scatter shields were always employed when i were a lard
www.allpar.com/mopar/shield.html
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I'll mention it bb. I'd be surprised if he hadn't thought of it himself.
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Don't be fooled Lud.
(sigh) I'm just passing on the numbers I was given NC. I am well aware and have been for many years that the figures given by engine tuners and rolling roads have a sort of elastic quality. As one would expect.
Are these figures so improbable, anyway?
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Are these figures so improbable, anyway?
The engine internals are standard, but it's possible the turbo or turbos aren't. I sort of half remember that they may be bigger. But I would have to check.
In any case I have the impression these engines can produce very hefty outputs. They aren't prized for nothing.
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I'm impressed at the honesty of these mechanical guru's Lud, admitting they might have been a little over enthusiastic with the spanners.
Some main dealer's workshops that feature anonymously here could do with reading your OP.
I test drove a GTR once, nice enough car but the harsh ride and rattly interior put me off...same result when i tested a Mustang couple of years ago.
Daresay i could live with the new GTR mind, (so long as someone else was paying the bills).
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impressed at the honesty
I am too gb. Enthusiasts not yet corrupted by the demands of business... Long may they remain so.
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NC: the turbos are standard factory issue.
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Thread drift alert! At the Reno air races R/R Merlin powered aircraft (1800 BHP) are tweaked to produce 4000 BHP, but not for very long between rebuilds! High power = High wear and High failure risk!
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>>(sigh)
Oh dear.
>>I'm just passing on the numbers I was given NC
I'm not suggesting otherwise Lud - not for a second.
A quick sanity check might suggest that losing 70BHP in the transmission would need a transmission cooling system as fitted to to a car of about 70 BHP power output. It's nonsense.
Helical gears are typically over 98% efficient, and lip seals won't cause more than about 0.25 Nm of drag each. The hypoid gears in the diff are a bit less efficient, but, not so inefficient as to lose any significant power.
Nissan would have to be pretty thick to spend time and money developing a powerful engine to then throw 70BHP away in the transmission!
I don't doubt the car is powerful and quick. What I do, stongly, doubt are the inflated numbers guessed at by people who run rolling roads. IMO, it's all rather spurious.
Edited by Number_Cruncher on 17/05/2009 at 20:15
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No doubt you have a point or two there NC. But transmission losses are going to account for something with a gearbox, two differentials (or three more likely) and all the driveshaft joints and wheel bearings and high-pressure gear oil churning around there.
I don't know how tuning outfits arrive at their rolling road and other figures. Reason suggests they would prefer methods that made their work look good.
But then there are other ways of exaggerating and being a tiny bit economical with the truth, aren't there?
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>>I don't know how tuning outfits arrive at their rolling road and other figures.
More often than not, I don't think they do either!
The only figure for flywheel BHP that I could place any trust in would be the results from an engine dynamometer running at constant engine speed for each point on the graph.
The only figure for power at the wheels which I could come close to trusting would be from a chassis dynamometer with rollers much larger than the wheels, running at constant speed for each data point. I don't trust these devices ability to estimate transmission losses at all.
>>Reason suggests they would prefer methods that made their work look good.
Yes, quite so.
Yes, there will be oil churning. These losses are much greater at low temperatures.
If there's any significant loss in a wheel bearing, then, the device doesn't deserve its name!, and I've never felt a driveshaft joint in good condition that got hot during use.
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A quick google of GTR 'transmission losses' and a look at some of the first pages displayed produced an estimate of 60bhp in another high-output bog standard (more or less) example (480 on the rollers, est 540 at the flywheel) on four-wheel rolling road to a whopping 28 per cent in a red-eyed, snorting, allegedly 900+bhp example.
I can't say I am over-bothered by a few bhp here or there having no hands-on connection with the thing. You are right to cast doubt on tuning company figures (and manufacturer ones come to that) in general. But I think you are guilty of underrating transmission losses in a 4wd system, for reasons at which I can only guess.
:o}
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>>But I think you are guilty of underrating transmission losses in a 4wd system,
70 BHP is a huge amount Lud - all as heat - where's it going?
>>for reasons at which I can only guess.
Just to highlight the BS used by these rolling road operators - all too readily believed by the car owner.
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all as heat - where's it going?
I don't think it has transmission oil cooling unless it's standard.
I do understand the car got a bit warm after a couple of aggressive laps. No doubt some of this transmission heat contributed...
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You can't underestimate Skylines. I saw one figured using calibrated timing gear at 0-60 in 3.4 seconds, 0-100 in 6.9, and go on to a 184 mph top speed. This was on a standard 2.6 bottom end too, with a remap different injectors, and some turbo trickery.
