Production Toyota FT-86 Details and Design Previewed by Toyota Sports Vehicle Boss

[serialk11r]

There's something called a gearbox...you can make any amount of torque at the wheels from any engine with one! This is the advantage of a high rev motor, you stick super short gears so you get more horsepower at a lower speed, and greater acceleration. Then if they gear it right you can also get good efficiency from the longer high gears. A large displacement motor needs to turn at super low rpm to produce less power efficiently except frictional and thermal losses become pretty big so it's not very efficient.

[madfast]

Originally Posted by serialk11r

There's something called a gearbox...you can make any amount of torque at the wheels from any engine with one! This is the advantage of a high rev motor, you stick super short gears so you get more horsepower at a lower speed, and greater acceleration. Then if they gear it right you can also get good efficiency from the longer high gears. A large displacement motor needs to turn at super low rpm to produce less power efficiently except frictional and thermal losses become pretty big so it's not very efficient.

great in theory, but not in practice... the car is already confirmed to have only 6 speeds. how can you gear it to be super short, and tall enough for fuel econ, at the same time without having noticeable gaps in the middle?

also how short is "super short". most manufacturers gear the car to hit 60 right before the 2-3 shift for the sake of 0-60 times... do you propose to hit 60 somewhere in 3rd? what top speed do you want?

[Levi]

7.000 RPM Redline is standard on all gazoline engines nowerdays. It has at least to be 7.500 RPM, like the Renault Clio R.S. engine, NA 2.0l I4, with 200 PS and 200 Nm.

[serialk11r]

Originally Posted by madfast

great in theory, but not in practice... the car is already confirmed to have only 6 speeds. how can you gear it to be super short, and tall enough for fuel econ, at the same time without having noticeable gaps in the middle?

So I don't have experience with performance driving or anything but I get the impression that you never hit 6th gear on the track? In that case they have the option of making the 6th gear the cruise gear. If not then we'd better hope they have some awesome way of reducing the pumping loss at part load.

[madfast]

Originally Posted by serialk11r

So I don't have experience with performance driving or anything but I get the impression that you never hit 6th gear on the track? In that case they have the option of making the 6th gear the cruise gear. If not then we'd better hope they have some awesome way of reducing the pumping loss at part load.

for all intents and purposes, 6th gear is almost always the cruise gear. so you now have 5 forward gears. how do you gear it to be "super short" while still tall enough to get ok fuel econ? like i said tq multiplication through gearing is great in principle, but there are a finite number of gears that we can realistically use, and there are fuel econ constraints in the market that lead us to gear the car taller and taller...

bottomline: gearing cannot replace engine tq in the real world. theoretically? yes. realistically? no.

[Traum]

Unless you are dealing with some diminutively sized engines (less than 1.5 or so?), the engine is gonna have enough torque to work well with some well chosen gear ratios. In my 5-speed pos beater, I rarely ever go beyond 3rd gear for city driving. On the freeway, I am more than happy to stay in 4th gear. Unless I am cruising on some Interstate-equivalent highways, I have no use of my 5th gear.

With a 2.0L engine, you can very easily gear 1st to 4th to be useful in the city, have 5th for the freeway, and 6th for cruising on the Interstate. It really isn't that hard to get it done, and it'd be easier still if you have a redline close to 8k. I just can't understand why manufacturers are so cheap that they intentionally chooses not to do it / do it right.

[SVTSHC]

Originally Posted by madfast

for all intents and purposes, 6th gear is almost always the cruise gear. so you now have 5 forward gears. how do you gear it to be "super short" while still tall enough to get ok fuel econ? like i said tq multiplication through gearing is great in principle, but there are a finite number of gears that we can realistically use, and there are fuel econ constraints in the market that lead us to gear the car taller and taller...

bottomline: gearing cannot replace engine tq in the real world. theoretically? yes. realistically? no.

I was going to disagree but then I gave it some more thought and realized you're right. realistically you couldn't shorten first, it'd be impractical making the amount of engine braking that happens and feathering you'd have to do in traffic enough to make you want to blow your kneecap off. Second you COULD shorten slightly and third a little more so but by the time to you hit 1 to 1 (4th) you'd have a good bit of ground to cover and being that this car is NA it'd feel like a huge power gap unless you were shifting out of third at like 5.5-6k. Problem is, the torque this motor will likely make isn't enough to start doing any worthwhile lengthening of the overdrive gears; due to where the powerband is likely to hit it's going to make the car feel like it has NEGATIVE balls in fifth and worse when you hit secondary overdrive (econogear 6th).

Or I could be totally wrong and missing something important

[serialk11r]

Originally Posted by madfast

for all intents and purposes, 6th gear is almost always the cruise gear. so you now have 5 forward gears. how do you gear it to be "super short" while still tall enough to get ok fuel econ? like i said tq multiplication through gearing is great in principle, but there are a finite number of gears that we can realistically use, and there are fuel econ constraints in the market that lead us to gear the car taller and taller...

bottomline: gearing cannot replace engine tq in the real world. theoretically? yes. realistically? no.

