Gunther

Does an engine see the same workload at 4500rpms in first gear, as it would in fourth gear? I would assume yes, but I was just wondering

internetautomar

iTrader: (30)

no it does not

Jeff92se

iTrader: (82)

I would have to agree w/ post 2

Brudda Bob

iTrader: (3)

I'm not a mechanic but I'm sure it doest. I think a simple analogy would be riding a ten speed bicycle. You start in 1st gear because it's very easy to pedal, as your speed increases you would need to change into a higher gear. Why? Because if you stayed in 1st gear you would become exhausted faster as opposed to changing into a "higher gear". i.e Your body is doing "less work" but youre moving faster because youve already gained that momentum from 1st gear.Depending on how fast you keep pedalling you may need to change into another higer gear and so it continues until you will find yourself barely pedalling yet youre moving really fast. You also wont start pedalling your cycle in the 10 gear because it's more difficult. It's the reason we start driving our cars in a lower gear to build that initial speed and then change it.

Engines have RPM (revolutions per minute) which is indicated on the tachometer. Look at your corresponding speed(mph) for the tach speed. You will notice that as your tach and engine speed increases you will need to shift into a higher gear. Same concept as shifting in the 2nd gear on the bicycle. Thats also why cars have a redline value because if you exceed that value for a considerably period of time you can risk damage to the engine.Thats like a cyclists becoming exhausted.

I think Hondas are most noteworthy for excessively high redline on their cars, some are 8000 plus on a FOUR cylinder engine which I think is an amazing feat. Then again Honda has tons of exper. R&D etc in their bikes.

Automatic cars shift themselved via complicated electronics.Manual shifts are done by the driver on 5 speeds.

Like I said I'm not a mechanic so I may be wrong.

maxitech

iTrader: (7)

Looks good from here, Bob!

renzokuken1227

does anybody have a front driver side window motor for sale?

Greeny

iTrader: (43)

http://forums.maxima.org/forumdisplay.php?f=62

bvtran

iTrader: (3)

the bigger the gear, the lesser the load it feels. That's why your able to drive much faster at higher gear than low.

Alex_V

What?

~Alex

mtcookson

iTrader: (2)

Low gear (high ratio) like first = low load/less work
High gear (low ratio) like fifth = high load/more work

MAXIMUS G EKSUS

Correct me if I'm wrong but the question states Does an engine see the same workload at 4500rpms in first gear, as it would in fourth gear? I would assume yes, but I was just wondering.

So taking the bike example, if one pedals at say 1/2 turn every second on 1st gear going at 5mph, does it take the same effort than someone pedalling 1/2 turn every second on 20th gear going 35 mph? I think yes ! Leaving the effort of staying balanced out of the equation.

I don't know if it makes sense, but to me it does,

Therefore, the engine work load should be the same in 1st gear or 4th gear going at the same 4500 rpm. Leaving the effort of going from a stop to moving out of the equation

jlars205

I think I get what you're saying. If the engine is going at constant speed (rpm-wise) in either gear, like 4500rpm, the wear on the engine in any gear should be the same, right?

MAXIMUS G EKSUS

Yes, because it has the same amount of rotation per minute ! (rpm)

But hey Gunther, what is the reason of asking such a question ?

mtcookson

iTrader: (2)

Negative... lets say we have a VE 5-speed with stock tires. 1st gear at 4,500 rpm would roughly be 15 mph. In 4th gear at 4,500 rpm it would nearly be 95 mph. There would be a higher load/more work on the engine due to aerodynamic drag, among other things.

Just to note, that's not to say fuel economy would be lower going 4,500 in 4th compared 4,500 in 1st. Basically you're going a further distance on the fuel used in 4th compared to 1st and therefore should get better miles per gallon even though the load is higher in 4th. Just thought I'd mention that just in case.

jlars205

Well, I guess the engine would be doing more work in physical terms (higher speeds in higher gears) but I don't think you'd be putting any extra wear on the engine if it's going 4500 rpm regardless of gear. But wear on tires and parts after the tranny would be higher because of the higer speeds. Is that what you were saying?

Hectic

iTrader: (20)

mtcookson

iTrader: (2)

We're talking about load on the engine i.e. the amount of work we're making the engine do, not wear. I wouldn't worry about wear as long as you keep maintenance up and don't hold the engine at redline for extended periods.

Gunther

I don't really think the bike example is that relevant, riding a bike at 50rpms up a hill is different than riding a bike at 50rpms on flat ground in the same gear.

