Launching the Automatic - Brake Starting
08-22-2007, 05:52 PM
#51
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08-22-2007, 05:56 PM
#52
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I do not know of anybody that "makes" a converter that you can simply buy. Most such things are custom made from a core part. You supply the shop with the converter, and they modify it for you. IPT transmission did mine.
08-22-2007, 06:49 PM
#53
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What did it run you? So if I bought a GM torque converter I could have a transmission shop build it up to a higher stall?
09-05-2007, 12:51 AM
#55
With my automatic Cobalt and its modifications I am often asked how to launch it. So I thought I'd make a sticky about the technique known as Brake Starting. Most drag racing cars use automatics, and this is the technique they use.
The brake start works like this: With your car positioned on the start line, hold your regular brakes (not the parking brake) and place the car in gear. This simple act is called Brake Torqueing. Apply full pressure to your brake pedal.
Now go to Wide Open Throttle (WOT). Your tach will stop increasing at a particular RPM. That RPM is known as Stall Speed. It the fastest your Torque Converter will allow the engine to turn without the wheels turning.
At this point, release the brake pedal. Car takes off.
General notes:
This practice causes your transmission fluid inside the torque converter to absorb all of the torque from your engine turning when the wheels are not. This generates a lot of heat, and will destroy your fluid if you hold the Stall Speed any longer then necessary. Once you achieve stall, you should be releasing the brake within a second. Vehicles that use this technique should install an extra transmission fluid heat exchanger. They are rather cheap.
Brake starting should produce a cleaner initial start then a manual clutch can. The reason is due to the fact that the torque is already at the wheels before you even begin moving. Only your brakes are preventing the wheels from turning. A clutch start sends a jolt of torque through the trans and axles at the launch, which can create huge stresses on parts, causing things like the commonly known broken axle.
Brake Torqueing works on all automatic trans equipped cars, front or rear wheel drive. However, on a rear wheel drive, you probably won't achieve Stall. The rear wheels will more then likely start to turn due to the rear brakes not having enough clamping power to stop the power being delivered by the engine.
Cobalt Specific notes:
The stock stall speed on the 4T45E torque converter installed in the Cobalt is about 2400 RPM. Additionally, the converter is the weakest part of the transmission, designed only to accept about 250 ft/lbs of torque while the trans itself can handle about 320. A typical stage 2 turbo system (when such a thing finally comes around) that doesn't require you to upgrade your drive train in any way will work fine in a stock setup. Anything over 250 ft/lbs however should upgrade the converter to a heavy duty 3000 RPM stall.
The Cobalt has traction control which will interfere with this kind of launch. To overcome that problem, select first gear, or "L" depending on your model year. There is no difference in the transmissions, only the label on the gear selector is different. This will turn off traction control. Also, the Cobalt will shift to second gear during WOT acceleration even though you are only in first. After this shift occurs, slide the selector into second. This won't change anything except to allow the car to shift to third. Just like before, even though your are in second, it will still up shift one gear. It will not shift to third however if only first gear is selected. Once the car is in third, select "D"
The 4T45E has an open differential. Brake starting will probably result in one wheel spinning while the other one stands still. Without an LSD, you will need to practice your starts and vary your brake torqued throttle launch speed to get good launch traction.
The brake start works like this: With your car positioned on the start line, hold your regular brakes (not the parking brake) and place the car in gear. This simple act is called Brake Torqueing. Apply full pressure to your brake pedal.
Now go to Wide Open Throttle (WOT). Your tach will stop increasing at a particular RPM. That RPM is known as Stall Speed. It the fastest your Torque Converter will allow the engine to turn without the wheels turning.
At this point, release the brake pedal. Car takes off.
General notes:
This practice causes your transmission fluid inside the torque converter to absorb all of the torque from your engine turning when the wheels are not. This generates a lot of heat, and will destroy your fluid if you hold the Stall Speed any longer then necessary. Once you achieve stall, you should be releasing the brake within a second. Vehicles that use this technique should install an extra transmission fluid heat exchanger. They are rather cheap.
Brake starting should produce a cleaner initial start then a manual clutch can. The reason is due to the fact that the torque is already at the wheels before you even begin moving. Only your brakes are preventing the wheels from turning. A clutch start sends a jolt of torque through the trans and axles at the launch, which can create huge stresses on parts, causing things like the commonly known broken axle.
Brake Torqueing works on all automatic trans equipped cars, front or rear wheel drive. However, on a rear wheel drive, you probably won't achieve Stall. The rear wheels will more then likely start to turn due to the rear brakes not having enough clamping power to stop the power being delivered by the engine.
Cobalt Specific notes:
The stock stall speed on the 4T45E torque converter installed in the Cobalt is about 2400 RPM. Additionally, the converter is the weakest part of the transmission, designed only to accept about 250 ft/lbs of torque while the trans itself can handle about 320. A typical stage 2 turbo system (when such a thing finally comes around) that doesn't require you to upgrade your drive train in any way will work fine in a stock setup. Anything over 250 ft/lbs however should upgrade the converter to a heavy duty 3000 RPM stall.