This car's owner claimed 650 bhp. I don't know how genuine this was, but to propel a 1550kg car with this kind of vigour, it can't have been far off.
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If you look at mpg figures of cars with 2wd vs the same except having 4wd you will typically see a reduction of around 10% - this is all lost as heat between flywheel and the road and may equate to 20-25bhp for a moderately tuned car (eg. Audi 2.0 TFSi).
I can believe 60-70bhp from a 400+hp 4wd car which will have at least 1 LSD, but other than bragging rights it is largely academic.
I imagine GT-Rs have oil coolers for engine, gearbox and rear diff as my old UK spec N/A 300ZX had them.
In reality most "serious" tuners don't care about flywheel HP, it's WHP all the way.
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And on the topic of the GT-R I seem to remember than each new version was quoted at 276bhp even though the torque figures and max revs would increase.
Nissan were almost certainly understating BHP as part of the 'gentlemen's agreement' between domestic Japanese manufacturers not to escalate to insane power in road cars.
I think the R34 GTR was dyno'd at 330bhp as standard, and I recall the current GTR being dyno'd in the states at just over 500bhp while Nissan say it has 473bhp.
Of course dyno's all vary and are only an approximation of bhp.
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>> it's WHP all the way.
Yes, that's what counts. But thinking they've got 510bhp at the flywheel must be a source of harmless, innocent satisfaction to owners. I doubt if they are as willing to accept any old allegation from the tuners as NC thinks.
Everyone knows that power varies with ambient temperature, pressure and humidity. Everyone knows that the rolling road mechanism and a car strapped down on it shredding its tyres take a lot of power to drive, so much that elasticity can be introduced into the figures more or less unconsciously, with a clear conscience... but so what? The proof of the pudding is in the way the jalopy goes, and the absolute figures only matter in the context of proper competition.
Of course there's only one way to measure flywheel output accurately, and even then someone will carp at the way the device is calibrated... They used to use a thing called a water brake I think.
:o}
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>>so much that elasticity can be introduced into the figures more or less unconsciously, with a clear conscience.
Lud, you sound like an MP "clarifying" his expense claims!
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Heh heh... but it's you who keeps going on about these people and their dodgy figures. I'm sure they all have good reasons for saying what they say. I don't expect the figures to be engineering gospel or believe they are. I don't suppose anyone does.
In the remark you quote, I was trying to imagine how these elastic figures come to get quoted with a straight face. But you must have twigged that.
It's all very well to pooh-pooh people's estimates of transmission losses, on the safe assumption that they are probably on the high side. It's quite another to make out that such losses are negligible, when as any fule kno they aren't.
To put it another way, if you want to expose tuning firms for trying it on, don't try it on yourself.
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>>I don't suppose anyone does.
You're kidding.....
......aren't you?
>>don't try it on yourself.
Identify any factually incorrect statement I've made in this thread, and I'll accept your criticism as valid.
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don't try it on yourself.
Identify any factually incorrect statement I've made
Any politician will tell you, NC, that it is possible to make out or imply or suggest that something that isn't the case is the case without actually making a 'factually incorrect statement'. In fact people talk staggering excrement day in day out without telling identifiable lies. And you have, in this thread, given us your own modest demonstration of how that is done.
Is it conceivable that you aren't aware of it? Only by a stretch of the imagination.
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>>Is it conceivable that you aren't aware of it?
I'm not aware of it - I don't see where I've misled anyone.
>>And you have, in this thread, given us your own modest demonstration of how that is done.
How?, where?
Any staggering excrement in this thread isn't my doing.
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From my very limited experience transmissions can get very hot when worked hard. The LSD on my Forester has a temperature sensor linked to a warning light with dire warnings to stop and let it cool down or damage will occur.
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This may be of interest and the last email reply at the bottom of the page appears to support NC's view of the amount of heat a large power loss would generate.
tinyurl.com/oklmnq
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I think Nissan would get quite upset at the accusation of designing and building a transmission system so rubbish that it caused 70hp of losses.
On the other hand it would be quite an engineering feat to make a transmission system that is compact enough to fit in a car but could dissipate that amount of power without melting (70hp = 60kW, electric kettle = 3kW). Titanium driveshafts would appear to be a requirement.
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At 160+MPH while churning out 400bhp "at the crank" the engine has already wasted at least 400bhp through thermodynamic inefficiency in combustion - this is (relatively) easily disposed of via the radiator/exhaust.
The tyres will be very hot as will the transmission fluids/components. Some is lost via the engine cooling system, some through heat transfer to the air (remember hot things lose heat energy at a rate proportional to the difference to ambent temperature).
