As usual, Dave, your spin is unique. I appreciate your
sharing your knowledge and experience. I look forward to the next "class."
Thanks, Dale C.
Subject: Re: Nitrous 101
wow have been tied up the last couple of days but here is my
take on this thread
Jon
Maybe the expert tune up does work fine for what they have
tested, about 1/4
mile..It probably makes the most power for that distance and
runs the best for
that distance but if you change the distance or time on I
think you need to
change the tune-up some too. Kind of like running nitro 100%
might be fine for
1/4 mile or less but for 5 miles might be pretty hard to
make it to the other
end. If your wrong tune up involves running slightly less
timing and slightly
more fuel then that wrong tune up is probably the safer one
in my mind. I can't
remember if it was last year or the year before we talked a
while about your tune
up, I had suggested starting back at a lower setting and
working your way back up
in power levels plus at the time you were running a lot of
ignition timing with
the nitrous if you compared the original output of the
engine compared to the
size of the hit. Are you now running a lot less advance than
you were? If you
don't want to reply to this on list I understand but am a
little curious if that
is the case. The whole nitrous tune up is relative to the
state of tune of the
engine before the nitrous, if you have 14/1 compression and
on the edge of
detonation with the ignition advance and everything is
optimized for running at
100 deg F and 4500 feet. then the changes you will have to
make to run a big load
of nitrous are a lot more drastic than a 9/1 engine setup to
run at 70 degrees
and sea level. Also if I add 100 hp to a 100 hp engine then
if you think taking 4
degrees of ignition advance is going to work you are sadly
mistaken. I would take
out at least 1/2 of the total timing to start. If you add
100 hp to a large
engine that is very inefficient
then taking out 4 degrees makes sense.
The only other question I might ask with your 'unusual tune
up' is what is the
bottle pressure during the run?? Are you chasing the bottle
pressure down the
track.
Tom you are only giving us about 10 degrees at best to
extract the power out of
the gasoline(or alky or nitro..) does that make sense to
you? With your numbers
peak pressure is at 20 degrees ATDC and it is over at 23..
Might have to spin
that one real high and need a lot of fuel to even make it
run..
Keith where do I start LOL...
at the beginning I guess..
Ve is interesting but there is mechanical, combustion,
thermal to consider too.
They all have to be good. You can pump lots of air and make
no power I have done
it and it is easy to fall into that trap.
With any engine you have to start the combustion so that
peak pressure is about
17 degrees ATDC. Before this point you are actually starting
to fight to a
certain degree the expansion of the gases. That is just the
best compromise that
makes the most torque(which is what we are trying to do make
torque hp is merely
a mathematical manipulation to express it in a different way
for other
comparisons). To take that to a different viewpoint you are
oxidizing a fuel to
make heat that will cause expansion by heating up the inert
gases and making them
expand. If you have no inert gases then you have less
expansion. That is why
nitrous is a case of diminishing returns in the first place.
You have a lot of
heat and nothing to expand, so things melt, the heat has to
go somewhere. If you
insulate and coat everything it might make it out the
tailpipe else something
will get too hot and fail.
Turbos and blowers..
Air pressure has nothing to do with anything at all in
this...
It is all about air density. A supercharged engine is no
more than a naturally
aspirated engine running at a different altitude period...
It is all about air
density, the Ve of the engine does not change one bit you
are just pumping denser
air. It has more weight per cubic foot. Same as when you go
up in altitude you
have less and make less torque. Well supercharging is going
down in altitude you
have more per cubic foot that is pumped. If you have more
mass then it takes
longer to burn so the power stroke is longer. Also you have
more gases to expand
so that takes longer as well and will extract more energy
from the combustion.
Further for your theory of air pressure to work inter
coolers would be both
un-necessary and actually cost power. They convert hot
compressed air to cooler
air at a lower pressure. In this process they increase the
density. The cooler
the air and the denser the air the better. As an aside to
this as the charge air
density goes up the speed of the combustion process also
speeds up, that is the
reason you run less timing with a supercharged engine as
well as to a certain
degree a nitrous engine( this is why the size of the engine
run on nitrous has an
effect on timing irregardless of the size of the hit). To
carry that to an
extreme put a 50 hp hit on a 1100 ci engine and what are you
going to do with the
tune up? Probably nothing, ok now put it on your lawn
mower...
90 degrees ATDC...
Nothing special about this number other than it is about 18
degrees past peak,
the best mechanical advantage is about 70 to 76 degrees ATDC
with 72 being most
typical. It is a relationship of stroke and rod length.
Next time you have the
pan off and are degreeing a cam or have a degreed damper
turn the engine till the
rod on #1 cylinder is 90 degrees to the crank pin. Ought to
be around 70 to 76
degrees ATDC.
Nitrous is easy to explain
All bang no push. Reason being it has a lot of oxidizer and
fuel. But it has less
gas to expand, so it gets done sooner. Having a more dense
fuel/oxidizer mix it
requires less advance because it burns faster, plus it is
potentially cooler
further increasing density..
It is all about air density, pressure recovery and thermal
efficiency....
Ok class dismissed.................
Oh as for Dave Freiburger and Hot Rod Magazine
Copyright 2002 Engine Management Systems . All rights
reserved.
Dave Dahlgren
(The 'Flame suit' is on now) LOL
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