ultimatejay

iTrader: (1)

I've never heard of using the 55 DCOE booster venturi. Is there a benifit to it as opposed to the long IDA one, or do you just have to use it when you bore the IDA to 51.5mm?[/QUOTE]

It's an old school mod the VW's guys have been doing for a long time. More air and more fuel is more power. I went from 82mph to 86mph at the dragstip just from the carb change. That's quite a jump in horsepower, no dyno required, track is what really matters.

48 and 51 is too small for a 13bpport, yes you can get by but you are not making full power. From switching to 48 to 51 you can see gains of 10+ hp. Not a huge amount but every horsepower counts and it's a good reletively cheap mod.

I would disagree on that one EFi being easier than carb. They both are very easy to tune if you know what you're doing, but a carb set up, especially an IDA carb is easier to learn and set up then a EFI.

Lets see, top of the line carb- 1200.00 VS

Top of the line EFI setup- Where do I begin? ECU unit, laptop computer, upgraded fuel system, throttle bodies and custome intake manifold- 4000+

You do the math.

Hyper4mance2k

iTrader: (40)

Physics my friends you can't argue with physics. I'd get more specific, but I dropped out of college 5 years ago and can't remember exactly how it works or I'd share. Either way carbs FTMFW. Here is a fun question. Have you ever seen a FI car run 15psi non intercooled? I ran my turbo FB like that for 20k before it spun a bearing.

Shainiac

iTrader: (7)

It's called methanol

drewski86

I like that you have real world experience with this, but the fact that you're using a boosted application is apples to oranges. Maybe you can tell me why everything that I found about carburetor ice refered to it as a problem?

http://www.twminduction.com/ThrottleBody/carb_vs_fi.pdf

This article, written by Jim Mederer, shows that FI makes more and better power over Carbs.

peejay

Carburetors atomize the fuel a lot better than EFI.

That is it.

If having a venturi actually added power, then why not put a venturi in an EFI system's throttle body? Nobody does this, because it doesn't happen. The venturi is a flow restriction. Temperature drops because pressure drops. That is it.

DelSlow

iTrader: (2)

I disagree. EFI is superior in every way to carbs, with the exception of price and electronic complexity. Fuel injection sprays a fine mist of fuel at high pressure, a carb cannot acheive that. I call BS on the greater temperature drop as well, for the same reason as atomization.

Just look to the pinnacles of racing technology, I don't see anyone still using carbs and for good reason.

drewski86

This makes sense, I just haven't found anything that shows carbs make more power, then again my research was to show FI is superior. It seems like some say one makes more power and others say otherwise. The link I posted shows a direct comparison which used the same manifold.

On a side note, did anyone else notice that only 25mm shorter air horns were good for 5 hp.

Hyper4mance2k

iTrader: (40)

If I sold pepsi and wrote an article that said it was better for you than water youd buy it wouldn't you... lol at twms article. I gave the example of my old turbo because intake temperatures are usually at least 50*F hotter than NA. My current NA car does always done the same thing.

drewski86

Jim Mederer (co-founder of Racing Beat) wrote the article and oddly enough only sell carbs for 13Bs...

The article is from Drag Sport magazine. Of course TWM is going to use this to show the performance of their product.

Hyper4mance2k

iTrader: (40)

at·om·ize 1. To reduce to or separate into atoms.
FI does not atomize the fuel. All it does is spray it out... When fuel comes out of an injector it's still in a liquid state very little of the fuel is atomized. That's why many companies are spending hundreds of millions of dollars trying to make a fuel injection system that does. When fuel is drawn out of a float bowl it atomizes into a gas and cools. This change is a chemical process durring which the liquid fuel atomizes into a gasious state and all the heat energy that was in the fuel as a liquid is now spread over a larger suface area, if you will, therefore dropping the temprature of the fuel per it's density. It's not just the venturi and the lower pressure across it that drops the temps. It's the atomization of the fuel. I never said it was the venturi that added power it's the temprature drop. You cannot argue with physics... Colder gasious fuel is densor than warm liquid fuel spraied into the intake tract. There fore you get more fuel and cooler fuel per cubic inch then you get in a FI setup. You also get cooler denser air which leads to more fuel and air into the cumbustion chamber per stroke than with FI which leads to a bigger better burning mixture and more power.


Look at that power graph in that terrible article it's obvious the carb isn't tuned right. The carb falls flat on it's face at 6500 RPM. Why didn't they tune the carb too? Just from looking at that graph and my experiance I'm willing to bet the had 36mm chokes in the Del... Of course the TB is going to flow more air and make more power up top. That article can't be used for compairison unless you know for sure the carb was tuned to it's full potential, and from how flat that graph is after 6500 rpm it's stupid obvious that they didn't spend 5 seconds tuning the carb. The del made a bunch more power through the mid range until the chokes limited any further progress...


This is not a carb vs. FI thread if you want to start one and prove how wrong you are then go ahead otherwise please get back on topic.

