05RollaXRS

Yes, the rotational mass of the flywheel decreases (engine has to work less hard to spin up the flywheel) so the engine response is much quicker. It does not add new HP, but it reduces drivetrain loss.

The engine response especially in the lower gears is much better. In simple terms, the car will feel 150 lbs lighter due to sharp responses.

On the other hand, with the loss of inertia on the flywheel rotation, revs drop much quicker so the car will stop quicker since the revs will lose quicker (engine will brake quicker) and on the downside you have to shift well even in bumper to bumper traffic (a lot of people say they get used to it) and avoid sloppy shifts since it will stall. Uphill starts are tougher as well since if the clutch is not engaged properly (I generally use e-brake anyway uphills), the engine can stall.

RocketGuy3

iTrader: (1)

I understand that, but I thought he was saying that this wouldn't actually increase wheel horsepower (I know it doesn't effect the amount of power at the crank, though).

I was saying if it increases the torque at the wheels at a given RPM, wouldn't it increase the power there as well?

lobuxracer

iTrader: (2)

What I'm saying is, reducing weight will not change the amount of load the engine can support. It will change the engine's ability to change speed, but not its inherent ability to support a load.

I've owned lightweight flywheels and I think they're awesome, but I've never deluded myself into believing it added any horsepower. An inertial dyno will indicate a power increase from this weight loss, when in fact there is no power increase. It also does not reduce drivetrain losses as those are frictional and fluid drag related. It reduces inertia, and only inertia. Reducing inertia means you accelerate quicker, but again, the engine moves the same amount of air, the pistons produce the exact same amount of force on the crank, and the crank produces the exact same amount of torque, but since we've reduced the mass it has to accelerate, it accelerates faster. That's all.

RocketGuy3

iTrader: (1)

Would it be safe to say that it doesn't increase peak power, but it increases power in the rev band before peak power occurs?

ride450

No.. and yes.
The lighter-weight flywheel essentially is just reducing the amount of force needed to spin. Thus, the engines power is being used more efficiently, less on spinning the flywheel, more on spinning the wheels. The actual engine output will be identical, however, on the dyno you may see a slightly higher brake horsepower because their is less parasitic loss towards spinning the flywheel.

lobuxracer

iTrader: (2)

Once you have a 5 lb flywheel spinning at 1000 rpm, it takes no more energy to keep it at 1000 rpm than it does a 50 lb flywheel because the system is in equilibrium and the only forces you are fighting are friction and fluid drag. Friction is essentially the same (depending on bearing design) and so is fluid drag, so the only time it makes a difference is when you are accelerating and fighting inertia. If no acceleration happens (balanced resistive force and power production), then it takes no more energy to spin the 5 lb flywheel than it does the 50 lb flywheel. That's the fundamental flaw with the discussion on SuperStang. Horsepower isn't the ability to accelerate, it's the ability to do work over time. There is nothing in the horsepower math that addresses inertial loads because horsepower isn't related to load change, only the ability to support a load over a time period.

It might make a lot of sense to include inertia in these calculations from a practical perspective because it adds an important dimension for racers - the lighter system will absolutely be more responsive and will generate better lap times for a number of reasons. This is part of why the Dynojet showing a change isn't all BAD, but you have to take these things with a grain of salt and understand that the measurement systems have their own quirks and the only fair way to compare is by using the same measurement styles.

So, back to the original premise - if the 2UR-GSE is rated at 425 hp, I would expect to see dyno numbers around 360 hp at the rear wheel. I would not expect the competition to show a significantly better number because they are manuals, particularly because Toyota have focused on getting their automatics very efficient to avoid gas guzzler taxes.

Also interesting is researching later model Toyotas available with automatics and manuals. In many cases, the automatics are actually a few lbs lighter than the manuals. I know it's strange, but it's true. I suspect part of the reason is the adoption of dampened flywheels which very typically weigh in excess of 30 lbs, but even on the Scion tC with a solid flywheel, the auto version is 3 lbs less than the manual for the engine & transmission combo. Who'd've thought that? I sure didn't!

