TH-400 gearing
11-08-2007, 01:33 AM
#1
TH-400 gearing I am starting to hear that you could get a TH-400 in two different 1st and 2nd gear combos? What are they if this is true?
On the motor my car is shifting into 2nd at 7,000RPM at 70mph or a hair less.
Car is right around high 4XX rwhp from what I have seen and looks like has a 3.73 gear (nitrous car) with a 28 inch tall tire.
Could be custom geared.
On the motor my car is shifting into 2nd at 7,000RPM at 70mph or a hair less.
Car is right around high 4XX rwhp from what I have seen and looks like has a 3.73 gear (nitrous car) with a 28 inch tall tire.
Could be custom geared.
11-08-2007, 05:23 PM
#4
I am sure there are several manufacturers for these aftermarket gear sets. We use ATI among others for custom aftermarket gearsets in TH400's.
The standard low gear set ratio is 2.48. So do this math.... take the 2.48 and multiply it by the rear gear ratio you stated which is 3.73. 2.48 x 3.73 = 9.25. That 9.25 number is expressed as your SLR or Starting Line Ratio.
ATI offers a 2.10 and 2.75 low gear ratio set for the TH400.
So for kicks let's run the numbers on those low gear sets real quick to see what we can extrapolate!
2.10 X 3.73 = 7.83 SLR... Not so good right?
2.75 x 3.73 = 10.25 SLR Much better than the stock gears would be IMHO.
And if we take it one step further we can determine what rear gear ratio you would need to use in order to obtain that same SLR of 10.25.
Take the new SLR of 10.25 and divide it by the old low gear (2.48) and we get 4.13. You would get a net effect of a 4.13 rear axle gear on the hit in 1st gear!
Suuuuhhhweeeet huh!
The catalog I have is vague, so without calling my rep, from what I can tell those gears with an aluminum carrier would cost around $700.00.
However, one thing to consider here is the Shift Extension, or the RPM drop between 1st and 2nd. And I can't realy help you with that one because I don't know enough about your combination and I could only guestimate that one as the converter will dictate that.
So yes there are some options to consider.
g
The standard low gear set ratio is 2.48. So do this math.... take the 2.48 and multiply it by the rear gear ratio you stated which is 3.73. 2.48 x 3.73 = 9.25. That 9.25 number is expressed as your SLR or Starting Line Ratio.
ATI offers a 2.10 and 2.75 low gear ratio set for the TH400.
So for kicks let's run the numbers on those low gear sets real quick to see what we can extrapolate!
2.10 X 3.73 = 7.83 SLR... Not so good right?
2.75 x 3.73 = 10.25 SLR Much better than the stock gears would be IMHO.
And if we take it one step further we can determine what rear gear ratio you would need to use in order to obtain that same SLR of 10.25.
Take the new SLR of 10.25 and divide it by the old low gear (2.48) and we get 4.13. You would get a net effect of a 4.13 rear axle gear on the hit in 1st gear!
Suuuuhhhweeeet huh!
The catalog I have is vague, so without calling my rep, from what I can tell those gears with an aluminum carrier would cost around $700.00.
However, one thing to consider here is the Shift Extension, or the RPM drop between 1st and 2nd. And I can't realy help you with that one because I don't know enough about your combination and I could only guestimate that one as the converter will dictate that.
So yes there are some options to consider.
g
11-08-2007, 05:34 PM
#5
There are several vendors who sell the gears but only a couple who actually make them.
You want to stay away from the TCI 2.75 gearset for a TH400.
http://forums.performanceyears.com/f...d.php?t=538337
Good info on the gearsets...
You want to stay away from the TCI 2.75 gearset for a TH400.
http://forums.performanceyears.com/f...d.php?t=538337
Good info on the gearsets...
11-09-2007, 09:19 PM
#7
I've also recently seen the 3.00:1 planetary gear set...Its 3.00:1 1st, 1.57 2nd and 1:1 3rd...The set is around $625 and would be the hot ticket for those of us who love the 3.06:1 1st gear of the 4L60E...The 2.75:1 set is nice, too and is cheaper thru Summit made by TCI for $419...
I researched this for a while when I considerd going to a TH400 when my output shaft in my 60E went on vacation last week...but I'm sticking with the 60E...for the time being...I like my OD and like my lock up at WOT...
--Alan
I researched this for a while when I considerd going to a TH400 when my output shaft in my 60E went on vacation last week...but I'm sticking with the 60E...for the time being...I like my OD and like my lock up at WOT...
--Alan
Trending Topics
11-10-2007, 05:28 AM
#8
So I assume its the higher the number the better just like rear gears for drag? Not like I have to worry about running out of gear 
Just giving your car more gear throew the first two gears...
I wonder what the 3.00:1 with a 3.73 on a 28" tall tire in first gear would be like with my 3800ish stall........
Car allready screams out of the hole.
Don't miss overdrive at all. at 60mph I am at 2800RPM with a 3.73 gear. Its like 300rpm more then if I had an overdrive.
Just giving your car more gear throew the first two gears...I wonder what the 3.00:1 with a 3.73 on a 28" tall tire in first gear would be like with my 3800ish stall........
Car allready screams out of the hole.
Don't miss overdrive at all. at 60mph I am at 2800RPM with a 3.73 gear. Its like 300rpm more then if I had an overdrive.
11-10-2007, 07:05 AM
#9
TECH Resident
iTrader: (8)
Join Date: Jul 2006
Location: Florida
Posts: 826
Likes: 0
Received 0 Likes
on
0 Posts
It may be debatable, but for all out performance wouldn't it be better to keep the tranny gear spacing closer together and use the rear end gearing to keep the car in it's power band?
