beaterstanger said:
A new 05 GT with 4.55 gears and slicks ran real low 12's. People say that 4.10's and higher are "not streetable". WTF??? Just for comparrison the final drive ratio on a honda civic is 4.31. I used to have a civic and I guess it feels wierd to not shift so often, just the opposite of what i'm reading here. Stock gearing has a top speed of like 160 mph, but who needs it. Your a f**king idiot if you go any faster than 125.
There's no one that said you can't do it, it's a matter of preference. Most people out there want to change their gears and not loose so much MPG. If you change to 4.10's, it's still streetable, but your gas mileage is going to suffer, and you'll be running in the 3000 rpm range, vs the 2100 RPM range.
The reason 4 cylinder cars have different gear ratios is for a few reasons. One is that they can turn higher RPM's and are still economical at higher RPMs. My eclipse redlined at 7250, so cruising at 3200 wasn't a big deal (came factory with 3.94's). When you're in a mustang that redlines at 6000 (or 5800, or whatever), you're at over 50% of the motors usable RPM's, it starts to kill your gas mileage.
Another reason is that 4 cylinders don't have the torque that we have, and don't start building power until higher in the RPM range (3500+), so they need different gearing to help it pick up better.
Look at diesel engines and their gearing. They typically only turn < 4000 RPM's.
**EDIT**
If you go from stock 3.27's (or whatever stock is), to 4.30's, or even 4.10's. Try driving around without using 5th gear and see how it is. It may be a little higher in RPM's than that when cruising.