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I supported Toymods
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Northern Beaches
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May 2002
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efi vs carby
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Mon, 07 October 2002 02:03
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Ok moving this topic into the tech section 
so which do u think is better and why? which is better for which applications?
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Location:
Carlingford, Sydney
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 02:43
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EFI is good carby is not good
very simple
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Location:
Brisbane / Gold Coast
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 03:31
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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.
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Club Member
Location:
sydney
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 04:25
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Seeing as this question was started in my for sale post I suppose I had better respond.
But before I do lets take an actual engine to base this discussion on, and as the parts were for a 4AGE lets use the bigport variant for the example using the standard factory EFI vs a twin sidedraft setup.
OK now weve got that sorted...
lets talk about the way these two systems introduce air in to the manifold.
I am sure some of what I will say here is not 100% correct and is based on conversations Ive had with more technicaly minded people who could also be wrong, but as I have understood it a carby uses atomisation to deliver an air fuel mix where as injection tends to use vapourisation by aiming the injector at a hot surface like a valve or the head itself and the fuel vapourising when it hits that hot surface. Of course some of the air is atomised on the delivery as well.
Obviously the vapourisation effect relys on a lot of variances like temp air speed etc to make it work effectively which is where its drawbacks are...fortunately the use of a computer and sensors overcome the poor mixing problems
(I havent taken in to account squish area here as that is something I understand little of at this point although I do know it does have an effect, but that effect would be advantagous no matter what delivery system you would use)
..without those injection would not nearly be as efficient or controlable. On the other hand a carburettor atomising the fuel from a much smaller jet further away from the valve can have a better mixing effect if everything is tuned correctly. Basically the size of the fuel particles are much smaller (better mixed) than straight out of an injector (where the particles are larger until they hit a hot surface)
The main advantage of injection is as has been stated before its ease of adaptability over varying conditions. Obviously if you had a computer able enough you could have a million maps to use for just about any given situation to overcome the mixing issue. Plus the fact that these days emmissions and fuel economy are big issues so this favours injection as well.
IMHO a carb will deliver a better throttle response (particularly low in the rev range where velocity is slower and the injected fuel struggles to vaporise) over all.
As an example try towing a trailer with a small load in a 4AGE powered car at 100Kmh in 5th gear, put your foot down and see the response..Ive done it many times towing trail bikes and generally the response from a standard engine is very slow ( the computer trying to figure whats going on with such small changes indicated from its sensors)
basically the EFI just decides to dump max fuel but this seems to bog the engine a little (flooding?) and the car is slow to recover and gain speed, where a carb delivers a much quicker response and the car starts to pull away at a much greater rate than the efi variant (no other changes were made to this engine BTW)possibly because you can control with your foot the fuel supply better but also because of improved fuel mixture (obviously more modern engines than a 4AGE have improved some of the mixing issues!)
ok thats enough typing for now...Ill wait for Bill to respond as I expect he will before I go into this any deeper
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Location:
Brisbane / Gold Coast
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 04:50
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A better example is Formula Atlantic engines of a few years ago. I was talking to a guy that used to build them, and he said that when they went from twin Webers to EFI, they went from 238hp to 242hp. That's pretty much dyno error ...
But at 6,000rpm he got 20hp more!
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.
If you want to compare a stock EFI 4AGE to a twin Weber one, make it fair and compare them the other way as well - A quad throttle body EFI one compared to one with a stock inlet manifold and something like a 2" SU hanging off the front of it. Pretty obvious which one would be better. 
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Registered:
June 2002
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Re: efi vs carby
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Mon, 07 October 2002 05:17
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In my experience, good carbies, such as webers, dellortos, mikuni flatslides etc can be just as good as injection for power, sometimes better, but, heres the thing, they will only be better or as good in a certain revrange- you can tune your carbies to give for example 1.the same top end power,or 2.same bottom end grunt, but either will compromise the other, due to the fact that the tuning- jetting, float levels etc- is basically static, where as an efi system can adjust the way and amount of fuel being delivered far more widely. You can also theoretically set up a carby for just as accurate mixing as efi, but again it will only be at a specific rev/load point, where as with efi you can have the ability for constant adjustment according to load, temperature, barometric pressure etc. Carbies operate in a very narrow band of operating conditions for peak efficiency, and can't compensate for most of the things that efi can. And, due to changing engine temps and other factors, its harder to accurately tune a carby,even on a dyno, but it can be done.
