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Old 06-18-2004, 09:01 PM   #16
Ki2AY
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i have a clue onto what you are trying to explain.. but its still not clear to me (not the fact that you didnt explain it well, its the fact that i dont know much about manual cars, actually anycar being the clueless guy i am).. i really appreciate ur informartion.. atleast i know now that it has more to do with the engine rather than just the breaks haha

anyways well done pal!
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Old 06-18-2004, 09:08 PM   #17
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cinqyg

You did well, Thanks for all the info guys. Now I know about the 1500.

John
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Old 06-18-2004, 09:52 PM   #18
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Quote:
Originally Posted by Ki2AY
i have a clue onto what you are trying to explain.. but its still not clear to me (not the fact that you didnt explain it well, its the fact that i dont know much about manual cars, actually anycar being the clueless guy i am).. i really appreciate ur informartion.. atleast i know now that it has more to do with the engine rather than just the breaks haha

anyways well done pal!

Shall we start from scrach, a typical petrol engine idles at 600-900 rpm (yeah the numbers are probly wrong so some 1 can put me right later) and for a most production:
V8's run stop liking you after about 5000rpm probibly a little less
V6's, I6 and I4's range upto about 7500-8000rpm

Within this range of revs there a maximum HP output and a max torque output. Torque is the turning force, HP is the power, they are distinclty diffrent.

One way to imagine torque is with a winch, as you pull your boat onto the road trailer for example its how hard it is to turn the handle.

BHP = torque x rev's ( the sets of units change with metric and imperial so im not going to get into that)

So on a auto it changes the gears for you, all to do with torque convetters and things which i dont like and not reallyinterested to learn about, there are lots of people on here who can help with autos' dodge, wally, chrisv to name a few.

The idea of a clutch is to be able to continue to run the engine while the car is stationary. There are lots of diffrent types and aragements for example a viscos coupleing is a type of clutching system. but have a look at

http://auto.howstuffworks.com/clutch.htm (is that alowed bav?)

So now you know what a clutch is

Well imagine you are driving along in 5th gear@ 60mph. The engine is turning they flywheel and clutch plate and this is conected to the friction plate on the gearbox, and they are firmly held together.

So now the gear's in the gearbox are turning anf then this is output through the differential to the 1/2 shafts (or prop if its rear wheel drive) and finally to the wheels.

dont worry about the prop 1/2 shafts or diff for now. thats just so we can trun couners more easilt and power more than one wheel.

So your roling along at 60mph and you have 205/50r16 tyres so your wheels will have to turn 838 times a min. Your engnine is say 3000rpm and top gear is 1:1, so every time the engine turns 1ce the output of the gearbox turns 1ce and there for you have a diff of 3.58

So your engine like to rev between 2000-3500 rpm so thats all fine and dandy.

But lets say you want to go ooh 25mph so now your wheels need to go round 349 times a min so goes through the diff so if we have the same 5th gear the engine will only need to turn 1105.5 rpm's and we know it doesnt like that.

so you need to change gear to change the ratio that its turning at.

Well lets apply this principal in reverse. Your traveling at 60mph and you sudenly change gear from 5th to 3rd, the wheels are still going around but now the engine has to turn alot faster. so rather than the engine driving the wheels the wheels are trying to drive the engine this is engine breaking.

Now on a modern car to change gear, you back off the throttle, press the clutch down disconecting the engine from the gearbox and wheels then move the gear lever from 5th gear's notch to 3rd gears notch ussaly they would be next to each other on a standard H patten.

As you push the stick into the notch for 3rd it makes you wait, this is th syncros comeing into play, so as you move the stick the gearbox gets the diffrent gears to start to move at the same speed, you then engage the clutch by lifting your foot off.


