Mythbusters.

[8VALVE-zn]

20) 16valves are for people that dont know how to make power with a 8v

thats not myth , thats FAX!!!!


8v FTMFW

an 8v that makes 108wkw and 217nm(standard bottom,standard head just a 288 Thabla inside) here at the coast will mince most ABF's ....Tried and tested!!

[slakkie]

20) 16valves are for people that dont know how to make power with a 8v

thats not myth , thats FAX!!!!


8v FTMFW

an 8v that makes 108wkw and 217nm(standard bottom,standard head just a 288 Thabla inside) here at the coast will mince most ABF's ....Tried and tested!!

I beg to differ.

Take any 2 liter 16v vs any 2 liter 8v (both N/A and modded to the max and who will win?)
Take any 2 liter 16v vs any 2 liter 8v (both boosted and modded to the max and who will win?)

Strei?

[johnnynguyen]

Thanks GtiTuned, 6 is a my favourite ones.
_________________
AtlasBX Battery

[8VALVE-zn]

20) 16valves are for people that dont know how to make power with a 8v

thats not myth , thats FAX!!!!


8v FTMFW

an 8v that makes 108wkw and 217nm(standard bottom,standard head just a 288 Thabla inside) here at the coast will mince most ABF's ....Tried and tested!!

I beg to differ.

Take any 2 liter 16v vs any 2 liter 8v (both N/A and modded to the max and who will win?)
Take any 2 liter 16v vs any 2 liter 8v (both boosted and modded to the max and who will win?)

Strei?

When money is no longer an obstacle then maybe that statement will hold true!! An abf will cost around R19000 were an 8v will cost R7500- bump that difference into an 8v (R3500- gasflow port, R2000-288 cam, Big Valve-R3300, and wow still a spare R2700 for tuning and other small odds and ends), which would you say would be faster? Unless fast for you means making numbers on the dyno...

[SebastianS]

sounds like we may have a tie if we factor in a turbo 8v vs 16v n/a

[Wolfburger]

29 - Idling a car when cold. Mmm - not really good or recommended. What you want is the engine to get to temp as fast as possible. An idling engine actually takes a long time to warm up and while it's doing that it basically sits with a very rich mixture as most managements and even carbs will enrich the mixture to get them running. A rich mixture at idle washes the bore with unburnt fuel and this ends up in your oil and it promotes wear on the sleeves. What you want to do is start and basically move off as soon as you are ready. This also allows the drivetrain to warm up as well. Basically just keep the rpm down and boost down if a turbo car and this will let the motor heat up much sooner.

Interesting!!! here am i thinking I'm doing it right all these years

[SebastianS]

30) 8V engines make more torque than 16V engines. Crap: some 8v engines are tuned for low-down torque, they pull hard, but got nothing at the top end, and will get wasted by a 16V in a 1/4mile

[Golfdriver]

Bigger discs with standard calipers will make your Mk1 stop quicker!

[THANAS]

Bigger discs with standard calipers will make your Mk1 stop quicker!

This isn't a myth, moving the stock calipers outwards to accomodate a larger disc increases the lever arm of the force applied, resulting in a greater torque/moment on the brake disc and hence the wheel. Assuming the tyres are capable of gripping the road adequately, the larger stopping torque combined with the increased heat capacity of bigger discs means that it very well should stop your mk1/citi from speed, quicker.

[Abnormal]

Bigger discs with standard calipers will make your Mk1 stop quicker!

This isn't a myth, moving the stock calipers outwards to accomodate a larger disc increases the lever arm of the force applied, resulting in a greater torque/moment on the brake disc and hence the wheel. Assuming the tyres are capable of gripping the road adequately, the larger stopping torque combined with the increased heat capacity of bigger discs means that it very well should stop your mk1/citi from speed, quicker.

That is key.


In reality I can already lock up the front wheels with the standard setup.

[THANAS]

Bigger discs with standard calipers will make your Mk1 stop quicker!

This isn't a myth, moving the stock calipers outwards to accomodate a larger disc increases the lever arm of the force applied, resulting in a greater torque/moment on the brake disc and hence the wheel. Assuming the tyres are capable of gripping the road adequately, the larger stopping torque combined with the increased heat capacity of bigger discs means that it very well should stop your mk1/citi from speed, quicker.

That is key.


In reality I can already lock up the front wheels with the standard setup.

True, but can you lock them up from 150/170 kph or after 2 or 3 substantial braking events. The bigger discs come in useful when braking hard from higher speeds. Under normal driving conditions, up to 100 kph or so, the additional braking effort isn't necessary, I agree, as there is enough effort to lock a wheel. High speed braking where the wheel momentum and contact with the road form a much larger resistive force, or repetitive braking in track conditions is a different story.

Not to get too sidetracked though, saying that bigger discs won't make you stop faster is not a myth, but it also isn't true in every condition (as you pointed out above).

[Abnormal]

Bigger discs with standard calipers will make your Mk1 stop quicker!

