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hemi twofifteen turbo Regular Location: Melbourne Registered: October 2003	Re: efi vs carby Sat, 22 October 2005 01:29 OK some things people have neglected to mention: A carby's venturi (well more like any venturi) increases air speed to create a pressure drop to draw fuel into the incoming air stream. All venturi's will be a restriction. EFI doesn't have this problem. Also on single carby setup on a 6 cyliner and sometimes 4 cyl depending on inlet design will usually favour the inner cylinders, and the outers will run lean. But depending on manifold design this can be overcome, but usually not too much of an issue for stock cars. This is most easily overcome with the use of multiple carby's so that each port feeds of a single throat of the carby. (but does require a bit more precise tuning to equalise both (3 for 6cyl) carbies. Older EFI systems with the air flap type meter are absolute crap, and a properly set up carby will make more power everywhere. "Apart from the cost, there's absolutely no reason at all why you'd ever want to run carbies over EFI. EFI is better in every way that you can think of." -- what about reliability, say your wishing to cross the nullabor, and your EFI pump shits itself, or a sensor goes (crank angle etc), or even an injector. Worst case scenario with a carby is not life threatning. In a police chase where they shoot the tazer on your car to fry the electrics, it's all over unless you got a carby. 4wd's in mud etc, water, dirt 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." Depending on carby choice, say for a 4bbl, you have primary and secondary jets. Primarys you drive on most of the time, then secondaries when you give more than 1/2-3/4 throttle (also adjustable) Say with a Quadrajet you also have metering rods, which lift out as the air flow changes in the secondares. Thus you can floor it at idle, and the seconaries won't open unil a certain amount of air is flowing , and as more air flows, the metering rods lifts out higher and higer. There are machined steps in the rod which dictate fuel delivery which can be changed, allowing you to set how much fuel you would like delivered at any given airflow. "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)." Every carby I have ever seen has at least 1 accelerator pump. Sometimes 2 or more. And 4 nozzles or so, which are all adjustable simply by changeing a spring or bending a rod. I've never had any trouble tuning for throttle response on a carby. In fact a carby will instantly squirt in fuel with throttle change since they are mechanically linked. The charge in the inlet manifold is already mixed with fuel, so flooring it allows this premixed mixture to go straight into the cylinders and burn, follwoed in the next combution event with a richer mix to increase power. On an EFI car if you floor it the entire inlet manifold is full of only air, this air then is able rush into the cylinders, with a squirt of fuel that was inteneded for the last measured amount of air (say cruise). The MAP response time is definaly not instantanous, neither is AFM since the colum of air in front of it will 'stretch' before it registers the increased air flow. All this is split second, and probalby not a noticeable difference in either system, but that is one thing a carby may have over EFI. Albeit a very small thing. "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). " Non sequential EFI will also leave fuel on the back of the valve. As far as I have reseached this only results in slighty higher emmisions, and does not effect power. As for carbies pouring in fuel, it's sucked in, in proportion to the air flow past the venturi. low air speed, low pressure drop, low fuel entry. With very lumpy cams carbies do have trouble with atomization/idle. On the upside it does sound pretty tough though. (same prob with MAP and lumpy cams) As for LPG, as Remedy said is quite good. I recall someone wanting to put the quad cam v8 lexus into an older car with a manual, LPG carby won hands down, no emmisions test, so no need for cat convertor etc, (in older cars in vic u need to make the car compliant to the newer engines emmisions specs for RWC) -- LPG meets emmisions tests by default. Also all the wiring got thrown out the window, a carby needs no sensors. A dyno tune with a simple igntion computer is all that was required. For someone that did not know how to wire, or want the hassle or upgrading fuel lines, surge tank etc etc etc) it was a good choice. Forced induction carby? -- I've seen a lot of good setups making big power with carbies, and being reliable. One thing carbies will never have is what bill said: "You don't need a million maps to make a good EFI system, all you need is the right compensation maps to adjust for temperature (which a carby can't do), elevation (which a carby can't do), water temperature (which a carby can't do), air temperature (which a carby can't do), and the engine will run just fine over a large range of conditions very well indeed. " A carby can be tuned to it's peak for any given condition, any deviation in these conditions will result in less than optimal power output, but still is not a major problem except if your on the strip. (in which case you'd be changing jets/rods etc all the time anyway) I'd be interested to see how many people have their aftermarket EFI setups calibrated for 'all conditions'. So in conclusion, Carbies are good, EFI is good, depening on application. [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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