British warships in Gulf to be renamed AA and RAC

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Carlton green
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Re: British warships in Gulf to be renamed AA and RAC

Postby Carlton green » 17 Jul 2019, 12:07pm

Tangled Metal wrote:Limiting power to 100bhp? Interesting!

Domestic use of vehicles isn't the only use, there's trade, commercial and industrial use. Take trade use, which means vans. There's often power break points at 90, 100 and 115/125 bhp depending on the van. Looking at vauxhall vivaro for example the standard powers are 89/90, 99/100 and 114/115 bhp. There's also a biturbo at 120bhp.

Which is the most fuel efficient and least polluting option? The 120bhp not the 90bhp van. The 90bhp van is actually the highest carbon emissions and lowest fuel efficiency. The best on both counts is the biturbo.

I read an article on the website of a fleet car trade journal that's highly relevant here. The fleet manager for the whole of BT wrote about serious fuel efficiency and emmisions reductions that are possible by remapping vehicles. By remapping for more power, savings of 15% on fuel costs / use in vans and 8% in cars. Crazy right?

In fact the guy wrote that it could be advantageous for large fleets to mass remap their vehicles and then put them through type approval. What that means is the remapped vehicles become recognised as a new model with better fuel / emmisions figures. Advantage being lower personal tax for company cars. They don't because it's really only an advantage to the employee.

I'm no car expert but this guy was so I've no basis to dispute his article. I just think power isn't a good measure for limiting cars. There's evidence that it's a bad measure to use.


I completely see your point and of course arbitrary limits rarely make complete sense, they are (or are best treated as) but a line in the sand from which to work. Of course, in some small defence of my comment, I did specifically say cars and did not mention vans. Commercial vehicles do need considering too but that’s a more complex conversation for another day.

BHP is to an extent a false indicator anyway - it’s meant to be a start point - because what matters more to the user is the amount of torque produced by an engine. (For the reference of others Power = Torque x engine speed, the maximum torque available can vary considerably through an engines’s operating speed range). To my mind 100 BHP is quite a generous limit; whilst 100 isn’t much these days it was in the past and cars of half that power and less have covered very large mileages. Here’s an example of what was a very popular family car that had under 100 bhp : https://en.m.wikipedia.org/wiki/Volkswagen_Golf_Mk3. And here’s an iconic vehicle that mobilised masses of people and yet must have had less than 50 bhp under its bonnet: https://en.m.wikipedia.org/wiki/Renault_4.

I’ve always wondered about engine (performance and efficiency) mapping and am not surprised that after market improvements are possible. Whilst typically manufactures want to make good products they make products for sale and profit, ultimately their goal is to make make money and if product efficiency suffers along the way then that’s businesses as we allow it to function. At the moment we don’t know why the more powerful engines you mentioned are more efficient, but my instinct is that they are more recent designs funded by customer desire for more power. It’s a nice thing for the Marketing Team too that the most expensive model happens to be the most fuel efficient and have the lowest emissions .......

Power might or might not be a useful indicator but it is easy for Goverments to use and so is engine size (eg. 125 cc motor bike of less than ‘15’ bhp is deemed acceptable for a learner to use and 400cc? of less than 33 bhp is OK for recently qualified motor cyclists to use). In general cars with smaller and less powerful engines are more fuel efficient than more powerful vehicles, what’s needed is a trend effect and sometimes, for the greater good, you have to carefully and selectively set anomalies to one side.

Tangled Metal
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Re: British warships in Gulf to be renamed AA and RAC

Postby Tangled Metal » 17 Jul 2019, 2:58pm

115bhp and 125bhp are not powerful vans. 170bhp are such as ford custom msport and the equivalent in other makes from citreon to vw.

IIRC the 113bhp vivaro went up to 115 when the engine size dropped from 2.0 litre to 1.6 litre. At the same time fuel economy went up by a couple of mpg at least.

