What makes MFI so good?

[PorscheGuy79]

I hear people rave about MFI and the throttle response, it seems to be a lot of peoples first choice for fuel management. Why is that, what makes it so much better? MFI vs. EFI, wouldnt EFI be that much better(pros and cons of each)?

Well besides MFI looking very cool...

[michel richard]

Something I can say a few words on . . . I just spent all morning fine tuning the MFI on my car, and I'm getting real close to where I want it.
I think that the major thing about MFI is a Mount Everest sort of thing: it's a challenge to master it, and it has a lot of history. It was the very top end, high performance, induction system for some of the glory days of auto racing.
This being said, it certainly is not better than the most modern engine management systems with wideband oxygen sensors etc . . .
Well set up, it adds a few horsepower to an engine, even over Webers, it does have good throttle response, is sequential etc . . . It is quite a challenge to get it there, though, and will make your engine run like c*** if it's not all adjusted properly, many people give up on the way (Everest again).
Oh, and it can be pretty expensive if you have to start rebuilding pumps or throttle bodies.
FWIW.

Michel Richard
914/6 2.2E MFI

[Wayne 962]

Simply put, the MFI system is an older-style fuel injection system that doesn't really compromise performance for emissions control. The engines that run with MFI can run with higher lift, longer duration camshafts - you can't run these with CIS. These cams mean more power, but also crappier emissions. This is the main reason why MFI went away.

As for MFI vs carbs - a finely tuned MFI system will give you better metering and mixture control than carburetors. The improved mixture control is basically the only real advantage that MFI has over carbs - simply bolting on an MFI system in place of carbs does not generate horsepower. By regulating the mixture more effectively, it allows the engine to perform more efficiently, and thus will give you better gas mileage and better horsepower over parts of the RPM range. A properly configured MFI system, and a properly jetted carb will give you about equal HP on the same motor at the peak - it's in-between where the MFI system shines.

Still, it's very difficult to tune and modify the MFI system for custom engines (you need to design / modify the space cam in the MFI pump), and also match the throttle boddies and the stacks to the engine's displacement). That is why most people with modified engines go with carbs - they are very flexible and easy to change the jets on.

Nothing beats a individual throttle-body electronic engine management system for throttle response and performance. The reason why the CIS system is a bit "slow" on throttle response is because the air needs to travel through the engine and activate the main sensor plate. This isn't as immediate as slamming open the throttle boddies on an MFI system or carbs.

-Wayne

[randywebb]

Bingo.

re CIS I'd add that the plate has mass so it takes longer for the air to move it than, say, for air to cool down a hot wire (the latter superceded the plate as a sensor)

[304065]

Carburetors neck down the inlet tract with a venturi in order to generate the vaccum signal to make the carb work. As a result, you don't move as much air. Since you're moving 14.7 pounds of air for every pound of fuel, the reduced restriction translates into greater performance.

[obrut]

and don't forget ease of (dyno) tuning - we did four runs in an hour a few weeks ago.

all you need to do to change the a/f is remove a plate and turn a screw. to do the same thing with carbs (changing jets etc) would take a weekend.

[Jay Auskin]

Don't forget the wonderful noises it makes. Matt, you need to go for a ride in my car. It makes me smile everytime I hit the loud pedal.