Now imagine you didnt have the syncros, so now you have to get them to spin at the same speed.

so what you do is first you take it out of 5th gear. easy enough. push the clutch down pull it out of 5th into neutral. So in the gearbox the gears arnt conected together any more. but now you have to get the new gear to spin at the same speed as the drive gear, so the only way to do that, is to use the engine, so we have to engage the clutch again, so we lift our foot off and now the engne is enged with the one 1/2 of the gearbox.

so now step on the throttle to get the gearbox spinning and then to engage 3rd, we have to apply the clutch agan to disconect the engine from the drive, so step on it again and pull it into 3rd, now re engage the engine and so now lift your foot again. ie double decutching, you have to de clutch twice!
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Old 06-18-2004, 10:05 PM   #19
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Well explained… thank you. Ill probably have to read that a couple more times to understand it fully. But really you've help me allot with your knowledge, thx!
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Old 06-18-2004, 10:14 PM   #20
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Quote:
Originally Posted by Ki2AY
i have a clue onto what you are trying to explain.. but its still not clear to me (not the fact that you didnt explain it well, its the fact that i dont know much about manual cars, actually anycar being the clueless guy i am).. i really appreciate ur informartion.. atleast i know now that it has more to do with the engine rather than just the breaks haha

anyways well done pal!

Ki2AY

Ok, I?ll try to handle engine braking.

As you drive down the road, at say 3000 rpm, @ 50 mph there are explosions going on inside the cylinders. When you release the throttle, the explosions become smaller and not as often. Just lifting your foot off the gas causes the car to suddenly slow down. This is ?engine breaking?. The same explosions used to move the car, can be used to stop the car. The smaller explosions, now occurring in the engine provides a back pressure or force tending to stop the car. By shifting to a lower gear, you are providing a mechanical advantage to the engine and the power the engine is producing provides greater stopping power. Double clutching is simply a method used, to be able to move from one gear to another by matching the speed of the input shaft with the gear set, being selected inside the transmission.

cinqyg
If we keep this up, we're going to get the point across. You just keep doing most of the work.



John
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Last edited by jcutsh : 06-18-2004 at 10:20 PM.
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Old 06-18-2004, 10:25 PM   #21
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Originally Posted by jcutsh
Ki2AY

Ok, I?ll try to handle engine braking.

As you drive down the road, at say 3000 rpm, @ 50 mph there are explosions going on inside the cylinders. When you release the throttle, the explosions become smaller and not as often. Just lifting your foot off the gas causes the car to suddenly slow down. This is ?engine breaking?. The same explosions used to move the car, can be used to stop the car. The smaller explosions, now occurring in the engine provides a back pressure or force tending to stop the car. By shifting to a lower gear, you are providing a mechanical advantage to the engine and the power the engine is producing provides greater stopping power. Double clutching is simply a method used, to be able to move from one gear to another by matching the speed of the input shaft with the gear set, being selected inside the transmission.

cinqyg
If we keep this up, we're going to get the point across. You just keep doing most of the work.



John

You know we could teach him to stop really quickly
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Old 06-18-2004, 10:38 PM   #22
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Quote:
Originally Posted by cinqyg
You know we could teach him to stop really quickly

LOL well before doing that, you might want to teach me how to drive a stick much better.
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Old 06-18-2004, 10:44 PM   #23
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We could send him a cinderblock and a rope.
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Old 06-18-2004, 10:48 PM   #24
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Quote:
Originally Posted by jcutsh
We could send him a cinderblock and a rope.

If he wants to master double declutching then i think a pre 1937 fordson TE20 would do the trick!

Well once you get the hang of double declutching it means you can put you car in reverse at 70mph lol!
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Old 06-18-2004, 11:09 PM   #25
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Originally Posted by cinqyg
If he wants to master double declutching then i think a pre 1937 fordson TE20 would do the trick!

Well once you get the hang of double declutching it means you can put you car in reverse at 70mph lol!

Gosh that's the hard way. Hay kid, tape an egg to the bottom of your left foot. When you get to where you can walk around for a week with out breaking the egg, come back and see us.
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Old 06-19-2004, 03:16 AM   #26
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It does not make a difference, and here is why in logical terms.

If your trying to determine how fast a car will stop, you won't be lightly using the brakes. Assuming it has Anti-Lock brakes, under hard braking conditions the rear wheels will lock up on most if not all braking systems in most or all vehicles. Now, power or no power being outputted to the rear wheels(or front), if they are locked up and not turning what difference would it make?
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Old 06-19-2004, 03:20 AM   #27
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Quote:
Originally Posted by cinqyg
you can use engine breaking with manuals, but you probibly can with some autos, most just free wheel. As bav said if you dont have ABS then manual is more handy in slipery conditions.

