R35 Horsepower Figures

[ras1983]

I'm saying trim the weight back 100Kg or so and you guys are reading build a stripped out racecar the size of a lotus elise.

Are previous GTR's too uncomfortable and compromised? They weigh considerably less than the R35; yet i don't hear many complain about their structural integrity or the interior space. Nissan could have easily kept the weight of the car down; the only reason i can see for them to avoid doing this is cost since lighter weight and higher strength material would cost more. Bear in mind the new engine is probably a lot lighter than the RB series and i'm guessing most of the components in the driveline are also lighter and stronger. Which brings me back to my original question, where has the extra weight come from?

[dr1ft.jp]

While it may have moved the weight to a better place I wonder how much extra weight the new gearbox and the massive "nose shaft" add.

20x9.5 and 20x10.5 wheels and massive tyres can't be light no matter what they are made out of, the brakes, everything. The car really is a monster in every sense of the word.

[Bumblebee]

loss is approx 25% no matter the power output...

Its more of a how well things are designed to keep power loss to a minimum.. but most RWD cars have a 25ish % loss through drivetrain.. awds going through a hydra transfer case lose more.

350kw makin 280 @ all wheels.. keep dreamin buddy

[Bumblebee]

but i still want the new GTR.. its fkn SEX

[ras1983]

Yeah i'd still sell a kidney and a lung to own one.

[hrd-hr30]

I would suspect a similar loss in power from the wheels to the engine as previous models (~80hp). Therefore, basing this assumption on an accurate 480hp at the wheels measurement, the GTR probably has about 560bhp (415kw at the flywheel).

Why do people think that drivetrain loss = 25%? It isn't proportional to the amount of power the car is making...

percentage is the best approximation for drivetrain loss.

helical cut gearsets in the box and diff(s) generate side loads proportional to the input torque. So you have a percentage loss there straight away.

frictional losses (in engine, box and diff) increase exponentially with speed. % loss doesn't really model that, but its a hell of a lot closer than just calling it 80bhp loss.

a simple straight bhp loss in the drivetrain doesn't do anything to approximate those factors. besides, I can turn a GTR gearbox and diff by hand, and even Arny wouldn't make 80bhp!

my mates' Landrover Discovery turbo diesel only makes 85bhp and it manages to move a big heavy constant awd vehicle without any problems. amazing what you can do with 5bhp left after drivetrain losses hey?

[Sydneykid]

Harry says % for losses is better and gives some good reasoning. Perhaps the fixed amount method deserves equal time, some reasons are;

If I double the horsepower do I double the losses? If I have a 200 kw engine it looses 50 kw (using a 25% loss), when it makes 400 kw does the same gearbox, tailshaft, diff, driveshafts, tyres, wheels etc suddenly loose an extra 50 kw?

Since energy can neither be gained nor lost, where does the extra 50 kw go? Heat? Keep in mind that 50 kw is a heap of heat (think 50 x 1 kw heaters). I would have boiling gearbox/diff oil all over the place in no time.

Personally I think it is somewhere in between, whilst keeping in mind that it is torque (not horsepower) that turns the divetrain. Hence any horsepower losses would be rpm dependant. Think of Harry's turning the gearbox by hand example, I can't do it at idle speed (750 rpm) let alone 7,500 rpm.

Merry XMas

Gary

[Brockas]

If I double the horsepower do I double the losses? If I have a 200 kw engine it looses 50 kw (using a 25% loss), when it makes 400 kw does the same gearbox, tailshaft, diff, driveshafts, tyres, wheels etc suddenly loose an extra 50 kw?

Since energy can neither be gained nor lost, where does the extra 50 kw go? Heat? Keep in mind that 50 kw is a heap of heat (think 50 x 1 kw heaters). I would have boiling gearbox/diff oil all over the place in no time.

Exactly my point. Although I do like the point about the helical cut gearsets! Hadn't thought of that before...

I guess both are simply an approximation.

[hrd-hr30]

you also have to remember that torque is not an energy, its a force. and helical cut gears lose a % of that force in a different vector. this loss doesn't go directly to heat, its absorbed by the housing or carrier.

