If you got quality speakers, you shouldn't get distortion. They may be a little louder due to the lower impedance, but I'm not sure if the stock head unit will actually push more power with lower impedance, it may not. If you want to get the most out of the speakers you just bought, an amp will probably be required, the stock head unit will probably not push the power the speakers can handle...
Stand back, layman explanation here: The stock amp will indeed push more power if presented with lower resistance speakers. Roughly 2x more if the impedance is cut by half. That is where the trouble can begin though and where amp stability is a factor. It's going to run hotter and may not be able to handle the reduced load. Being that GM made internal changes to the amps in '92 and then went with a whole other radio in '95, I don't think our OP will have a problem driving 4 ohm speakers as I certainly don't have any issues driving my 2.5 ohm units. Distortion though, that's always possible with any amp and what is usually responsible for killing any speaker. Some factory radios like what I've got in my '89 attempts to self attenuate itself when it detects peak/overload. It was noticeably worse with my pre '92 amp section, I'd see the display dim out and the volume would automatically decrease. What it is doing is trying to create enough "headspace" for the sudden transients that occur in the material you're listening to. If you've got the volume all the way up, there isn't any headspace left to cover those and it overloads the amp, essentially then allowing it to run a DC signal to the speaker and burn out the voice coil in the woofer or tweeter. Home stereos are notorious for this as they usually expect the owner to leave some headspace as opposed to turning the thing all the way up. Now, if you want louder speakers, go for ones which have significantly higher dB sensitivity ratings. I tend to like Infinity for that reason, especially with stock amps. Go for anything over 95dB, anything lower, meh. With speakers which have low sensitivity ratings, even doubling the power sent to them will not double their output, it's a mathematic logarithmic thing. It's my opinion you're always better off going for speakers that are high sensitivity.
Does anyone know the wattage output of the stock head unit because i got "factory upgrade" speakers and there not high wattage or anything but they are higher than stock. Like 35w front and 75w rear or sum like that
Never believe whatever garbage is on the box. WTF is meant by "Factory Upgrade?" Your ears will determine that. A specific scene of Chris Farley and a box of brake pads comes to mind here... I've never measured the output of the factory deck but I bet it's something close to 10 or 15 watts. Which when paired with a sensitive speaker like I've done, is more than enough to sound better than the factory speakers and "go louder." Put a link to the speakers you bought and I'll have a peek-a-loo at 'em. Doesn't really matter to me what the power handling capabilities are, it's generally better to over power a speaker than it is to underpower one though. I'm assuming 35w front and 75w rear is their peak rating? If it were me, I'd just make sure all speakers are the same ohm wise.
