Fuel Injection Vs Carburetor: What Makes More Power?

[900HP]

Ok I'll be the devil advocate. So IN A PERFECT WORLD ONLY where ultimate hp is the only goal a carb will always make more power. Before I get jumped on let me explain. Ltent heat of vaporisation is the key. I also believe that it is next to impossible to achieve a perfect setup with a carb but with EFI one can get alot closer. So in a perfect world a carb wins. in the real world the EFI wins.

Shower injectors take care of that, however and can produce a finer mist than any carb booster.

The question I have is a "finer mist" always more desirable though? There can be a lot to droplet size and atomization, finer isn't always better.

[twl]

I look at it this way.
It's a matter of what gives the best F/A mixture for the power.
The difference can only amount to how much better the mix can be made by one particular technology or other.
IF the carb is doing well, and the tune is getting nearly as good as it can get for a particular engine, the EFI is not going to be any significant amount better.
If the carb and tuning sucks, the EFI can be a lot better. If the EFI and tuning sucks, the carb can be a lot better.

A good example that I saw very recently was a team that went to Bonneville last month with a bike that had a very expensive and exotic EFI system put on it, and the team consisted of people who were supposedly very top level experts with these EFI systems. However, it sucked, and carbed versions of that bike are much much faster. It ain't always the tech, but more often it's the implementation, and how the rest of the engine is working all together to produce max.

[jet1]

Ok I'll be the devil advocate. So IN A PERFECT WORLD ONLY where ultimate hp is the only goal a carb will always make more power. Before I get jumped on let me explain. Ltent heat of vaporisation is the key. I also believe that it is next to impossible to achieve a perfect setup with a carb but with EFI one can get alot closer. So in a perfect world a carb wins. in the real world the EFI wins.

Shower injectors take care of that, however and can produce a finer mist than any carb booster.

I dissagree. With any fuel injection you are creating heat by pressure to vaporize the fuel regardless of injector type. In a carb you are removing heat from the fuel and air as it vaporizes. Like I said perfect world only carb wins.

Here is a thought. What if a guy pressureized your fuel to a higher pressure (150 psi) then ran it through a heat exchanger to remove the heat created by the pressure. Then when it was injected it would actully remove heat from the charge.

[140Air]

Ok I'll be the devil advocate. So IN A PERFECT WORLD ONLY where ultimate hp is the only goal a carb will always make more power. Before I get jumped on let me explain. Ltent heat of vaporisation is the key. I also believe that it is next to impossible to achieve a perfect setup with a carb but with EFI one can get alot closer. So in a perfect world a carb wins. in the real world the EFI wins.

I think that FI wins by a hair over a Dominator or Predator setup when the injectors are mounted high. It is possible to get near perfect mixture distribution. But those carbs are very hard to beat and are simpler and probably easier to use.

[140Air]

Ok I'll be the devil advocate. So IN A PERFECT WORLD ONLY where ultimate hp is the only goal a carb will always make more power. Before I get jumped on let me explain. Ltent heat of vaporisation is the key. I also believe that it is next to impossible to achieve a perfect setup with a carb but with EFI one can get alot closer. So in a perfect world a carb wins. in the real world the EFI wins.

Shower injectors take care of that, however and can produce a finer mist than any carb booster.

I dissagree. With any fuel injection you are creating heat by pressure to vaporize the fuel regardless of injector type. In a carb you are removing heat from the fuel and air as it vaporizes. Like I said perfect world only carb wins.

Here is a thought. What if a guy pressureized your fuel to a higher pressure (150 psi) then ran it through a heat exchanger to remove the heat created by the pressure. Then when it was injected it would actully remove heat from the charge.

Hmmm. Liquids do not compress when pressurized, so do not heat up from that cause alone. They can be heated from inefficiencies in the pump and plumbing. The injectors heat the fuel in the process of breaking it up into fine particles and this may be the primary source of heating.
You could start with chilled fuel, but that works for carbs too.

[vannik]

Just to clear one thing up - injectors atomize the fuel (small droplets) which than evaporates (vaporizes) as it travels down the inlet and this latent heat of evaporation gives the cooling effect. Depending on the length of the inlet tract from the point of injection one can play with droplet size to "control" this cooling effect.

For port injection to match a carbed setup requires a slightly longer runner (higher temp) and slightly bigger diameter to compensate for the lower density.

Damn, I promised myself not to get involved in this thread!!

Vannik

[900HP]

Just to clear one thing up - injectors atomize the fuel (small droplets) which than evaporates (vaporizes) as it travels down the inlet and this latent heat of evaporation gives the cooling effect. Depending on the length of the inlet tract from the point of injection one can play with droplet size to "control" this cooling effect.

For port injection to match a carbed setup requires a slightly longer runner (higher temp) and slightly bigger diameter to compensate for the lower density.

Damn, I promised myself not to get involved in this thread!!

Vannik

Class is now in session children

[900HP]

I have posted this graph before. It is our 2013 Engine Master's Pontiac. This was early in our testing but here is the comparison of our EFI vs. our Carb. The problem with this comparison is I believe with more work and testing BOTH systems could have been made to work better. We had a pretty well sorted carburetor but plenum volume, runner inlet, spacer, etc. could have all been played with. The injection needed the injectors higher in the runner and "layed back".

Also remember we had a lot of rules to follow so this is not a 100% maxed carb effort or is it a 100% maxed EFI effort because of the rules we were dealing with.