So If its a constant high rev application,or a setup where all out power is to be chased, well, there may be little difference. however if a smooth torque curve or general driveability is a factor, and , really, when isn't it, efi will be best.
Cost comes in too, of course- I'm working on a 4age powered something (chosen the engine, unfortunately not the car...probably escort mk2) which will more than likely use twin webbers, dell ortos, or hopefully mikuni flatslides. Its simply a dollars thing for me though, any of those will outflow the standars setup, but will have nothing like the driveability and sacrifice the power in some areas.
Thats my two cents, I hope I was on the right track....
cheers,
floody
[Updated on: Mon, 07 October 2002 05:20]
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Location:
Perth
Registered:
July 2002
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Re: efi vs carby
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Mon, 07 October 2002 05:29
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I remember about 10 years ago reading a tech article including an interview with the head design engineer for Honda Motorbikes.
At the time all bikes still used carbies and his reason was that they had not yet been able to get fuel injection to provide the immediate throttle response that carbies could.
Obviously very important for a bike.
These days a different story, all decent bikes have FI, technology has progressed far enough to make carbies redundant.
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I supported Toymods
Location:
Berowra-Sydney
Registered:
July 2002
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Re: efi vs carby
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Mon, 07 October 2002 05:32
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I'll always rather the sound of a Side draft weber at full throttle then an efi motor 
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Registered:
June 2002
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Re: efi vs carby
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Mon, 07 October 2002 06:15
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Carbies are redundant...tell that to kawasaki.
Motorbike carbies are somewhat more advanced than the state of 4 barrels or sidedraughts. The manufacturers have not been able to yet build an injected bike that has *quite* the rideability of a carby one- even now there is just that little bit of abruptness and hashness in the throttle response from injected bikes that makes the power delivery of something like a zx-9r a bit nicer than an injected fireblade. And sidedraught vs injected, yeah I'm mostly with you there, but slide injected motors and one throttle per inlet port engines sound damn good.
cheers,
floody
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Location:
South Australia
Registered:
July 2002
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Re: efi vs carby
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Mon, 07 October 2002 06:41
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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.
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I supported Toymods
Location:
Northern Beaches
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 08:21
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A bit more to think about with aftermarket computers which my 4age is running, just did some comparing from Rod's carby 4age on dyno day 3.
The 2 linking motors were Mos's 4age sprinter as it was the only one I could see run on both dyno day 3 & 5
Dyno Day 3
Rodney T - 4AGE TA22 Celica - 57.8kW (Carby)
Luke S (MOS) - 4AGE AE86 Sprinter - 57.5kW (Standard I think)
Dyno Day 5
Mos - 4AGE - 55.5
Matthew Robisin - 4AGE - 62.3 (Aftermarket computer)
So are aftermaket computers better than carbys?
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Location:
Brisbane
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 08:24
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| GIN51E wrote on Mon, 07 October 2002 15:32 |
I'll always rather the sound of a Side draft weber at full throttle then an efi motor
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Quad throttle EFI sounds every bit as good as twin sidedraughts! Throttle response is just as good too. The best of both worlds.
As for cost, the difference between well setup twin sidedraughts and a decent EFI system isn't much these days. In fact in some cases EFI can be cheaper! Keep in mind that a pair of Weber sidedraughts costs around $1500, and then you've got to pay someone to tune them properly. Hardly what I'd call "cheap"!
