RE: New 'vette V8

[jbi]

that would be US gallons so...

27 mpg Imperial @ 100mph

[DonkeyApple]

Wondering if a 2007 car is a LS2 rather than the LS3 being discussed?

[irocfan]

edb49 said:

Max_Torque said:

Custard, bring out the Custard!!

Science says:


at 100mph and 26.2mpg on gasoline (32mJ/litre energy density), it takes you 36sec to do a mile, burning 0.173litres, which is 0.163mJ/sec, which is 163.6kW. A very typical figure for overall efficiency of a spark ignition internal combustion engine is 25% (especially considering that 163kW isn't WOT!), so that's 40.9kW usefull flywheel power. We will conveniently ignore drivetrain and tyres losses (which would knock off another 10% or so). So, back calculating the vehicles CdA (again ignoring rolling losses like tyres etc (another ~4%)) results in a max Cda of 4.955 Sqr feet (on a std atmospeheric day).

That, in effect, is how "slippery" your car must be to do "26.2mpg" at 100mph.

Here's a link to an article which measures the CdA for some corvettes:

http://www.corvettefever.com/techarticles/corp_090...


I'll leave it up to you, the reader, to determine if you believe those mpg claims are achievable.

Good post. Fundamentally 30mpg/100mph ain't going to happen due to the square law with wind resistance.


I think it may be easier to try and win the argument a slightly simpler way though:

http://www.youtube.com/watch?v=udE3zXtTYZM

Trip computer shows 21-23mpg at a 100mph cruise.

QED.

awaiting the twunt brigade whinging about the accuracy of trip computers now lol

[blahblop123]

31mpg is believable just as long as it still has the LONG 0.5 top gear. at 60mph, the old c6 spun 1100rpm, which is almost idling. as light as the 4.4 twin turbo v8 ? i'm pretty sure it would be, i mean, it has 2 turbo's hanging off it..

[irocfan]

doogz said:

You guys are all grown men, yes?

Maybe, act like it? I don't think I've ever seen such a petty thread. Twunt brigade? Come on.

If you disagree, why don't you agree to disagree?

I agee it's a childish/petty thing to say but while you can argue the relative merits (or otherwise) of cars/engines/transmissions when you get to the stage that people are being told their assertations of mpgs are incorrect regardless of the fact that we've actually experienced the bloody FACT then you just want to give up being factual, or indeed grown-up

[DonkeyApple]

blahblop123 said:

31mpg is believable just as long as it still has the LONG 0.5 top gear. at 60mph, the old c6 spun 1100rpm, which is almost idling. as light as the 4.4 twin turbo v8 ? i'm pretty sure it would be, i mean, it has 2 turbo's hanging off it..

It seems very 'top end' of expectations. But, I think it's more about looking at supposed 2v old tech US V8 versus say, a modern DOHC, 4v, VVT, DI, etc European engine and seeing if all that fantastic tech actually delivers results of noteable benefit over the LS unit, especially in contrast to cost?

I actually think you get a more meaningful answer if we look at the engines in 'trucks'. Rather than in a sportscar you are looking for more low down torque and do not require a large rev range, so a 2v pushrod certainly isn't out of place.

So, taking the Escalade v the FFRR:

2011 Escalade: 6.2L VCT 2v pushrod 403bhp 417ft-lb 6sp auto
13 City
15 Combined
18 Highway
Curb Weight: 2,630kg

2011 FFRR: 5.0L SC 4v DOHC Direct Injection 503bhp 413ft-lb 8sp auto
12 City
14 Combined
18 Highway
Curb Weight: 2,810kg

These are US MPG figs from: http://www.fueleconomy.gov/

Other stats from Wiki

It's worth noting that the non FI 5.0L AJ unit produces 375bhp and 375ft-lb

[K2MDL]

blasos said:

Pistonheads said:

That'll mean even the entry car will, it's claimed, accelerate to 62mph in under four seconds. So what they're saying is that it'll match the drag times of today's 205mph ZR1, which is pretty impressive for a car that'll cost around $50,000 in the States (£31,000).

