Question about gears, trannies, and hp

This may sound stupid.. but I'm curious..
Saw the post on the tranny swap, and I got thinking:
I am wanting to change up my transmission. It's 2nd on the list for what i'm saving up my pennies for. But how does that translate to the dyno, if at all?
I'm also wanting to consider changing my gear ratio. I'm not sure what I'm at, but it's something I think might be worth looking into. I know the Cougar came out of the factory with a 2.75 gear, but i'm not sure what's been done to it before it got to me, if anything. I'm also wanting to change from the stock auto merc-o-matic to a (suggested by Rick) T5, as i'd like to go manual in it.

Either way, the engine's putting gout the same power. Sure a new transmission might be smoother (have less resistance), so more energy might be able to seep through to the wheels..
but what would I expect on the dyno? Same hp, different curve? What's bad about 2.75 vs 4.10, etc etc..

unless you modify the engine...HP & torque remains the same

what gearing & a tranny change does is it changes the way

the HP & torque is used...eg 273 gears gives better fuel economy

but the cars slower accelerating...whereas a 373 gear gets you off the line quicker

at the sacrifice of fuel economy...if you go auto trans...you lose some HP thru the converter

this wont happen with stick...there is some loss but its minimal...if youre unsure of the rear

end gear ratio...it will say on the tag on the diff if its still there...but the best way is to

pull the cover off...the numbers are stamped on the ring gear

It probably has a 9" rear. There's no cover to pull off. Jack it up, put the rear axle on stands and mark a tire with chalk. Mark the driveshaft with chalk. put her in neutral and crawl under. Rotate the driveshaft and count the turns until the tire rotates once. This assumes it has limited slip or at least both tires are rotating evenly. If not keep one tire stationary and rotate the driveshaft until the other tire does 2 turns. The number of rotations of the drive shaft to do this will be your gear ratio.

For the trans and gear selection if you have a 3 spd auto it won't be overdrive. If you go modern t-5 etc or a 4 spd auto they will have overdrive. It will allow you to run a better gear. your hwy rpm will still be low enough to drive it regularly but acceleration will be hugely increased!

A conversion that includes a 5 speed trans and gear ratio in the 373 range will put a grin on your face that'll take a lifetime to remove. Car will feel and act like you just got a ton more h/p and torque + lost a bunch of wt.
Remember how happpy the new look and performance under the hood made you feel? Mulitply that by several times, now you get the idea.

I put maybe 300 miles on it a year, so i'm not worried about mileage or anything.
0-60 acceleration is what I would want to focus on most.

right now it's got crazy torque off the line. I spin too easily.. but once it grips, there's a lot to be desired. I'm hoping these changes will help that.
So is 3.73 a good goto number?

Yes.

Quote:

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Originally Posted by bluetoy

It probably has a 9" rear. There's no cover to pull off. Jack it up, put the rear axle on stands and mark a tire with chalk. Mark the driveshaft with chalk. put her in neutral and crawl under. Rotate the driveshaft and count the turns until the tire rotates once. This assumes it has limited slip or at least both tires are rotating evenly. If not keep one tire stationary and rotate the driveshaft until the other tire does 2 turns. The number of rotations of the drive shaft to do this will be your gear ratio.

For the trans and gear selection if you have a 3 spd auto it won't be overdrive. If you go modern t-5 etc or a 4 spd auto they will have overdrive. It will allow you to run a better gear. your hwy rpm will still be low enough to drive it regularly but acceleration will be hugely increased!

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never even thought it wasnt an 8.8

I swapped out 2:73 gears for 3:73 gears on my 95 GT. Seat of the pants was night and day. Car still had no power to speak of but it felt like it did and at the end of the day that's what counts in a street car. IMO

Quote:

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Originally Posted by Uncle Buck

I swapped out 2:73 gears for 3:73 gears on my 95 GT. Seat of the pants was night and day. Car still had no power to speak of but it felt like it did and at the end of the day that's what counts in a street car. IMO

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Sounds like a plan!
Still a bit confused how that wouldn't change the output on a dyno, but i'll take it.

Quote:

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Originally Posted by 70XR7

Still a bit confused how that wouldn't change the output on a dyno,

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you are too hung up on the dyno thing.

IMO, changing from auto to manual is because of the driving fun-factor.

I got it. Turns out that hp is a calculated between the torque vs RPM from a 1:1 ratio.

Changing to stick would change dyno results as there is not as much hp loss through a stick as an auto tranny, difference is probably about 5%.
Changing gears would not change the dyno results but the fun factor will go up 200%!!
As stated, changing both will make you happier than a kid at Christmas!