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Old 03-05-2011, 09:32 AM   #1
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wobble rotors

Stock car racers have for many years known that they could increase performance with numerous tricks, some of which are useful to us, and some of which are not.
One of the tricks that has significant benefit is to take your brake rotors and turn them with a .005 shim or so stuck in one side of the machine so the rotor ends up with a wobble. This wobble is not the same as a warped rotor, as the two faces of the rotor are still completely flat and parallel, but the result is that the rotor pushes the brake caliper piston back so the pads are not in full contact with the rotor until you step on the brakes. Disk brake calipers do NOT retract as drum brake shoes do, they just lose their clamping pressure when you let off. There can be a shocking amount of brake drag on vehicles with disk brakes.

Another stock car racer's trick is the windage tray, which is inside the oil pan, and reduces the "motoring torque" of the engine. That means the power required to spin the engine over.

Engine accessories also gobble up power... water pump, power steering pump, alternator, even the oil pump which is constantly bypassing during operation. We don't need the power steering really...... A proper steering ratio makes power steering an unnecessary accessory except for wimpy people, but modern steering is too quick and steers hard without it as a result. As someone mentioned, a deep cycle battery could eliminate the need for a charging system. That sounds like a great idea....but in fact the alternator does not draw any significant power except for it's cooling fan, unless it's charging. An electric clutch just like an AC compressor would be the cat's meow here! Electric water pumps exist...... but generating power and then using a motor introduces two points of loss. A water pump is a centrifugal pump, and centrifugal pumps draw the most horsepower when their outlets are wide open, and the least when the flow is choked off, opposite of what one would expect, but the formula is horsepower = Flow in GMP * pressure in PSIG / 1710, divided by the efficiency factor of the pump. There are two ways in which we could reduce the load of a water pump. One is to use an efficient pump. These probably have an efficiency down around 15-20%, and the other is to choke down our coolant flow to unload the pump..... flow just as much water as we actually need to keep the engine cool. The two together could have a significant effect on efficiency, but controlling flow is the only place we can EASILY have an effect here. That said, the impellers for reasonably sophisticated pumps are readily available as replacements, and often are of similar overall dimension. It seems to me that a pump could be manufactured which would be significantly more efficient. These pumps move a lot of water, and of course burn significant horsepower doing it........... How much do they really need to move? Supposing we used a small, high efficiency belt driven pump........
Another thing I have observed, having built somewhere well over 100 gas engines, and numerous heavy industrial and agricultural diesels, is tightness makes a difference. Engines for my own use, I have always built very loose. Large bearing clearances, loose piston fit, etc, and the run loose and easy from day one, without the "break in" period, and tend to be more efficient. They seem to last just as long as engines built to tighter tolerances. If the piston clearance spec for example has a range spanning 2.5 thousandths from tight to loose, I will bore and hone to near max. Likewise, my crankshaft grinder knows I want the journals ground on the small end of the scale for more clearance rather than less. It does make a difference!

Howard
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Old 03-05-2011, 09:39 AM   #2
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Re: wobble rotors

Quote:
Originally Posted by Howard View Post
Stock car racers have for many years known that they could increase performance with numerous tricks, some of which are useful to us, and some of which are not.
One of the tricks that has significant benefit is to take your brake rotors and turn them with a .005 shim or so stuck in one side of the machine so the rotor ends up with a wobble. This wobble is not the same as a warped rotor, as the two faces of the rotor are still completely flat and parallel, but the result is that the rotor pushes the brake caliper piston back so the pads are not in full contact with the rotor until you step on the brakes. Disk brake calipers do NOT retract as drum brake shoes do, they just lose their clamping pressure when you let off. There can be a shocking amount of brake drag on vehicles with disk brakes.

Another stock car racer's trick is the windage tray, which is inside the oil pan, and reduces the "motoring torque" of the engine. That means the power required to spin the engine over.

