Is my car worth modding??

[SeverAMV]

how bout....
for $7500 why doesn't someone just buy this?
http://www.automarket.com.au/vehicle...hicleNo=254605
hmmm, must be a typo or something!!!

lol, f*** yeah, i'd take that for 7.5, haha

[IZY-10]

how bout....
for $7500 why doesn't someone just buy this?
http://www.automarket.com.au/vehicle...hicleNo=254605
hmmm, must be a typo or something!!!

its not worth it! if you want to go fast get a carby

[AzKik-R]

yeah, i hear it has better atomization

[AzKik-R]

Mostly because it's impossible to meet modern emission control requirements with carbies. If it wasn't for the imposition of stricter and stricter emission controls then we'd still mostly be using carburettors, at least on cheaper cars.

And even with more expensive cars, the injection wouldn't be either as good or as reasonably priced as it is now mostly due to the development the manufacturer's have been forced to undertake to meet emissions on their mass market cars.

agreed.

Carbys are great for dumping loads of fuel into the engine ie big v8's, i think top fuel & funnies still use them, injectors are restricted to their rating ie 380/450/550/1000cc

injected engines can also run upside down and do not rely on gravity
as technology evolves injected is the cleaner more precise/stoich method

[SeverAMV]

from what i can understand about the physics of it, carbs have better atomisation due to the non-stop intake flow, whereas with efi you gotta wait for the spray. most drag racers tend to use carbs because it has better atomisation, physics of it seems hazy, but they seem to be able to make their cars go faster with carbs, so obviously something is going right.

[AzKik-R]

from what i can understand about the physics of it, carbs have better atomisation due to the non-stop intake flow, whereas with efi you gotta wait for the spray. most drag racers tend to use carbs because it has better atomisation, physics of it seems hazy, but they seem to be able to make their cars go faster with carbs, so obviously something is going right.

and this has plus points for the speedy delivery of the fuel to the chamber
there is one problem, being that the valve's are not always open, sooo while the fuel is still spreying everywhere and the valve is closed, where does the atomized fuel go to?
injectors are part of the EFI electronic fuel injection system
they squirt the fuel at the time that the valve is open, they aim the fuel directly into the engine, and then stop spreying the fuel when the valve is closed.
this is how injectors are a cleaner more precise or stoich method of fuel delivery.
stoich is something like 1:14 fuel:air or 14.3, cant remember off hand, any more fuel then this is running it rich, and less fuel is running it lean, lean leads to pre-ignition. stoich is optimal, and very little benefit is found from runnnig too much higher then stoich.
cars like top fuel's dont run a complete combustion cycle, they're very in-efficient, because they just dump fuel into the engine like you wouldn't believe haha

[IZY-10]

we are talking 4cyl carbies here though. A V8 carby i must admit you can not beat the sound they make as well as power

[SeverAMV]

and this has plus points for the speedy delivery of the fuel to the chamber
there is one problem, being that the valve's are not always open, sooo while the fuel is still spreying everywhere and the valve is closed, where does the atomized fuel go to?
injectors are part of the EFI electronic fuel injection system
they squirt the fuel at the time that the valve is open, they aim the fuel directly into the engine, and then stop spreying the fuel when the valve is closed.
this is how injectors are a cleaner more precise or stoich method of fuel delivery.
stoich is something like 1:14 fuel:air or 14.3, cant remember off hand, any more fuel then this is running it rich, and less fuel is running it lean, lean leads to pre-ignition. stoich is optimal, and very little benefit is found from runnnig too much higher then stoich.
cars like top fuel's dont run a complete combustion cycle, they're very in-efficient, because they just dump fuel into the engine like you wouldn't believe haha

ideally its 14.7:1 air to fuel, but most motors only get around 12:1 from factory, and thats efi motors included. this is probably due to air being mostly nitrogen, whilst fuel needs pure oxygen to combust ideally.
at the speed motors rotate at, the bottlenecking isnt quite noticeable, and it can be quite useful for instantaneous response spikes, but with vacuum physics, the bottlenecking is minimised as it only sucks in the mixtures when the valves are open, much like injectors only spray when the valves are open.

i'll admit carbs arent quite efficient at producing more power from less fuel like efi motors, but carbs can be pretty good power wise. downside with carbs is you cant have both fuel economy and power, its either one or the other.

[JohnL]

from what i can understand about the physics of it, carbs have better atomisation due to the non-stop intake flow, whereas with efi you gotta wait for the spray. most drag racers tend to use carbs because it has better atomisation, physics of it seems hazy, but they seem to be able to make their cars go faster with carbs, so obviously something is going right.

There's no waiting with an injector, it fires precisely when the cylinder needs it, in the quantity required, already well atomised and then further atomised by turbulence. With a carby the fuel leaves the jets in a fairly un-atomised state, then largely relies upon turbulence to do the rest. The constancy of the carby air flow may help to some very slight degree (doubt it though), but won't make up for the other defecits.

Also, the best carby set ups are generally considered to be those that provide a dedicated venturi per cylinder (e.g. multiple Webers, Dellortos, Amals, Mikunis, Keihins etc), so these venturi and their jets will see just as pulsating an air flow as the injectors on a multi point EFI set up, which tends to upset the constant flow theory...