I was asking because I don't wanna blow my engine driving too fast on the highway

(and because I just like to know things)

jlars205

I agree. The only thing is that bigger gears are work multipliers. At high velocity you'd be doing more WORK with a bigger gear (ie going faster) but it doesn't take any more EFFORT (ie force) on the part of the engine than to maintain that engine speed in a lower gear. See what I mean? I think there needs to be a distinction between work and effort.

Jeff92se

iTrader: (82)

I think more effort is needed to keep the car at a higher speed due to wind resistance.

Gunther

I understand that part, my question isn't do I need to step on the gas more to make the same amount of gain in a higher gear, but if the engine is 'working harder' at a certain RPM level in different gears.

So for instance, is it more risky to redline the engine in fifth then in first?

Brudda Bob

iTrader: (3)

Interesting to say the least!You do have a point and I totally understand what youre saying.I think Youre approaching it from the perspective of a ratio. 1/4 is the same as 100/400.

However I doubt whether youre factoring the final mph of both vehicles after a period of T=time I’ll give you MY basic definition of workload and how it applies to the situation.
WORKLOAD: How heavy is the work, how much work energy is applied to produce a specific result.Specific result will be the final speed in mph
Work energy is what’s being done by the engines to achieve the specific result and which of those engines is working more than the other.

SCENARIO1: 1ST GEAR @4500RPM final speed is say 50 MPH.
SCENARIO 2: 4TH GEAR @4500 RPM final speed is 75 MPH

However we need the same resulting speed for both gears! WHY? Because we are measuring the workload. The input and output needs to be the same since were trying to determine whether the engine is working more@4500 in 1st or 4500@4th for the same final speed. If you can carry 50 blocks in 1 hr. and I can only carry 50 in 2 hrs, then who is working harder?You are! So your workload is heavier and youre working harder.All things being equal.
With this in mind we readjust the rpm in 4th to match 50 mph. Lo and behold the engine rpm drops to about 3000!!!!

Lets take 2 new 5 speed vehicles with everything being equal on them.We shall exclude acceleration and deceleration since you wanted to.
CAR#1 starts and reaches 4500 rpm for a resulting speed of 50 mph.We set the CC and leave it there.
CAR # 2 starts and we reach 50 mph, however we’re in 4th gear but only doing 3000 rpm.We also set the CC and leave it.
Which of the vehicles is working more, or being overloaded as opposed to the other?

CAR 1 with rpm’s @4500 or car 2 whose engine is doing 3000 rpm’s for the same resulting speed.

SCENARIO1: 1ST GEAR @4500RPM final speed is 50 MPH.
SCENARIO 2: 4TH GEAR @3000 RPM final speed is 50 MPH

Difference in rpm for the SAME speed but in DIFFERENT gears=1500.
Therefore we can deduce that gear 1 is working @1500 MORE RPM to produce the SAME OUTPUT.

If we allow those cars to run infinitely, which engine will wear/work more? If we have the exact cars (all things being equal) and you always drove your car to 4500 rpm and kept it there to give you 50 mph,and I always drove my car to 4th gear to obtain the SAME SPEED that youre at (my rpm’s will be lower), whose engine is being overloaded?

Maybe someone come forward with the formulaes.We can plug numbers in and see the result

braxsusriely

This thread is getting pretty funny....

lets say we are in... "space" and there is no air drag.....
TPS: or your throttle position sensor tells the ECU how far you pedal is pushed
RPMs: your ECU reads this and with some math of the Pedal postion and speed determines the load on your engine which in then turn changes your fuel and air required. Like if you go up a hill, you slow down until your ECU calculates how much more air and fuel is required to maintain the speed like when you are in cruise control. If you step on the gas you are upping the load.

Alex_V

The slower the tach moves for the same throttle position the heavier your engine is loaded simple as that.

and we have redlines and multipul gears because at 10K rpm there is a ALOT of force acting on the engine. 1/10 scale rc cars have redlines (well they stop making power) between 30-40 THOUSAND rpm's. Balancing these engines is super critcal and they wear out very fast. They make a crap load of power though. And untill recently most r/cs were a single speed so you had to wind them out, thats very bad for reliability (sustaining high rpm's).

1st gear tops out at about 30MPH. 4th is good for something like 120. So your engine is going to be at about 12K rpm in 1st gear while in 4th gear its only 3K rpm. And the forces on pistons and rods go up exponentially after about 6K-7Krpm's its very significant.

