Which uses less fuel?

[jimmy__riddle]

Ok, someone told me that when slowing down on a slipway off a motorway or similar change down early and engine brake as it uses less fuel than clutch in and brake. what are peoples opinions on this, ture or false.

NB, this was in a car but i guess it will apply for bikes as well

[Viney]

Clutch in and use the brakes only. The engine will use less fuel at tickover in theory

[MiniMatt]

Would have thought that any difference would be measured by the thimbleful.

Either way, engine braking probably leaves you in more control, clutch in and coasting with application of the brakes doesn't sound particularly settled.

[Biker Biggles]

I reckon engine braking but not quite as you describe it.What really uses less fuel is getting off the throttle earlier and hence using less brake.Brake is simply converting moving energy(which you have paid for to get up to speed)into heat dissipated at the brake disc.Get off the throttle sooner and you have used less fuel before you need to slow down.

[jambo]

Depends on the fuelling system. Top Gear took a V8 diesel Audi to Edinburgh and back on a tank of fuel a couple of years back. With the modern FI in that if you coasted with your foot off the gas the FI put no fuel into the engine at all, as the engine braking was keeping it turning. A similar system was much criticised on Yamaha's FZ1 when it came out as it led to a hesitation as you went from negative to positive throttle while cornering.

Carbs, of course will always add a little fuel as long as the engine is turning, but using smooth, gentle throttle in the correct gear and not building up speed that you then need to scrub off helps fuel economy.

If all else fails, fit a Sid Squid, annoyingly this makes more difference to fuel economy than anything else I've tried.

Jambo

[the_lone_wolf]

With the modern FI in that if you coasted with your foot off the gas the FI put no fuel into the engine at all, as the engine braking was keeping it turning. A similar system was much criticised on Yamaha's FZ1 when it came out as it led to a hesitation as you went from negative to positive throttle while cornering.

in any car from the past decade this is probably the case, cars don't have the lurching problem because the inertia of the vehicle dampens the movement, they also have had more stringent emissions regs that bikes are only getting now so it's almost certainly going to be more fuel efficient to leave the engine in gear and slow down using engine braking and the brakes as required

[Stu]

I'll see your Sid Squid and raise you 55mpg :D

[Grinch]

Clutch in and use the brakes only. The engine will use less fuel at tickover in theory

Yep, I think the same... but your just end up spending your savings on pads.

[yorkie_chris]

Curvy carbs have TES which dumps fuel in on the overrun. But I don't like coasting as then you're going to end up in the wrong gear when you need some power. Engine braking at about 5krpm means it's easy to get out of someones way when they do something silly. Try that when you're at 30mph with clutch in and still in 5th gear!

[Stu]

OK, now that's answered that engine braking uses no fuel so is the perfect economical way to slow down. What is more fuel efficient when you don't want to slow down? Engine braking using no fuel or clutch in & coasting far longer/faster? :)

[jimmy__riddle]

some mixed answers!

I should add its not about me penny pinching, not fussed about that at all. i was just wondering from a engineering/science point of view.

[yorkie_chris]

The answer is a massive "it depends"

[jimmy__riddle]

yeah i thought it might, the vehicles we were originally talking about were a 2.5TD L200 and a 2.2 petrol (carbed) Hilux.

[yorkie_chris]

Well a standard (not common rail) diesel has fuel flow proportional to engine speed and throttle position. So not much difference.

[startrek.steve]

If all else fails, fit a Sid Squid, annoyingly this makes more difference to fuel economy than anything else I've tried.

Jambo

Whats a sid squid?

[yorkie_chris]

Who's got that .gif of him with the lightbulb on his head?!?

[Biker Biggles]

Its a sort of automatic pilot that drives your vehicle around without using any fuel.
We should market it really.

[Daimo]

As said, when an engine is idling, its still using a lot of fuel to turn the engine over.

When using engine braking, the momentum is still turning the engine and not forcing any fuel in.

Our VXR does 0.2mpg when on idle, but you leave it in 6th and slow down it'll ratain max of 999.99 (therotically, no fuel used at all).

[breakz187]

I thought that the engine braking causes the vacumn to build up massively, reducing the amount of pressure within the fuel pressure regulator. I thought this was how it worked on injected petrol engines anyway. Obviously the injectors will have different control logic but i dunno...

[yorkie_chris]

Depends if it's a 2port reg or 3port ... compensated or not... (obv a 3port won't be compensated...) Basically ECU logic can cut fuel flow entirely on the overrun if programmed to do that.

[SoulKiss]

Whats a sid squid?

This is a Sid Squid (http://forums.sv650.org/member.php?u=188)

[Daimo]

I thought that the engine braking causes the vacumn to build up massively, reducing the amount of pressure within the fuel pressure regulator. I thought this was how it worked on injected petrol engines anyway. Obviously the injectors will have different control logic but i dunno...

Think thats a fair bit old on the early injection engines.
Things have come ona long way since then.

But on a modern engine, rolling + in gear uses no fuel, but taking it out of gear and idling uses quite a bit of fuel.

[Jdawg]

Tend to agree with Jambo, modern Fuel Injection systems will not inject any fuel into the combustion chamber when at 0% throttle, however in older FI engines this may not be the case. Anything with a carb will use fuel on 0% throttle.

[Sid Squid]

Depends on the fuelling system. Top Gear took a V8 diesel Audi to Edinburgh and back on a tank of fuel a couple of years back. With the modern FI in that if you coasted with your foot off the gas the FI put no fuel into the engine at all, as the engine braking was keeping it turning. A similar system was much criticised on Yamaha's FZ1 when it came out as it led to a hesitation as you went from negative to positive throttle while cornering.

Carbs, of course will always add a little fuel as long as the engine is turning, but using smooth, gentle throttle in the correct gear and not building up speed that you then need to scrub off helps fuel economy.
He's right. As for the later comment about the Yamaha, all FI systems go 'dry' on high vacuum/shut throttle.

If all else fails, fit a Sid Squid, annoyingly this makes more difference to fuel economy than anything else I've tried.
There's no substitute for being fiscally sensitive, ;).

[Spikenipple]

Are you sure no fuel is injected (FI bike obviously) when the clutch is out and you're engine braking?
That would effectively be the same as flicking the kill switch, which is completely different than just using engine braking (on my bike anyway, it slows you down a lot faster). I was under the impression that it will inject just the amount of fuel it needs to stay at idle speed.

[metalmonkey]

He's right. As for the later comment about the Yamaha, all FI systems go 'dry' on high vacuum/shut throttle.


There's no substitute for being fiscally sensitive, ;).

So whats the going price in today's climate for Sid Sqid after maket mod? What does the bidding start at?

[arcdef]

i read somewhere that with carbed engines it makes a difference to the fuel usage when coasting but with the electronic injected engines they use more fuel when coasting than if you stay in gear as the injectors shut down or something btu i may be talkign out of my bum.....