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| Re: Fuel Injection |
Subject: Re: Fuel Injection
by andrewjdonoghue on 2002/1/1 6:26:00
This "EFI makes more power theory" is pure BS, as is much conventional wisdom. Don't jump on me, but if you're interested read this through. EFI is better, but don't think it's a miracle
horsepower cure. Unfortunately this is very long and will take multiple postings.
If you don't want to know, please skip over them.
Andrew
There's no doubt fuel injection is heaps better, but not necessarily in outright power. The only limit to outright power is how much air and fuel can get in, and can they achieve the correct
mixture. Obviously with heavily modified carby V8's (or even turbo rotaries) running around getting sufficient air/fuel, there's not going to be a limit that a 1200 engine (or even a 1500
engine) is going to hit. Anyone think that an A series engine is capable (with ANY mods) of making more power than these types of engine is sadly mistaken.
Get the carby big enough to flow enough air, and get the jet sizes right, and it will get exactly the same PEAK horsepower as an EFI engine. (Assuming both can supply correct spark at the
correct time). Possibly, the carby engine could even make a slight power increase, due to the additional load that running heavier alternators makes on the EFI engine.
However, having said that - where fuel injection is better than carbies is basically EVERYWHERE else that the carby is not optimised for (in this case our carby engine was calibrated for max
hp).
A very simplistic view (*see carby addendum 1 - next posting ) is that a carby can be tuned for approximately 3 points - flat out, idle speed, and usually one more point in between.
A fuel injection system can be tuned for whatever the resolution of the fuel injection system allows. An extreme example of this is on some of your top end fuel injection systems, like MOTEC,
where you can set ignition timing, fuel delivery for every single mapping point on the power curve (by individual RPM, throttle opening, air density etc).
This is where fuel injection wins out. It can be tuned for so many more load points, effectively increasing at each of those points: Driveability, fuel economy, tuneability, throttle
response, reliability, power, torque. Wider power bands, more torque and often power are normal responses to EFI - but this is because factories don't usually set up their cars as undriveable
beasts with max horsepower the only goal. Because of the better tuning resolution of the EFI system, everything else can be setup for more peak horsepower (if that's what the factory wants),
without making the same sacrifices a carby engine tuned for peak power has to make.
The actual horespower figures are going to vary based on the state of engine tune, and how good the carb tune is versus how good the EFI system tune is.
Even retuning a stock EFI car (if the computer is retunable, or getting a rewritten chip if possible) can significantly improve horsepower, and replacing a FACTORY fuel injection computer
with a more powerful aftermarket computer can improve it further.
Hope you can use the info. In short, the only real way to find out how much "horsepower" it can improve your car's engine is to try. There were injected L series 4 cylinders and they're a
good example to use in this forum. You can usually guess at perhaps 20% and work up or down from there (CA20 vs. CA20E is very close to this mark). But also remember that it effectively
cannot improve the maximum horsepower to any more than the right carby and tuning could anyway, but where you'll see the benefits is EVERYWHERE else.
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