I think doubling the engine power would almost double your drivetrain loss. Its a pretty good approximation anyway. Certainly alot better than a fixed value loss. eg if you make almost double the torque to double the power as you can do with a turbo car if you have to then you've definitely doubled amount lost through the helical gears. and they will try to push themselves and their housings apart, or in the case of difffs the pinion will try and climb the crownwheel. On the other hand, if you almost double your revs to double the power, you probably will loose that extra 25kw in heat through frictional losses. If you double the power with some combination of the two (torque and revs) as is the case most of the time in the real world, then you'll loose parts of the increase to each - some extra lost force vector and some to heat. Mind you, you're not at that full power very often, so those extra 25 1kw heaters are only all on at the moment in time you make that peak power figure. The more you're at and around that peak power, the more heat you'll make. hence why serious race cars will have oil coolers on boxes and diffs as well.

Edited December 24, 2007 by hrd-hr30

[R32zilla]

Actually it does an 11.6 with a clutch frying launch. No owner would launch like that repeatedly because you'll either fry your clutch or break your gearbox.

GT-Rs were heavy enough as it was; in tighter corners their weight could really be felt and could prove to be quite tricky to handle in some situations (mainly in a series of tight corners where the weight of the car is shifting from one side to the other and/or front to rear; and also when entering a corner hard under breaks, the front would could push wide because of the weight).

Even though Nissan seem to have engineered the car very well, imagine how much faster it would be had they kept the weight down.

actually no it did an 11.3 in private testing. using launch control system

[philta]

we are really getting off subjects here.

most of the power loss in the drive trains is through the transfers of energy. every time u transfer energy or force through gears or a change in direction (on different axis of rotation) u lose power/energy (read up acceleration, momentum and rotational forces). now how much u lose depends on the the design of the drive train and friction blah blah. BUT back on the weight of the gtr guys.

i reckon the gtrs weight issue is its drive train. u don't get a 11 1/4 car with ordinary steel, most of the parts that nissan used are either/or heavy and tough alloys. they simply cant afford use light weight, high strength alloys that would simply but the gtr closer to the 911 prices. im pretty sure the v-spec will be equipped with cf parts along with carbon ceramics brakes which would be lighter than its iron slap.

Edited December 24, 2007 by philta

[hrd-hr30]

I love OT nazis. Mate, the thread topic is "R35 horsepower figures", nothing to do with weight.

[Sydneykid]

you also have to remember that torque is not an energy, its a force. and helical cut gears lose a % of that force in a different vector. this loss doesn't go directly to heat, its absorbed by the housing or carrier.

I think doubling the engine power would almost double your drivetrain loss. Its a pretty good approximation anyway. Certainly alot better than a fixed value loss. eg if you make almost double the torque to double the power as you can do with a turbo car if you have to then you've definitely doubled amount lost through the helical gears. and they will try to push themselves and their housings apart, or in the case of difffs the pinion will try and climb the crownwheel. On the other hand, if you almost double your revs to double the power, you probably will loose that extra 25kw in heat through frictional losses. If you double the power with some combination of the two (torque and revs) as is the case most of the time in the real world, then you'll loose parts of the increase to each - some extra lost force vector and some to heat. Mind you, you're not at that full power very often, so those extra 25 1kw heaters are only all on at the moment in time you make that peak power figure. The more you're at and around that peak power, the more heat you'll make. hence why serious race cars will have oil coolers on boxes and diffs as well.

So the gearbox/diff continues to stretch? I don't think so, eventually it reaches its limit of elasticity and either breaks or stops stretching. Since it doesn't break, we can assume it stopped stretching. So where does the (lost) engergy go then? It must be heat, there is no kinetic energy going anywhere else but driving the car.

Anyway, I think were are talking a bit at cross purpsoses, losses increase with RPM, I think we both agree on that?

It's when the rpm is constant that we dissagree. So let's concentrate on that issue.