The Cobalt has traction control which will interfere with this kind of launch. To overcome that problem, select first gear, or "L" depending on your model year. There is no difference in the transmissions, only the label on the gear selector is different. This will turn off traction control. Also, the Cobalt will shift to second gear during WOT acceleration even though you are only in first. After this shift occurs, slide the selector into second. This won't change anything except to allow the car to shift to third. Just like before, even though your are in second, it will still up shift one gear. It will not shift to third however if only first gear is selected. Once the car is in third, select "D"
The 4T45E has an open differential. Brake starting will probably result in one wheel spinning while the other one stands still. Without an LSD, you will need to practice your starts and vary your brake torqued throttle launch speed to get good launch traction.
09-30-2007, 10:27 AM
#56
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Breaking loose - burning tires
I realize it's a difficult concept to read and understand, but if you just go out and do it once, you'll see how it works. Here, do this:
Go out on some open road. Put your car in normal old ordinary "Drive" and floor it. The car will accelerate in first gear all the way to around 6500 RPM where it will shift automatically to second and continue accelerating. Just like it should.
Now...One more time...Try this...
Put the gear selector in first or low depending on how your selector is labeled. Its the furthest position back you can move the selector.
Floor it. The car will accelerate in first gear all the way to around 6500 RPM where it will shift automatically to second and continue accelerating. EVEN THOUGH THE SELECTOR IS STILL IN FIRST! Then, simply continue accelerating at WOT and slide the selector up to second. NOTHING WILL HAPPEN. The car is already in second and still accelerating. Doing this will allow the trans to now shift to 3rd, EVEN THOUGH THE SELECTOR IS STILL IN SECOND!
The whole purpose of doing this is to turn T/C off for your launch. That's it!
Go out on some open road. Put your car in normal old ordinary "Drive" and floor it. The car will accelerate in first gear all the way to around 6500 RPM where it will shift automatically to second and continue accelerating. Just like it should.
Now...One more time...Try this...
Put the gear selector in first or low depending on how your selector is labeled. Its the furthest position back you can move the selector.
Floor it. The car will accelerate in first gear all the way to around 6500 RPM where it will shift automatically to second and continue accelerating. EVEN THOUGH THE SELECTOR IS STILL IN FIRST! Then, simply continue accelerating at WOT and slide the selector up to second. NOTHING WILL HAPPEN. The car is already in second and still accelerating. Doing this will allow the trans to now shift to 3rd, EVEN THOUGH THE SELECTOR IS STILL IN SECOND!
The whole purpose of doing this is to turn T/C off for your launch. That's it!
02-27-2008, 12:38 AM
#59
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my stock 2.4L will only spin a few times (depending on surface), then take off, It's still faster then a dry start with no power brake. Now when I get tuned,header,exhaust,intake, that may be a differnt story.
03-05-2008, 08:05 PM
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My R compounds dont slide at all 
I kill everyone at launch.
Oh and I also read something about the burnout box, unless you have R-compounds or specific drag tires you dont need to waste time with it, If you have any type of tread, dont waste time with it, I always go around it because treaded tires(especially on weak little cars like we have) dont spin enough to make steam and smoke and the water sits in the treads of the tires until you stop spinning and while waiting at the line drip onto the track surface until you do your run(hitting it and loosing traction).
I kill everyone at launch.Oh and I also read something about the burnout box, unless you have R-compounds or specific drag tires you dont need to waste time with it, If you have any type of tread, dont waste time with it, I always go around it because treaded tires(especially on weak little cars like we have) dont spin enough to make steam and smoke and the water sits in the treads of the tires until you stop spinning and while waiting at the line drip onto the track surface until you do your run(hitting it and loosing traction).
03-06-2008, 12:51 AM
#61
My R compounds dont slide at all I kill everyone at launch.
Oh and I also read something about the burnout box, unless you have R-compounds or specific drag tires you dont need to waste time with it, If you have any type of tread, dont waste time with it, I always go around it because treaded tires(especially on weak little cars like we have) dont spin enough to make steam and smoke and the water sits in the treads of the tires until you stop spinning and while waiting at the line drip onto the track surface until you do your run(hitting it and loosing traction).
I kill everyone at launch.Oh and I also read something about the burnout box, unless you have R-compounds or specific drag tires you dont need to waste time with it, If you have any type of tread, dont waste time with it, I always go around it because treaded tires(especially on weak little cars like we have) dont spin enough to make steam and smoke and the water sits in the treads of the tires until you stop spinning and while waiting at the line drip onto the track surface until you do your run(hitting it and loosing traction).
06-05-2008, 03:43 PM
#62
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Going into the left lane?
I don't know whats going on.... since Ive installed the Jet GM Module, if I attempt a brake torque launch from L-1, both front wheels are spinning through first gear and the car is slithering into the left lane and nearly off the road to the point I have to let off... at that point the car jerks to the right as the tire get traction since I've been steering to the right trying to avoid going off the left side of the road. Obviously going WOT on brake release is NOT the way for a low ET. Anyone had this problem? My build sheet does not show LSD but it sure acts like it.