Try balancing a VG so it can go up to 9K-10K rpms. Then try again for 12K. The load of the cars weight and aerodynamics will be easier to carry in lower gears (look up mechanical advantage of gearing) but if there was only one or 2 short gears the engine would quickly destroy its self at sustained high revs.

Theres so many aspects of load on an engine we could be here for months.

In the end the engine will be less "loaded" in lower gears because the transmission multiplies its torque depending on the gear. But its not feasible to have super short gears due to forces acting on the engine internals.

~Alex

jlars205

Here's an experiment that would settle it.

Get two identical cars with equal amounts of gas off their wheels (on a lift or something so they don't actually move, experience external friction, or wind resistance). Then run one in 1st gear at 4500 rpm, the other in 4th gear at 4500 rpm. That one would need a fractional amount more gas to get up to speed. Then see which one runs out of gas first. Whichever one does has the higher load.

Any volunteers? Just kidding, but in all honesty this thread has really gotten me to think. It's like I'm back in physics class or something.....

jaguax

iTrader: (1)

I've have two random questions that I've always pondered.

Why are transmissions typically only 4-7 speed? Why not 10+ speed? In other words, why can't we have really high gears that allow our cars to reach 300 MPH? Is it just for practicality reasons, since people will never actually go that speed (unless it's a giant straightaway race)...

Or is it that the engine just can't handle anything higher than 7th? I'd imagine that most modern high horsepower/torque engines should be able to, even though acceleration in 8th+ gear would suck hardcore.

Another question. Why don't boats [or at least the typical boat] have transmissions?

CapedCadaver

iTrader: (8)

A 450-HP Daytona/Talladega stock car cannot go faster than 190mph. Gearing it for higher speeds would be useless, because at the redline it's at its top speed, and if you gave it more gear you'd hurt acceleration witout improving top speed. There comes a point at which all the power your engine has is overtaken by wind resistance and other frictions and stuff. The theoritcal top-speed gearing in 6th of a Dodge Viper is 314mph, but it can't go but about 185 in real life, because it takes too much power to overcome resistance. Heck, even the 1001 HP Bugatti Veyron proves that. "It takes just 270 HP to make this car to move 155mph, but the next 100mph from 155 to 253 takes an extra 730. That's because the faster I go, the more every force in nature is trying to slow this car down." said James May, who definitely knows a lot about cars. The engine can't make enough power to justify a 400mph gear, unless you plan on running 1100rpm down the interstate. And think of the increased weight of the transmission to make that many more gears. And how hard it would be to have 5 gates instead of 3 on your stick shift. Or how much more crap the A/T computer would have to think about to pick the 'right gear'. Lexus is putting 8-speed auto on their new LS460 sometime soon. You can make a 20 speed transmission and run it on a car, as long as you space the gear ratios closely. Then you shift from like 2500-2400 instead of 2500-1900 on a normal car's shift.

CapedCadaver

iTrader: (8)

I'd say 1st gets the easy job, because even though your RPM is the same, the workload is really all about how much gas pedal you have to use to maintain the car's speed on level ground. If you reduce it to say 2000rpm, just look how high your engine revvs if you do that and hold the gas pedal steady, then quick step on the clutch, or knock it into neutral. What's your RPM now? In 1st gear it'll climb to about 2400rpm after the load is removed. Going 50mph in 4th A/T and about 40mph M/T in 4th at that 2000rpm you'll see it climb to about 2900-3100RPM, which shows you the comparison in load between 3100 unloaded and 2400 unloaded. Using 5000RPM in 5th and 1st you'd see the engine overspin to about 7500+rpm if you clutched it in 5th, and you'd redline in 1st but not go into the red.

Thherefore, the higher load is in the higher gear.

Alex_V

Also the more gears you have, the more power it takes to turn all of them. That means less power to the wheels to actually move the car and thats lower top speed.

~Alex

Alex_V

What? If you were above 30ish mph in any other gear, and some how get the shifter into 1st (wont happen) and dump the clutch, you'll be in the XX,XXX range and blow your engine. Just not possible.something like 3-2 when you wanted 3-4 happens all the time and lots of engines die of that.

~Alex

Jon94SE

This is retarded, try taking off in fourth gear as opposed to first. As far as the rpm's are concered what happens when you shift from first at 4500 directly to forth, i'm sure the workload would increase quite a bit?

