Re: Simultaneous Application of Gas and Brake Pedals

Yes, many of the muscle car era cars were deliberately under-rated. The SAE specs have changed some, but HP is still HP. The definition has not changed. What HAS changed is the way HP is produced today. The muscle car era engines put out prodigious torque at pretty low speeds, many of them dropping off quite markedly above, say, 4000 RPM.

Today's engines, being smaller displacement, pruduce less torque, but they continue, due to advanced tuning and design, to produce that same torque, or very close, up into the 6000 RPM range and well above. Since the formula for HP is lb-ft of torqueXrpm/5252, the horsepower available from some of these "mighty mouse" engines is increadible . You just have to wind them pretty tight to get it.

They do not give you quite the "seat of the pants" "grunt" the 455SDs and street hemis, and 427 Shotguns, or 428 CobraJets did. Particularly from a dead stop withouthigh-p-revving heroics.

The parrot effect, I'm guessing.

You are correct. They don't.

Well, to be perfectly semantic about it, the only "manual brakes" out there are the ones on vehicles specially modified for the handicapped. But yes, I agree with you, a properly set up and dialled-in unboosted disc system cannot be beaten in terms of pedal feel.

Unboosted discs are terrific in slick winter conditions, too. We're looking at deleting the brake booster from my '92 Spirit R/T clone. It'll doubtless take a different master cylinder, but there's an enormous variety of MCs that'll fit.

I think the mistake most people make is in thinking that power brakes without boost are the same as unboosted brakes. They're very definitely not. The mechanical advantage of the brake pedal over the cylinder is much greater in an unboosted setup than it is in a power setup.

DS

amplification,

Probably because the vast majority of disc brake cars do have power assist - dating back to the first installation of modern discs on American passenger cars in the '63 Studebaker models, where the disc brake package came with a mandatory power booster.

handicapped. But

wonderful,

definitely

True, although with a reasonably heavy car it does become almost a necessity to have the power booster because you are trading off pedal travel against line pressure, and both need to be kept at a reasonable level.

Personally the only car I've driven with unboosted discs was my '71

914/4, and the feel is spectacular...

nate

Absolutely, the pedal LINKAGE is often different in addition to a different bore size in the master cylinder when comparing power brake and non-power systems for the same model car. In the case of Mopar B-bodies like my '69, the power brake cars had a bellcrank mechanism that moves the master cylinder piston FASTER than the pedal moves. The loss of leverage is more than offset by the power booster... UNTIL the booster quits working and mashing the brake pedal is like stepping on a block of lead. The manual brake pedal linkage is a direct connection from the pedal to the MC piston and has much more mechanical advantage, at the cost of more pedal travel. All other power brake cars have a similar mechanism for reducing pedal travel, or simply attach the pushrod closer to the pedal rather than closer to the pedal hinge (another way of changing leverage)I LIKE the added pedal travel- for one thing it makes "sudden acceleration" a lot less likely (just to tie two threads in a knot... ) ;-p

I agree that 1 horsepower is still 746 watts, but that's where agreement ends. If you could magically bring an LS-1 back through time and let GM rate it in 1969 *exactly* the same way they rated the '69 302 smallblock, I think you'd be surprised how similar they are. Of course the LS-1 can get 28 mpg in a Camaro, which the 302 never did.

4000 RPM was right through mid 50s maybe. Even many big-block muscle car engines of the 60s were good to 5000 to 5500 RPM. Not the long-stroke monsters like the Olds 455, but quite a few others. Some short-stroke engines like the Chrysler 383 could happily reach nearly 6000 RPM as built in the 1960s. If I were to build a 383 with available off-the-shelf pistons today, its simple to make it work beyond 7000 RPM. And we all know that many of the 60s smallblocks were real screamers too- Ford 283s and Boss 302s, Mopar 273s, and the Chevy 302 that was good to nearly 8000 RPM come to mind

No, they produce LESS torque up there, but since HP goes as the product of torque and RPM (as you pointed out), they can produce similar horsepower. Not necessarily MORE horsepower, but similar. There is only a tiny percentage of production cars today that can produce the same real-world horsepower as a Buick 455 Stage I or a Mopar 440. LS-1s do. Vipers do. The 5.7 Hemi comes close, and the 6.3L Hemi (coincidentally about 383 CID- aint that cute?) promises to do as well or better. Ford Modulars don't (except the 32-valve Cobra which is about a tie). Only the rather exotic BMWs and Benz's do.

