From: jws@billy.mlb.semi.harris.com (James W. Swonger)
Subject: Nitrous Oxide Engine Mods
Date: Mon, 14 Dec 1992 14:57:14 GMT
Organization: Harris Semiconductor, Melbourne FL

 Nitrous Oxide setups are fairly easy to install and inexpensive, but they
can easily make up for the latter if you enjoy them too much or do not set
them or the engine up properly. Newer systems seem to be a bit better
engineered than the earlier ones. A basic system consists of a "bottle", a
solenoid valve or two, high pressure line and aither a plate or set of
injectors to mix and deliver the N2O and fuel. Adding N2O requires that you
add fuel as well. Excessive leanness under nitrous injection can damage an
engine very quickly.

 As far as engine preparations go, they range from minimal (if you're putting
in a small setup, maybe 75 - 100HP) to total (dragsters). At the low end, 
you want to be starting with a sound block, but have at least a fuel system
which delivers consistent flow and pressure. A mechanical "suck through"
fuel pump can give a decreasing pressure-vs-RPM profile; this is the
opposite of what is needed. The foggers/plates generally meter fuel via
a simple orifice; this depends on a consistent fual pressure to maintain
consistent mixture. If your fuel pressure falls off and the nitrous pressure
doesn't, you can end up doing damage. The best arrangement is a good "pusher"
electric fuel pump and a "fuel log" with a return line and bypass regulator.
This arrangement maintains a set pressure at a common feed point and returns
excess gas to the tank. The pump, lines and regulator should be sized to
allow constant fuel pressure to be maintained over the operating RPM range.
Some newer setups may come with their own fuel pressure regulator but that
still needs a reliable supply to work from.

 If you're setting up an engine specifically for forced-induction or N2O,
the heads can be done a little differently. In particular, the exhaust
valve can be enlarged preferentially over the intake, because there is
less intake flow per HP but exhaust flow remains the same per HP (so will
increase). Since there is only so much area for valve sizing, the I/E
bias should be adjusted in the most beneficial direction. Another benefit
of keeping smaller intake valves is a slightly broader torque curve and
maybe better economy when you're not "on the bottle". Naturally, if you
enlarge the exhaust valves, you'll want to install hardened seats, port
the exhaust passages and take a look at the rest of the exhaust system.

 The engine's components should be selected for the appropriate levels 
of RPM, HP and torque expected. For higher levels of performance, the usual
things apply - forged pistons, maybe moly rings (just in case you run into
occasional detonation), good bearings and well-set-up oiling system, maybe
a specialty crank and con rods (if you're running past 7000RPM), and 
definitely the best head gaskets you can find. O-ringing the block & heads
may be necessary past the 500HP range, especially if the engine is already
a high compression type.

 Nitrous systems seem to be used more and more with some sort of ignition
retard system. The goal is to absolutely prevent pre-ignition/detonation.
There are a number of products out there that are aimed at this application.

 The out-of-the-box nitrous system may require some setting up to reach
optimum performance. Most important is getting the boost mixture right on.
It's better to work from the "too rich side". 

 As a final word, there are several books out which deal with this subject.
Your local speed shop should be happy to oblige.
-- 
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Newsgroups: alt.autos.rod-n-custom