From: John De Armond
Subject: Re: Chevie Engine Performance
Date: Wed, 10 Nov 1999 01:16:11 EST
Newsgroups: alt.rv,rec.outdoors.rv-travel

prsmith@navnet.net wrote:
> 
> I have a 91 Fleetwood Cambria with a 454 Chevie engine.
> 
> I have heard that there a number of things i can do to improve its
> performance and gas mileage.  For example, using 

>split fire plugs, 

No

>K&N filters,

Maybe.  See below

> newer chips in the throttle body injection system

Probably not

>, upgrading the
> exhaust manifolds, etc.

Possibly

I'm an ex-race engine builder so keep that in mind as I type.  There
are things that you can do improve performance but while evaluating
the various products on the market, it is important to keep in mind
that the conditions in your MH are vastly different than those of a
street hotrod or even a drag racer.  A car has a relatively high
power to weight ratio and so the engine spends a relatively low
amount of time at wide open throttle.  OTOH, the engine in your MH
will spend much of its life near or at wide open throttle.  This has
a profound impact on reliability.  For instance, a common method of
increasing power output is to raise the peak HP RPM with things such
as cams, larger intakes and exhausts, etc.  In moderation, this is
safe to do on a street engine because the added thermal and
mechanical stress is short-lived.  OTOH, the MH engine, already
operating much of the time at full power, may be overstressed by the
small additional output.  You may find problems with overheating or
shortened engine life or both.  And you may find you develop
problems with the transmission because the tranny may already be on
the edge.  With that to think about, I'll offer the following
suggestions:

A better exhaust system will almost always help things, usually at
the expense of more noise.  The manifold is probably OK. 
Larger/dual exhausts with balance tube(s) will do the most good. 
Don't however, underestimate the effects of more noise on your
coach.  I once went to Daytona with a friend who owned the local
Winnebago dealership.  He had equipped the engine with dual
glasspacks.  The cabin resonated strongly with these things.  By the
time we got to Daytona, we were all stir-crazy and he paid to have
conventional mufflers installed before we returned.  A favorite high
performance muffle of mine is the stock muffler used on the early
60s Cadillac.  This muffler looks like the popular Corvair Turbo
muffler, only about twice as long.  It is very quiet but flows as
well as any of the expensive performance mufflers.  Thrush is now
even packaging the muffler as a hotrod muffler - with a suitable
price increase, of course.

A chip probably won't do you any good, as the MH engine should
already be tuned for the best output since the emissions
requirements are much less stringent than for a car or light truck. 
The Holly ProJection replacement throttle body fuel injection system
has gotten great reviews for use on MH engines.  I bought one of the
early units and found it to be garbage because of the very poorly
designed analog ECU.  Holly has bought up an independent EFI mfr and
has incorporated their ECU into their ProJection products so most of
the problems should have been fixed.  A 4-barrel system will clip
you for about $1200, more or less, and will take a whole day to
install.  Note that this will not work if your chassis uses an
electronic transmission with the transmission ECU incorporated into
the engine ECU.  I think your MH is old enough not to worry but
you'll have to check.

I *HATE* K&N air filters!  We once tried a K&N on a racing motocross
bike my shop sponsored.  There was contingency money involved so we
used it despite my misgivings.  Lost a brand new engine in one
race.  Not to a blown-up engine but a complete wear-out caused by
all the trash the filter passed.  An old racer's trick is to smear
the inside of the air box with a thin layer of grease.  This grease
will trap a small part of any dirt passed by the filter and will
show you if the filter is not working.  The grease on that engine
was like grinding compound!  Use at your own risk.

Whether any sort of aftermarket filter will make any difference at
all is hard to tell.  In all likelihood, not. There may be some
performance improvement possible with modifications to the air
cleaner housing but even that will involve some fairly sophisticated
testing.  I have the test equipment (precision pressure transducers,
flow transmitters, data loggers, etc) to do this testing but most
shops don't.  I tend to recommend people shy away from modifications
that require extensive testing to make work, particularly when a
poor design can have such serious consequences.

Several companies advertise cams especially designed for MH use. 
Generally they boost the peak RPM a bit but mostly bolster the low
end torque. Never used any of the products so I cannot recommend
anything and can only call your attention to their existence.


> What is the best repair manual I can buy to increase my understanding and
> help me maintain this chevie chassis and drivetrain?

Helm Publishing publishes the factory manual for your vehicle.  Hard
to beat the factory manual.  Look in the back of your chassis
manual.  Mine gives the phone number and address of Helm.  If yours
doesn't, contact me and I'll look it up.

John