Changing 410 posi trac gear in 89 Mustang LX

If this is your daily driver, going down to a 3.73 is going to do very little to ease your gas woes. I mean it will help a little on the freeway but if that's what you have to resort to, then the stang shouldn't be your DD.

stevesLX said:

I've been looking for a 5.0 stock with lower mileage but that has been near to impossible. Also I only have $4000 to spend. I am getting this LX from a neighbor new tires wheels custom paint job cal induction hood and the rebuilt motor with 15000 miles for $3800. The only downfall is that gear in it and the mods to the motor. Do you have any suggestions?

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In your case, I would suggest finding another car as a daily driver. You drive quite a bit each day and gas being an obvious concern for you makes the mustang a poor choice. I mean even changing to a 3.55 or 3.08 gear is not going to make too big of a difference on gas. It's still a V8 with motor mods, it will burn gas.

You WILL waste a lot of time and money switching from a 410 to a 373. Leave the 410, you will be fine.

The only reason I can suggest stepping down from 4.10's to 3.73's is that you'll possibly get better times in the 1/4 mile, actually. My car's pretty close to the same as yours - same year, gears, driveshaft, tranny - and I'm at about 5800 RPM when I cross the traps. Getting traction is a major pain, so unless you're running DR's or slicks, you're gonna have to get damned good at your launching technique to make those 4.10's worth it. Your cam and injector setup may change the powerband on yours, but I'd imagine it's likely to make it even worse off in that you'll be redlining before you even cross the traps. Taller/wider rear tires might be an easier/cheaper way to help balance things out than a gear change.

As far as mileage, I average about 22 MPG city/highway mix (mostly highway). The most I've ever seen was one freak occurrance of 26 MPG; the lowest average was about 16 MPG. Switching to 3.73's might gain you 1-2 MPG, tops. I don't have a clue as to how the cam you have will affect your mileage, but I'd imagine it won't be good. I drive about 70 miles a day, myself, so I feel your pain as far as gas cost goes; last month, alone, I spent $210 just in getting to/from work.

At 75 MPH, I'm turning about 2400 RPM - not too high, and actually pretty nice that it keeps it far enough up in the powerband that I can just lay on the gas to get around a slowpoke on the highway, or jam right up a steep incline, without downshifting.

Tge easiest thing to do, although it may not seem like it, is to get another rear, housing and all, and put some gears in it that will give some gas mileage, and sway when you want to play.