TH400 low gearset

[325DR]

I know that the 400 has a different low gear gearset than the 200. For a mid-high 10 second car, is it wise to have the low gear changed to something closer to what the 200 has? What does a bigger number do anyway (lengthen or shorten the gear)?

200:
1st- 2.74
2nd- 1.57

400:
1st- 2.48
2nd- 1.48


** Ratios edited **

 

[musclecar neal]

you have them backwards the 200r4 has the lower ratios

 

[G McCall]

I know of 9 and 10 second cars running the standard gear in their TH400 and having no problems at all, so they say. I am being told do not worry about a lower gear in a mid 10 second car.
So, I am at this time waiting on a new install of TH400 (Standard 1st gear) with transbrake and Quicksilver shifter etc etc.

I am tired of the 200-4R repairs.

 

[buickboy]

Greg-
Talk to John Martin. he installed a 400. Car was slower. He changed rear gears to 3.73's and car picked up to good numbers.
Mitch Smith

 

[G McCall]

Originally posted by buickboy
Greg-
Talk to John Martin. he installed a 400. Car was slower. He changed rear gears to 3.73's and car picked up to good numbers.
Mitch Smith

Mitch,

I'm running 3.90s with 28" tires now, so I hope it will be Okay.

 

[325DR]

Originally posted by musclecar neal
you have them backwards the 200r4 has the lower ratios

Thanks, I fixed my post.

Originally posted by buickboy
Greg-
Talk to John Martin. he installed a 400. Car was slower. He changed rear gears to 3.73's and car picked up to good numbers.
Mitch Smith

This is what I am talking about. If I have a 400 built I would like to have the same ratios as the 200. It will be a mid 10 at best anyway, not a 9 sec car.

 

[chris718]

each application is different .however a car with more weight will benefit from the additional ratio of a numerically higher gear ratio.we use stock ratio at high hp levels to gain traction and stall speed with an unmodified suspension in a dual purpose street strip car.for a complete list of ratios for the th 400 check url below.

 

[G McCall]

I agree with Chris that each aplication is different.

I'm also counting on this advise with my soon to be TH400 setup.
Keep stock 1st gear with my 600 +-HP car.
In the "higher" horsepower cars the convertor becomes more of the key than that 1st gear in the TH400. I was told than in more than one instance swapping 1st gear did not net any gains and that the convertor's ability to slip and tighten up became the key.

 

[325DR]

Every application is different which is why I posted that I am looking at mid 10's at best. So for a heavy 10.50-10.90 car should I use:

1.) Stock 400 gearset

or

2.) 200 Gearset?

 

[chris718]

a stock 2.48/1.48 will be a better choice with a small tire.by the way we dont use a 200 gear set to make our 2.75/1.57 gearset as others.the reason being the helix is backwards in relation to the rear planet which causes front axial thrusting ang a gear set that rips itself apart from the moment it begins to rotate.opposite helix is common in automatic transmission planetaries but only when they do not share a physical connection such as in a simple compound planetary gearset.they must be independant of one another for this principle to work and this is not the case with a th 400.

 

[325DR]

Originally posted by chris718
a stock 2.48/1.48 will be a better choice with a small tire.by

What do you consider small tire? I am using a 28". I do NOT want to change my rear end gear and what the trans to be as close to the 200 as possible. I cant afford rebuilding 200s and dont drive the car very much, so I want a 400. I dont want to put a 400 in and LOSE e.t. either. From what I understand, people loose with the 400 because it takes more power since the low gears are lower. If I have the gears close to the 200, I shouldn't loose, correct?

 

[chris718]

the inertia of a th 400 with a 2.75 gear set can overpower a 8.5 or 9.5 street tire on the track.some classes dont allow a slick and this can cause traction problems.we take gear out of the trans on any high powered car over 3500 lbs with a 10.5 inch tire capable of mid to low 10 sec ets and they go faster down the track .the convertor can be made more efficient in this approach and the car WILL go faster ,in the 11.9 to 11.0 arena this is a different story. and if you have a near stock rear suspension and are not running a transbrake the convertor will stall higher and the car will leave with the wheels glued to the track easier.i am going thru this right now with a customer going 10.50s and wanting a th400 with a 2.75 gearset.we have already proven to ourselves here the outcome of this combination with specific vehicle chassis and know what works best for it.