When the engine is producing power, efficiency is quite high, and the extra frictional loss is not very significant. The main concern is part power cruise, if you have to spin your engine at 4k rpm on the highway, you certainly do not need very much torque at all, and so you have a lot of losses from various places. One very long gear that lets us cruise with 50-60% of engine torque at freeway speed would give extremely high highway mpg numbers. Even around town when you're going on 35-45mph roads that super long gear will help. Porsche gets this extra long gear with a 7th gear so there's not a huge rpm gap between 5th and 6th, but I think they can do this in the name of fuel economy.

The sacrifice made would be that this long cruise gear would have "negative balls" as the above poster said, but that's why you can shift down to 5th for more power right? The whole point of more gear ratios is that you have more choices, not so you can sit in one gear and expect it to do everything.

EDIT: oh and a benefit of a short 1st gear is a slightly longer lasting clutch since you don't have to slip it as much to get started.

EDIT 2: I just remembered how most cars have pretty widely spaced gears, so you have to ask yourself, is the "big" gap between this hypothetical super fuel economy gear and the next gear down really that bad?

[Spaceywilly]

A wide torque band is definitely more important to me than having huge peak torque or hp. I'm hoping this car will feel like a GTI or Mini Cooper S to drive. Both are underpowered on paper, but if you actually drive one you would never know it. Torque is what you drive.

Here's a chart I made showing the difference between the 5spd WRX (red) and 6spd STI (blue) ratios. In this chart, flatter lines = higher ratio = more torque multiplication. As you can see, the line for the WRX gets steep very quickly as you go through the gears. This means you lose effective torque to the wheels more quickly. In the 6spd, the lines stay flatter, meaning you are able to keep the torque going as you build speed. If you were to watch a side-by-side video of an STI and WRX accelerating, even if you had the same engine in both, the WRX would fall behind after the shift from 1st to 2nd, because a)the engine would fall out of the peak torque range and b)torque multiplication is less in the WRX 2nd gear. The 5sp car does have one advantage in that it requires one less shift to get to a given speed, but this doesn't make up for the relative lack of torque for acceleration. Notice also that the slope for 6th gear is similar in both cars, meaning you don't sacrifice much fuel economy for the 6spd. Other things to notice, 1st gear is the same in both, and 3rd gear in a WRX = 4th gear in an STI.



Here is the site I used to look up the ratios:
http://spda-online.ca/modules/tinyco...ite/tc_28.html

[madfast]

Originally Posted by serialk11r

When the engine is producing power, efficiency is quite high, and the extra frictional loss is not very significant. The main concern is part power cruise, if you have to spin your engine at 4k rpm on the highway, you certainly do not need very much torque at all, and so you have a lot of losses from various places. One very long gear that lets us cruise with 50-60% of engine torque at freeway speed would give extremely high highway mpg numbers. Even around town when you're going on 35-45mph roads that super long gear will help. Porsche gets this extra long gear with a 7th gear so there's not a huge rpm gap between 5th and 6th, but I think they can do this in the name of fuel economy.

The sacrifice made would be that this long cruise gear would have "negative balls" as the above poster said, but that's why you can shift down to 5th for more power right? The whole point of more gear ratios is that you have more choices, not so you can sit in one gear and expect it to do everything.

exactly my point. theoretically you can do this but realistically no manufacturer will. porsche basically had to use a 7th speed because they simply wouldnt dare to use 6 speeds and have a "negative balls" gear.

right, the point of more gear ratios is more choice, but like i said there is a realistic limit. with a manual tranny it looks like porsche's 7 speed is the most in a new car. but do you realistically see 8 speed manuals in the near future? with auto's 8 and 9 speeds will soon be commonplace. but obviously with an auto the computer shifts for you, and you will never get stuck in a "negative balls" situation as the tranny would just shift down a couple of gears automatically.

[serialk11r]

But look at your chart, the 6th gear on the STI is geared SHORTER than the 5th gear on the WRX! Basically they are sacrificing efficiency and quietness for acceleration. What I'm saying would be analogous to taking the 6th gear, and instead of having nice even ratios between the gears, boost it past the wrx 5th gear so it can get extra good fuel economy.

I still don't think people's complaints are about the torque being peaky. Look at the Honda K20, which people complain about having not enough torque. The VTEC system's 2 profiles each have an optimal rpm. The lower cam is more fuel economy oriented so its torque isn't quite what it could be, but the peak is almost at exactly the same torque level as the max torque of the motor. I'm using this chart: http://hondanews.com/media_storage/GIF/S2_Civic_2.gif

As you can see the torque almost peaks at 3000 rpm as well as 6000ish. At 3000rpm the engine SHOULD be able to hit a higher torque figure because there are less frictional losses and pumping losses, but Honda gave it lower duration to improve fuel economy.

