Atomisation Re: Intake manifold construction, intercoolers

[Dave Williams]

-> So do "conventional"[1] port injectors at any point in the rev/load
-> range produce better fuel delivery then carbs?

 "Better" in the sense of "more appropriate for the driving conditions
at hand?"  Yes; port injection (more particularly, timed or "sequential"
port injection) can give better cold start and cold idle emissions and
driveability than a TBI or most carburetors.  The old side
constant-vacuum SUs and the like with appropriate manifolding would come
danged close, though.


-> (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

 True.  Most carbs were the cheapest things that would do the job.  Just
like most modern fuel injection systems.  Different problem set,
different solution set, you know.


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

 They don't *have* to, particularly if the injectors are small enough to
run a decent pulsewidth at low RPM, but the atomization of most
injectors is very poor, and will result in unburned fuel going past the
exhaust valve.

 There are people who believe that port injectors shoot at the back of
the intake valve, which is hot and vaporizes the fuel, but in most
engines this is not true; the injector simply squirts a stream on the
port wall or floor, where it's picked up by passing air,
catch-as-catch-can.  Take a look at any 5.0 Mustang or Tuned Port Chevy
and note the injectors are nowhere near the valves.  A few new-design
engines *do* shoot more or less at the valves, but they're still a
minority on the road.
                                                                                                     
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