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      09-06-2007, 12:47 PM   #1
damian
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How long is it going to take me to learn to launch RWD style?

It took a long time to learn how to properly launch a turbo AWD car. Jumping into a 135i, I'm guessing I'm going to just sit there spinning my wheels unitl i get used to the difference. Any tips?
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      09-06-2007, 01:24 PM   #2
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Why do people want to drag race cars that are not designed for this purpose. Buy a Cobra or the new Comaro if you want to drag race. The 135i is more of a track/drivers car. It is not intended to be drag raced.
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      09-06-2007, 01:28 PM   #3
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Guys, please treat your fellow members in a respectful manner. The question damian is asking is on the face of it completely innocuous and a legitimate question.
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      09-06-2007, 01:29 PM   #4
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You still sometimes need to launch a car in every day driving, and sometimes it's fun to just do. Wanting to take off fast without spinning the wheels is a perfectly valid wish. In an AWD turbo, you get bogged down if you're not careful and it's like you're driving a 5000 pound car. With the 135i it's going to be just the opposite with a mountain of torque available right away, and RWD susceptible to wheelspin.
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      09-06-2007, 01:33 PM   #5
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Well as I do agree with Madjack here but I would still want to know how or what RPM's to take off at. That's like saying I'm intrested in a Viper but don't care how fast it gets from 0-60 or do the 1/4 mile.:iono:
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      09-06-2007, 01:35 PM   #6
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Quote:
Originally Posted by dsm9 View Post
That's like saying I'm intrested in a Viper but don't care how fast it gets from 0-60 or do the 1/4 mile.:iono:
Exactly! Many of us plan on driving the car hard from time to time, at all speeds. That's the point. If my only concern was cornering I'd get a miata.
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      09-06-2007, 02:43 PM   #7
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No ones going to be able to tell you how to launch your car properly. Once you get it, you'll get the hang of it after several practice launches. Practice makes perfect, you just need to find the happy medium between launching without bogging down and just sitting there spinning your wheels.
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      09-06-2007, 03:02 PM   #8
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Make sure you turn off the traction control before trying to launch, otherwise the car will apply brakes and retard spark and it will bog down.

Make sure you buy an aftermarket LSD, so at least you will have 2 wheel drive instead of 1.

Practice a few times - dropping the clutch from around 3k revs and adjust revs for best results.

Prepare to buy a new clutch...
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      09-06-2007, 03:27 PM   #9
damian
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Quote:
Originally Posted by grant View Post
Practice a few times - dropping the clutch from around 3k revs and adjust revs for best results.
That seems kinda high when you're getting mega torque at 1.4k revs.
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      09-06-2007, 04:41 PM   #10
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Quote:
Originally Posted by bradford View Post
The question makes it sounds like you are just learning to drive.
No, the question sounds like it's coming from someone that's driven almost exclusively AWD sports cars for almost a decade. I explained exactly why i was asking the question.

You telling me the 14000 threads asking the difference between leather and leatherette are so valid, yet something like this is deserving of your derision? Gimme a break, it's what discussion forums are for.
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      09-06-2007, 04:47 PM   #11
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My answer was coming from someone who has owned two heavily modified Quattro A4s. *shrug*
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      09-06-2007, 04:49 PM   #12
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Quote:
Originally Posted by damian View Post
Eh, in every performance car I've driven, it's much more subtle than that. It can be a somewhat complex dynamic.
Only two ways we can go with this statement:

1) Assume you are correct. If so, as everyone else in this thread as stated numerous times, no one has driven the car and had a chance to report on the "complex dynamics" of the throttle and clutch. Additionally, what you are asking seems more inline with someone asking how to learn to drive a stick. You really cant teach someone how to drive a stick without getting them in the car and feeling it for themselves. Everyone has a different experience and finds different ways to drive a stick. Therefore, it is nearly impossible to get the answer you are looking for.

2) Assume you are incorrect. If so, then launching the car is a "somewhat simple dynamic". Even here, the fact that no one has driven the car means that even this simple task is still unknown. Let's give you the benefit of the doubt and assume that it is a simple process and that we all have driven the car numerous times. Even now, the problem, as discussed in #1, is that driving a stick is something that you can not teach someone in words and is not something that is going to be the same for everyone in the world. With all of these assumptions, we still dont have the "answer" you are looking for.

In my personal experiences, I have never had a problem with any car specifically because of the drivetrain layout. However, judging by your comments, I think it would be safe to say that if you struggled to learn AWD, you would be more likely than not to struggle again learning RWD.

BUT, we dont have the car available to drive yet and discussion like this seem very premature and extraneously silly.
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      09-06-2007, 04:51 PM   #13
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Hmmm - maybe someone with a 335i might be able to offer some launching guidance - same engine.
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      09-06-2007, 04:57 PM   #14
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Why do you hate miatas?!? They are great drag cars....hater! Same responses threads over there.... "If you want power get a different car our car is built for _________ (insert closed minded activity here)



I think this car is going to take a gentle touch to get it going with out lighting up that one tire. It is supposed to have an electronic "LSD" that uses the brakes to prevent wheelspin. No idea how well it will work.

My guess it to skim some of the 335i boards and see how they are doing it.,..

good luck!



Quote:
Originally Posted by damian View Post
Exactly! Many of us plan on driving the car hard from time to time, at all speeds. That's the point. If my only concern was cornering I'd get a miata.
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      09-06-2007, 05:25 PM   #15
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Damian, if you have a buddy with a decently powered RWD car, ask if you can take it for a spin (no pun intended). Obviously, it's not going to show you how to take off in a 135i specifically, but it might indicate how hard/easy of a time you'll have with it when the time comes...