Hyper4mance2k

iTrader: (40)

Maybe nexttime I go for a drive I'll make some gasoline snowcones for all the disbelievers. lol. I don't get that much ice.

Shainiac

iTrader: (7)

I dont understand how the fuel from the carb could be cooler consider the pressure differential from the carb to the intake is only ~5psi.
The fuel pressure on an FI motor is 8 times that. Forgetting about the venturi for a second, wouldn't this be a much more dramatic decrease in temperature than from a carb?

DelSlow

iTrader: (2)

I didn't say it atomizes the fuel, I said it sprays a fine mist of fuel at high pressure. This increases the fuel surface area in contact with the air and allows the fuel to atomize much easier. The carb and fuel injector both do the same thing, but the fuel injector does it more efficiently.

ultimatejay

iTrader: (1)

I would say most drag racers today are still using carbs. Most pros with big sponsers and big money are using EFI because when they travel to different parts of the country they have programs on their computer to tune their car for that track much faster and precise than a carburetor. As far as total horsepower output between the two their really isn't a big difference. It all depends on the tuner.

rnz520

iTrader: (10)

This is a very interesting thread, and before I ask my question I just want to add that a properly set carb will make as much power or more than FI, but driveability on the street will suffer, along with midrange, and how it reacts to different temperatures and altitudes.
F1 and top racing teams use FI because how easy it is to adjust from one to the other and how much easier it is to monitor and control and datalog how an engine is behaving at every RPM.

On another note, I want to do a full bridge on my 13B, would a 48 IDA suffice for fueling or do I NEED the 51?

Hyper4mance2k

iTrader: (40)

And that is the problem. It doesn't atomize. It's just spraied liquid fuel. Gasoline DOES NOT burn as a liquid. It only burns as a gas. I've thrown lit cigaret butts in an open can of gasoline, and you know what happens? The cigarette goes out. I'm not saying to go try this cause if there is a great enough concentration of gasious gasoline above the liquid it could ignite for a big boom. If you spray water out of a spray bottle no matter how fine the mist it's still not steam. The fuel injected from fuel injection cars doesn't drop in temprature because the gasoline is still in liquid form, it hasn't atomized into a gasious state. The fuel injector does not atomize the fuel as well as a carburetor does. Direct injection is the closest to atomizing fuel and that's using 20,000 psi fuel rails. In fact fuel injected cars do such a bad job of atomizing the fuel manufacturers put the injectors as close to the cumbustion chamber as they can get them. They do everything they can to counteract the problem of the still liquid fuel recombining into larger clusters of gasoline and puddleing in manifolds. That's one of the reasons why the casting is left inside manifolds. It keeps the air turbulant along the runner to assist in not letting the liquid drops of fuel reaccumulate in the bottom of the runner.

The fuel pressure on a carb has nothing to do with this. Fuel pressure to a carb is only to regulate the amount of fuel that gets past the inlet and into the float bowl, and how fast the float bowl can refill. Apples and oranges. Raising the fuel pressure on a fuel injected car can cause the injector to spray a finer mist of liquid gas that might have a better chance to evaporate into a gasious state, a.k.a. atomize. But on a carb all the fuel pressure does is control the amount of fuel available in the float bowl. No matter how high you turn up the pressure on a fire hose water is never going to come out as steam. it has to go through a chemicle change to atomize into steam. In waters case it needs to be heated. With gasoline it needs to evaporate or expand in the atmosphere. The low pressure across the chokes and emulsion chamber which is attached to the fuel feed in the float bowl allows the gasoline to atomize almost instantly as if it was in a vacuum.

I don't know how to better explain this so you can understanding this...

drewski86

Of 5 back to back dynos I found comparing FI vs. Carb, FI came out on top 4 times. We can argue theory all day, but it's hard to argue against test data.

ultimatejay

iTrader: (1)

I would say then that you don't know how to tune a carb., or the carb manifold setup is not up to par. What carb did you use in your comparison against what efi setup?

And what comparison are you talking about? We are talking about max horsepower.

drewski86

Since I have never tuned a carb you would probably be correct. I did not do the comparison. These were comparisons I found on the web, like the one I posted earlier.

DelSlow

iTrader: (2)

I'm sorry, but the ICE classes I have taken and the textbooks from them say exactly the opposite of what you are claiming concerning atomization. The liquid droplets in the fuel spray WILL evaporate(atomize) and the finer the spray the quicker this will occur (hence the reason ultra-high pressure direct injection is even better, it is just a step up from fuel injection). The fuel injectors are placed closer to the engine because the fuel does in fact atomize quicker than from a carb and will not displace as much air. Injecting fuel further upstream will allow more complete atomization, but will also displace more of the intake air, slow throttle response, and could also actually lead to a hotter intake charge once the mixture reaches the combustion chamber. What you say about the rough intake surface is true, but only because liquid fuel will not evaporate as quickly once it sticks to the walls. The tendancy of the fuel droplets is not to reaccumulate and puddle, but instead to continue to evaporate into a vapor until combustion occurs.

