Gear selection

[1987MCSSAeroCou]

I am trying to figure out what gearing to use when I convert my monte to the Turbo6. I have 3.73s stock. If I go to the GN rear I will have 3.42s. Either of these is ok, but is there a good reason not to go to 4.10s or even 4.56s? The way I have calculated with the 200-4R the 4.56 gears would allow for 9sec 1/4mile ~145MPH, which is about the fastest I would want a street car to be. Would having a gear like the 4.56 affect launch that much (reduce the boost I could launch with), and would it be good or bad. I am aware that fuel economy will suffer (I switched a non-SS Montes 2.29 gear to a 3.73, hehe)

Thanks for any help

 

[azgn]

not too many 9 sec cars have 2004R's in 'em.....the tranny of choice is a TH-400......3.73's are good to the very low 10's with it...bigger tires (29,30, et al) may require 4.10's....for the vast majority using 2004R, the stock 3.42's will work just fine into the high 9's

 

[Chuck Leeper]

4.56!!

There best be a COMPLETE Stage 2 setup in the swap if you expect:
1: to run 9's
2. Keep it in 1 piece w/ that kind of rpm!!

 

[1987MCSSAeroCou]

What RPM can you get out of a slightly worked 3.8 (head work, cams,etc)?

 

[Chuck Leeper]

Stock RPM?/

You MAY get 6000, for a few WOT blasts and hi boost... Then it's time to be initiated into the DOTC club!! 5200 to 5600 is a safer bet.
Gear the car w/ the 3.42's and the 200 and it'll stay together a bit longer...

 

[1987MCSSAeroCou]

According to my calculations 5500RPM in 4th with a 26" tire and 4.56 gears yeilds 144 MPH. Of course 4.56 gears would mean 2686RPM at 70mph which I bet the guys running TH350s or TH400s are used to. The way I see it I shouldn't need to go much past 140, as the nose will probably feel very light around there, and it would help improve the acceleration characteristics (assuming minimal wheel spin).

And no, I don't expect to run 9s without bulletproofing the tranny and doing some major engine stuff. One thing which I would have to do is reduce the vehicle weight from its current 3600+lbs, I think goinfg to the V-6 instead of the V8 will help, removing A/C (maybe), smog stuff, power steering, and a battery relocation.

How much horsepower will a well-built 200-4r take?
And what is the DOTC club?

 

[Chuck Leeper]

Da bottom line!!

You won't make enuf ponies out of a production GN engine to push a brick like a G body to 144 MPH, and keep it together.

The DOTC is: drive over the crank club!!
My combo runs 10.20 @132 @ 6000 w/ a T-400, 3.42 gears and a 28" tire. Go figger!!

 

[Four-Four-Two]

Originally posted by 1987MCSSAeroCou
I am aware that fuel economy will suffer (I switched a non-SS Montes 2.29 gear to a 3.73, hehe)

Thanks for any help

Not to switch the subject here, but I thought 3.73 posi was standard equiptment on all AeroCoupes.

 

[1987MCSSAeroCou]

Sorry, This was in reference to amy first monte, a '85 CL...
And actually RPO G80, which was the posi rear, was not available on the '86 Aerocoupes (only 200 made), but was an option on the 87 (I think most 87 Aeros are posi).

 

[1987MCSSAeroCou]

Chuck, what are the geasr ratios for the 400?

 

[kenny]

Originally posted by 1987MCSSAeroCou
According to my calculations 5500RPM in 4th with a 26" tire and 4.56 gears yeilds 144 MPH. Of course 4.56 gears would mean 2686RPM at 70mph which I bet the guys running TH350s or TH400s are used to. The way I see it I shouldn't need to go much past 140, as the nose will probably feel very light around there, and it would help improve the acceleration characteristics (assuming minimal wheel spin).

Why do you want to go through the traps in overdrive? Ideally you should go through the traps at redline (or damn close) in whatever gear 1:1 is. In the case of the 2004r, that would be 3rd.

TH400 gears:
2.48:1
1.48:1
1:1

2004R gears:
2.74
1.57
1:1
.67:1

 

[ThikStik]

TH 400 gearing=2;48, 1;48, 1;1. A deep first gear set with a 2;75 first is available from TCI. Hope this helps.

