Doug & netters,
The main reason for using a turbo instead of the supercharger is that a
supercharger relies on cannibalizing horsepower from the engine to make
horsepower, where the turbo uses "free" horsepower derived from the exhaust
pulses of the engine. The supercharger renders horsepower at the cost of some,
and they are not controllable for the amount of boost like the turbo is. They
are usually configured and then "on" all the time. Turbos can be set so to
speak. Typically where people run into problems with overheating and such is
1) the restriction in the free flowing exhaust "backs up" heat into the engine,
& 2) the heat introduced into the fuel/air mixture due to the heat generated
from compressing the air. Number one complaint has typically been solved by
increasing air flow around the exhaust area, and making boost at higher rpms
where the momentum of the turbo can be sufficiently built up to actually begin
to help scavenge exhaust out of the engine. Number 2 is dealt with by using low
compression pistons, higher octane fuel, delayed turbo response, intercoolers,
or combinations of those things.
All that having been said, and at the risk of making an oversimplification,
if one were to use the ONLY for normalizing the engine, and therefore have a
manual wastegate that allowed the pilot to only "activate" the turbo above a
density altitude of say 3-4000 feet, than the engine should just behave as if
it was still at those altitudes, if one did not allow the manifold pressure to
grow beyond the inches that are experienced below that altitude. One would
then "trick" the engine into believing it was still down lower. I think most
problems are encountered when the temptation to try and tap the additional
performance increases offered by the turbo at lower altitudes that gets most
pilots into trouble. The additional heat, AT ALTITUDE would be a beneficial
thing, both being added to the cowling temp, and the mixture, as it would help
the engine from being too cool at altitude (above say 5000feet), and would
assist in good air/fuel atomization or mixing as well. Remember, even in our
modern cars, there is a certain amount of engine heat that must be added to the
air/fuel mixture in order to prevent the gasoline from "falling out" of the mix
due to condensation within the intake manifold. This is where some have had
tuning problems due to the surging and rich/lean running because the fuel falls
out and then puddles, then gets sucked into the next cylinder as too rich and
the engine surges, and cuts out, sometimes minor, sometimes major.
One other caution about turbos: make sure you know what kind you have, blow
through, or draw through. A blow through design lacks the seal necessary to
draw air/fuel mixture through the carb, where the turbo would be mounted AFTER
the carb, but before the engine. The other design draw through has these
seals. Most turbos are the blow through design, and draw outside air in, then
compress it and send it on to the carb or fuel injection system. Also turbos
typically allow for the elimination of any kind of muffler due to their
quieting effect.
Flame as necessary......lol
Colin & Bev Rainey
KR2(td) N96TA
Sanford, FL
[email protected]
or [email protected]
http://kr-builder.org/Colin/index.html
