Re: Performance Mods

[Scott Fisher <sfisher71@domain.elided>]

Nash,

Here's a partial answer for you.

As a VERY VERY GENERAL rule of thumb, compression
ratio increases will give you about 4 bhp per full
point of increase.  This is why, for example, IAP
cites a 5 bhp increase when going with their 10.4:1
pistons (up from 9:1 stock CR) -- on a ~120 bhp car,
4% is about 5 bhp.  

Furthermore, one point made by an engine builder I
consulted some ten years ago on the subject was that
compression increase gives you additional power
THROUGHOUT the power band -- off idle to redline. 
Some other changes (particularly cam changes) can have
little or even negative effect on one part of the
powerband -- typically a high-lift, high-duration cam
loses response in the bottom half of the powerband,
but provides additional power in the upper half.

As for guessing about the benefit as a result of cams,
porting heads, big valves, etc. -- there's so much
variation among builders, and the eventual
effectiveness is so dependent on installation, that
there may be no easy equivalency.  However, given the
Alfa engine layout with the cams right up top, it's
much easier to change cams than to change pistons, so
you have to factor that in when you consider bang for
your buck.  

One of the things I'm looking for, and one of the
reasons I'm collecting info at the moment, is a "path"
for the one-mod-at-a-time enthusiast -- which I think
is more to your point.  That is, if I have this much
money now, what's the best use of it -- what should I
do first, what should I do next, etc. etc. etc.?

The answer appears to be, so far, that the FIRST
several hundred dollars you spend on your Alfa should
be to have a knowledgable shop adjust everything as
well as possible, preferably on a chassis dyno so you
can see that you're getting this much more here (and
this much less somewhere else, and you can then make
the choice).  There is absolutely no doubt in my mind
that if Charlie Rockwell was still in business, the
first $200 I'd spend would be to have him dial my
cams, ignition, and Spica to give the best result on
the dyno, for the RPM range of my choosing.  

So, Portlanders, who's the local Charlie Rockwell
clone?  Who can degree in my cams, frob the dwell and
timing to work with the cam timing, and make the Spica
just *so*, and either do this on a dyno or otherwise
(say, by doing some acceleration runs with a G-Analyst
or Vericom) give me some documentary assurance that it
isn't just a lot of hooey?

--Scott Fisher
  Tualatin, Oregon



--- NashBap@domain.elided wrote:
> It is interesting to read about all the performance
> mods. that various digest 
> members have performed on their vehicles. I have,
> however, always wondered 
> what performance gains are obtained by what
> modifications. For example, do a 
> set of hotter cams  give a bigger performance gain
> than say, high compression 
> pistons or a head shaved to increase compression.
> Where is the most bang for 
> your buck ? 
> 
> Could you racers out there please enlighten me.
> 
> Thanks.
> 
> Nash Bapasola
> 75 Montreal
> 81 GTV6
> 
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