This isn't a myth, moving the stock calipers outwards to accomodate a larger disc increases the lever arm of the force applied, resulting in a greater torque/moment on the brake disc and hence the wheel. Assuming the tyres are capable of gripping the road adequately, the larger stopping torque combined with the increased heat capacity of bigger discs means that it very well should stop your mk1/citi from speed, quicker.

That is key.


In reality I can already lock up the front wheels with the standard setup.

True, but can you lock them up from 150/170 kph or after 2 or 3 substantial braking events. The bigger discs come in useful when braking hard from higher speeds. Under normal driving conditions, up to 100 kph or so, the additional braking effort isn't necessary, I agree, as there is enough effort to lock a wheel. High speed braking where the wheel momentum and contact with the road form a much larger resistive force, or repetitive braking in track conditions is a different story.

Not to get too sidetracked though, saying that bigger discs won't make you stop faster is not a myth, but it also isn't true in every condition (as you pointed out above).

yeah it will help in repeated attempts to stop.

So if
saying that bigger discs won't make you stop faster is not a myth :head exploded:

then you saying that bigger discs will make you stop faster is a myth

[Golfdriver]

The basic physics equasions apply, few of which you are extrapolating correctly. The larger disc may conduct more heat away which is useful in racing to minimise fade but not in street use. It all boils down to the physics of inertia, momentum and mass. Therefore a larger disc will accelerate slower, and will decelerate slower. Unless you increase the pad area, there is no benefit in street us. they just look nicer inside a bigger wheel.

[Abnormal]

The basic physics equasions apply, few of which you are extrapolating correctly. The larger disc may conduct more heat away which is useful in racing to minimise fade but not in street use. It all boils down to the physics of inertia, momentum and mass. Therefore a larger disc will accelerate slower, and will decelerate slower. Unless you increase the pad area, there is no benefit in street us. they just look nicer inside a bigger wheel.

So you saying that there would be no benefit from the additional leverage.

[THANAS]

saying that bigger discs won't will make you stop faster is not a myth :head exploded:

then you saying that bigger discs will make you stop faster is a myth

Oops, you know what I meant!

The basic physics equasions apply, few of which you are extrapolating correctly. The larger disc may conduct more heat away which is useful in racing to minimise fade but not in street use. It all boils down to the physics of inertia, momentum and mass. Therefore a larger disc will accelerate slower, and will decelerate slower. Unless you increase the pad area, there is no benefit in street us. they just look nicer inside a bigger wheel.

By extrapolating I assume you mean applying. There is no need to extrapolate something that is directly applicable. In any case, the inertia of the disc itself is miniscule in comparison to the inertia of the vehicle, so the comment about accelerating/decelerating slower isn't that relevant to the discussion. Pad area does form part of the equation, but then you might as well include the number of pistons in the caliper, size of the master cylinder, restrictions in the brake line, lever on the brake pedal, etc etc.

Your statement that 'increasing the size of the discs, with the same calipers, helps a mk1 stop faster is a myth', is untrue. To help visualise the problem consider two situations, one where the disc is tiny, and the caliper is right up against the hub, and one where the disc is very large (think larger than the wheel), with the caliper on the end. Which, intuitively, would be expected to stop faster?

[Golfdriver]

leverage plays no part in this scenario. For example: Take your standard disc with a standard caliper and pad, spin the disc up to a known rpm and measure the power and the time used to spin it up. Now bring it to a stop using the maximum force available from the caliper and measure the time taken to do this. Now go to an extreme to illustrate. Change the disc for one of 1000mm in diameter made from the same material and spin it up to the same rpm in the first trial. Notice that a) much more power will be required to spin it up. If you use the original amount of power then much more time will be needed to spin it up. Now bring it to a stop using the same caliper and it will stop approximately 3.5 slower than in the first example. Therefore leverage and moment arm do not apply. Its not the size of the disc that matters but rather the size of the hand that's grabbing it. The only reason to increase the disc size is so that you have the room to fit a larger caliper and pad. In order to stop the disc quicker, you need to increase the friction. Increasing the size of the disc on its own does no accomplish this. Rather it is detrimental from a mass and inertia aspect.

[Golfdriver]

Extrapolte - To predict an outcome using known facts. In this case, inertia, momentum mass and friction. So using a larger disc with a standard caliper will make your Mk1 stop faster is indeed a myth. You can disagree with me as much as you like but is doesn't change the maths. Of course one must never underestimate the power of the placebo effect.

[Neuk]

I am with THANAS on this and would love to hear @Golfdriver explanation of how a clearly lengthened moment arm has zero effect on the braking force applied to the wheel/tyre?

[Golfdriver]

Because the equation is based only on inertia, mass. momentum and friction. Leverage is not part of the equation because it has no effect. In order to effect a rotating mass speed you can only use the peramaters that I have noted. you can stand as far away from it as you like and use the longest lever that you can find but it does not effect the outcome.

