Audio Systems: car audio, skinned knuckles, 4 ohms

Question
The problem I am having is after installing this system I am unhappy with the sound. I wired two 4 ohm speakers in series  each side (right and left)  thus obtaining 8 ohms and the system seamed to sound better. But I dont have the room for the added speakers
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Followup To

Question -
I am attempting to improve the sound of the stero in my truck it is a Sony 45WX4 with a Pyramid amp with Pioneer 4 inch 4 ohm 80 watt speakers in the front and Blaupunkt 4 inch 4ohm 105 watt speakers in the back. The speakers are mountecd in the original places hence the need for 4 inch speakers.
My question is can I some how wire a resister into the speakers to change them from 4 ohm into 8 ohm speakers?

Answer -
Good question.

Absolutely,
  You can always add two resistors together to get a higher total resistance down the line.  Just make sure you run in series, from "plus" to "minus" on each.  You should only need one additional wire.  
(Follow up with me if you need further explanation on what that means).
In audio signals post-amplifier, you also should make sure you have a resistor rated for the power (in watts) you're looking for.  In your case, a 50W resistor should do.  "Ohmite" or similar brand is fine.  Expect something relatively large, the common small PCB resistors you might find at Radio Shack can't hack the power.

My question to you would be why?
This is a highly unusual thing to do.
Car audio systems are designed for 4-Ohms, raising resistance will deplete you of power and slew for marginal damping gains.  I would hate to think you'd go through all the trouble and skinned knuckles just to find you like the sound even LESS with resistors in line.
If you can describe what goal you are trying to acheive or what problem/symptom your trying to overcome then perhaps one of our car audio experts can recommend a better strategy.

I can't move on without pointing out that in theory, a transducer (such as a speaker) doesn't behave exactly like a resistor, speakers have very differnet resistence/reactance/inductance (amongst other electro-mechanical properties) at different frequencies.  In practice it's usually OK to approximate, but I highly recommend Vance Dickason's "Loudspeaker Cookbook" if you'd like to learn more.  

Answer
Great!  You have some experimental evidence to build on.  

I have two recommendations:

Option 1)  
Use only two channels (one L&R stereo pair) on your amp, and wire your two speakers in series (per channel).
-The improvement you percieved may be much more due to the interaction of the two speakers electronically as it is about "8-Ohms" across the amp.  I see that allot with "cascading crossovers" and other wierd wirings.
-The downside to this is that you lose "fader control" of front-to-back balance.  Other than that you lose nothing - unless you're playing DVD's allot your "4x" system is just two identical stereo audio channels, so you're not missing out on any audio.
If it were me I would go for this option.  Simple and Elegant is almost always better.

Option 2)
Add in the 4 Ohm resistors as discussed before.
-On the upside, you get fader control for front-back volume balance.
-The downside is that the resistors are more or less linear resistance, so I can't say with any certainty that you'll experience the same benefits as before.  Also it requires more $ and soldering.

I wish you luck!