I had to make a choice a few years ago when I realised the factory Solex's on my 18R-G were beyond repair - should I fork out for 45mm Webers or convert to factory EFI? I chose the latter, and it ended up costing me less than $500 total. The grumpy old 18R-G now starts and idles like any modern EFI engine, gets twice the fuel economy, AND has more power from idle to redline! It's possible that the Webers might have given me a fraction more peak HP, but at the expense of mid-range drivability. That might be worthwhile on a race car, but for a street car? No way, EFI every time.
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I supported Toymods
Location:
Berowra-Sydney
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July 2002
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Re: efi vs carby
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Mon, 07 October 2002 08:27
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ok this is getting long and becoming a bit hard to understand, but how about this, plug all your sensors up to a weber, replace the jets in the weber with injectors and plug in a computer then your getting your computer adjustment depending on air temp and so forth but also having the fuel "mix well" with the air as its getting more churned up on the way to the cylinder??? 
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Location:
North Sydney
Registered:
May 2002
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Re: efi vs carby
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Mon, 07 October 2002 09:20
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No way id be doing that!
What your proposing to do is make "Sinlge Point Fuel Injection" which is crap. Its what they had on shitbox Holden Camira's(worst cars ever).
Thats what they had in the begining of fuel injection (Single point). Then they realised using multi-point is better for over 10 obvious reasons. Multi-point being what you see on cars with injectors firing into each port. It gives better atomisation, more even fuel saturation throughout the air etc etc etc.
Personally i think EFI rocks. For what we are dealing with anyway. Carburetors are great for 2000hp and up engines as its easier to supply the massive amounts of fuel the engines require. Dont think anyone round here will be even cracking 1000hp! Imagine the size the injectors would be on Victor Brays drag car if you could get injectors that big!
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I supported Toymods
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I renounced punctuation
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I supported Toymods
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melbourne.victoria.austra...
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June 2002
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Re: efi vs carby
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Mon, 07 October 2002 10:39
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u forgot one argument. fuel type
i ran a gas research carb on a 202 holden POS motor. not only did the carb make more power than the EFI variant - in ran 100% smoother as well (as the convertor convers the liquid to a gas - mixing with air is no problems...)
i think there are pro's and cons for both systems to be honest
carbs can be a bit grouchy on cold starts, EFi i've never had a problem with....
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I supported Toymods
Location:
Berowra-Sydney
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July 2002
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Re: efi vs carby
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Mon, 07 October 2002 13:49
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this thread is the same as saying "which is better? front wheel drive or rear wheel drive" one is always going to have an advantage over the other in some way, and it also comes down to personal choice,
fuel injection is good,
but so are Carbs.
and i'll always like the sound more,
like the sound of an old carb V8 sounds much nicer then a new V8.
but then again its personal choice and i enjoy hearing the fuel get sucked into the engine when you floor it
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Location:
Finland
Registered:
June 2002
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Re: efi vs carby
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Mon, 07 October 2002 15:19
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To my mind the upside in getting twin carbies is that they are somewhat plentyful out there on used market. Yes, second hand units.
Those few units I've been involved with were in good condition, nothing was broken. Only re-alignment of butterflies was needed, and of course re-jetting them.
If we compare cost of independent throttle bodies with all relevant gadgets to a pair of used twin carbies - our imaginery weekend racer's decicion may very well turn to favour of carbs.
To get carbies run well we need to sort out ignition management. That'd preferably be a 3-dimensional model. This will jack up the price of carbie setup. This feature is standard in EFI setup.
No arguments there, EFI is the best. I'm not aware of recent price developement but I know of domestic racers paying like 3000 AU dollars for EFI.
A pair of used twin carbies with inlet manifold is rarely more than 700 AU dollars (over here). For race use regular ignition distributor can be tweaked to work decently well on used rpm band.
It's really a case of what is sought from upgrade. An everyday ride with occasional drop at local track - EFI is the way to go.
For a car that is solely raced on track and built up with limited budget, carbs are good. Some difference in top rpm performance when compared over to EFI, but not really worlds apart. Like Mr. Sherwood said, Atlantic engine gained 20hp at 6000rpm when EFI'ed. But don't those engines rev like crazy, so 6000rpm would present an rpm range just off idle -?