What is true and what I think you're getting at is that the garden-variety sedan V6 of today (say, a Chrysler 3.5 or a Buick 3.8) produces more horsepower than a garden-variety 2-bbl sedan v8 of 1975. But who really cares about that?

Which is exactly what make them BORING.

I've seen a Dodge Aspen do this. True, it was a 1980 model police package with the 360 4-bbl and a monster exhaust. It could be held with the brakes and spin both back tires.

-- Jeff Wieland

Well, a self-energizing drum brake does take significantly less line pressure than a disc to develop the same torque at the wheel... I'll grant you that the explanation given above is inaccurate, but in a typical disc with floating shoes and an anchor pin at the top, a lot of the torque generated actually comes from the rotation of the drum forcing the primary (trailing) shoe into the anchor pin.

nate

I had a new 1975 Fuel injected Beetle when I was a kid. There was no clutch lockout to start the vehicle. My dad went to move the car cause it was blocking his car's access to the garage in the driveway. Temperature was below freezing, but not by a lot. Throttle stuck open after he touched the pedal ( he was not used to fuel injection cars and had "tapped" the gas pedal like a regular carb car to set the choke for cold weather start.) In gear the car was it started and raced through the garage door. ( remeber

1st and reverse are very low ratios ) Turns out the slush and snow build up had accumlated and frozen in the tube that carried the throttle cable back to the engine. So after he had "Tapped" the pedal partially, the cable remained stuck while the pedal returned to normal (springloaded) position.

Even though it caught him by surprise he did hit the brakes but being in a low gear the car (even tho it was a low horsepoer car - ie: a beetle) managed to build up enough momentum to break through the garage door before stopping.

In addition I have had several cars that have had momentary surges or throttle sticks that required great effort to prevent catastrophe. I had a

66 Coronet with a transplanted 413 that once every three or four months would race for no reason ( eventually I ditched that carter and got a remanufactured one to solve the problem.

All I am getting at is there are a lot of reasons why something 'could" interfer with fuel line, mechanical or electrical throttle body or electronically controlled engines.

I think anyone who dismisses such a claim awithout fully investigating is only furthering the mass hysteria often caused in the driving world by those that don't know...

The poor man was honestly looking for an answer at the beginning of all this and everyone seems to have taken the subject personally.

I think it could be argued that for a commercially successful main-stream consumer vehicle of today, they do.

Yes - achieved with much smaller diameter, longer travel master cylinder pistons to gain back some of that mechanical advantage. That comes at the "cost" of much greater pedal travel, which has the upside of greater sensitivity (i.e., being able to modulate the pedal more precisely).

I guess my comment was about what 95+% of people drive on the road today. Apparently the mfgrs., for good or bad, feel that the public wants short pedal travel for *perceived* quick reaction time and

*perceived* safety.

The car stops

If there is no type of boost at all, then it is, by definition and the laws of physics, at the price of longer pedal travel and the advantage of greater control - again - by playing games with the master/slave piston diameter ratios.

The reason that they don't have power boost is that (1) there is not adequate vacuum to guarantee boost under all critical conditions, and (2) The weight penalty of a separate electrically powered vacuum pump is too high. The obvious solution for that niche application is to utilize the adaptability and quick reflexes of the drivers and have a bonus of greater sensitivity (modulation control) as a bonus.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

No. The reality of modern consumer vehicles that will be driven by quite a range of ages, mental quickness, and physical strength.