Engine accessories also gobble up power... water pump, power steering pump, alternator, even the oil pump which is constantly bypassing during operation. We don't need the power steering really...... A proper steering ratio makes power steering an unnecessary accessory except for wimpy people, but modern steering is too quick and steers hard without it as a result. As someone mentioned, a deep cycle battery could eliminate the need for a charging system. That sounds like a great idea....but in fact the alternator does not draw any significant power except for it's cooling fan, unless it's charging. An electric clutch just like an AC compressor would be the cat's meow here! Electric water pumps exist...... but generating power and then using a motor introduces two points of loss. A water pump is a centrifugal pump, and centrifugal pumps draw the most horsepower when their outlets are wide open, and the least when the flow is choked off, opposite of what one would expect, but the formula is horsepower = Flow in GMP * pressure in PSIG / 1710, divided by the efficiency factor of the pump. There are two ways in which we could reduce the load of a water pump. One is to use an efficient pump. These probably have an efficiency down around 15-20%, and the other is to choke down our coolant flow to unload the pump..... flow just as much water as we actually need to keep the engine cool. The two together could have a significant effect on efficiency, but controlling flow is the only place we can EASILY have an effect here. That said, the impellers for reasonably sophisticated pumps are readily available as replacements, and often are of similar overall dimension. It seems to me that a pump could be manufactured which would be significantly more efficient. These pumps move a lot of water, and of course burn significant horsepower doing it........... How much do they really need to move? Supposing we used a small, high efficiency belt driven pump........
Another thing I have observed, having built somewhere well over 100 gas engines, and numerous heavy industrial and agricultural diesels, is tightness makes a difference. Engines for my own use, I have always built very loose. Large bearing clearances, loose piston fit, etc, and the run loose and easy from day one, without the "break in" period, and tend to be more efficient. They seem to last just as long as engines built to tighter tolerances. If the piston clearance spec for example has a range spanning 2.5 thousandths from tight to loose, I will bore and hone to near max. Likewise, my crankshaft grinder knows I want the journals ground on the small end of the scale for more clearance rather than less. It does make a difference!

Howard
WOW Lots of great information!!! I really enjoy reading your post's.
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Old 03-05-2011, 06:20 PM   #3
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Re: wobble rotors

Quote:
Originally Posted by Howard View Post
Stock car racers have for many years known that they could increase performance with numerous tricks, some of which are useful to us, and some of which are not.
One of the tricks that has significant benefit is to take your brake rotors and turn them with a .005 shim or so stuck in one side of the machine so the rotor ends up with a wobble. This wobble is not the same as a warped rotor, as the two faces of the rotor are still completely flat and parallel, but the result is that the rotor pushes the brake caliper piston back so the pads are not in full contact with the rotor until you step on the brakes. Disk brake calipers do NOT retract as drum brake shoes do, they just lose their clamping pressure when you let off. There can be a shocking amount of brake drag on vehicles with disk brakes.

Another stock car racer's trick is the windage tray, which is inside the oil pan, and reduces the "motoring torque" of the engine. That means the power required to spin the engine over.

Engine accessories also gobble up power... water pump, power steering pump, alternator, even the oil pump which is constantly bypassing during operation. We don't need the power steering really...... A proper steering ratio makes power steering an unnecessary accessory except for wimpy people, but modern steering is too quick and steers hard without it as a result. As someone mentioned, a deep cycle battery could eliminate the need for a charging system. That sounds like a great idea....but in fact the alternator does not draw any significant power except for it's cooling fan, unless it's charging. An electric clutch just like an AC compressor would be the cat's meow here! Electric water pumps exist...... but generating power and then using a motor introduces two points of loss. A water pump is a centrifugal pump, and centrifugal pumps draw the most horsepower when their outlets are wide open, and the least when the flow is choked off, opposite of what one would expect, but the formula is horsepower = Flow in GMP * pressure in PSIG / 1710, divided by the efficiency factor of the pump. There are two ways in which we could reduce the load of a water pump. One is to use an efficient pump. These probably have an efficiency down around 15-20%, and the other is to choke down our coolant flow to unload the pump..... flow just as much water as we actually need to keep the engine cool. The two together could have a significant effect on efficiency, but controlling flow is the only place we can EASILY have an effect here. That said, the impellers for reasonably sophisticated pumps are readily available as replacements, and often are of similar overall dimension. It seems to me that a pump could be manufactured which would be significantly more efficient. These pumps move a lot of water, and of course burn significant horsepower doing it........... How much do they really need to move? Supposing we used a small, high efficiency belt driven pump........
Another thing I have observed, having built somewhere well over 100 gas engines, and numerous heavy industrial and agricultural diesels, is tightness makes a difference. Engines for my own use, I have always built very loose. Large bearing clearances, loose piston fit, etc, and the run loose and easy from day one, without the "break in" period, and tend to be more efficient. They seem to last just as long as engines built to tighter tolerances. If the piston clearance spec for example has a range spanning 2.5 thousandths from tight to loose, I will bore and hone to near max. Likewise, my crankshaft grinder knows I want the journals ground on the small end of the scale for more clearance rather than less. It does make a difference!