How was that conclusion reached? The ZR1 has an official 0-62mph time of 3.6s. Sub-4s is not necessarily 3.6s. And even if that were the case, that is just one acceleration figure and it is, at best, disingenuous to state "it'll match the drag times of today's 205mph ZR1". An exaggeration to fill the the story, nonsense.

+1

[anonymous-user]

swerni said:

If you want a proper fast one, it needs to be red.

Quite.

[AER]

According to an EPA report I googled a few minutes ago, a Corvette needs approximately 580N tractive effort to travel at 50mph. Now given that this report was written in 1980, we can assume things have moved on a bit. It might be a little lower than that now, but not a huge amount due to fatter tyres etc. Let's say 500N for a nice round number

500N at 50mph is 2000N at 100mph, which is 89.4kW at the wheels. At the flywheel it could be 10-15% more, so say 100kW for another nice round number...

Now, despite Max Torque's protestations, I know for a fact that the LS series engines produce some pretty impressive fuel consumption figures on an engine dyno. I would expect this new one to be even better, but let's say that 250g/kW.h is doing pretty damn well at a modest part load point. This is feasible, but remember, many diesels dont do much better than this, with the best cracking the 200g/kW.h threshold only at their best point.

100kW at 250g/kW.h is exactly 25kg fuel per hour. At a density of 0.74kg/L, this is 33.8L/h or, at 100mph, is 13.456mpg

Check my maths if you like, but 26mpg at 100mph is better than diesel territory... (and I don't mean the Ford Territory Diesel!)

Edited by AER on Thursday 1st November 14:01

[AER]

By the way, I just have returned from Austria to Stuttgart as a passenger in a relatively quickly driven E60 M5 and having suffered repeated accelerations and decelerations to accomodate noddy MPV drivers on the autobahns, and having just calculated what 100kW gets you on four wheels, I can't for the life of me understand why we don't fly more, as in personal aircraft. With a relatively modern airframe, 100kW will move four people and their luggage point-to-point at 200mph.

Attempting to travel fast on the ground is a mug's game, IMHO

[AER]

The reason cars are cheap is because the cost is spread over millions of examples and also most people are blind to the true running cost of motoring (depreciation)

Normalise both of those factors and invest in the infrastructure, technology and regulation to the same degree and you'll see you can fly cross-country much more cost effectively and at lower environmental cost than driving...

Edited by AER on Thursday 1st November 15:08

[Kozy]

Max_Torque said:

Custard, bring out the Custard!!

Science says:


at 100mph and 26.2mpg on gasoline (32mJ/litre energy density), it takes you 36sec to do a mile, burning 0.173litres, which is 0.163mJ/sec, which is 163.6kW. A very typical figure for overall efficiency of a spark ignition internal combustion engine is 25% (especially considering that 163kW isn't WOT!), so that's 40.9kW usefull flywheel power. We will conveniently ignore drivetrain and tyres losses (which would knock off another 10% or so). So, back calculating the vehicles CdA (again ignoring rolling losses like tyres etc (another ~4%)) results in a max Cda of 4.955 Sqr feet (on a std atmospeheric day).

I thought gasoline was 47.3mJ? Might rather skew the calculations in the favour of 30mpg at 100mph. Not all the way of course, but maybe slightly...

Also, with these engines having such long top gears, the power required to do whatever speed is going to come at a wider throttle opening than a lower geared car, so less pumping losses and greater thermal efficiency from the increased effective compression ratio...

Not arguing against you at all, just thought you might want some banter more on your level, rather than childish name calling.

[DonkeyApple]

DonkeyApple said:

It seems very 'top end' of expectations. But, I think it's more about looking at supposed 2v old tech US V8 versus say, a modern DOHC, 4v, VVT, DI, etc European engine and seeing if all that fantastic tech actually delivers results of noteable benefit over the LS unit, especially in contrast to cost?

