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RWDboy Forums Junkie Location: South Australia Registered: July 2002	Re: efi vs carby Mon, 07 October 2002 06:41 I am not a smart-arse engineer so this could be a stuffed up argument. Both carburettor and electronic injection operate on the principle of atomisation. The main difference is in the way they use pressure to create the air:fuel ratio. Carby uses a low pressure air stream (ie a flow of air past the jets) to suck the fuel out of the jets and into the air stream which then flows into the head/cyliner etc etc. This has a few reprocussions (?) as the jet size stays the same, hence the chance for good atomisation of fuel is low except for a certain revs. It's like a hose cleaning a car, for a given amount of water flow rate, you will only get decent cleaning with a certain aperture (ie putting your finger over the end), **especially at low water pressure**. On top of that, when there are sudden changes in the air flow, there is no pressure pushing the fuel out, so for split second there, the mixture will lean out, and the timing will be wrong due to the slightly lean mixture (faster burning), and this can cause your car to "bog down" alot. This is why some cars have a vacuum retard system (like the solex carbies on a 2T) just so the car doesn't lose too much power. Most sidedraft carbies have an accelerator pump which temporarily enriches the mixture by putting the fuel under a little pressure but this doesn't solve the problem completely. Things tend to expand in a vacuum, this is why the fuel partially atomises with carbies, but it's not a very reliable method and will not always work perfectly, the atomisation is very inconsistent. Carbies are tuneable only in a certain rev-range! Carbies also will always pour fuel as long as air is flowing, this means that at low revs, droplets can form in the manifold when the valve shuts and this will cause the fuel mixture to be inconsistent, this is a tuning problem and will affect power (but only minorly). The main problem with carbies is that the fuel delivered is very unmeasurable, tuning the ignition can only be done on a dyno and can't be done on the run, when things like air temperature, pressure and temperatures in the cylinder change, there is very little done to compensate for it Fuel injection works on the idea of a high pressure fuel stream being pushed out into a low(er) pressure air stream. The nozzles for fuel injection are designed so the the fuel mixture gets squeezed through them, and broken into a very neatly atomised stream (compared to a carby). The duration of the injection spray is the measure of how much fuel is put into the combustion chamber. This is obviously a much better way of measuring the fuel put into the combustion chamber! For starters, the pressure in the fuel system remains constant, and the flow rate of the nozzle stays the same as well, the effect the low pressure air stream has on sucking the high pressure fuel is very low. The computer essentially knows how much fuel is going in. On top of that, there is usually an air volume meter. Whatever air goes into the system, will have to make its way to the cylinder eventually, this means the computer can know exactly how much air and fuel there is, all it has to do is calculate how much fuel to deliver (usually based on the stiochiometric ratio). With sensors for air temperature, water temperature, exhaust gas oxygen the car can tune itself on the fly, the ignition can be adjusted for good clean burning etc etc. I have to go to work now, so I can't explain everything, but you can see how the accuracy of fuel injection will create a FAR smoother engine, genuinely better torque curve, and much more tuneable engine that can respond to varying conditions better. My personaly preference is EFI, but it is more expensive. Although, the standard 4A-GE EFI is pretty basic, an aftermarket computer and some dyno tuning to optimise the map would produce more power for that car. Sidedraft carbies are good for cheap power, though, on older cars. [Report message to a moderator]

	Subject	Poster	Date
	efi vs carby	Ribbo	Mon, 07 October 2002 02:03
	Re: efi vs carby	EMP-2TG	Mon, 07 October 2002 02:43
	Re: efi vs carby	Bill Sherwood	Mon, 07 October 2002 03:31
	Re: efi vs carby	IRA11Y	Mon, 07 October 2002 04:25
	Re: efi vs carby	Bill Sherwood	Mon, 07 October 2002 04:50
	Re: efi vs carby	floody	Mon, 07 October 2002 05:17
	Re: efi vs carby	Blown86	Mon, 07 October 2002 05:29
	Re: efi vs carby	GIN51E	Mon, 07 October 2002 05:32
	Re: efi vs carby	floody	Mon, 07 October 2002 06:15
	Re: efi vs carby	Norbie	Mon, 07 October 2002 08:24
	Re: efi vs carby	gianttomato	Mon, 07 October 2002 10:18
	Re: efi vs carby	RWDboy	Mon, 07 October 2002 06:41
	Re: efi vs carby	GIN51E	Mon, 07 October 2002 08:27
	Re: efi vs carby	Ribbo	Mon, 07 October 2002 08:21
	Re: efi vs carby	SUPRAGTE	Mon, 07 October 2002 09:20
	Re: efi vs carby	Grega	Mon, 07 October 2002 10:39
	Re: efi vs carby	GIN51E	Mon, 07 October 2002 13:49
	Re: efi vs carby	5KinKP60	Mon, 07 October 2002 15:19
	Re: efi vs carby	justcallmefrank	Tue, 08 October 2002 00:20
	Re: efi vs carby	mrshin	Tue, 08 October 2002 00:34
	Re: efi vs carby	thetoyman75	Tue, 08 October 2002 00:39
	Re: efi vs carby	mrshin	Tue, 08 October 2002 01:34
	Re: efi vs carby	chrisss	Tue, 08 October 2002 09:18
	Re: efi vs carby	Remedy	Tue, 08 October 2002 10:03
	Re: efi vs carby	GIN51E	Tue, 08 October 2002 10:31
	Re: efi vs carby	chrisss	Tue, 08 October 2002 11:24
	Re: efi vs carby	rjenman	Fri, 21 October 2005 22:24
	Re: efi vs carby	rjenman	Fri, 21 October 2005 22:25
	Re: efi vs carby	hemi twofifteen turbo	Sat, 22 October 2005 01:29
	Re: efi vs carby	Bill Sherwood	Sat, 22 October 2005 07:28
	Re: efi vs carby	September_Squall	Sat, 22 October 2005 05:24
	Re: efi vs carby	170bhp	Sat, 22 October 2005 08:03
	Re: efi vs carby	oldcorollas	Sat, 22 October 2005 08:07
	Re: efi vs carby	170bhp	Sat, 22 October 2005 08:15
	Re: efi vs carby	river	Sat, 22 October 2005 10:26
	Re: efi vs carby	170bhp	Sat, 22 October 2005 10:41
	Re: efi vs carby	170bhp	Sat, 22 October 2005 10:44

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