Carb jet changes and fuel efficiency

[LoserShoes]

Actually, there are even more efficient carb designs out there. The problem is that they are owned by the oil companies.

I've always wondered what one of these mystery carburators could do that can't be done with electronic fuel injection? Seems that the software gives total control over all the parameters.

Steve

[HobbyMan]

The technology for fuel injection has been around for a long time. Only, it hasn't become popular until recently. While the world was running mainly on carburated engines, serveral things wouldn't have been soo significant. Maby the energy crisis wouldn't have happened, emissions wouldn't have been soo much of a problem, etc...

[Snow]

The 1957 Corvette C1 had fuel injection

http://en.wikipedia.org/wiki/Chevrolet_Corvette_C1

[mainlylinux]

and for mileage, how about not just having electronic fuel control but also spark control that is "integrated" with the fuel control? That way when you make jetting changes you are able to have the spark adjusted to it's best potential right along with it.

BTW, with fuel injection you can shut the fuel off completely on deceleration; as long as the vaccum and rpm are where they need to be, the computer just turns the injectors off. Not only that, but @ 45 PSI your fuel is pretty well atomised for a better burn, wasting less fuel. And with an 02 sensor your machine can continually sample exhaust and adjust itself for optimum efficiency.

One big boost for efficiency I've read about is high compression ratios. Not much is written about it; but from what I understand, even though max power isn't increased greatly, part throttle (where most people drive) efficiency is increased a good deal.

How about this: a manual transmission that has a one way clutch, so that when you let off the gas you can coast, without the engine having any drag on the coasting.

[Crazcnuk]

Part of the function of the transmission is to act like a brake. It saves a lot od wear and tear on the brake linings.

However, your idea of shutting the fuel right off on deceleration is an intersting one. Then at least you aren't wasting fuel while decelerating.

If you are going to build for efficiency, the first thing you want to do, if possible, is increase compression. However, it's a real bit of science to know how much any particular engine can take without self destructing, or, more commonly, starting to preignite the fuel (knock).

Most engines these days, v8s at least, are anywhere from 7.8 - 9.0:1 compression. High performance factory engines can be 10:1 or better. The upper limit, w/o a lot of headwork, etc., is usually around 11.5:1.

IF your thinking of using a turbocharger or supercharger, however, you may be better off to build the engine for around 8:1, and then using the charger to boost you up to whatever you want it to be. Very high performance turbo engines are often 6:1 then run very high boost pressures.

It's a trade off between efficiency and performance. A very low prime compression engine tends to run poorly off idle, even though it may go like a bat out of hell as the rpms climb.

Biggest problem is that every engine design is slightly different, so it takes a lot of trial and error to get the best combination.

One common misconception is that fuel injection is more efficient than carbs. This isn't actually true. A properly tuned and sized carb is every bit as efficient. What fuel injection saves is all the adjusting needed to keep a carb in tune.

The reason that early mechanical fuel injection didn't catch on was that it was very complicated to tune, and none of the regular corner garages ever bothered to learn how. If you wanted your 59 Impala, or 57 vette F/I tuned you almost had to take it back to Detroit!