Alex_V

Like I said. Its mechanical advantage of the higher gearing in the lower gears. The more reduction a gear has the more wheel TQ the tranny puts out and the less load the engine has.

~Alex

mtcookson

iTrader: (2)

5,000 rpm in 5th shifting 1st would be 20,700 rpm to be somewhat exact.

To add on to this, in lower gears the engine itself is actually producing less torque than if you were in the higher gears.

Back to the bike example again... if you were in first gear on the bike you can just peddle lightly without even getting off the seat to start moving. Put it in a higher gear though then you start having to put more weight on the peddles, even your body weight sometimes. More or less the same thing.

renzokuken1227

i need a new window motor for the front drivers side. does anyone know where i can find one local or online? i live in houston

internetautomar

iTrader: (30)

http://internetautosupply.com/catalog/
I think I actually have a used one in the garage.

CapedCadaver

iTrader: (8)

I wasn't referring to shifting. I meant that if you take your car up to 5000 in first and hold steady, the amount of throttle you use to hold steady in 1st at 5000revs will see your RPM shoot up to around redline if you depress the clutch. If you get your car into 5th gear and up to 5000 revs in 5th and hold steady, you are using so much more throttle, that if you depress the clutch your RPM would go as high as the engine could spin without hitting a rev limiter or something, because of how much throttle it took to maintain 5000RPM in 5th.

I'm not saying to get to 5000RPM in 5th then shift into 1st.. that'd kill everything, like you said. The second time I ever drove a manual I hit 5-4 but it turned out I really did 5-2. It was OK because I wasn't going but about 40-50mph at the time, and I think 2nd gear can go about 65mph on that car (1991 corolla 1.6L).

Tquick

I'm sorry, but having more gears doesn't decrease the amount of power that the engine can deliver to the wheels. If it did, then I seriously doubt tractor trailers would have transmissions with 13 or more gears in them. Lower gears (which have higher numerical gear ratios) give the engine greater mechanical advantage (leverage) over the car, like pedaling up a hill in 1st gear on your bike. The engine runs fast, the car moves slow, but it can go up nearly any hill. Higher gears (which have lower numerical gear ratios) allow the engine to move the car at a higher speed, like cruising along in 10th gear on your bike. The engine can move the car very fast, but it can't develop much rear wheel torque, so it is hard to maintain speed going up hills. High gear means more load on the engine.

CapedCadaver

iTrader: (8)

Yeah, but due to the very narrow power band on a large diesel, they have to keep their RPM in a narrow window and thus need lots of gears to make the thing go. Gasoline engines typically have much larger power bands thus the gear ratios don't have to be as close to make the car move properly. So it'd be cost-ineffective to run a 18-speed on a passenger car. Though a synchromesh manual gearbox would lose some power due to added friction from the synchromeshing gears, but other than that it'd have no effect on the sheer power. It would, however, affect the curb weight and the power-to-weight ratio adversely.

And "if you gave it more gear you'd hurt acceleration witout improving top speed" I said "more gear" as in "more [theoretical top-speed in your top] gear", not "more [physical] gears". Easy to misread.

Alex_V

Tquick-Yes it does. Ask in the advance section if a 6speed transmission gives less WHP then a 5 speed. Same thing for the new 7speed autos. Think a 350Z 6speed and 240sx 5speed eat up the same power? Not really.

Caped- the best ratio in 5th is one that has redline just after your absolute top speed (maybe 20-50rpm) That way you have the shortest ratio possible and still can go top speed. How ever that might not be good for highway milwage depending on your cars HP.

Example. A stock 5speed max may only go 142mph. Boost it and your max speed is redline in 5th. Lengthen 5th and it'll go up, but thats only with high power cars.

What your suggesting is exactly what he said. having less reduction hurts acceration and gives more top speed. Only good for mpg and cars with enough HP to hit top speed.

~Alex

mtcookson

iTrader: (2)

Actually, in many cases of turbo charging a vehicle, wider gearing actually improves acceleration due to the way the engine produces the torque compared to an n/a. If you go the turbo route and have a wider gearing setup not only would you have a higher gear limited top speed and potentially better fuel economy but it should accelerate faster as well (unless the torque curve remains somewhat narrow like on many n/a cars... then there is a chance acceleration would hurt.)

We don't really have any good options for wider gearing minus that the VG-5 is slightly wider due to the diff. compared to the VE-5. If you happen to be doing a rwd setup though, that'd be something to mess with.