[Diy_efi] TBI, heat riser, crossover passage

[Michael J Flaherty]

Hi all,

I've been wondering about the importance of maintaining an exhaust heated
intake with TBI and a cast iron manifold.

EGR aside, is this as necessary for cold weather driveability as it was with
carburetors ?  I'm hopeful that I can do away with the heat riser on 2 EFI
retrofits that I've been thinking about.  Obviously the shape of the intake
won't have changed (sharp turns at the bottom going both ways), which would
still tend to cause the fuel to want to puddle at the bottom of the cold
manifold, causing lean stumble until such time as the intake is warmed by
either the crossover exhaust gases or heat radiating from the block below
(which takes at least 5 times as long to warm the intake as a functioning
heat riser/crossover, especially in the coldest weather).

Is the superior atomization (smaller, lighter fuel droplets) that is/are
achieved with injection enough to counterbalance this tendency to puddle ?
In other words, all other things being equal, will the gasoline make it
around the corner ?  Even at an idle or accelerating from a stop with a cold
engine and a tall gear at -10 Fahrenheit ?

I'd like to be able to achieve this (reasonable cold weather driveabilty)
without resorting to prolonged start-up enrichment and the bad for the
engine things that go along with it.

I do a lot of short trip city driving, which makes this a fairly major issue
for me.  With carbs, I've had to take great pains to keep crossover passages
clear and heat risers and thermostatic air cleaners freed up and
functioning.  This is becoming impossible as you can no longer get parts for
this stuff.  I'm pretty sure that I bought the last small block Chrysler
heat riser kit in the Americas, for example.  FWIW, I had to order it from
Thunder Bay, Ontario...

Thanks in Advance,

Mike

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