Bridging front rear channels

HI,  hope you can help with a simple question;

I have a four channel car radio/cassett player (left-right/front-rear speakers) but only want to run 2 speakers.  Each pair of positive left and right outputs have a single negative (common).

If I bridge the 2 left (front-rear) positives and 2 right (front-rear) positives will I get a power gain?

Shoud I drive a 4 or 8 Ohm load (speaker)? Why?

No, I would not advise you to "bridge" your outputs on your HU, it isn't designed for that and presents too much of a load on the amplifier in the unit and will cause premature failure.

4 ohm speakers are generally designed for car audion applications while 8 ohm are generally for home audio. Though there are certain applications that this may not remain true. But if you are just looking for two speakers to wire to your HU, then I would suggest 4 ohm speakers. Reason being, you will get more power out of your HU with a 4 ohm driver than an 8 ohm. And from the way it sounds, you want to get the most you can out of your HU, you will not get it with an 8 ohm driver.

Thanks for the quick replys.  The Aplifier IC is a Toshiba TA8210AH (20watt duel channel)  I have found the following discussion on this chip at http://www.epinions.com/content_82003529348 which appears to be about an amp that bridges the IC to a single speaker.

As the chip is only a duel amp IC, does that indicate that front/rear fading is only a resistive circuit sharing the same source? I can not see any (4) Power Amp IC's inside the unit so I guess that bridging the front/rear will make no difference at all to gain and only short out the fader pot.

My initial thoughts where divided between the ecconomics of mounting 4 small speakers or 2 large ones.

Think I will just tape up the front speaker positives and remember to keep the fader biased to the rear (40w) speakers.  The IC is only ever going to put out 20w into 4 ohm's anyway....