 

[1987MCSSAeroCou]

Originally posted by kenny


Why do you want to go through the traps in overdrive? Ideally you should go through the traps at redline (or damn close) in whatever gear 1:1 is. In the case of the 2004r, that would be 3rd.

So if I had aT-56 equipped Vette or Camaro SS I would want to only shift into 4th (1:1)?
If there is a good reason not to use overdrive let me know please, that is one thing I am trying to figure out. Maybe I could put the 2.29 gears in and just use 1st and second gears.

So far looks like the 3.42s are the most common choice. All this info is helping me, so thanks, and keep it coming.

 

[kenny]

The higher the gear (numerically), the higher the torque multiplication. Overdrive is simply when the output is spinning faster than the input. Because the output is spinning faster you get no torque multiplication - in fact, you lose power because of the force needed to turn the output (this is made up by the rear gear).

For example, say you have a car with the 2004R and a 3.42 rear gear. In third gear the final gear ratio would be 4.42:1 (1:1 + 3.42:1) and forth would be 4.09:1 (.67 + 3.42). 4.42 > 4.09, so you would have more torque multiplication in third.

If you only want to use two gears, run a powerglide. It only has two gears.

Hope this helps. I'm off to bed.

 

[ThikStik]

Sorry for the redundant info on 400 ratios. I got interrupted before hitting submit . Anyway, keep in mind that a taller rear gear will overtax your trans. and u-joints. The total GN powertrain is what ya need. Some guys will tell ya they have regretted changing the 3:42s for 3:73s. That is true up to deep 11's anyway.

 

[ThikStik]

I was kinda thinking the ratios would be as follows; third=3:42x1=3:42
Fourth=.67x3:42=2:29

 

[1987MCSSAeroCou]

Originally posted by kenny

For example, say you have a car with the 2004R and a 3.42 rear gear. In third gear the final gear ratio would be 4.42:1 (1:1 + 3.42:1) and forth would be 4.09:1 (.67 + 3.42). 4.42 > 4.09, so you would have more torque multiplication in third.

Then the Torque multipliction, as you call it, for the 4.56 in 4th would be 4.56:1 + .67:1 = 5.13:1, and 5.13 > 4.42, so wouldn't that be advantageous?

But basically what you are saying is it is better to have the rear gear do more work than the tranny gears? I thought it might be the other way around, that the loss of power would increase the furthur down the drive line (If that makes sense).

 

[ThikStik]

MULTIPLY DON'T ADD!

The eye roller wasn't sufficient to call attention to the math problem I see.

To get gear ratios MULTIPLY the internal trans ratio x the rear end ratio. For example in a TR, first would be 2:75 x 3:42=9:405. Meaning the motor's crank gets to spin 9:405 times for each revolution of the rear wheel ( torque converter slip being ignored).
Try to strike a balance with torque multiplying members. Any member should't bear all the tork multiplying or it will snap. The stellar times you call for will require th 400 and chevy 12 bolt/Ford 9 rears. How about a deep geared, switched pitched TH 400 from Postons, then hiway cruising wont be so bad.
Good Luck.

 

[1987MCSSAeroCou]

Well, 9s are not in the near future for me, as all the requirements (including the 600+ HP for a heavy car to run 9s) add up to a lot of $$. I do enjoy stoplight racing though, and figure a 4.56 gear would help put some mustangs and ls1s to shame with a mostly stock GN motor. I think by about 100 MPH (which would be the top of 3rd gear w/4.56) most of them would get the picture. Another thing I would hope for would be decent launches from idle rather than building boost up on the line, so by the time they realize they are racing a turbo it's too late (don't know how well that would work, I'm not real familiar with turbo cars myself) I assume there is little whine from the turbo at idle...

I'll probably end up using 3.42 or my current 3.73 gears considering what I've seen here.

Edit: or maybe a 4.56...

 

[kenny]

Rick is right. I don't know what I was thinking. It was late.

Of course it is multiplied... that's why it's called torque multiplication... duh.