Howard
The problem with the rotor trick is that they can sometimes back the pad pretty far from the rotor ("knockback"), causing problems in panic stops. You may need to pump the pedal a couple of times for the pads to make stiff contact with the rotor. I have seen issues in races in which a driver overshot pit road or his pit stall and blamed it on pad knockback. I am also not sure if modern master cylinders will allow that much variation in fluid levels from "brakes on" and "brakes off/knockback." An engineer, I am not, so I may be wrong here. I do know that it does reduce brake drag, at least... if it didn't, why would they try it on the race track?

As far as the loose engine tolerances go, do you notice any piston slap or wear issues when driven in cold temperatures?

As far as the power steering, I both agree and disagree. I had 2 cars without power steering (Civic VX, del Sol S). Both were light weight and no trouble to park. They both had very slow steering, though (almost 4 turns lock-to-lock). My 1999 Civic Si shared the steering ratio, but had power steering, which was a waste, even with its much-wider tires. However, after driving my Fit and 2005 Civic Si, I do not want to go back to a vehicle with steering that slow. I could probably be OK without power steering in my 2 vehicles, but I wouldn't want to try it on something heavier or with wider tires than my Si. ...and almost every new car on the market seems to be heavier and have wider tires.
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Old 03-06-2011, 08:38 AM   #4
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Re: wobble rotors

"Knockback" is a problem that idiots who felt that if a little bit was good, a lot was better ran into. The amount of wobble I am talking about does not result in significant take up. The pedal will be just slightly closer to the floor, something you will soon not even be aware of. The world is full of stupid people. and the percentage that are stock car racers is about the same, as any other group.

I personally have no problem with manual steering.......nor do I like fast steering at all. Fast steering increases risk of wrecking a vehicle in panic situations. It requires a level of control that is beyond most people in an emergency, or impending emergency, and in my opinion results in a lot of wrecks directly from "over controlling". That is particularly true out here where the vast majority of highway fatalities are single car roll over accidents on our many thousands of miles of narrow two lane highways. I am reminded of two cars I had....... One an Aerostar, which had the best steering of any vehicle I ever owned....... It seemed that you could take a nap, and wake up and it would be motoring right down the middle of the lane, the other was a Subaru Impresa (93), and the steering was so quick that it was dangerous unless you had 100% of your attention on the road all the time. Reach down to adjust the radio, and you were in the other lane, look at what's going on alongside the road, and you were headed for the ditch. Two pickups I drove a lot are another example... My 1960 F100 4x4, steering rato 6 turn (manual), and a 1979 Ford F350 4x4, steering ratio about 2.5 turn. Our highways around here are two lane, and have frost heaves and rutting and such. Driving the 1979, you had to drive with two fingers on the bottom of the wheel, allowing your upper body to sway with the highway independently of the two fingers that were driving. Driving the 1960, with it's 6 turn manual steering, you could keep both hands on the wheel and the little bit it moved made no significant difference....... It had virtually zero play in the steering. Sudden radical changes resulting from small control inputs are a liability in my opinion, and cars that behave that way are far more stressful to drive, particularly long distances. An example of a vehicle I had with manual steering that was an excellent compromise, was a 1977 Datsun king cab pickup....... ratio was excellent, steering effort low, highly controllable............. You can have your race car steering.......I don't want it, and the price of the fuel it costs is more than I want to pay really. I've also driven big trucks with manual steering for years, the steering is not "quick", nor is it difficult unless you aren't moving. My yard truck, a cab over international CO1800 with a Hiab 6000lb knuckle boom on the rear has manual steering, and can be a bearcat if it's not moving, but is a joy to drive down the road with the large steering wheel and good steering ratio.