To what I've been told, hp figures are very close to one another in 4-cyl rally engines revving to about 8000rpm.
-A.
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I supported Toymods
Location:
Perth
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May 2002
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Location:
Montrose, VIC
Registered:
May 2002
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Re: efi vs carby
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Tue, 08 October 2002 00:34
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First of all, don't get me started on LPG carbs 
Personally, I'd go injection every time over carbs. Thing is, there are different ways injection is done.
Multi throttles are good things, plain and simple. They sound good, and have the throttle response they should. But a lot of it comes down to the computer. Most aftermarket set ups are done with a MAP sensor, not an airflow meter. Why? easier to set up, cheaper, and no inlet restriction. But a MAP sensor obviously can't give the precise measurement/response of a proper air flow meter. Allow me to be sacrelidge for a moment and mention Nissans. The RB26 has got six throttles and twin air flow meters as standard. It sounds fairly good, and has good throttle response without flat spots etc. However, people try and fit aftermarket management to these cars, and in the process ditch the air flow meters. Because of often large cams combined with short stroke engine and multi throttles, running them purely MAP sensed makes them run like something Briggs&Stratton would even avoid. So the first thing people do is ditch the multi throttles and stick one big one on, in an attempt to get a bit more vacuum happening. Yuck!
So do it right, use air flow meters and multi throttles along with a decent computer  Of course, there is the (significant!) issue of cost...
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Club President
I supported Toymods
Location:
Sydney
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May 2002
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Re: efi vs carby
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Tue, 08 October 2002 00:39
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Ok, I really wasn't going to get into this as this is a old debate that is never answered to either sides satisfaction.
A few things to consider - Cost and availability.
Firstly you do need to decide what you want out of your car/engine and what you are prepared to spend.
A well set up set of Carbies will provide excellent power delivery and can quite easily provide a smooth running bottom end. It is all in managing the entire Carby set up from air speed to choke size, manifolds the whole package.
For an EFI set up to compare to Carbies in the top end performance side of things you need to have individual throttle bodies with well set up manifolding and of course a GOOD programable efi Computer.
Compare the cost on both and you will deffinatly be infront with the carby setup.
Now if you can actuially afford the leter mentioned EFI set up then yes thatwould be my choice ! An electronic carby
A cheaper EFI set up will be more restrictive than a basic carby set up. Stock intake manifolds are designed to flow for a standard engine NOT a modified one. Factory runners are generally resticive and flow poorly. Stock Throttle bodies also have a limit (Altho this is generally alot higher than the rest of the manifold)
Facts are a stock 4AGE EFI system is shit for a performance engine and so if your serious about your performnce its need to be changed. Which direction you go is up to you.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: efi vs carby
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Tue, 08 October 2002 01:34
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A little off the topic, I've just made a custom intake manifold for my 4ag turbo. I'll let you peoples know if it does anything when I get to try it, hopefully in the next few days.
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Location:
melb
Registered:
May 2002
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Re: efi vs carby
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Tue, 08 October 2002 09:18
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I agree with Rod and 5kinkp60.
if for example you had 2 people with 2TG's
- 1 with a carby version
- 1 with a EFI version
and they both want to put in a decent set of cams and port the head etc. which will be the cheapest to get running with the correct mixtures throughout the rev range?
- the carby set up is better in this situation.
efi is best on a stocky setup tho, for economy/drivablity benefits.
also I have a bluetop 4ag and these efi computers cannot even be rechipped. it drives pretty good though in everyday traffic.
but if I had a delco(holden) equipped efi setup, I could take it to just about any performance workshop and get them to remap it quite economically.
an efi 4age is not ecomically modified because of the efi system and that is why most people convert to a 4agze when serching for more power.
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Location:
Southern Sydney
Registered:
August 2002
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Re: efi vs carby
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Tue, 08 October 2002 10:03
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I'm suprised no one's thrown this into the conversation yet....
