Atomisation Re: Intake manifold construction, intercoolers

[Mos]

On Sun, 9 Dec 2001, Dave Williams wrote:

> -> So what you are saying is that carbs (I guess not all) have better
> -> atomisation than port injection? and consequently lower BSFC? (As a
> -> generalised statement - feel free to go into much detail).
> 
>  Running throttled, steady state - yes.  A TBI system can match a
> carburetor under those conditions, but a port injection setup can't.
> Conventional Bendix-type injectors do a poor job of atomization, and too
> much of their output is in gobbets too big to be fully consumed during
> the power stroke, and the unburned portion goes out the exhaust valve.
> This is not normally an issue for EFI cars since most of them use
> catalytic convertors and the fuel is burned in the convertor, keeping it
> hot enough to function when exhaust flow is low.
> 
>  Just because it's new and complicated doesn't mean EFI is better under
> every condition.  Eventually rail pressures will get high enough to do a
> better job of atomization, but right now all injectors are pretty much
> the same.
> 
>  Part-throttle cruise is where carbs and TBIs rule, but that doesn't
> play much of a part in EPA smog or mileage testing.  They assume
> everyone lives in an anthill of traffic.  However, for some of us, part
> throttle cruise is the dominant driving mode.

Ok, thanks for that. 

So do "conventional"[1] port injectors at any point in the rev/load range
produce better fuel delivery then carbs? (I'm thinking 'result in lower
BSFC' but possibly that is not entirely accurate?)
(You did say "doesn't mean EFI is better under every condition" implying
some conditions exist where efi is superior [without defining 'better']).

(I'm presuming that the carbs' superiority only holds true for a small
subset of available hardware, and does not extend to mass market carbs
factory fitted to older non-performance cars - is that correct [in
general]?).

Does it follow that port injected engines without cats spit some amount of
unburnt fuel out the exhaust?

Apologies if the questions offend, but I'd like to improve my
understanding rather then make erroneous deductions.

Mos.

[1] ie every day, mass market injectors.

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