I know someone will say 'but what about Holleys etc', but IMO this sort of carb generally isn't quite as good as single choke per cylinder set ups, and are largely used because a common plenum chamber is easy to package on 'V' engines, and thus a multiple choke single carb is easier to use with quite good results.

I once saw a GTHO Falcon fitted with four 50mm DCOE Webers on manifolds that criss-crossed above the engine, could barely see the engine for carbs and plumbing! That car was truly ferocious. Ferrari used DCOE Webers on all their carburetted 'V' engines, I once did some work on a 365GTC4 with six of them, and I can tell you the carbs got in the way of doing just about anything on that motor!

I'm not really up on drag racing (not my cup of automotive tea), but I vaguely recall that at least some of the classes use carburettors because it's mandated in the rule book(?).

There's no reason you can't make as much (or nearly as much) power with a carb as with EFI, but it will tend to be over a more restricted rev range and the response to changing conditions won't be as good. It's relatively easy for a carb to give optimum power over a narrow rev range, harder to do it at just above idle all the way to the red line, and harder still to do it with good fuel consumption and emissions.

[SeverAMV]

coincidentally, i managed to get my hands on a pair of dual sidedraught skracing carbs, dcoe40. apparently they integrate the best bits of the mikuni and weber designs so they shouldnt be too bad for my d15b. (i'd have bought genuine dcoe45 webers if they didnt cost half a motor each).

but yeah, these are purely mechanical carbs so they cant adjust to change in conditions as well as the keihin cv carbs already in the civic. but as i recall, one advantage of running carbs is the simplicity of the tuning for high revving applications. with most efi ecu's that are capable of handling high revs (say 10krpm), you need to program in the entire fuel map up to that point in the rev range, whereas with the carbs, you just tune it so it can supply enough fuel at that revs, and it will be able to perform decently at those revs (albeit a little richly until then).

but for street driving and daily driving, its better to tune it for a more narrow but useable rev range as JohnL has stated. why tune a daily driver motor for 10k rpm when you probably wont even hit anywhere near that on the street. imo, for street applications, its best to tune for good bottom end and midrange response, because frankly, how often does anyone stay in the top end before upshifting?

im not too sure about the calculations with regards to the atomisation rate of carburetor over efi, but someone on the d series forums should be able to shed some light on it.

[JohnL]

and this has plus points for the speedy delivery of the fuel to the chamber
there is one problem, being that the valve's are not always open, sooo while the fuel is still spreying everywhere and the valve is closed, where does the atomized fuel go to?

You mean the un-atomised fuel? It partially collects on the plenum and manifold walls and then dribbles into the various cylinders in uncontrolled quantities, and in different uncontrolled quantities in different cylinders. The un-atomised (or poorly atomised) fuel is also in relatively heavy droplets that in engines with a single carb are pulled this way and that with changes in air direction as the different valves open and close, but since the droplets have relatively high mass they tend to get 'left behind' by the airflow and end up not being evenly distibuted into all the cylinders.

Old straight six Holden engines were notorious for this, i.e. cylinders 1 and 6 would run rich and the others progressivly nearer the middle run lean and leaner. This happened because the heavy droplets would rush along the manifold but then fail to turn the sharp corners as they passed the openings to the middle cylinders, and more fuel ended up in the end two cylinders. This wasn't helped by the manifold passages for cylinders 3 and 4, whereby the air / fuel had to negotiate a cast-in baffle that meant the mixture had to initially travel toward each end of the manifold but just before the port openings for cylinders 2 and 5 had to make a sharp 180° turn before heading back toward cylinders 3 and 4! Needless to say cylinders 3 and 4 generally ran lean, especially at higher rpm (or what passed for high rpm with these engines), and the fuel that should have gone to cylinders 3 and 4 ended up in 1, 2, 5 and 6 (mostly in 1 and 6).

stoich is something like 1:14 fuel:air or 14.3, cant remember off hand, any more fuel then this is running it rich, and less fuel is running it lean, lean leads to pre-ignition. stoich is optimal, and very little benefit is found from runnnig too much higher then stoich.

Except under harder acceleration, a richer than stoichiometric mixture (yes, I looked up the spelling!) up to a point produces more power, but at the expense of fuel economy. When cruising you want a perfect stoichiometric ratio as you don't need max power but you do need max economy.

A stoichiometric ratio occurs when all the fuel and all the oxygen is consumed in the reaction (burning) with none left over unused. For petrol and air this ratio is roughly 14.7 X the mass (weight) of air to fuel mass. A ratio less than 14.7 of air to 1 of petrol is rich, and more than 14.7 to 1 is lean (looked those numbers up too, just to be certain you understand!).

I don't know what is considered to be the ideal ratio for a rich mixture for hard acceration, it's substantially richer but there is a point at which power starts to drop away, and I'm pretty sure this is very different for different fuels or blends.

cars like top fuel's dont run a complete combustion cycle, they're very in-efficient, because they just dump fuel into the engine like you wouldn't believe haha

Way over stoichiometric, so much that drag engines are often in danger of destroying the engine due 'hydraulicing' on fuel if something goes even a little bit wrong. Keep in mind that the brews used in drag racing are usually quite exotic and are obviously intended to be run at very rich ratios.