Stupid things non petrolheads say... Vol 2
Discussion
From my wife this morning:
Wife: "Who do we have to speak to about our car serviced"
Me: "It doesn't need a service it was done about a month ago""
Wife: "but I keep getting a message to top up washer fluid, what washer fluid does the car need?"
Me: "Seriously????"
Wife: "What do you mean?"
Me: "washer fluid, is screen wash or if we have none in the garage. Water"
Wife: "Oh. Got a job for you when you get home!"
Wife: "Who do we have to speak to about our car serviced"
Me: "It doesn't need a service it was done about a month ago""
Wife: "but I keep getting a message to top up washer fluid, what washer fluid does the car need?"
Me: "Seriously????"
Wife: "What do you mean?"
Me: "washer fluid, is screen wash or if we have none in the garage. Water"
Wife: "Oh. Got a job for you when you get home!"
Luis Nazario said:
WarrenB said:
Saw something on TwiXter that made me chuckle, 'using premium fuel lowers your revs on the motorway'.
Isn’t this correct though, all other things being equal?Higher octane (petrol) fuel means the spark can be delayed (because of greater resistance to knock), meaning greater compression, meaning more torque, meaning fewer revs to produce the same bhp?
The difference would perhaps be marginal, but I don’t think the statement is incorrect?
Talking to a guy at one of my work sites today. He asked how often I go to the petrol station. Said usually once every week or so, I do anywhere between 400 and 600 miles a week normally. He looked confused. Asked why he asked. 'I have to go every single day!' Asked him why, surely he doesn't do that many miles in a day... Turns out he never puts more than a tenner in at a time, it's cheaper that way. Apparently.
WarrenB said:
Luis Nazario said:
WarrenB said:
Saw something on TwiXter that made me chuckle, 'using premium fuel lowers your revs on the motorway'.
Isn’t this correct though, all other things being equal?Higher octane (petrol) fuel means the spark can be delayed (because of greater resistance to knock), meaning greater compression, meaning more torque, meaning fewer revs to produce the same bhp?
The difference would perhaps be marginal, but I don’t think the statement is incorrect?
WarrenB said:
Luis Nazario said:
WarrenB said:
Saw something on TwiXter that made me chuckle, 'using premium fuel lowers your revs on the motorway'.
Isn’t this correct though, all other things being equal?Higher octane (petrol) fuel means the spark can be delayed (because of greater resistance to knock), meaning greater compression, meaning more torque, meaning fewer revs to produce the same bhp?
The difference would perhaps be marginal, but I don’t think the statement is incorrect?
Talking to a guy at one of my work sites today. He asked how often I go to the petrol station. Said usually once every week or so, I do anywhere between 400 and 600 miles a week normally. He looked confused. Asked why he asked. 'I have to go every single day!' Asked him why, surely he doesn't do that many miles in a day... Turns out he never puts more than a tenner in at a time, it's cheaper that way. Apparently.
See, for example, the article from Car and Driver at:
https://www.caranddriver.com/features/a28565486/ho...
They tested 4 cars using higher octane fuel and lower octane fuel and measured, amongst other things, the hp produced by those cars in those two different scenarios.
A couple of the statements made in the article:
"A higher octane rating indicates greater resistance to knock, the early combustion of the fuel-air mixture that causes cylinder pressure to spike. When higher-octane fuel is flowing through its injectors, the engine controller can take advantage of the elevated knock threshold and dial in more aggressive timing and higher boost pressures to improve performance."
"Tapped into the Ford's CAN bus, we recorded a peak boost pressure roughly 1.9 psi lower during acceleration runs on regular gas, down more than 10 percent compared with the 18.1-psi peak on premium."
Then some of the results of the tests:
Honda - 87 octane fuel: max 164 hp
Honda - 93 octane fuel: max 172 hp
BMW - 91 octane fuel: max 604 hp
BMW - 93 octane fuel: max 617 hp
Ford - 87 octane fuel: max 360 hp
Ford - 93 octane fuel: max 380 hp
Dodge - 87 octane fuel: 318 hp
Dodge - 93 octane fuel: 332 hp
If these gains are brought about as a result of an increase in boost pressure (which can be achieved because the higher octane fuel has greater resistance to knock) - as the article seems to suggest - then there is no reason to suspect that the gains are the result of the engines revving to a higher RPM.
If that is correct, it would seem that at any given RPM (once the cars come on boost), the cars will be producing more hp on the higher octane fuel than on the lower octane fuel.
Therefore, if a car on lower octane fuel produces 50 hp at say 1,500 rpm, it would seem that the same car on higher octane fuel would produce the same 50 hp at a lower rpm (say 1,450).
A car will need a certain amount of hp ("X") to allow it to achieve a certain mph ("Y") in a certain gear.
If the inferences I have drawn from the Car and Driver article are correct, then the car running higher octane fuel will achieve X hp (and therefore Y speed) using fewer revs than the car running lower octane fuel.
As I said in my first response, the difference would perhaps be marginal (or very marginal), but I don't think the statement in question from the Twitter / X user was stupid.
Dracoro said:
Quite, not only that, if the car is doing 70mph at 1500 rpm, it wouldn’t make a single bit of difference whether the car has 100BHP or 900 BHP, it would still do 1500rpm at 70mph
I don't follow that.Take remapping as an example. In the below dyno graph, wouldn't the remapped Porsche (i.e. the one with higher bhp) be travelling faster at, say, 7000 rpm than the stock Porsche (i.e. the one with lower bhp) at 7000 rpm (assuming that in both cases the car is in the same gear)?
It wouldn’t be marginal at all.