I actually think you get a more meaningful answer if we look at the engines in 'trucks'. Rather than in a sportscar you are looking for more low down torque and do not require a large rev range, so a 2v pushrod certainly isn't out of place.

So, taking the Escalade v the FFRR:

2011 Escalade: 6.2L VCT 2v pushrod 403bhp 417ft-lb 6sp auto
13 City
15 Combined
18 Highway
Curb Weight: 2,630kg

2011 FFRR: 5.0L SC 4v DOHC Direct Injection 503bhp 413ft-lb 8sp auto
12 City
14 Combined
18 Highway
Curb Weight: 2,810kg

These are US MPG figs from: http://www.fueleconomy.gov/

Other stats from Wiki

It's worth noting that the non FI 5.0L AJ unit produces 375bhp and 375ft-lb

You can also contrast it to a direct and deliberate competitor of the 5L Coyote engine used in the F150.

That is a DOHC, 4v with VVT, 6sp auto and I believe direct injection and achieves comparable outputs to the L92 engine it is pitched 100% against.

Yet fuel consumption is only marginally better and this is a lighter vehicle.

[anonymous-user]

Kozy said:

Max_Torque said:

Custard, bring out the Custard!!

Science says:


at 100mph and 26.2mpg on gasoline (32mJ/litre energy density), it takes you 36sec to do a mile, burning 0.173litres, which is 0.163mJ/sec, which is 163.6kW. A very typical figure for overall efficiency of a spark ignition internal combustion engine is 25% (especially considering that 163kW isn't WOT!), so that's 40.9kW usefull flywheel power. We will conveniently ignore drivetrain and tyres losses (which would knock off another 10% or so). So, back calculating the vehicles CdA (again ignoring rolling losses like tyres etc (another ~4%)) results in a max Cda of 4.955 Sqr feet (on a std atmospeheric day).

I thought gasoline was 47.3mJ? Might rather skew the calculations in the favour of 30mpg at 100mph. Not all the way of course, but maybe slightly...

Also, with these engines having such long top gears, the power required to do whatever speed is going to come at a wider throttle opening than a lower geared car, so less pumping losses and greater thermal efficiency from the increased effective compression ratio...

Not arguing against you at all, just thought you might want some banter more on your level, rather than childish name calling.

it is ~47MJ per kg, however, 1 litre of gasoline (as i used in my calcs) doesn't weigh 1 kg.......

[Kozy]

Well that settles that one then!

[Gixer]

It would only be an argument if the people he was arguing against actually said that in the first place, however nobody he's been arguing against actually did.

It's a shame that MaxTorques skill set falls short of being able to read.

I've asked him again and again to quote where I said 30mpg. Of course he has been unable to as I didn't say that anywhere at all.

But there you go this is PH where facts don't matter.

[DrTre]

You didn't, someone else did. That MT quoted you in a response doesn't negate his numbers, if they're true...

chilled901 said:

Yeah, no. I have verified that the LS2 corvette doing a steady 100mph will give you 22 free world MPG which would be 26 2 mpg for you.

Cue in the naysayers.

[Gixer]

DrTre said:

You didn't, someone else did. That MT quoted you in a response doesn't negate his numbers, if they're true...

chilled901 said:

Yeah, no. I have verified that the LS2 corvette doing a steady 100mph will give you 22 free world MPG which would be 26 2 mpg for you.

Cue in the naysayers.

Nope. He's been painstakingly arguing that 30mpg isn't possible. As I said, nobody has said that.

[DrTre]

Gixer said:

Nope. He's been painstakingly arguing that 30mpg isn't possible. As I said, nobody has said that.

No he hasn't he's been painstakingly arguing 26mpg isn't possible at 100mph. Someone else threw in 30mpg.

ETA, that's from what I can see/have followed. Maybe I'm wrong.

Edited by DrTre on Thursday 1st November 19:59

[Gixer]

Either way, he's been arguing with the wrong people.