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10-17-2008, 02:10 PM | #23 | |
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10-17-2008, 08:38 PM | #24 |
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If you like a fast 0-60 & 0-100 times & can live with not being able to hit the very top speed the M3 is capable of (if you removed your limiter) then DO IT!!!! It is one of the best NA motor mods.
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10-17-2008, 09:37 PM | #25 |
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People are missing the point that you will need to shift at a lower vehicle speed with the shorter ratio. That means, after the shift, the stock car will still be on top of the gear the modified car just shifted from--hence, more torque at the wheels--at the same speed. In other words, you also need to consider where you'll land on the torque at the wheels curves after the shift.
The simplist way to consider all this is to look at power, which, by definition, takes all of this into account. The shorter diff does not give you more power. In a drag race, it does affect the effective power band though by shortening it, but at the cost of shifting more. I doubt that it will make a significant difference except for the start of the race, where the cars are far away from where they'd like to produce power. Meaning, the car with the shorter ratio will get to the power band quicker, and the rest will not matter all that much. But the start of a drag race is traction limited anyway, so I don't know that more torque would make much difference. On the track, it might be a different story, but that would most likely be function of the track layout. And I don't see how shifting more often can help in that case either. I definitely would not want overall reduction in 2nd gear to be higher. I don't see how that would be useful on the track at all. 3rd gear, however, can be shorter IMO.
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10-17-2008, 10:45 PM | #26 | |
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10-17-2008, 10:56 PM | #27 | |
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EDIT: I caught an error in my previous reponse on this one. LSD does not change the width of the effective power band during a straight acceleration run as gear spacing is maintained. What I was really referring to is making the 3rd gear shorter, and hence dropping less rpms during the 2->3 shift, and staying more to the right of the power graph after the shift. The statement above, the first statement of this post is true though, which is the main point.
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10-17-2008, 11:26 PM | #28 |
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I see what you mean. Dainan doesnt have it for DCT yet but I've been talking to some people to do this to mine by the time I get the car back from RdSport. Thanks for the info.
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10-17-2008, 11:49 PM | #29 | |
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Good luck! -Rich |
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10-17-2008, 11:51 PM | #30 | |
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10-18-2008, 06:46 AM | #31 | |
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Gearing is probably the biggest bang for the buck upgrade especially in how it makes the driver feel. Power is torque x rpm / 5250 anyway, more torque multiplication won't hurt. |
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10-18-2008, 06:56 AM | #32 | ||
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On the other side of that incline, there is another incline with a radius which you go up in 3rd, and at the crest you are at about 80 mph. I spent the entire day trying to figure out how much throttle I can possibly use, and if I can go WOT there. Despite my best effort to apply the throttle really gradually, I lost and pulled in the back end once at 70 mph, which is not fun. Clearly, torque is not the limiting factor there either. Would be nice to have more when all is hooked up though on the straights, and that's why I'm saying I would rather have the 3rd gear slightly shorter. And for fuel economy reasons, I don't see why 6th can't be longer (the new LSD decreases total reduction in 6th even further). Who uses that on the track or in a drag race anyway?
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10-18-2008, 08:12 AM | #33 |
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I was just reading that the M-DCT doesn't have an overdrive gear. That sucks for highway cruising although this car was not really built for that.
I did the gear calculations using the stock 18" rear tire size. 4.10 - 33; 54; 73; 94; 113; 131; 158; 4250rpm @ 80mph 3.62 - 37; 61; 83; 106; 129; 149; 179; 3750rpm @ 80mph 3.15 - 43; 70; 95; 122; 148; 171; 205; 3250rpm @ 80mph I think the 3.62 would be a good compromise for most of us as far as cost, daily utility, and performance. Why not get a Z06 or even a Z51 if you really want a car that will kick @ss out of the box in a drag race?
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10-18-2008, 12:05 PM | #34 |
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Is the E46 M3 diff a direct swap for the E9x M3?
