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Carbs vs. Fuel Injected

Discussion in 'Mechanical & Technical' started by beansbaxter, Oct 13, 2004.

  1. I love my fuel-injected 12...but I was just curious...

    Is there any pro's of having carbs over fuel injection?

    Just curious.
     
  2. :shock: With carbs you will never get close to the proper air/fuel ratio, that you can with fuel injection. And never have that efficiency of fuel injection,ie. mpg, lower emissions ease of modification for torque/HP, altitude changes.etc.
    Plus the parts in a carb set wear out, by vibration and use, faster than a throttle body does. It just goes on and on the differences.... 8)
     

  3. Agreed. I'm not spending $11K to convert my cobra to EFI because it's cool :tard:

    electronic fuel injection analyzes all the engine variables such as :

    Coolant temp

    Vaccuum

    Exhaust gasses (OXY sensor, it's mounted on my headers in the cobra)

    Intake air temperature

    Etc..

    And decides what level of fuel to deliver, etc.. a vast improvement over carbs. If I Mad Max my V Max, I will likely go with EFI (there's a new sequential port injection version for the 'Max, in the works) I hate carbs, I just don't have the knack of keeping them properly tuned like my dad and bro could !
     
  4. I understand that elevation does effect carbs but it's "not" supposed to effect F/I. But why is it then that I have obviously less power when I go up into the mountains? I'm assuming it's because the air is thinner....less oxygen means smaller combustion???
     
  5. Because lower air pressure means you're getting less air volume in the engine, and as far as I know most modern sport bikes lack an o2 sensor so they can't accurately adjust for changing air pressures.
     
  6. That's what I figured, thanks.
     
  7. no matter if its fuel injection or carbs less oxygen means less hp. with fuel injection the computer changes the air fuel mixture to run at its best as where with carbs the higher in altitude you go the richer your bike will run. we used to have this problem with snowmobiles because if you tune to run at higher altitudes when you drop down in a low valley you run really lean and we burned up a few motors.
     
  8. Thats the way it is suposed to work but without an o2 the computer doesn't have enough info. I think the VFR is running an o2 and probably some of the big expensive bikes (goldwing, fj1300, ect..) but the sport bikes have to rely on a pre-mapped fuel map.
     
  9. Here's the difference between a "closed loop" and "open loop" system (as best I can remember...no reference material on-hand...). A closed loop system lacks the O2 sensor, and is therefore "locked in" to the FI/ignition mapping it already has.

    The open loop system is more versatile due to the O2 sensor, and is able to adjust the FI air/fuel ratio accordingly, also due to the nature of the FI/ignition mapping built into the ecu.

    ZX
     
  10. ok, a few misconceptions here but its mostly right :)
    the o2 sensor is only there for emissions and fuel economy, it has nothing to do with power. in fact it is ignored (system goes into open loop) above a certain load (based on throttle position, rpm, etc). the lack of emissions testing on bikes in most places explains the lack of an o2 sensor.
    FI systems have some means of reading barometric pressure so that they can compensate for the lower oxygen content of higher altitudes. this may be a completely seperate barometric sensor or it will read the map sensor at key on before the engine is started. the former method is obviously better since it constantly updates, the latter will only update if the engine is turned off and restarted.
    and yeah, i would most definantly take FI over carbs, me and carbs dont get along :rant
     
  11. The link below is for a build it yourself FI unit that has been used with varing success in a lot of different applications. Since it is build it yourself, the results reflect the builders ability as well as the design qualities of the unit. There is a lot of feedback from various different builders.
    FI system

    And thanks xrattiracer - Yes an FI system can compensate for atmosphere density at altitude and dial fuel back to keep the ratio in balance.
    Mass air flow sensors are one way to do that, and combining map, baro, and tps inputs will do the same thing a different way.
    An O2 sensor will help, but is generally considered a switch between open loop and closed loop modes of operation, with a feedback signal in closed loop.
     
  12. I don't know of a barometric sensor? Some use a mass airflow sensor and an air temperature sensor to get that job done. As far as the o2 doing nothing for power I'm going to have to do some more research to be convinced. I do remember reading something to the effect that the o2 regulates a subtle flip-flop from rich to lean to increase a catalytic converts efficiency.
     
  13. a barometric sensor is actually just a map sensor that is open to the atmosphere rather than hooked to the intake manifold. 80s and early 90s chrysler products actually used just one map sensor, but used a vacuum solenoid to expose the sensor's input to atmosphere briefly at key on and during overrun conditions (coasting).
    no narrowband oxygen sensor contributes anything to the power output of an engine, it really is just there for emissions and economy (causing the cat conv to run more efficiency falls into the emissions category). *some* systems do use the adaptive stuff that it learns in closed loop to adjust the overall fuel ratios (called long term fuel trim) but its pretty rare and doesnt have much affect. now wideband sensors are a whole different story, they are quite capable of controlling then engine to a very exact air/fuel ratio even under a load. but they are expensive and dont last as long so arent used much (yet) in oem applications.
    Trust me on this stuff, I know engine management :) I spend alot of time calibrating and even reprogamming the code for the ecu in my car.
     
  14. I want to say you're wrong but I don't have proof at this point.. merely that my
    Holley 950 Commander system demands an o2 senser, and it's basically a universal hotrod EFI conversion. The way I understood it (for my system) is the o2 sensor tells the CPU whether the mix is fully burning and it can therefore adjust fuel flow (injection) and ignition advance, to compensate

    Maybe I don't really understand that part, though..

    PS: I have basically open sidepipes with NASCAR auger baffles, no Cat converters..and I have one MAP
     
  15. I agree with max, but I will research to make sure I'm not full of poo.
     
  16. Your hp drops with altitude increase because of the lower air content, or more specifically, less MANIFOLD PRESSURE. Some piston engine aircraft overcome this with turbos, to keep the manifold pressure higher, thus reaching peak power even at high altitude.

    Hp drops with altitude increase and several other factors. See this chart, page I-3: http://www.ametektmd.com/pdf/Sectioni.pdf
     
  17. Not to sidetrack the discussion, but to prove that last point, some WW2 aircraft used NOS injection systems to give extra emergency boost/speed at high altitudes
     
  18. Interesting!
     
  19. Carbs pro= I can adjust them myself

    Fuel injection pro= they adjust themselves

    Carbs con= they don't adjust themselves

    Fuel Injection con= I'm still learning how to properly configure it to my likeing and wish I had a dyno to play on.

    T
     
  20. Right.. my cobra will be trucked to a very professional group called Blood Enterprises in Auburn, after the final hardware install (I have a fuel cell issue now and have to return it for the second time to make things right) to program the CPU. Although I am a former R & D technician in the high tech field, (and could wing it if I were so foolish)

    As Dirty Harry said: "A man's gotta know his limitations"

    get a pro to dyno/program it, they do it everyday 8)
     
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