Forced induction? I find it hard to believe a carby would be better than efi when there is a turbo bolted on.
Whats peoples opinons?
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I supported Toymods
Location:
Berowra-Sydney
Registered:
July 2002
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Re: efi vs carby
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Tue, 08 October 2002 10:31
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i think efi is better with forced induction simply because its able to run off maps and so forth where it has to constantly change its fuel injection acording to the amount of boost the car i running at the time. but thats just a theory i have no real idea
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Location:
melb
Registered:
May 2002
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Re: efi vs carby
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Tue, 08 October 2002 11:24
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oh here we go...
this discussion has reached the pointless stage..
let the first issues be addressed before bringing new ones up..
carbies on turbos are not good but for completely different reasons..
oh I also agree with rod on this point - "I really wasn't going to get into this as this is a old debate that is never answered to either sides satisfaction"
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Registered:
September 2005
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Re: efi vs carby
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Fri, 21 October 2005 22:24
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| chrisss wrote on Tue, 08 October 2002 19:18 |
I agree with Rod and 5kinkp60.
if for example you had 2 people with 2TG's
- 1 with a carby version
- 1 with a EFI version
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ah sorry to dig this up, but back with the old 2TG, carbies were better because the EFI system was old and not so advanced, this is a bad example
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Registered:
September 2005
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Re: efi vs carby
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Fri, 21 October 2005 22:25
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lol i didn't realise this was a 2002 thread
i was googleing
i think i can get away with this cos i'm new. sorry. lol
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Location:
Melbourne
Registered:
October 2003
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Re: efi vs carby
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Sat, 22 October 2005 01:29
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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.
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Location:
Melbourne, Australia
Registered:
March 2005
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Re: efi vs carby
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Sat, 22 October 2005 05:24
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| rjenman wrote on Sat, 22 October 2005 08:25 |
lol i didn't realise this was a 2002 thread
i was googleing
i think i can get away with this cos i'm new. sorry. lol
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3 years!!!1111oneone wOOt! roflcopter
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Location:
Brisbane / Gold Coast
Registered:
May 2002
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Re: efi vs carby
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Sat, 22 October 2005 07:28
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| hemi twofifteen turbo wrote on Sat, 22 October 2005 11:29 |
"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.
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Reliablility is precisely why you'd choose EFI carbies every time. They are far more fault tolerant than carbies are, and have multiple failure modes that let the engine keep on going despite not much working at all.
If the pump shits itself, then it'll stop a couple of seconds faster than a carby-type car will. If an injector stops, then there's lots more to keep the engine going. I doubt the majority of the public would even notice an injector drop out on most engines these days under most conditions.
The gear that makes up a modern EFI setup is tested under far more dire conditions than carbies can handle. Most of the electronics can be completely submerged and there's no adverse effect at all, for example.
Do you think the people that build the Paris - Dakar off-roaders would choose carbies because of reliablity?
Um, no.
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Registered:
January 2004
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Re: efi vs carby
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Sat, 22 October 2005 08:03
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Hemi twofifteen turbo has hit the nail well and truly on the head, by design the carburettor relies on air speed across a venturi to create a low pressure, the faster this airspeed across the venturi the greater the pressure drop, now the fuel bowl has atmospheric pressure acting on it, and this difference in pressure is what causes the fuel to flow from the bowl thru the jets into the carburettor throat, here lies it's downfall.....IT RELIES ON AIRSPEED ACROSS A VENTURI!!! Fuel injection doesn't due to the fuel being pressurised, now with a carb if we want a good strong signal at the venturi, either the venturi has to be small or the airspeed has to be high, if you have every played with Weberes and replaced the venturis(removable, often called chokes) and replaced for larger ones to increase the amount of air that can be flowed at higher rpm, you will find that due to the lower air velocity across the venturi at lower rpm we get a weak pressure signal and not much difference between the pressure at the venturi and pressure acting on the float bowl, this causes bad mixing of the air fuel ratio(basically said!!), of course with fuel injection you can also run into problems where the air speed is also low, but back to back if you had two motors one efi and one carb and airspeed was low, the efi engine would be the more drivable. You could go on and on about this topic in depth but it all comes back to one very important factor.....