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10-18-2008, 04:08 PM | #36 | |
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10-18-2008, 04:10 PM | #37 | |
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I don't have an issue with traction, especially when moving, but if these cars do than what do the people with much larger, torquier RWD cars do? The car will enter its powerband more quickly with these gears, and I think the advantage would be greatest on the racetrack. The shorter spacing may be a chore with the manual, with the DCT it will be faster and a non-issue. |
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10-18-2008, 06:41 PM | #38 | ||
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There is not such thing as "the" powerband for a car. However, as I said earlier, the new LSD will narrow the effective powerband between gears, so there will be a slight benefit from this. There is no such thing as "the" powerband. However, as I said earlier, the new LSD will narrow the effective powerband, which will provide a slight advantage. As I also said earlier, if you can manage traction, it will help you get to that rpm range quicker as well, but that's just from a dead stop, 0 rpms, which doesn't happen more than once on a track. If you read what I wrote earlier, you'll see that we agree on this one.
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10-18-2008, 07:47 PM | #39 | |
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I never said you would have 13% more power, but power is a function of torque. There is such thing as the powerband, to be specific since you seem to not want to use your common sense, the area where the car makes its power (high revs). With shorter gears you get to this area quicker, rather simple. I am WOT as soon as it won't upset the balance of the car, I think you need to attend a performance driving school if you are having issues applying this level of power. I'll be inquiring about the 3.62 shortly, it will blow a car with stock gearing away and the car will feel livelier and torquier, best bang for the buck upgrade. |
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10-18-2008, 08:34 PM | #40 | ||||
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What I am saying is 13% change in final drive will not result in 13% average acceleration during the 1/4 mile, as calculated by trap speed/1/4 time (delta velocity/delta time). If what you are saying about "always 13% more torque at the wheels" was true, it would have to lead to 13% higher average acceleration, but it won't. I told you why, but you are avoiding the issue. I agree the car will feel liverlier during regular driving though. In that case, one is operating the engine in a limited vehicle speed range, and what happens after you shift is not a major consideration.
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10-18-2008, 09:07 PM | #41 | ||
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Yes, it would be great if someone knew...bump. Quote:
Thanks for clarifying that. I agree, the 3.62 seems like the best of both worlds.
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10-19-2008, 01:23 AM | #42 |
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Hmmm...
You are not gaining any more power with gearing, you are simply 'moving' the RPM band to the left (referring to a dyno graph). So, in a drag race moving to a 4.10 should will improve your 60' but reduce your trap speed. On a road course, you will be able to accelerate 'quicker' out of slow/throwaway turns but ultimately 'slower' in an extended straight. Of course, this depends on the track...i.e. short gearing should help in shorter technical courses between and hurt in longer high-speed courses. Again, to each their own. I still think there are better ways to spend $3k to reduce lap/track times...i.e. reducing rotational unsprung weight and increasing overall grip. -Rich |
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10-19-2008, 08:45 AM | #43 |
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OK guys, I took the time to plot wheel torque vs vehicle speed as some folks really do think that switching final drives ALWAYS gives you more torque at the wheels, which is not true, and which has been my minor contribution to this discussion. I don't know how else to illustrate that fact apart from plotting the numbers.
Your car simply will NOT accelerate faster on a, say, 0-200 km/h run by 6.5% simply because your final drive has been changed by 6.5%, and this graph illustrates why. As can be clearly seen in the graph, you are NOT always putting down 6.5% more torque at the wheels during the run. After the shifts, the modified car actually has significantly LESS torque at the wheels for a vehicle speed range (see blue line about 30% higher than the red line after the 2->3 shift). The net result is that you will end up accelerating somewhat faster, but not by 6.5%, so it won't be what some people think. The difference is especially pronounced in the 1st gear since both cars need to go through the entire rpm range during that interval. There are also some finer points such as when the race ends. If it were the end at 170 km/h, the stock car would have an advantage for instance since it can still stay in 3rd gear whereas the modified car needs to shift into 4th and lose its torque multiplication advantage. This is all aside from the point that on a track, 2nd gear is used coming out of turns (never mind the fact that 1st gear is used once), and there are traction limitations which bring up the issue of how much of that torque you can actually put down without completely losing the back end. Sticky thinks I should take yet another performance driving class. I should perhaps relay that suggestion to Will Turner whose E90 M3 also seemed to be traction limited turning in second gear going up the hill I had issues with so that he can benefit from Sticky's advice as well (never mind the fact that his car had track rubber). EDIT: The 4.01 on graph title and legend are typos. The calculations used the 4.10 ratio. I will fix that text and upload the new graph.
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Last edited by lucid; 10-19-2008 at 11:34 AM.. |
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