The only way to get the torque that everyone wants is to increase displacement (sacrificing fuel economy), or sacrifice fuel economy with more aggressive cams (though I don't think this would solve the problem, seeing that people complain when the torque is just as good down below as it is up top). Optimizing valves only gets you so far. Or you can add a turbo which poops out before the redline so you feel like there's more torque down below. Which also hurts fuel economy. I think it's a psychological thing, when people think they have more torque when the engine is revving high, because clearly the difference isn't that big. So what people are really clamoring for is a bigger engine.

[Spaceywilly]

Yes, they are not exactly the same, but they are pretty close. If you take a typical cruising speed of 75, there is only a 200RPM difference (3000 in the WRX vs 3200 in the STI). That wouldn't have a noticeable affect on fuel economy or noise. I can speak from experience that 5th gear in a WRX still very "usable." I am still able to pass people on the highway without downshifting. Yet it isn't revving so high as to be annoying. Obviously it can't cruise at 1600 like a V8 can, but it also gets much better fuel economy even with the fairly short gearing. The turbo and engine tuning have much more of an affect on fuel economy than gearing does. Without a turbo and with DI this car should get somewhere in the mid 30 MPGs easily.

[serialk11r]

Originally Posted by Spaceywilly

Yes, they are not exactly the same, but they are pretty close. If you take a typical cruising speed of 75, there is only a 200RPM difference (3000 in the WRX vs 3200 in the STI). That wouldn't have a noticeable affect on fuel economy or noise. I can speak from experience that 5th gear in a WRX still very "usable." I am still able to pass people on the highway without downshifting. Yet it isn't revving so high as to be annoying. Obviously it can't cruise at 1600 like a V8 can, but it also gets much better fuel economy even with the fairly short gearing.

Right but the thing is, that level of fuel economy still isn't enough, not if car manufacturers are supposed to hit the new requirements. If we can cut rpm 20%, we increase the amount of torque we need by 25%. If we're talking a traditional throttle plate controlled engine, this 25% could be a huge decrease in pumping loss. A taller gear also has less frictional loss, and the lower rpms mean the engine has less frictional loss. Thermal losses go up, which is why those big engines that cruise in the 1k rpms still have trouble putting down good fuel economy when they theoretically should be able to do better, but with a 2.0L engine you wouldn't be that low anyways.

Personally I feel like a 7 speed gearbox is about right. Current 6 speed gearboxes on sports cars aren't keeping the rpms low enough at highway cruise speeds. Adding one extra gear with 20-25% higher gear ratio would put us close to the optimal engine efficiency zone. Technologies like Valvematic would put the efficiency peak at lower torque levels, landing it right next to where 7th gear would place us. This fuel economy gain is probably the easiest one for manufacturers to tap. Engine technology improvements, weight reduction, aerodynamics, all cost money, this virtually does not.

[madfast]

Originally Posted by serialk11r

But look at your chart, the 6th gear on the STI is geared SHORTER than the 5th gear on the WRX! Basically they are sacrificing efficiency and quietness for acceleration. What I'm saying would be analogous to taking the 6th gear, and instead of having nice even ratios between the gears, boost it past the wrx 5th gear so it can get extra good fuel economy.

I still don't think people's complaints are about the torque being peaky. Look at the Honda K20, which people complain about having not enough torque. The VTEC system's 2 profiles each have an optimal rpm. The lower cam is more fuel economy oriented so its torque isn't quite what it could be, but the peak is almost at exactly the same torque level as the max torque of the motor. I'm using this chart: http://hondanews.com/media_storage/GIF/S2_Civic_2.gif

As you can see the torque almost peaks at 3000 rpm as well as 6000ish. At 3000rpm the engine SHOULD be able to hit a higher torque figure because there are less frictional losses and pumping losses, but Honda gave it lower duration to improve fuel economy.

The only way to get the torque that everyone wants is to increase displacement (sacrificing fuel economy), or sacrifice fuel economy with more aggressive cams (though I don't think this would solve the problem, seeing that people complain when the torque is just as good down below as it is up top). Optimizing valves only gets you so far. Or you can add a turbo which poops out before the redline so you feel like there's more torque down below. Which also hurts fuel economy. I think it's a psychological thing, when people think they have more torque when the engine is revving high, because clearly the difference isn't that big. So what people are really clamoring for is a bigger engine.

fwiw that dyno is comparing the 2005 si (ep3 with K20a3) and the 2006 (FG2 with the k20Z3). the k20A3 had NO vtec lobe. its vtec worked by connecting both intake valves. when not in vtec only 1 valve fully opens, while the other is cracked open to prevent pooling behind the valve.