DEREKBENOIT

I have 5 speed gt and plan on changing gears. I know it revs around 1900rpm's at 60 right now. Was planning on going with 4.10's. If anyone out there already has them what are your rpm's at now at 60? How's highway driving at higher speeds?

281GT

Highway with 4.10 gears is still pretty good because of the overdrive 5th gear. It will really make a huge difference in the acceleration. The only time I might not consider a 4.10 is if I planned on doing some really high speed crusing such as 90+ mph for extended periods.
The engine has a nodular iron crank, cross bolted mains, hyperutectic pistons with full floating pins. It can easily take the rpms.

DEREKBENOIT

d

281GT

The C&L and Predator tune will help alot. Should be good for 25 - 27 hp. It will work well the exhaust changes. You won't realize the full benefit of your exhaust mods unless you improve the air intake as well. I think you be happy with these changes and with the gears it will feel like a different car.

delurker

I'm going with 4.10 for my MT. Got them ready to install.

don_w

I'm also going with 4.10s...

I've posted this before, but here it is again... to calculate RPMs at a given speed:

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RPM = GR X MPH / Dia / .002975 (GR is rearend gear ratio; MPH you make up; Dia is rear tire diameter in inches - let's assume 27" here, approx. same as stock tire)

For example: 3.73 X 80mph / 27" / .002975 = 3,715 rpm
Or, 4.10 X 80mph / 27" / .002975 = 4,083 rpm

However, that calculation would work for 4th gear (1 to 1 ratio) but not with overdrive. With a 5-speed automatic, 5th gear is 0.75 OD and the manual has a 0.67 OD. So, multiply your OD times the rearend gear ratio to come up with the final gear ratio, as follows (for the automatic):

(3.73 X 0.75) or 2.7975 X 80mph / 27" / .002975 = 2,786 rpm
(4.10 X 0.75) or 3.075 X 80mph / 27" / .002975 = 3,063 rpm

Tres Wright

Keep in mind that the lower gearing is really only a benefit out of the hole. I hear some people talk about how much better the acceleration is on the freeway, but you get the exact same benefit by driving around in 4th gear! I understand the guys who like to go drag racing at the track wanting (and needing) the lower gears, but for anyone that's just playing around on the street you need to ask yourself what the value is. Back when I used to street race a lot it was very rare to go from a dead stop. It was almost always from a roll, and from a moderate roll if you have 4:10's you'll start in 2nd gear, if you have 3:55's you'll start in first!

don_w

I don't street race... but, the 4.10s will plant you in the seat a little harder than the stock gears. That's what I'm talking about!! [sm=gears.gif]

davidmac12

What's the best place to look for 4.10's?

281GT

It's simply a matter of torque multplication. The 4.10's will give you better acceleration at all speeds in all gears. You may not even loose any top end. Depending on the particular vehicle. For example, a typical 70's pos with 2.73 gears would actually have a higher top speed if you changed to say a 3.55 ratio. Reason being is that with the 2.73 gears the car encountered too much wind resistance before the engine could gain enough rpm to overcome it. Change the gears so the motor could get into it's power band before the wind resistance became too great and you actually gained top speed as well as acceleration. With the 05 Mustang I am not sure if in 5th gear with the stock 3.55's this would be the case though, but then again, the car does 143 mph stock. I think that's enough for most of us. It sure is for me. I would drive it that fast so rarely that if I lost a little top end with the 4.10's that it wouldn't bother me. But that's just me.