At 1500rpm the car (depends on the gearing of course but in this example…) is going at 70mph then how much power it complete irrelevant. There’s no “marginal” at all!
You could add a billion horsepower to that same car, it would still do 1500 rpm at 70 mph.
At 1500rpm the car (depends on the gearing of course but in this example…) is going at 70mph then how much power it complete irrelevant. There’s no “marginal” at all!
You could add a billion horsepower to that same car, it would still do 1500 rpm at 70 mph.
Luis Nazario said:
Dracoro said:
Quite, not only that, if the car is doing 70mph at 1500 rpm, it wouldn’t make a single bit of difference whether the car has 100BHP or 900 BHP, it would still do 1500rpm at 70mph
I don't follow that.Take remapping as an example. In the below dyno graph, wouldn't the remapped Porsche (i.e. the one with higher bhp) be travelling faster at, say, 7000 rpm than the stock Porsche (i.e. the one with lower bhp) at 7000 rpm (assuming that in both cases the car is in the same gear)?
The speed is REVS * GEAR RATIO. It’s that simple. How much power it had makes absolutely 0% difference.
The extra power means it can get up to 70 more rapidly, use differing amounts of fuel etc.
Geoffcapes said:
From my wife this morning:
Wife: "Who do we have to speak to about our car serviced"
Me: "It doesn't need a service it was done about a month ago""
Wife: "but I keep getting a message to top up washer fluid, what washer fluid does the car need?"
Me: "Seriously????"
Wife: "What do you mean?"
Me: "washer fluid, is screen wash or if we have none in the garage. Water"
Wife: "Oh. Got a job for you when you get home!"
I have similar conversations with my wife about the washing machine. Wife: "Who do we have to speak to about our car serviced"
Me: "It doesn't need a service it was done about a month ago""
Wife: "but I keep getting a message to top up washer fluid, what washer fluid does the car need?"
Me: "Seriously????"
Wife: "What do you mean?"
Me: "washer fluid, is screen wash or if we have none in the garage. Water"
Wife: "Oh. Got a job for you when you get home!"
Except that it’s me that sounds a bit thick.
Luis Nazario said:
Very interesting, thanks.
So my whole, longwinded reply should be chalked up as “stupid things a PistonHead says”.
Damn.
In fairness, I think the only thing you missed is that throttle application is variable. So a remapped car or higher octane fuel might well be capable of making more power at a given rpm but only if you use it. But unless the clutch is slipping, you change gear or you have a CVT, revs and speed are directly linked. So my whole, longwinded reply should be chalked up as “stupid things a PistonHead says”.
Damn.
robinessex said:
In any vehicle, engine output is in proportion to throttle opening. The rolling resistance and aerodynamic drag are constant at a steady X mph. Regardless of the fuel used, the engine hp at any given rpm will be the same.
Are you sure? HP is a function of torque and rpm. Does a more energetic fuel create more torque? If it doesn’t why do drag racers and F1 cars use specially formulated high octane fuels?
Edited by blueg33 on Saturday 25th May 21:14
blueg33 said:
Are you sure? HP is a function of torque and rpm.
Does a more energetic fuel create more torque? If it doesn’t why do drag racers and F1 cars use specially formulated high octane fuels?
Is high octane fuel more energetic though? As far as I’m aware the octane number relates to fuel’s ability to resist knock which means you can advance the timing/up the boost and in turn produce more power. Does a more energetic fuel create more torque? If it doesn’t why do drag racers and F1 cars use specially formulated high octane fuels?
Edited by blueg33 on Saturday 25th May 21:14
832ark said:
blueg33 said:
Are you sure? HP is a function of torque and rpm.
Does a more energetic fuel create more torque? If it doesn’t why do drag racers and F1 cars use specially formulated high octane fuels?
Is high octane fuel more energetic though? As far as I’m aware the octane number relates to fuel’s ability to resist knock which means you can advance the timing/up the boost and in turn produce more power. Does a more energetic fuel create more torque? If it doesn’t why do drag racers and F1 cars use specially formulated high octane fuels?
Edited by blueg33 on Saturday 25th May 21:14
Edit to add
Google says you are right. Every day is a school day.
Luis Nazario said:
Very interesting, thanks.
So my whole, longwinded reply should be chalked up as “stupid things a PistonHead says”.
Damn.
As said before, yup. Extra power from a higher octane fuel means that instead of topping out at 6000 rpm in the top gear to reach its max speed, the car might be able to get up to 6100 rpm and go a little faster, and also reach the rpm required for a specific speed faster in a lower gear so improve its 0-60 time. It wouldn't change the revs required to keep it at a specific speed in a given gear. So my whole, longwinded reply should be chalked up as “stupid things a PistonHead says”.
Damn.
Geoffcapes said:
From my wife this morning:
Wife: "Who do we have to speak to about our car serviced"
Me: "It doesn't need a service it was done about a month ago""
Wife: "but I keep getting a message to top up washer fluid, what washer fluid does the car need?"
Me: "Seriously????"
Wife: "What do you mean?"
Me: "washer fluid, is screen wash or if we have none in the garage. Water"
Wife: "Oh. Got a job for you when you get home!"
I remember reading and article about a woman who went into a spares shop and asked for water for her windscreen washers but insisted it had to be FIAT water, becauseWife: "Who do we have to speak to about our car serviced"
Me: "It doesn't need a service it was done about a month ago""
Wife: "but I keep getting a message to top up washer fluid, what washer fluid does the car need?"
Me: "Seriously????"
Wife: "What do you mean?"
Me: "washer fluid, is screen wash or if we have none in the garage. Water"
Wife: "Oh. Got a job for you when you get home!"
her car was a Fiat 500!
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