Howard

Quote:
Originally Posted by Fetch View Post
The problem with the rotor trick is that they can sometimes back the pad pretty far from the rotor ("knockback"), causing problems in panic stops. You may need to pump the pedal a couple of times for the pads to make stiff contact with the rotor. I have seen issues in races in which a driver overshot pit road or his pit stall and blamed it on pad knockback. I am also not sure if modern master cylinders will allow that much variation in fluid levels from "brakes on" and "brakes off/knockback." An engineer, I am not, so I may be wrong here. I do know that it does reduce brake drag, at least... if it didn't, why would they try it on the race track?

As far as the loose engine tolerances go, do you notice any piston slap or wear issues when driven in cold temperatures?

As far as the power steering, I both agree and disagree. I had 2 cars without power steering (Civic VX, del Sol S). Both were light weight and no trouble to park. They both had very slow steering, though (almost 4 turns lock-to-lock). My 1999 Civic Si shared the steering ratio, but had power steering, which was a waste, even with its much-wider tires. However, after driving my Fit and 2005 Civic Si, I do not want to go back to a vehicle with steering that slow. I could probably be OK without power steering in my 2 vehicles, but I wouldn't want to try it on something heavier or with wider tires than my Si. ...and almost every new car on the market seems to be heavier and have wider tires.
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Old 03-06-2011, 01:05 PM   #5
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Re: wobble rotors

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Disk brake calipers do NOT retract as drum brake shoes do, they just lose their clamping pressure when you let off.
The seal on the piston is supposed to distort and then provide retraction upon brake release.

"New Generation" calipers supposedly have return springs... I've seen pics of them but haven't studied them to be able to say how they work such that the clearance tween pads and rotor is neither too small nor too great.
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Old 03-06-2011, 02:11 PM   #6
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Re: wobble rotors

Nice info, thanks Howard.

Here's a pic of the pad return spring from a 2003-2011 Mitsubishi EVO.



FYI the pad on the right is installed backwards! You can also see a nice crack forming in the spring. The spring has two wedge shaped arms that go out to the sides and apply a slight outward force. It also keeps tension on the pad so it doesn't rattle.

I've thought about making a low tension pad retraction spring from a piece of thin stainless steel wire, such as a bicycle spoke. The brake pads on my car have a slot in the middle, so it would be easy to bent a spoke into a squared U shape and insert it in the slot. Just bend it differently to adjust tension.
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Old 03-07-2011, 12:31 PM   #7
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Re: wobble rotors

I don't believe the wedge shaped arms have any retraction effect at all. Remember that only one pad moves, and the caliper itself floats, but the pieces you are speaking of are bearing on the caliper itself, NOT on the pads. The caliper itself does NOT open and close. I believe if you examine it closely. These springs are just anti rattle springs.
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Old 03-07-2011, 10:09 PM   #8
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Re: wobble rotors

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I don't believe the wedge shaped arms have any retraction effect at all. Remember that only one pad moves, and the caliper itself floats, but the pieces you are speaking of are bearing on the caliper itself, NOT on the pads. The caliper itself does NOT open and close. I believe if you examine it closely. These springs are just anti rattle springs.
Hmmm, perhaps I should describe the pic better.

The Mitsubishi EVO uses the same brake spring design on front and rear brakes. The EVO uses fixed calipers with 4 opposed pistons up front, twin opposed piston fixed caliper at the rear. The pistons act directly on the pad. The brake pad in the pic has a shiny black backing plate, and the wedge shaped part of the retraction spring is in contact with the inner edge of the backing. There is a small gap between the caliper and the outer edge of the retraction spring. The flat vertical portion of the spring is held in tension by 2 horizontal bars, which pushes the center of the spring against the pad.
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Old 03-07-2011, 10:45 PM   #9
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Re: wobble rotors

The real question is, if you jack up an Evo wheel and give it a whirl, is the brake not dragging at all?
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Old 03-08-2011, 08:52 PM   #10
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Re: wobble rotors

i thought GM back in the early 80's had a idea like this where there was a little rise in thickness in the rotor or something that as it spun would bump the caliper piston back JUST enough.

i swear thast what my chevettes brakes do haha. stupid GM and thier solid steel rotors!!!
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