by the factory we can simpy short cut that longer statement to: Power to weight is the key metric in determining a cars performance. Another way to help realize this is simply that F=Pxv. Given two cars each at the same velocity the one producing more power (at that velocity, i.e. using the best (lowest) gear and highest rpm) will produce the most accelerative force. When you look at it this way gearing and torque disappear from the equations! Again another way to look at this is that the M3 on WOT operates typically from 7000-8400 rpm (not counting the very begining of a launch) and thus is producing a minimum of ~350 hp (7/8.4 x 414). The 1M never even produces that much! Well if under rated, its peak might be just about that much. Again the power of high redline and broad torque curve is infinitely more important than peak engine or wheel torque. Hope this all helps.
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12-12-2010, 05:08 PM | #33 | |
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Speed at RPM can be calculated by using: RPM x 60 / gear ratio / final drive / Tire revolutions per mile) = MPH So for the 1M in 6th gear: 7000 rpm x 60 / .846 / 3.154 / 790 = 199.2 mph For the M3 DCT in 7th: 8400 rpm x 60 / 1.00 / 3.154 / 790 = 202.3 mph Tire revolutions per mile can be found on the tire rack for the specific tire used, but in this case they are the same, so we can agree they will grow by the same amount. Thus the 1M is geared 3 mph shorter than the M3, but your "guaranteed" numbers show it as about 6 MPH taller. Please explain why?
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12-12-2010, 05:26 PM | #34 | |
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Your graphs show 3500 for the 1M and 3800 for the M3, but we calculate 3846 for the 1M and 3566 for the M3. This is why I've asked that you post the numbers you are using.
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12-12-2010, 10:03 PM | #35 | |
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12-13-2010, 01:44 AM | #36 | |
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12-13-2010, 02:07 AM | #37 | |
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If M team did not address the power drop off it's fair to assume something has gone awry at BMW and I'd sell sell sell and go straight to a P-car.
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12-13-2010, 02:57 AM | #38 |
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Great thread Thanks to everyone who provided information (especially Swamp and Pete).
Besides the "height-issue" in the "Drive Power in Gears" diagrams (as Pete mentioned in Post #36), the 1M's drive power seems to fall too fast ... To me it looks like the simulation doesn't take into account that the torque curve is almost flat at 450Nm between 1500 and 4500 rpm. |
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12-13-2010, 03:28 AM | #39 | |
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I was using the non overboosted torque figure whereas you used the overboosted. Neither is entirely correct since the car can't maintain this peak across a full acceleration run. However, if you do only want peak values your numbers were closer here. This does put the peak accelerative force of the 1M > than that of the M3 (and hence the force/weight at an even larger advantage). However, your numbers are not entirely correct either though as you can not calculate using the same loss figure for both most parasitic losses are a function of rpm. The M3 will take a bigger torque loss hit at its peak torque since it is at a higher % of redline. The torque loss in the M3 in absolute terms at their respective peak accelerations will be about double that of the 1M! This alters the initial acceleration vs. time curves I showed simply by slightly amplifying the advantage already shown for the 1M in my initial graphs. It also makes me revise my statement about how long the 1M could get the jump on the M3. It could do so for a bit longer, but only up to about the 4-5 second range or at about the 60 mph point. To determine this you need the position vs. time graphs, you absolutely can't see this from the times from 0-speedx results, since the M3 is still winning those contests. Seems a bit contradictory but it isn't. Also it will only be truly pulling harder for about the first 1.5 seconds after launch. You need the true acceleration curves (a vs. t) to see this (which I have posted). You CANNOT read nor determine this from a wheel torque per weight vs rpm graph. After this 4-5 second range the story is exactly the same as I posted prior, the M3 will walk it. Again of course that conclusion is based on the car having a real power output consistent with the claimed output. Any under rating (which is likely IMO) will allow the 1M to keep up a bit longer. Due to the really strong torque of the car, if you can launch it well, it will do a very good job getting the jump on a lot of cars. Despite some minor adjustments here and there my prior comments about the curves you posted misrepresenting the true real world advantage of the 1M still stand. Power to weight is all that really matters (again except a bit for low speed stop light races). I've also posted another comparison of the M3 vs. 1M again assuming 370 ft lb all the time for the 1M.
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12-13-2010, 03:56 AM | #40 |
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@Robert and Madozu. Here is the torque curve I used assuming 369 ft lb (the graph kind of sucks and it would be visually easier to read in Excel but this is how CarTest belches stuff out...).
Ultimately the shape of the curve is not too vital to getting a good simulation. And obviously the sharpness of the peak here in my curve is entirely non physical. Also, if you assume 332 ft lb peak instead of 369 ft lb you do get a more flat torque plateau. The higher peak torque though will have to drop faster less the peak hp number could not be the same... Either way Pete's curve probably is a more accurate guess. I did not waste any time at all bothering with making a really accurate prediction of this since it makes such littler difference. Get the peaks for torque and hp correct and get the rpms at which the peaks occur and you are pretty good to go.
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12-13-2010, 04:30 AM | #41 |
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I knew the M3 hits almost 110 in 3rd. Pretty crazy.
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12-13-2010, 04:48 AM | #42 | |
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I have gone ahead and picked up a copy of cartest, available here for those interested: http://www.cartestsoftware.com/index.php I'm not a big fan so far, as I'm used to Bosch lapsim (free and very good). This is easier to use, however, and has many cars pre-loaded. Be careful using them, though- a number of them are wrong. I set up an apples to apples comparison in the software using the specs I first published on this thread. I have copied the specs below so eveyone knows what I'm doing and can spot any mistakes. I've used the published specs for everything, expect as noted before I added +15 hp an TQ to the 1M to account for the WHP dynos of the 35is cars we have seen so far. All of the performance variables, shift times, etc are the same. The results are below. Now I will quote my earlier post: "The 1M is clearly going to kick hard when the boost hits, pulling harder than the M3 until about 35 mph when the torque rolls off and the M3 keeps pulling. The 1M is again slightly ahead up until about 60 mph in 2nd. In the higher gears, however, the M3 spends more and more time in front, and it's always in front above about 115 mph due to the higher top end power." I am more than happy to answer any questions about how I set this simulation up.
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12-13-2010, 08:41 AM | #43 | |
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12-13-2010, 09:02 AM | #44 | |
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There are a number of dynos floating around to model from, such as these for the 320 hp 35is. Obviously the 1M is going to breath better up top than this, so I may have been conservative killing power about 6000 as fast as I did in my estimated dyno. http://www.bmwblog.com/2010/09/12/dy...vs-n55-engine/ BTW, I think your weight number above is off.
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