05RollaXRS

Scion TC
(5 speed): 2905 lbs
(auto): 2980 lbs

Camry 4 cyl:
(5 speed): 3265 lbs
(auto): 3310 lbs

Definitely does not look like the autos are even close. Where did you see it? I checked Toyota website and Scion website and tells a different story. My 2ZZ-GE XRS is old, but it weighs 2650 lbs. If there was an available 4 speed auto, it would have weighed ~2720 lbs or so (based on weight difference between 6 speed Celica GTS and auto GTS).

lobuxracer

iTrader: (2)

The New Car Features manual gives the weight of the engine and transmission assemblies. The autos are lighter for sure.

[EDIT]I remember seeing this in the Scion manual and marveling at it. Now I can't find it, and everything else points to the autos (as is normal) being heavier. Weird. My brain must be on vacation, or I need one, or something...[/EDIT]

05RollaXRS

Most luxury car makers still have autos heavier than manual (335 has auto heavier than the manual). I checked Acura as well and the same story there.

The one car I found where the auto was lighter than the 6 speed manual, was the Lexus IS250. The auto also gave slightly better gas mileage than the 6 speed manual. It is mostly because of the gear ratios. However, the manual is very noticeably quicker than auto despite being heavier (Lexus' officially claims almost half a second quicker) against most likely due to gear ratios.

I test drove a red 6 speed manual IS250 with X-package and absolutely loved it. Very fun to drive with great luxury. The X-package made it a serious handling machine. It was willing to rev up a lot more to redline than the auto and the handling was absolutely superb.

p.s. In Canada, the IS250 gets a limited slip differential with the X-package.

TRDFantasy

There has been much debate about this "LSD". From what I understand, it's not a 'true' LSD but some sort of electronic "semi-LSD" that I heard US IS models also get. Don't know what the reality is though.

lobuxracer

iTrader: (2)

https://www.clublexus.com/forums/sho...2&postcount=29

Yes, there is a Torsen limited slip available for the IS250 RWD.

RocketGuy3

iTrader: (1)

Lobux, what you said in those first couple paragraphs makes sense (I think), but that's why I'm so confused here, heh.

I mean if the lighter flywheel allows the car to accelerate quicker, then that means there is more torque at the wheels when accelerating, right? So forget steady state conditions... if the car is accelerating, then at 1000 RPM, it has more torque available at the wheels than it did with the heavier flywheel. If there is more torque at the wheels than before, and the wheels are spinning at the same speed as before, doesn't that mean that the wheels are putting out more power than before? (Wow, that whole paragraph sounds very redundant.)

Again, this isn't talking about staying steady at 1000 RPM; this is referring to the instantaneous torque/power when accelerating through 1000 RPM. So if you take a differential of the car's speed to get acceleration, and then use that to calculate torque at the wheels, and then use that to calculate power, the wheels ARE generating more power, aren't they?

Or are you saying there is an inherent flaw in that very method of calculating power?

TRDFantasy

Thanks for the clarification on that . Lexus specs are a bit vague regarding that.

maxnix

No, it means a particular torque producing value is achieved quicker (due to less rotational inertia , but that maximum peak torque is not changed.

However the area under the torque curve is increased ever so slightly because the maximum torque is achieved earlier.

What really counts is not the calculated HP, but the torque vs. rpm, and in particular the area under the torque curve within the engine's operational limits. All this presumes the gearing and transmission's operation is not affecting the engine's performance negatively compared to another engine and transmission's operational characteristics.

This is why an undersquare engine like the 355 does so well with it's more efficient use of energy courtesy of its turbo charger, especially at lower rpm, the area under the torque curve is greater than if it were naturally aspirated.

Lobux understands what is important, and why dynamometer runs are hardly indicative of much across different machine, barometric pressure and temperatures, different rolling coefficients of friction, and different fuel formulations. Too many variables to control.

Yeah!

So no one knows how much of a drivetrain loss there is w/the 8-speed auto?