A CARBY RELIES ON AIRSPEED ACROSS A VENTURI TO CREATE A LOW PRESURE!!!
This effect is also how front spitters work on cars, fast moving air has a low pressure, so when this fast moving low pressure air hits the front of the car, it slows down and it's pressure comes up, this higher pressure acts on the splitter like a leverage arm, also if any air goes underneath the splitter we want to accelerate this air as it's pressure will reduce(fast moving air has a lower pressure remember) which will help the pressure onto of the splitter force it down....make sense??
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: efi vs carby
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Sat, 22 October 2005 08:07
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but with the aforementioned (years ago ) bike CV carbs keep Constant Velocity across the jet, and the jet is also variable with airspeed, removing many carb downfalls, and is why they are still used on bikes today..
car carbs suck, bike carbs suck better, but for tuneability and flexibility, EFI always wins...
ever heard of a closed loop carby? (LPG excluded )
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Registered:
January 2004
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Re: efi vs carby
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Sat, 22 October 2005 08:15
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oldcorollas, oh I've heard of CV carbs....ever heard of an SU???........Hmmmmmm don't see ANY sports bikes with CV's anymore!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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Location:
Land of Oz
Registered:
June 2004
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Re: efi vs carby
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Sat, 22 October 2005 10:26
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Hi,
Carbs are great. They look good, they sound good and they work good.
The biggest issue with carbs is you need to keep them tuned, and they're expensive to manufacture - with all those fiddly bits and gaskets etc. Also it takes someone with skill and time (and therefore money) to tune them.
If you got a well tuned carby set-up, especially if you got a venturi per cylinder, then your engine will work fine over the entire rev range. Carbs have been around since the birth of the petrol engine, and if your engine has flat spots or other issues 'cos of your carbs, then they're out of tune or not set-up properly.
Ultimately, EFI is easier and cheaper to manufacture and maintain. And that's the reason why cars have them now. Not because they're better or provide more HP than carbs. They work well and stay working well through the life of the engine, without requiring expensive periodic tune-ups.
Airspeed across the venturi isn't its weakness, rather, that's its strength and simplicity. While the engine turns and there's an atmosphere, the carby will work. Even when well out of tune they work - sure it may not be at the optimum for the engine, but they'll still deliver atomised fuel. Carbs are designed to deliver the proper fuel/air ratio from idle to max revs - it would be pointless if it didn't. Although their operating principle is simple, the modern automotive carb is a complicated piece of equipment. Proplerly designed, and tuned for the engine it is attached to, it will provide as good as operation as EFI.
I drive both a carby engined and an EFI engined car. Before the carbs were tuned the EFI car had the goods in response, idle and revving. Once the carbs were tuned on the other car, it's just as responsive as EFI. Most people wouldn't know the difference when driving a car whether it has carbs or EFI, unless the carbs are out of tune or the EFI setup is wrong.
Although automotive carbs may not be responsive when talking about temperature and pressure differences, the large aviation carbs that were attached to the aircraft of WW2 were designed to adjust to pressure and temperature, and they worked a treat. It's just that for your normal car and the normal driving habits of people, you don't need this extra complexity in your cars carbs. The temp/pressure variances for most driving conditions make bugger all difference to normal driving conditions.
The bottom line.... EFI is cheaper to make and maintain. That's why we have them. Carbs are more expensive and require periodic maintenance - that's why we don't have them now. Both deliver the goods just as well as each other. Again, I am talking about your average car and average driving habits.
seeyuzz
river
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Registered:
January 2004
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Re: efi vs carby
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Sat, 22 October 2005 10:41
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Sorry River, Airspeed across it's venturi is it's weakness!!!
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Registered:
January 2004
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Re: efi vs carby
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Sat, 22 October 2005 10:44
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If it's not then all I learnt when I did my Mech eng degree many years ago is wrong
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