If you had a RWD, and were in slippery conditions, using a low gear for engine braking would make your back end "loose" - that makes handling worse, not better.
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Old 06-19-2004, 03:25 AM   #28
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Quote:
Originally Posted by jcutsh
Ki2AY

Ok, I?ll try to handle engine braking.

As you drive down the road, at say 3000 rpm, @ 50 mph there are explosions going on inside the cylinders. When you release the throttle, the explosions become smaller and not as often. Just lifting your foot off the gas causes the car to suddenly slow down. This is ?engine breaking?. The same explosions used to move the car, can be used to stop the car. The smaller explosions, now occurring in the engine provides a back pressure or force tending to stop the car. By shifting to a lower gear, you are providing a mechanical advantage to the engine and the power the engine is producing provides greater stopping power. Double clutching is simply a method used, to be able to move from one gear to another by matching the speed of the input shaft with the gear set, being selected inside the transmission.

cinqyg
If we keep this up, we're going to get the point across. You just keep doing most of the work.



John

No, it's compression that provides engine braking. Not combustion. The piston never moves up on the Power Stroke.(in theory it does, because the fuel gets ignited on the upward, compression stroke, but it doesnt provide any pressure until the piston is after tdc and on its way downward.)
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Old 06-19-2004, 05:32 AM   #29
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No, it's compression that provides engine braking. Not combustion. The piston never moves up on the Power Stroke.(in theory it does, because the fuel gets ignited on the upward, compression stroke, but it doesnt provide any pressure until the piston is after tdc and on its way downward.)

Easy to check. turn the key off at sixty and see how long it takes to stop the car. Then try it with the key on.

Make this test with a stick tranny. See which method stops the car faster. With the engine running the car will stop about 30% faster. Must have something to do with all those little explosions. Of course compression helps but that is nothing compared to an engine starved of fuel, trying its best, and producing power of about 50/70 hp, to spin the crank at 700/800 rpm. That's 50 hp trying to stop the car. At the same time the car is trying to spin the crank at 2000 rpm. The crank is really turning faster then the explosions. The crank is turning so fast the combustion happens BTDC. The little explosions really hate this and fight all the way, still trying to make all that mass return to idle. Like I said above: Get a stick, mark out a spot. take the car to 60. let off the gas till it comes to a dead stop, then do the same thing but this time when you hit 60 just turn off the key.
I think if you grafted the flame wall inside the cylinder on a milisecond basis, then you would see some very strange things happening (pwr vs crank position). As far as can a manual stop faster then an auto. If you hard lock the brakes then no difference. If the wheels aren't turning then they aint turning. However in a emegency stop and driving an automatic with one foot, like your suppose to. The time it takes to move your foot from the gas to the brake pedal can be .5 to .8 sec. It can take an engine up to 2 seconds to return to idle. Those few seconds can propel the car another 50/60 feet at 60 mph, even though the engine is returning to idle it is still driving the wheels until it gets there and your foot may still be in the air. In a stick though, we use both feel and disengage the engine and brake at the same time. This gives the stick a little faster stopping time. Most racing schools teach students to kick the automatic into neutral in case of trouble or when trying to stop on snow and ice.

Sorry for the confusion.

Great car by the way. wish I still had my 69 RT.
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Old 06-19-2004, 05:37 AM   #30
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this is the first time i hear about double declutching, so this thread has got me psyched up about finally learning something pretty technical thats not too simple. its a simple concept to understand, but u just have to use ur brain (which i havent had the chance of doing for a long time.... that n im feeling lazy :P).

anyhow, i was wondering, has the whole engine braking or double declutching anything to do with the whole heel and toe braking? just like in many races, specially drifting where it gets done alot (but for different reasons there), the driver uses the brakes normally but at the same time steps on the gass with the heel while using his toes for the brake pedal (hence, heel and toe), so he revs the car once while hes working the clutch and the shift stick..... kinda thought the whole engine braking and double declutching had something to do with this too.
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