I used to drive an International Travelall (similar in size to a Chevy Suburban). Unfortunately the mfgr. figured it didn't need power steering - but, man, you should have tried to parallel park that thing - quit4e a feat even for a teenager. I think there would be similar problems selling a modern vehicle with unpowered disk brakes as selling ones without power steering just due to human factors.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

I guess I have to ask why you snipped the rest of that paragraph where I essentially said exactly that. Continuing from where you snipped my post: "...your vacuum reserve is depleted, and you essentially have no (or extremely weak) brakes - this could become critical if a sudden acceleration situation arises (due to driver error, floor mat jam, or vehicle controls failure). The mechanics of the drum brake is totally immune from that loss of amplification."

A person in such a panic situation is not only possibly going to pump the brakes, but will very likely do so, only to find the brakes getting very weak by the first pump, and for all intents and purposes, totally gone by the second or third, and the remainder of the event, whatever it turns out to be, will be over in mere seconds.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Obviously you meant "but in a typical drum with floating shoes..." 8^)

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Bingo! An experiment that the naysayers refuse to try or don't want to admit the results when they did. Under those conditions, by the second or third pump, most boosted disc brakes are less effective than the typical parking brake at slowing the vehicle down.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my adddress with the letter 'x')

Sometimes I amaze myself. Sometimes even in a good way. Sometimes... well, I just amaze myself.

nate

I don't understand the thinking behind that.

If you jam on the brakes, and you haven't locked up the wheels (because you don't hear the tires squeeling), then why would the typical person *let up on the brakes* and perform a second (or third, etc) application?

In a panic situation where you know you haven't locked the wheels, I bet the typical person would keep his foot planted on the brake pedal until the desired degree of deceleration has been achieved.

Rawk! Yes.

Right, 'cause women and little old men *never* drove before what you arbitrarily consider the "modern" age. Pfft.

No, the original owner decided it didn't need power steering. In any event, that's irrelevant to the topic at hand, which deals with *brakes*.

Not hard enough, as it seems.

Arguability and truth are not the same thing, and the former does not imply the latter. Most consumers don't know or care what-all goes on under the hood and under the car. Give them a car that works (even marginally, viz. brisk-selling garbage from GM and Ford) and they'll buy it.

7/8" bore vs. 1-1/32" bore, so the "much" smaller diameter amounts to a whole five thirty-seconds of an inch. And that's only on certain vehicles. In some years and on some vehicles ('70 and earlier A-bodies for one example), the same 1" bore was used with or without a booster.

Hydroboost

Hydroboost

Why would you pump the brakes if you were trying to stop a car with the throttle stuck open?

Matt

P.S. To the owner of the TransSport, better get those brakes fixed.

We're talking about the market place - not subject to rigid rules as are the laws of physics. That's why claims made about it are subjective. Certainly you aren't going to claim that you can predict what the "market" will do in response to some subtile technical change - yet there likely will be a repsonse to that change. There's just no formula to calculate the impact.

So that's a 40% increase in piston area = 40% increase in pedal-to-caliper piston force multiplication. Nice trick using a throwing out a linear parameter in an attempt to minimize what is a square law effect. 40% is a big difference when you're talking braking effort.

Which does away with unobtainable vacuum requirements and gets the boost from an "always on" source: the power steering pump. Thanks for reinforcing my point that vacuum source for brakes is unreliable in certain critical situations like stuck throttle, which is what I believe we were talking about.

Once again, my points about the difference between drums and disc brakes were in the context of the cars that 95+% of consumers and no doubt those here drive. I stand by what I said.

The more commmercially viable vehicle will have power assisted disc brakes on the front if not on all four wheels - right or wrong, that's what today's market has determined. It has obviously not always been that way, nor will it likely always be that way in the future.