40-45kW lost through transmission/chassis at 160+ mph is quite plausible.
At low speeds (eg. 1st/2nd gear) these losses will be much smaller, but I think the point N_C is making best is that dynamometers are a complete fudge when it comes to 'flywheel' bhp.
By increasing the 'transmission' losses, the tuners/dyno owners can make a car seem more powerful than it is. They may have a vested business interest in this, especially if a customer has spent £££ tuning an engine.
Whether the losses are 20, 50 or 100bhp they are significant - but impossible to measure accurately with a dynamometer!
There's a reason a GTR has radiators for the gearbox and read-diff. There's a reason why a Veyron has 10 (I think!) radiators.
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On a different tack, there was a dyno test of a new Yamaha R6 in Performance Bikes recently.
They were testing the effects of aftermarket exhausts on power & torque, so they did dyno plots at both full throttle AND half throttle (i.e. twistgrip held 50% open) to get a feel for the effects at full power and "real world" use.
The runs were done in 4th gear. The results of the standard factory bike were:
Full throttle: 109bhp at 14,500rpm
Half throttle: 101.5bhp at 14,500rpm
Torque figures were comparable too -- at half throttle, the bike was putting out over 90% of the torque at full throttle.
Admittedly the R6 has a fairly state of the art fuelling system with fly-by-wire throttle, mulltiport injection etc, but I was still surprised to see that a 50% throttle opening gave 93% of peak power.
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>>at half throttle, the bike was putting out over 90% of the torque at full throttle.
That is surprising.
So in effect, the second half of the throttle travel on an R6 is just for show. This is just throttle mapping, surely. Probably done to make the bike feel searingly quick on small throttle openings.
This is a trick some of the car manufacturers use as well. Used to some extent on the VAG PD diesels where the "throttle" response is not linear. Engine does far more in the first half of travel than the second. Makes it feel really perky.
Edited by DP on 18/05/2009 at 13:30
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@ DP -- yes, it must be the mapping & fuelling that gave these figures.
It would be interesting to see how a carb-equipped engine would perform in the same dyno tests.
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Any staggering excrement in this thread isn't my doing.
Yes it is. You said the estimate of 70bhp power loss was excessive, to flatter the flywheel output of the car. You didn't suggest what the loss might be because you didn't know, having not measured it. But you implied very strongly in at least one post that it would be more or less negligible. You didn't say so, you just gave efficiency figures for various sorts of gear and said wheel bearings didn't lose much power. This clearly amounts to exaggeration and can be described as staggering excrement.
Why do you do argue in this PITA manner? No one said they took tuning company figures as gospel or doubted that such companies would try to make the figures look good. You simply didn't need to go on making that point. You don't have to be annoying to make people take you seriously.
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Why do you do argue in this PITA manner?
Possibly because he's highly likely to be correct?
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>>But you implied very strongly in at least one post that it would be more or less negligible.
You've made the mistake of choosing to infer this from what I said, and have been digging in deeper staggering excrement ever since.
I quantified the easily quantifiable sources of loss - yes, I can't quantify the more difficult case of oil churning losses because that's gearbox specific, and hence it wasn't in my post. Losing such power to oil churning in a gearbox would be very wasteful design, and I don't believe Nissan would do that.
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I quantified the easily quantifiable sources of loss <<
You mention the loss of 2% through helical gears, and another unspecified amount through the differentials.
This hints at perhaps 5-6% total through the transmission ?
Well, if you take a couple of standard cars that come in both 2WD and 4WD formats, that are otherwise identical we can see that this is possibly not correct:
Fiat Panda 70hp diesel 2WD: 114g/km CO2, 0-60 13sec.
Fiat Panda 70hp diesel 4WD: 136g/km , 18sec
-------> almost 20% less efficient having drive going to the rear as well as the front.
Audi A4 3.2 SE petrol 2WD: 194g/km CO2
Audi A4 3.2 SE petrol 4WD: 213g/km CO2
-------> almost 10% less efficient (sl better 0-60 either because of better traction or because Audi don't want to advsertise their more expensive model as being slower!)
These figures presumably are from cars on the same tyres (same specs so same OE wheels) so the extra inefficiency must come from additional losses purely in the 4WD rather than 2WD transmission.
Obviously a dynamometer max power test is not directly comparable with an EU emissions test as the engine will run through a completely different rev-range
What does appear to be the case is that relatively less power is lost as power output increases (not just as I've shown above - www.pumaracing.co.uk/coastdwn.htm explains it a bit better).