Also, remember that when you're taking off from a stop, there's going to be some rearward weight transfer, and this is a RWD car... so you're not going to be as bad off as you would be in a FWD car with the same hp & torque. Granted, it won't be the *grip and go* of a WRX or STi (I'm a former WRX guy myself), but I don't think that it's going to be advanced trigonometry.

Besides, half of this battle is how you have your car set up, anyway (LSD, TIRES, etc.)
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      09-06-2007, 10:54 PM   #16
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Quote:
Originally Posted by damian View Post
That seems kinda high when you're getting mega torque at 1.4k revs.
The 135i will make very little torque at all at 1.4k when it's not under load (torque curves on turbo motors are very dependent on load, unlike n/a motors which only depend on revs). Turbo motors only build boost when under load - when they're doing work (not when revving motor in neutral).

They actually launch much better with conventional torque converter automatics where you can brake torque (put car in drive and press throttle while holding car still with left foot braking). When launching a turbo with manual gearbox, you need to rev it up pretty high. Even then launches are not very impressive. Launching a turbo works MUCH better from a rolling start...
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      09-06-2007, 11:04 PM   #17
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Quote:
Originally Posted by grant View Post
The 135i will make almost no torque at all at 1.4k when it's not under load (torque curves on turbo motors are totally dependent on load, unlike n/a motors which only depend on revs). Turbo motors only build boost when under load - when they're doing work (not when revving motor in neutral).
Although I do have to say that the torque curve for the n54 engine is very impressive.



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      09-07-2007, 12:04 AM   #18
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Quote:
Originally Posted by grant View Post
The 135i will make very little torque at all at 1.4k when it's not under load (torque curves on turbo motors are very dependent on load, unlike n/a motors which only depend on revs). Turbo motors only build boost when under load - when they're doing work (not when revving motor in neutral).

They actually launch much better with conventional torque converter automatics where you can brake torque (put car in drive and press throttle while holding car still with left foot braking). When launching a turbo with manual gearbox, you need to rev it up pretty high. Even then launches are not very impressive. Launching a turbo works MUCH better from a rolling start...
I do a very harsh thing with my turbo A4 for a better launches. I guess what you said about needing load for turbo engines to build power really explains why it works. I've never really thought through the engine dynamics behind it, and needing to have load to build power.

I heel/toe the gas and brake at the same time while slipping the clutch right before launch. It works like this: I level the gas to get the RPM to around 3500 RPM with the clutch all the way to the floor and the brake firmly applied. Then I start letting out the clutch until the RPM's start to drop to around 2800 RPM while easing on a bit more gas. When I hit about 2800 RPM, I swivel off the brake and floor the gas while letting the clutch all the way out at the same time.

This is all done in one quick motion over about 1-2 seconds. I don't hold the clutch at 2800 RPM for any time at all, I just go straight to launch the moment the engine starts really pushing hard against the brakes.

I'm going to guess that I will burn the tire off if I try that in a RWD turbo 135i, so I'm feeling damian's pain. I know how to launch a turbo engine with AWD, and I know how to launch a torquey NA 6-cyl 535i with RWD. (Just start feeding it gas and then play out the clutch to keep it at a fairly constant launch RPM and let the engine do all the work. No planning ahead is needed, it's all just the feel of the moment.) But I'm not sure how to launch a turbo engine with RWD.

I'm going to have to figure out how to build load before launch and then transfer to acceleration without the harsh clutch release -- and without too much clutch slip. It would be easier if I didn't need to load the turbos to make power before launch. It doesn't sound like higher RPM's is going to be a good substitute for generating load. I don't think just reving up the RPM's is going to get the turbos to full boost.

I'm not sure about asking the 335i guys on the 335i boards. Everything I've read there seems to indicate that manual 335i owners really aren't getting good launches. The Autos seem to be doing much better, like grant said. Especially the 335i's with mods like Shiv's Proceed. They have been putting down fairly poor runs at the strip compared to what you would expect from the power boost of the Proceed. I'm going to guess that part of the problem is a lack of boost/load at launch.
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      09-07-2007, 12:18 AM   #19
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Quote:
Originally Posted by Nixon View Post
I do a very harsh thing with my turbo A4 for a better launches. I guess what you said about needing load for turbo engines to build power really explains why it works. I've never really thought through the engine dynamics behind it, and needing to have load to build power.
If your A4 has a stock flywheel you can just blip the throttle a few times to build some boost. The resistance of the flywheel to motion will make the ECU see some load.

That being said, my best times at the strip in my A4 were by just getting the perfect combination of a tiny bit of clutch slip and the right throttle application tempo.

This was my best ET at 12.8, but not my best 60' time at all...(I'm on the right obviously)

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      09-07-2007, 12:36 AM   #20
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Quote:
Originally Posted by bradford View Post
If your A4 has a stock flywheel you can just blip the throttle a few times to build some boost. The resistance of the flywheel to motion will make the ECU see some load.
Ah ha! That actually adds more pieces to the puzzle. I've got an ECS RA4 lightweight aluminium flywheel. 2.9 kg instead of 11.1 kg. I developed this lauch style soon after I installed it...

So that leads to the question of how heavy will the 135i flywheel be?

I think we'll just have to wait and do some launches before we will know if something special will be needed to build load.
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      09-07-2007, 12:38 AM   #21
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It won't get you a lot of boost though, just a few PSI.

Also - the resistance of a flywheel (which may be a dual mass or not) would not be nearly as much of a load to a 3.0L V6 as it would to a 1.8L 4-banger.

In any event, like has been said in this thread several times, we're all just pissin into the wind until we can actually DRIVE the car.
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      09-07-2007, 03:42 AM   #22
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Try 2500 rpm's, throttle, then feather out the clutch to manage the wheelspin. Here's a great site for finding good shift points. http://www.my330i.com/gears.php

Good luck.
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