Carburetor vs Injection.

Carburetor vs Injection

                                                             

   This article covers an opinion of why fuel injection out performs carburetors. This is still a touchy subject for many people because they still think that the carburetor is the only way to go. This was the same type of reasoning that people had when ignition distributors with points were being replaced with electronic ignition. I remember hearing people say “Dual point distributor would out perform electronic ignition any day”. This type of thinking usually comes from a lack of knowledge, and understanding of how the system works.

Unfortunately, the American motorcycle manufactures use old automotive technology and are years behind the automotive industry standards. Fuel injection has come as standard equipment on many automotive manufacture’s automobiles since the 70’s, mostly from the European automobiles.

I will use “AMM” (American motorcycle manufactures) to keep from violating copy rights by mentioning manufacture’s names. The Delfi FI (fuel injection) is a very good system for motorcycles. It can be manipulated very easily with the correct software. There are several good manipulation software programs, piggy back devices, and aftermarket ECU replacements on the market today.
  One of the problems with the V-Twin engine is the restrictions of the placement of the engine, because it has to be configured around the frame and other obstacles. There is also the lack of space to incorporate newer technologies such as variable valve timing, turbo charging, variable exhaust tuning, variable intake runners, mass air flow meters… the list goes on. This is just scratching the surface of potential technologies that could be utilized in the motorcycle industry.

The ETM (electronic throttle module) has been standard equipment on most of the European automobiles since the year 2000. You are now seeing ETM technology applied to some 2008 AMM. Since there are restrictions such as frames, floor boards, foot pegs… the V-Twin exhaust has to twist, bend and turn so it can be routed around these obstacles. This creates a problem with VE (volumetric efficiency) of the engine. VE is different between the front and rear cylinders. There are other things that cause differential VE between cylinders such as slightly different compression between cylinders (leaky valves, worn rings, imperfect combustion chamber cc’s, imperfect piston domes, cylinder temperature …). Anything that can cause a difference in the amount of power being produced in each individual cylinder is where the carburetor cannot compete against EFI. 


  As we all know the amount of air pulled through the venture of a carb. is what determines how much fuel is needed to flow through the jets. One problem with this is that most motorcycles feed both cylinders with one carb and one divided intake runner. A carb cannot meter the correct AFR (air fuel ratio) needed to obtain maximum power because the VE is not the same on both cylinders. Even if there were one carb per cylinder, the carb couldn't meter optimum AFR through the complete RPM range and at different throttle positions. This is where fuel injection has the advantage (when it can be manipulated).
Most of these devices and softwares use a spread sheet design so that you can change the optimum fuel mixture for each cylinder at any throttle position, RPM, and MAP (manifold absolute pressure). The MAP sensor monitors the changes of intake vacuum and pressure due to engine load and throttle plate position. This means that more power can be produced if the optimum AFR is reached. Lets say that 13.2:1 AFR (13 parts of air mixed with 1 part of fuel) makes the most horsepower which would be the optimum AFR. Now we need to adjust the jet sizes to shoot for 13.2:1 from 2,000 – 6,000 RPM. So change the jet size in the carb to obtain optimum AFR at WOT (wide open throttle) on the rear cylinder at 2k. 2.25k, 2.5k, 2.75k, 3k, 3.5k, 4k, 4.5k, 5k, 5.5k, 6k,6.5k RPM… Now do the same for the front cylinder. There is no way to obtain optimum AFR with a carb. To make it even worse, now jet the carb at different throttle positions such as 0, 2, 5, 7, 10, 15, 20, 25, 30, 40, 60, 80, 100 %. Even worse, change altitude and or ambient temperature. It’s impossible to obtain optimum AFR unless you have a fuel injection. You can map any fuel mixture at any of these throttle positions and RPMs and it can adjust to temperature and altitude changes. If you have two engines exactly alike, but one engine doesn’t have optimum AFR and the other does. Which one will produce more horse power?  

This is what a typical FI map looks like. If the AFR was not correct at 20% throttle at 2500 RPM, then you would increase or decrease the number (61.5) in the graph at the point where the RPM and TP meet.

This is what a typical FI map looks like. If the AFR was not correct at 20% throttle at 2500 RPM, then you would increase or decrease the number (61.5) in the graph at the point where the RPM and TP meet.



This is what a typical FI map looks like. If the AFR was not correct at 20% throttle at 2500 RPM, then you would increase or decrease the number (61.5) in the graph at the point where the RPM and TP meet.




Not only can FI make more power, it can be manipulated to run smother, run better cold and hot, easier starts, and better fuel mileage. I’m a big fan of the SE Race Tuner. The software can manipulate: AFR both cylinders, VE mixture either cylinders, Ignition timing either cylinders, warm up enrichment, cranking fuel, idle RPM, IAC warm up steps, closed loop bias, acceleration enrichment and deceleration enleanment.

Another advantage of this software is that it comes with a very detailed data recorder. This recorder records everything that the ECU sees. It can read engine codes with descriptions. It has a speed / distance calculator, ¼ mile calculator, and dyno graph capability. I have found that the dyno graph hasn’t shown accurate horsepower readings compared to actual dyno graphs, but is very helpful in comparing glitches in the graph lines to the data recorder.

The speed / distance calculator is extremely useful. You can record 2,000 RPM to red line (or what ever RPM you want to record), make changes and compare them to your next run. These recordings include: distance in feet, distance in miles, elapsed time, and average G force. Pretty Cool! There are a lot of people that don’t like this software. It is because they don’t understand how to use the software and don’t realize it’s potential.

In conclusion, to make optimum horse power
you must have optimum fuel mixture.

Credits: http://www.hemrickperformance.com