06-06-2008, 06:14 PM
#63
I'm old school
Thread Starter
First, what is the Jet GM module? That doesn't sound good.
Second, If you are losing traction coming out of the brake torque, then you are starting off with too much accelerator. Back off from WOT a bit a find the spot the gives you traction at brake release. The floating out of your lane thing is completely caused by the traction thing. Get rid of one, fix the other.
Second, If you are losing traction coming out of the brake torque, then you are starting off with too much accelerator. Back off from WOT a bit a find the spot the gives you traction at brake release. The floating out of your lane thing is completely caused by the traction thing. Get rid of one, fix the other.
06-07-2008, 06:28 PM
#64
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Jet GM Module
First, what is the Jet GM module? That doesn't sound good.
Second, If you are losing traction coming out of the brake torque, then you are starting off with too much accelerator. Back off from WOT a bit a find the spot the gives you traction at brake release. The floating out of your lane thing is completely caused by the traction thing. Get rid of one, fix the other.
Second, If you are losing traction coming out of the brake torque, then you are starting off with too much accelerator. Back off from WOT a bit a find the spot the gives you traction at brake release. The floating out of your lane thing is completely caused by the traction thing. Get rid of one, fix the other.
06-07-2008, 08:42 PM
#65
I'm old school
Thread Starter
Okay, thats what I thought. I don't like those signal modifier chips. They usually just resistors that mess with the IAT signal. But anyway, I doubt it has anything to do with your traction issue.
If you are spinning the tires, then the traction control should be off. If the T/C off indicator is on, then the traction control is off. If you are launching using this method in this thread, then the T/C is off.
You need to find the sweet spot in the accelerator that gives you the most torque your tires will hold at brake release. If you lower the tire pressures in the front, you can get more starting traction and hence more torque at the launch.
If you are spinning the tires, then the traction control should be off. If the T/C off indicator is on, then the traction control is off. If you are launching using this method in this thread, then the T/C is off.
You need to find the sweet spot in the accelerator that gives you the most torque your tires will hold at brake release. If you lower the tire pressures in the front, you can get more starting traction and hence more torque at the launch.
06-08-2008, 07:44 PM
#67
I'm old school
Thread Starter
12-20-2008, 01:58 PM
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i thoguht i had it but now im more confused i have a 2.2 auto lets say i was racing i keep it in drive floor thebrake and keep the accelerator from 3500-4500 then just release the brake right? well better yet what rpm should i keepp it on for wen i lift off the brake?
12-20-2008, 02:11 PM
#69
i thoguht i had it but now im more confused i have a 2.2 auto lets say i was racing i keep it in drive floor thebrake and keep the accelerator from 3500-4500 then just release the brake right? well better yet what rpm should i keepp it on for wen i lift off the brake?
12-20-2008, 02:22 PM
#70
i thoguht i had it but now im more confused i have a 2.2 auto lets say i was racing i keep it in drive floor thebrake and keep the accelerator from 3500-4500 then just release the brake right? well better yet what rpm should i keepp it on for wen i lift off the brake?
Don't worry about the RPMs, they are dicated by the design of the torque converter, temperatures, engine torque at given rpms, all factors beyond your control. Just full brake, full gas, release brake. Away you go
12-20-2008, 06:55 PM
#71
I'm old school
Thread Starter
i thoguht i had it but now im more confused i have a 2.2 auto lets say i was racing i keep it in drive floor thebrake and keep the accelerator from 3500-4500 then just release the brake right? well better yet what rpm should i keepp it on for wen i lift off the brake?
As those above have stated, you can not physically get the RPM that high from a stop. The stock stall speed is 2400.
And you don't start in "D". You start in either "L" or "1" depending on how your car is labeled.
12-29-2008, 01:45 PM
#72
If this is what you are doing, then you are doing it wrong.
As those above have stated, you can not physically get the RPM that high from a stop. The stock stall speed is 2400.
And you don't start in "D". You start in either "L" or "1" depending on how your car is labeled.
As those above have stated, you can not physically get the RPM that high from a stop. The stock stall speed is 2400.
And you don't start in "D". You start in either "L" or "1" depending on how your car is labeled.
02-26-2009, 11:31 PM
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02-27-2009, 12:52 PM
#74
I'm old school
Thread Starter
I will recap the first post for you. It says that on the Cobalt specifically (that's important, because it means it doesn't apply to your silly Camaro) the traction control system will interfere with a good launch. So by simply starting in "L" instead of "D", you fix the problem.
Last edited by Halfcent; 02-27-2009 at 07:47 PM.
02-27-2009, 02:04 PM
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It is truely amazing me to come back to my own threads and see how people post without even reading just the very first post in the thread.
I will recap the first post for you. It says that on the Cobalt specifically (that's important, because it means it doesn't apply to your silly Camaro) the traction control system will interfere with a good launch. So by simply starting in "L" instead of "D", you fix the problem.
I will recap the first post for you. It says that on the Cobalt specifically (that's important, because it means it doesn't apply to your silly Camaro) the traction control system will interfere with a good launch. So by simply starting in "L" instead of "D", you fix the problem.
Last edited by Halfcent; 02-27-2009 at 07:47 PM.