Since my race car is at 100% throttle for over 75% of every lap and never gets out of the 5,000 rpm to 7,250 rpm range, the heat build up in the % loss method must go somewhere. I have not changed the transmision coolers on the race car since we doubled the power output and the transmission fluid temperatures have not changed noticeably, we log them. So where is this doubling of heat going? A lot of heat mind you, 50 kw of it.

Cheers

Gary

[Brockas]

So the gearbox/diff continues to stretch? I don't think so, eventually it reaches its limit of elasticity and either breaks or stops stretching. Since it doesn't break, we can assume it stopped stretching.

Exactly, it will reach its yeild point, where additional stress on the metal will not result in additional deformation.

Obviously a gearbox of different metallurgical construction will perform differently, and will require a different amount of stress before it reaches this yeild point.

[RNS-11Z]

if the car weighs 1700kg, and does the quater in 11.6 @ 121mph, it definately has 350kw or more at the wheels. A car that weighs 1400-1500kg with 290-320rwkw does the quater in low 12s high 11s at 120-125mph.

[hrd-hr30]

So the gearbox/diff continues to stretch? I don't think so, eventually it reaches its limit of elasticity and either breaks or stops stretching. Since it doesn't break, we can assume it stopped stretching. So where does the (lost) engergy go then? It must be heat, there is no kinetic energy going anywhere else but driving the car.

no, it is wasted force, not energy. go exert a force against a wall and see if it generates any heat on the wall.

Anyway, I think were are talking a bit at cross purpsoses, losses increase with RPM, I think we both agree on that?

It's when the rpm is constant that we dissagree. So let's concentrate on that issue.

Since my race car is at 100% throttle for over 75% of every lap and never gets out of the 5,000 rpm to 7,250 rpm range, the heat build up in the % loss method must go somewhere. I have not changed the transmision coolers on the race car since we doubled the power output and the transmission fluid temperatures have not changed noticeably, we log them. So where is this doubling of heat going? A lot of heat mind you, 50 kw of it.

Cheers

Gary

no, read my post agin. its only a fraction of the extra 25kW that will be translated to additional heat. force and energy are different things. heat remains similar because the friction in the drivetrain hasn't increased much. friction increases exponentially with speed and increases very little with additional load. so if the engine speeds haven't substantially altered, neither has the friction. the lost force from the helical gearsets has increased at a fixed percentage of the input force

Edited December 25, 2007 by hrd-hr30

[Laurence]

no, it is wasted force, not energy.

If you can make force with no energy then you my friend have just discovered perpetual motion. You can buy an R35 with the Nobel Prize money!

[hrd-hr30]

Don't confuse the work you do to create a force with the work done by the force you've created.

The energy transferred by a Force = the Work done. If a force is exerted on an object that is not free to move, no work has been done on that object, and therefore no energy has been transferred to it. The fraction of the input force transferred (and lost) to the casing of the box/diff, which is not free to move, has done no work and therefore has not transferred any energy or contributed to any extra heat.

force and energy ARE different things. that's why they have different names!

Edited December 25, 2007 by hrd-hr30

[Bumblebee]

geez this has gone pretty darn far now.. lol

who cares about loss. It loses a few kw's to heat friction blah blah...

It will always lose who cares. Now as for my vl turbo has 300kw and cant do 11s but the <250kw R35 can is simple...

The GTR has one of the lowest drag ratings to be released on a car.. it literally slips through the air.. so all that power doesnt have to overcome the amount of drag that say.. my gtr has to.. my gtr makes a hell of a lot more power than the new gtr, but id be damnd if i could hit 100 in 3.3 seconds or even 150 in like 5.3 secs... it'll do an 11 sec 1/4 but thats because its got loads of power...

Power isnt everything when it comes to Supercars.. 353kw and it goes over 300km/h.... id hit 300... but as comfortable as a GTR?? no chance..

[DRIFTER]

this is a really interesting thread, its been 10 years since i did physics, and i didn't grasp it very well then anyway. hasn't anyone done many back to back chassis vs engine dyno testing?

p.s don't forget the quarter mile time of the new GT-R is lower than it would be with a conventional gearbox due to the time saved with the DSG tranny (adds up over 3 gear changes)

Edited December 26, 2007 by DRIFTER