The 120bhp biturbo is more efficient because it has a large and small turbo with what I believe is an intercooler in the middle. Now from what I think I understood about it the turbo increases air pressure going into the engine making the fuel burn faster and more efficiently. The biturbo adds in secondary compression as it's needed, when higher has flows such as when the driver is accelerating away (potentially needed such a pulling into a busy road). The turbo heats the air which also lowers the pressure slightly. The intercooler between cools the air down increasing pressure again.

Basically, if I've read this right, the biturbo is increasing available air to the engine making it more efficient at burning fuel. This can give me power and better economy.

Remapping is basically re-writing the program for the computer that controls air and fuel to the engine. This allows for better use of the fuel. I never understood why the car maker never set the car up like this in the first place. If the maker got things right there would be no advantage in remapping surely?

Another thing, if a more powerful car is driven like a lesser powered car, which is using less fuel? If you had 200bhp you could drive it conservatively (not using all 200 horses if you like) and cut fuel and pollution, right?

I do not know for sure. I'm just trying to point out that power, fuel economy and lower pollution aren't always a simple formula where arbitrary power figures work out better for climate change reasons than higher figures.

Tangled Metal
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Re: British warships in Gulf to be renamed AA and RAC

Postby Tangled Metal » 17 Jul 2019, 3:04pm

One more thing, there's probably some very high powered cars that are more frugal with fuel than those old classics with sub 100bhp ratings. That's before you're into hybrid and evs of course.

Then there's type of driving. Top gear (that dodgy car show I don't actually like) did a trial. An audi A6 2.5l tdi drove from London to Edinburgh (possibly back) on a single tank. In doing so was more fuel efficient and less polluting than a prius hybrid. Prius is nothing special except on short, town based journeys. Open road they're just an inefficient small car.

kwackers
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Re: British warships in Gulf to be renamed AA and RAC

Postby kwackers » 17 Jul 2019, 3:09pm

Tangled Metal wrote:Remapping is basically re-writing the program for the computer that controls air and fuel to the engine. This allows for better use of the fuel. I never understood why the car maker never set the car up like this in the first place. If the maker got things right there would be no advantage in remapping surely?

Makers have to balance lots of things, not just performance and fuel economy.
Engines are a compromise and remapping invariably improves one thing at a cost to another.

That said it used to be that there was a 'hole' in the mapping at 56mph to maximise fuel economy at the expense of performance so the vehicle looked good on paper. Unless you drive at 56mph then probably not much use to you.
Don't know if it still exists.

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Pastychomper
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Re: British warships in Gulf to be renamed AA and RAC

Postby Pastychomper » 17 Jul 2019, 4:09pm

kwackers wrote:Makers have to balance lots of things, not just performance and fuel economy.
Engines are a compromise and remapping invariably improves one thing at a cost to another.

I was impressed - if that's the word - by one example of such a compromise. I ran a car with an 82bhp engine that various companies offered to re-map to give 110bhp. The rumour was that the manufacturer had turned down the power so they could add a 2l engine to the range without upgrading the gearbox, making the re-map expensive in the long run. Oddly enough they sold a 1.7l version with very similar power and mpg to the 2.0.

I wonder if there were any long-term downsides to remapping those BT vans. Maybe the manufacturer just made some wrong assumptions about the way they'd be driven.
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kwackers
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Re: British warships in Gulf to be renamed AA and RAC

Postby kwackers » 17 Jul 2019, 4:21pm

Pastychomper wrote:I was impressed - if that's the word - by one example of such a compromise. I ran a car with an 82bhp engine that various companies offered to re-map to give 110bhp. The rumour was that the manufacturer had turned down the power so they could add a 2l engine to the range without upgrading the gearbox, making the re-map expensive in the long run. Oddly enough they sold a 1.7l version with very similar power and mpg to the 2.0.

I wonder if there were any long-term downsides to remapping those BT vans. Maybe the manufacturer just made some wrong assumptions about the way they'd be driven.

I'm sure some of the "compromises" are commercial too.

TBH most remaps I've ever come across result in very little extra power. If you blueprint your engine then sometimes you can get a moderate increase simply because the manufacturer maps an average engine.

Only place I ever saw where big gains were possible was with turbo charged engines where the remapping altered the wastegate but you potentially had shorter life and more reliance on higher quality fuels.