In our circumstances, the EFI outperformed the carburetor, here is the difference.

efivscarb.jpg

[140Air]

Just to clear one thing up - injectors atomize the fuel (small droplets) which than evaporates (vaporizes) as it travels down the inlet and this latent heat of evaporation gives the cooling effect. Depending on the length of the inlet tract from the point of injection one can play with droplet size to "control" this cooling effect.

For port injection to match a carbed setup requires a slightly longer runner (higher temp) and slightly bigger diameter to compensate for the lower density.

Damn, I promised myself not to get involved in this thread!!

Vannik

Broken promises.

I think there is a little ambiguity in this: "For port injection to match a carbed setup requires a slightly longer runner (higher temp) and slightly bigger diameter to compensate for the lower density". Saying "match" and "compensate" implies the difference is neutralized.
The advantage of fogging with gasoline is an approximate 30 degree F drop in charge temperature while the air displacement with gasoline vapor is on the order of less than 2%. For low port injection without the air displacement from gas vapor the effect would be like running in 20 degree colder air. There is about a 3-5% hp advantage there. If you turn that around, say you have wrung all the power out of your engine you can get and then you have a race in the desert and its 20 degrees hotter. Can you just resize your intake tract and regain the lost power?

[jmarkaudio]

I have posted this graph before. It is our 2013 Engine Master's Pontiac. This was early in our testing but here is the comparison of our EFI vs. our Carb. The problem with this comparison is I believe with more work and testing BOTH systems could have been made to work better. We had a pretty well sorted carburetor but plenum volume, runner inlet, spacer, etc. could have all been played with. The injection needed the injectors higher in the runner and "layed back".

Also remember we had a lot of rules to follow so this is not a 100% maxed carb effort or is it a 100% maxed EFI effort because of the rules we were dealing with.

In our circumstances, the EFI outperformed the carburetor, here is the difference.

efivscarb.jpg

There are circumstances that may have helped the carb in that case. And limiting the carb throttle blades to 1.75" is not a fair comparison.

There are several things that have to happen to make the most out of either carb or injection. The fuel needs to be delivered in the amount each cylinder needs for all load and RPM changes. It needs to be delivered in a sufficiently homogenized mix that allows for a quick and even burn in the cylinder. and it needs to respond to changes as the engine needs change.

While there may be inexpensive systems available with injection that work over a wide range, they are not readily available to everyone and easily set up by most. Carbs will bolt on and usually run reasonably well if they are not excessively plundered and sized accordingly. And even when engine needs are a little different calibration time is minimal compared to injection.

As far as droplet size, I have yet to see a point where too small has hurt power on a single carb application. Everything I do that improves atomization has netted more equal distribution, uses less fuel, and makes more power.

[JoePorting]

I would think in a perfect world there wouldn't be any difference between the two. In the real world a carb is a lot easier to setup. Just take it out of the box and put it on and you'll have a motor running in 5 minutes. The big advantage of a carb is that it's self regulating. An FI system will take hours to setup and probably run worse than a carb when first setup. If an FI expert spends 1,000 hours on a setup, like an OEM engineer, then he can get it to run better than a carb. Better in terms of lower emissions and better response. Either way the difference between the two setups, assuming they're both done right, should only be around 2%, or within the dyno error rate. Therefore finding a material power advantage between a carb or FI system is a waste of time.

[900HP]

I would think in a perfect world there wouldn't be any difference between the two. In the real world a carb is a lot easier to setup. Just take it out of the box and put it on and you'll have a motor running in 5 minutes. The big advantage of a carb is that it's self regulating. An FI system will take hours to setup and probably run worse than a carb when first setup. If an FI expert spends 1,000 hours on a setup, like an OEM engineer, then he can get it to run better than a carb. Better in terms of lower emissions and better response. Either way the difference between the two setups, assuming they're both done right, should only be around 2%, or within the dyno error rate. Therefore finding a material power advantage between a carb or FI system is a waste of time.

The carb is easier is a common mis-conception. There is NO WAY that the above carburetor would have performed as well as the F.I. if it hadn't been for the extensive data acquisition package we had with the EFI including individual cylinder tuning and monitoring capabilities.

Yes, you can take a carb out of the box and it will run. To make it run as well as it can takes a bit more effort. Don't get me wrong, I love carburetors but I also understand if you want to maximize performance you will need a lot more than a carb, some jets, and a magnifying glass

[MrBo]

Just a related comments to consider:

I have read the term “dyno queen” to describe an engine quite a few times on the internet.
I am not really sure I believe such an engine exists. What moves a torque meter, should move a car, I would think.

I can see a huge difference in engine performance between dyno and track caused by G forces and float bowls not working together, and requiring band aid fuel mixture settings etc. though…

[900HP]

Just a related comments to consider:

I have read the term “dyno queen” to describe an engine quite a few times on the internet.
I am not really sure I believe such an engine exists. What moves a torque meter, should move a car, I would think.

I can see a huge difference in engine performance between dyno and track caused by G forces and float bowls not working together, and requiring band aid fuel mixture settings etc. though…

Absolutely. Why do you think the Pro-Stock guys would give both nuts to be able to run EFI. Think of how much fuel is going to the rear of the manifold on launch vs. down-track when G-force is down and now air-speed and pressure is up inside the scoop. Tuning nightmare.

[jmarkaudio]

And you don't think you can have distribution issues with injection as well? Unless you direct inject it's not peaches there either, and the higher the injectors the larger the issue can be. I would be curious to see back to back the difference.