Factoring in tyre losses (increases with road speed) I think energy wasted through putting power from the crank to the road is substantial - again, it is almost impossible to quantify it unless you can compare a known bench-tested engine with itself after installing it in the vehicle - I can't find good internet data regarding this as most tuners don't bench test, and those that do (manufacturers and racing engine builders) probably see the information as economically sensitive.
Most racing applications are RWD or FWD so it might be tricky to find 4WD data.
If anyone can find such a test I'd be intrigued to see it.
Edited by Lygonos on 18/05/2009 at 15:17
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These figures presumably are from cars on the same tyres (same specs so same OE wheels) so the extra inefficiency must come from additional losses purely in the 4WD rather than 2WD transmission.
Not to mention the extra weight of course!
Some 4wd Audis also have lower gearing than the 2wd ones.
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Absolutely!
And I guess maybe a wee bit more drag with a messier underchassis too.
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I quantified the easily quantifiable sources of loss
No you didn't. This is the substantive part of your most substantive post:
'A quick sanity check might suggest that losing 70BHP in the transmission would need a transmission cooling system as fitted to to a car of about 70 BHP power output. It's nonsense.
'Helical gears are typically over 98% efficient, and lip seals won't cause more than about 0.25 Nm of drag each. The hypoid gears in the diff are a bit less efficient, but, not so inefficient as to lose any significant power.
'Nissan would have to be pretty thick to spend time and money developing a powerful engine to then throw 70BHP away in the transmission!'
That doesn't quantify much as I am sure you can see. But it does suggest very strongly that the 70bhp figure is wide of the mark, very wide. You don't say how wide, because you don't know.
The effect of this tediously patronising tone - 'sanity check', 'nonsense', 'Nissan would have to be pretty thick' - combined with the parsimony of actual information is very plain to a rational person. It may impress Fotherington Thomas and other weeds and wets but it just annoys me. It's obvious you know your stuff, so why not just stick to that?
Other posters have said the GT-R does have transmission oil coolers. Assuming they are right, do you think Nissan just fitted them to impress their ignorant punters?
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....just don't ignore the noises OK.
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If it "loses 70BHP" in the transmission, that'd make it a pretty reluctant to move. Bung it in gear, press down the clutch, and try to tow it. Could a Polo pull it along the flat in top? I bet it could.
The only gripe I've got is the "losing BHP" statement, which might be better as "losing HP".
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www.consumerenergycenter.org/transportation/consum...l
Again not a test-bed engine vs in-car engine comparison, but give some %age figures of energy losses (not sure of the source, but anyways).
Drivetrain losses 5.6% (around the level I presume N_C was guesstimating) - this doesn't include rolling resistance which is suggested at 4.2%.
ie. 9.8% loss from flywheel to road.
I think due to the physics of the process, as speed rises the relative amount lost through the drivetrain reduces a bit, whereas rolling resistance increases as a function of velocity.
Any calculation is a fudge/guess/lottery, but a car losing say 10 hp (4% of 250 hp) at 50mph through rolling resistance is likely to be losing around 30 hp at 150mph.
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In fact the link above suggests driveline losses as 5.6% of the 18.2% of fuel energy reaching the flywheel ie., >25% of engine power output is lost.
/sigh.
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/sigh.
Heh heh. It's a minefield. Like a GTR with sheared flywheel bolts...
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It's a US source Lygonos. 4wd and three differentials, all, with the gearbox, substantial enough to transmit very large amounts of power, might account for a bit more than 5.6% don't you think? That would be 24 bhp at full power in a car returning 430 at the wheels.
I'm not a rolling road operator so I haven't a clue myself. But I don't see any reason why such people should be accused of making madly fanciful claims. They work for proper car fanciers after all, not barryboys.
There certainly used to be engine tuners who made pretty exaggerated claims, and there probably still are. But from what I know of the Skyline owner mentioned I don't think he would be going to one of them.
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The rolling road tests are usually in high gears as these should get a lower gearbox loss - tyre losses will be much higher though, as wheel speed is obviously faster.
www.youtube.com/watch?v=dQ27PL7WwM0
Looks like 4th is the chosen gear for the 'power run'.
Other vids seem similar.
What I would suggest re the 'run down' is the engine has a closed throttle (ie. foot OFF the accelerator) - surely this adds engine drag and will give an artificially high mechanical loss on a dyno run - wouldn't a better approximation be made if you killed the ignition and kept the throttle open during the 'run down'?
Maybe I'm FOS heh heh.
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I do think that wastegate tweet is charming. I've never been in this GTR but I am looking forward to it for that alone.
:o}
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the 4WD stuff weighs quiet a bit thats why the mpg is so much less.
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