[Neuk]

Because the equation is based only on inertia, mass. momentum and friction. Leverage is not part of the equation because it has no effect. In order to effect a rotating mass speed you can only use the peramaters that I have noted. you can stand as far away from it as you like and use the longest lever that you can find but it does not effect the outcome.

Please list this equation, I am now genuinely fascinated how the length from the centre of rotation to the point of application of the force causing or limiting the rotation, has zero impact.

[Golfdriver]

The length from the center of rotation to the point of application of the force in order to affect the rotation does indeed have an impact. The further from the center you go. this implies that the disc is getting larger therefore the further you go, the greater the NEGATIVE impact you will have on dissipating the kinetic energy. The friction between the disc and the pad is as a result of the caliper exerting a force on the pad. This force is transmitted via the hydraulic fluid from the master cylinder and is a result of the strength of your leg. We have noted that the original caliper is being used so the friction generated is a constant. If this friction remains a constant, then where is this additional leverage coming from that you refer to? There is no leverage as it does not form part of the eqation. If you want details of the equation, then look up the effects on a force applied to a rotating mass and the effect on kinetic energy in your physics book. I am not going to go into the maths as I don't believe a forum like this warrants it.

[Neuk]

The length from the center of rotation to the point of application of the force in order to affect the rotation does indeed have an impact. The further from the center you go. this implies that the disc is getting larger therefore the further you go, the greater the NEGATIVE impact you will have on dissipating the kinetic energy. The friction between the disc and the pad is as a result of the caliper exerting a force on the pad. This force is transmitted via the hydraulic fluid from the master cylinder and is a result of the strength of your leg. We have noted that the original caliper is being used so the friction generated is a constant. If this friction remains a constant, then where is this additional leverage coming from that you refer to? There is no leverage as it does not form part of the eqation. If you want details of the equation, then look up the effects on a force applied to a rotating mass and the effect on kinetic energy in your physics book. I am not going to go into the maths as I don't believe a forum like this warrants it.

You answered yourself earlier in your argument, using a larger disc necessitates moving the caliper further away from the centre of rotation of the wheel, increasing the moment or torque arm that is applied. Using the equation to calculate the torque applied which is the force applied multiplied by the moment or torque arm multiplied by sin (theta), and considering that the force applied by the brake caliper along with the friction between pad and disc remains constant, the only change is the moment or torque arm. Thus, a higher torque is applied to the drivetrain (wheels, tyres, driveshafts, etc.) by a larger disc setup with the caliper moved further out from the centre of rotation but whether that torque can be fully used is another story along with other benefits of running larger discs like heat dissipation.

Bring the maths, actually mechanics, this forum is a great place to discuss it.

[Golfdriver]

You answered yourself earlier in your argument, No I did not.
Using the equation to calculate the torque applied which is the force applied multiplied by the moment or torque arm multiplied by sin (theta), and considering that the force applied by the brake caliper along with the friction between pad and disc remains constant, the only change is the moment or torque armnot. Totally incorrect equation for this application.
Thus, a higher torque is applied to the drivetrain So much rubbish.
whether that torque can be fully used is another story It can't because it doesn't exist
So my final comment on this is: Go and fit your car with a set of 30 inch wheels with a set of 25 inch cast iron discs with the original calipers and then come back here and tell us how much shorter braking distance you have achieved. You must use the same width tyres.
And as I said, is you want the maths, go and look it up because I am sure that if I shared my calculations with you on this subject then you will probably argue about them as well.

[Neuk]

You answered yourself earlier in your argument, No I did not.
Using the equation to calculate the torque applied which is the force applied multiplied by the moment or torque arm multiplied by sin (theta), and considering that the force applied by the brake caliper along with the friction between pad and disc remains constant, the only change is the moment or torque armnot. Totally incorrect equation for this application.
Thus, a higher torque is applied to the drivetrain So much rubbish.
whether that torque can be fully used is another story It can't because it doesn't exist
So my final comment on this is: Go and fit your car with a set of 30 inch wheels with a set of 25 inch cast iron discs with the original calipers and then come back here and tell us how much shorter braking distance you have achieved. You must use the same width tyres.
And as I said, is you want the maths, go and look it up because I am sure that if I shared my calculations with you on this subject then you will probably argue about them as well.

So your argument basically amounts to, 'Because I said so but I can't be bothered to validate my argument!'

[Abnormal]

So forget leverage,
So lets say the friction is constant because its the same size of pad and caliper and brake booster and brake fluid friction in the lines and leg muscles.
For a standard disc of 239mm the circumference is 1501mm
Now for a larger disc of 280mm the circumference is 1759mm

Given that the same frictional force is being applied to the disc constantly in each case (friction)
with the standard disc you will be applying the force over a distance of 1501mm x (friction)
with the 280mm disc you will be applying the force over a distance of 1759mm x (friction) for each rotation of the wheel.
a difference of 258 (friction) per wheel rotation.


Maybe you need to fit a set and check out the placebo effect for yourself.