fuel injection vs. carbuerator

[MC85]

what are the major differences in power? which is a better buy? i have a 305 and i was wondering what are the major perfomance differences between them.

[Auto_newb]

I don't know too much about cars, but anyway:

Carbs:
Easy to fix
not good on gas
uneven engine wear -maybe not with today's modern carbs(delivers more of the fuel/air mixture to the cylinders closer to the carb)

I think you can also tune carbs for more horsepower, like making it run rich or something.

Cheaper
Probably better throttle response since it is mechanical

Electronic Fuel Injection:
Great on gas
costs a fortune to fix
if you put f/i onto it, the computer will adjust the engine to it
even engine wear
And I don't think the throttle response is as good as carbs
expensive

[quaddriver]

power is only dependant on the carb or FI system to the extent that it gets as much air/fuel as it can use. a 1000cfm TB will bog a 4.3L v6 just as fast as a 800cfm 4bbl on same for example.

Due to the 'fixed' nature of carbs, you can make one run steady rpm nearly as good as an FI system, as long as humidity, temp, baro pressure etc does not change. IF they do, a FI system can be made to adapt, a carb, as GM had shown with the E4ME and E2SE carbs and ford with the VV, can be made to adapt - but to a point. Once you start using mixture control solenoids, it has become a crappy TBI system.

For fuel metering accuracy, economy, emissions etc, they should be ranked in order: carb, TBI, CFI, MFI/PFI, SFI

[SaabJohan]

Carbs have only one advantage, they are cheaper.

Fuel injection has all the other advantages that includes; better idle, lower exhaust emissions, better throttle response, higher power output.

The reasons are quite simple, when using fuel injection you have better control of the fuelling, for example a fuel inejction system can add fuel during fast throttle changes, it can run closer the the limits of knock = higher power, don't need vacuum = better idle and so on.

[MC85]

i heard from a mechanic that early 90's fuel injection on camaros were horrible. is this true. what is the problem?

[quaddriver]

Originally Posted by MC85

i heard from a mechanic that early 90's fuel injection on camaros were horrible. is this true. what is the problem?

actually, the early 80's injection-abortion called 'crossfire' was the stupid one. After that the various port fuel systems got better and better, the 'L98 TPI' system of the late 80's early 90's was actually fairly good and easily modifiable and easy to retrofit to cars that came with nada (I know a 69 chevelle with an L98 350)

The system used on the LT1 motors (93-up) and the 'LS1' motors (98? and up) are simply followons with more precise controls. Of course with any system, the odds of it breaking down are proportional to the square of its complexity but quality control has also gotten that much better.

the use of OBD2, while extremely precise in controlling emissions, makes it very hard to fit the systems to cars not intended for.

[Steel]

A nice thing about carbs is that they can deliver a LOT of fuel if needed. Fuel injectors max out, and its an expensive bitch to get higher output ones, then to get a system to control them so they they arent flooding your engine all the time.

[replicant_008]

The main advantage of EFI was the more precise air/fuel mixture metering over a range of loads, revs and ambient air pressure. This helps with emissions and fuel economy especially @ idle of all times.

Single point fuel injection (the cheapest and simplest) form can be described as a float less carby - these effectively one injector doing the job of a jet and it's controlled by some ECU. The main issue is the capacity of the flow rate of the injector and it's ability to respond. They provided better emissions than carbs but were nasty cheap pieces of kit - incidentally they can provide better economy than MPEFI mainly because you don't have as much losses from injectors.

Multi-point fuel injection is more expensive and involves having numerous injectors. Sequential MPEFI basically provides for the injectors to open and shut above a valve port so that fuel is being jetted in the plenum above the port just before and during valve opening which is the usual rig these days although you can have MPEFI that are non-sequential ie squirt all the time.

There were some initial issues with the plenum/manifold sizes which meant the peak power of injected engines initially could be less than carbie ones - but that's improved immeasurably with more sophisticated maps and manifold design.

Part of the issue with trying to have more fuel is to change the ECU map (some OEMs make it difficult to help out with engine longevity), changing the injectors and in the case of the race car we built maintaining sufficient fuel pressure on the injector rail to provide enough fuel for the injectors when running a full capacity for 30 seconds down the long straight at the circuit.

There are a couple of DI (Direct Injection) engines using gasoline eg ALFA ROMEO JTA which operate direct injection into the cylinder head. These provide some advantages and is widely used in diesel and turbo-diesel applications.