Hyper4mance2k

iTrader: (40)

You are very correct. FI is amazing and it has advantages in every place over a carb except for temprature and atomization, which directly lead to power. The droplets spraied by an injector will evaporate and atomize but not at the same rate as they do in a carb. Okay here, when the pressure drops across the chokes it also drops in the emulsion chamber where the fuel is. Now both EFI and carbureted engines are always pressureized at 14.7 psi of atmospheric pressure at wot. Now, when air is rushing every where through a TB, intake manifold, carb, it's all still darn near atmospheric pressure. So when there is a pressure drop in the emulsion chamber it essentually creates a small vacuum just like in the engine. Now imagine how fast the gasoline is atomizing inside a vacuum, now its not a big vacuum, but something has to full that vacuum. The 14.7 psi of pressure areound that vacuum require it to be equalized and the fuel atomizes and fills that vacuum. The gasoline is atomizing much faster in the lower pressure area than it ever will evaporating in the airstream at 14.7 psi of pressure after being spraied out of an injector. So with a carb in say 1cubic inch of volume you have more atomized fuel than you would in a fi car because it atomized in a vaccume. A denser colder more atomized fuel for a bigger bang.

Race cars don't use carbs because the travel all over the world and it would take too long to tune and retune all the time. Plus you can get a broader tq curve with FI, more power through more rpms, and better gas mileage. But, peak power is for the carbs lol...

EpitrochoidalPower!

In order for a carb to function it requires this pressure drop across the venturi as you describe, this creates and lower pressure after the venturi which is a flow restriction which fuel injection does not have.

I disagree that the air be it carb or efi is all at atmospheric pressure as it rushes through TBI, carb etc. its very close on good efi setups as there isnt the flow restriction of the venturi and it doesnt require a vacuum to function whereas by the very nature of the design of a carburetor the air is going to be below that of atmospheric pressure and below that of fuel injection setups and therefore there is decreased volumetric efficiency.

You argue that because of this pressure drop a temperature drop is created, this is true... but

according to ideal gas law

PV = nRT

Pressure * Volume = number of moles of gas * universal gas constant * Temperature

Therefore if pressure drops for a constant volume of air the temperature drops according to basic physics, but the flaw in your argument is that the pressure is dropping after the venturi which is the limiting factor of the flow of air entering the intake manifold, therefore even though the air is colder, there is still the SAME amount of air and its even less dense than that of a fuel injection setup without this temperature drop and pressure drop.

Colder air is more dense than warm air at the same pressure, but in this case the temperature is dropping DUE to a pressure change and therefore it is not more dense.

The important thing to consider here is that the air is cooling AFTER the carb, it may cool, but it doesnt become more dense, more air cannot just be created after the carb, there is still the same amount of air as entered the carb, its just dropped pressure and therefore temperature.

So yes there may be more of a temperature drop in a carb setup compared to efi but this does not mean that carbs allow denser air to enter the engine. Assuming flow was equal between a tbi system and a carb system then the density of the air entering the engine would be the same, you cant create more air after the carb or tb, its impossible, all you will have is warmer, higher pressure air in the tb setup and colder low pressure air from a carb setup at the same density But you also have to consider that the flow between the two will not be equal as the venturi in a carb setup is a restriction to airflow which a tb system does not have and therefore tb will flow more air

And remember higher pressure means higher volumetric efficiency.

The cooling of the evaporating fuel would be very similar between the two, injectors atomize fuel very well, have you seen a fuel injector firing? its a very fine mist, looked at fuel coming out of a carb jet? very similar, and the argument that the vacuum aids in the evaporation doesnt work either as the pressure drop does exactly what you said and cools the air, so lower pressure but also lower temperature (Boiling temperature of a liquid changes with change in pressure) therefore evaporation is at the same rate as that of the warmer higher pressure air.

Carbs have less flow and lower pressure, fuel injection has great fuel atomization and far more precise fuel metering, carbs can come close to matching peak power of FI over a very small rpm range whereas FI will make more power everywhere and therefore greater acceleration, smoother power and better fuel consumption

Hyper4mance2k

iTrader: (40)

Youre wrong, and thanks for ruining a good thread with your consistent arguing, ********.

Shainiac

iTrader: (7)

The temperature change I was referring to was in the FUEL. Sorry I didnt state that. The relationship between pressure and temperature is direct. When pressure decreases, so does temp. What I was trying to get across is that the 40+psi fuel behind the EFI injectors quickly goes to near 0 and looses heat. Same concepts as an air conditioner. Carburetion really doesnt have this advantage.


I doubt many people will call this a ruined thread. Albeit off track, there are a lot of good points being pointed out.

But, It's hard to argue with physics. EpitrochoidalPower's post was on par with about every text book Ive read. No change is energy is free. The temperature drop after the carb is at a loss of kinetic energy.


Alex

Shainiac

iTrader: (7)

Edit: Sorry Hyper4mance2k, I didnt realize you were the OP. This really has turned into a royal threadjack.