Re[2]: Performance Mods

[Ed Lutz <edlutz@domain.elided>]

I'd like to add something to this thread. When starting off on a
performance modification project its very important that you have a
plan worked out before you begin. If you decide to start with some
head work, since the head is easy to get too, fine...but know what
other mods your going to do later. A motor isn't a collection of
unrelated parts put together on a whim but rather a series of
decisions all effecting each other decision. You need to design the
whole thing as a unit, not piecemeal. The cam you choose has a direct
correlation on any porting work. Porting relates to the cam. Piston
choice, as in its design and compression ratio effects all the above
and is effected. Carbs, fuel injection, manifolds, everything is
related. Before you jump in check with a knowledgeable builder with a
proven track record with the type engine you have. Discuss what you
want to end up with and see what they suggest. If you just start
building without a plan you may get lucky, but your likely to be very
disappointed and not just a small amount lighter in the wallet.

Ed

Thursday, February 14, 2002, 1:15:07 PM, you wrote:

SF> Nash,

SF> Here's a partial answer for you.

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

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

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

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

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

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

SF> --Scott Fisher
SF>   Tualatin, Oregon



SF> --- 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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SF> Send FREE Valentine eCards with Yahoo! Greetings!
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