Stock ratio th400, I believe I was told 84-85% of input shaft (fwd drum) rpm in the opposit direction. It won't be engine rpm as there is slip through the converter. But to answer your question, yes, that number is changed with aftermarket ratios. The closer the ratio you go (2.10/1.40 vs 2.48/1.48 ), the smaller that percentage is. So the closer ratio gear sets are nicer to the intermediate sprag. I believe that's where you were going with this.

 

Yep... That's where I was go'n ...

Thanks for that reply..

 

82% oem ratio, aluminum direct drum for any high rpm, over 6k is a great investment.

 

The drum speed does vary with ratio changes. If the majority of the ratio change is done in the intermediate planet the % goes up. If the reverse ratio is the only change made, the ratio goes down. Some of the low numeric ratio's which use conventional Simpson planet designs can exceed 100% while others are 50% using a non conventional design that works in a T400 case.


Hutch

 

Just when I think I understand something, hutch drops a bomb and I'm lost again.

 

Me too ...

Let me break it down like this....

If I switch out my stock 2.48 planet gear set, for a Coan 1.86 planet gear set.. Will my direct drum speed increase or decrease as related to my first gear engine rpms ??

 

It will increase. Now if you go to a 1.76-1.40 it will decrease substantially due to the design changes.



Hutch

 

Is there's rule of thumb that indicates what that fwd drum to direct drum difference of rpm will be? Or do you have to count the teeth on the planets and sun gear and bust out a calculator? I'd honestly believe you if you just said "I'm that good, I just know Cameron"

 

You need to know the tooth counts to determine the sun gear speed which is ultimately the direct drum speed. The 1.86 ratio is 96% , the 1.95 is 91% the 2.10 is 85% the stock 2.48 is 84% and the 2.32 is 76%. Its amazing how these ratios change the loads on the internal components of the trans. Anyway , from this you should be able to see what ratios offer more drag in low gear.

Now there are non conventional sets which are 2.08-1.56 that have a 45% anti rotation. This would also make a killer second gear leaver. Has a nice first and a good second ratio. The conventional 2.10-1.40 kinda sucks to use a second gear leaver.
The 1.77-1.40 is 53% , the 1.66-1.34 is 56% , the 1.60-1.31 is 58%




Hutch

 

You need to know the tooth counts to determine the sun gear speed which is ultimately the direct drum speed. The 1.86 ratio is 96% , the 1.95 is 91% the 2.10 is 85% the stock 2.48 is 84% and the 2.32 is 76%. Its amazing how these ratios change the loads on the internal components of the trans. Anyway , from this you should be able to see what ratios offer more drag in low gear.

Hutch

With that being said.... It looks like the 1.86 gear set would be the hardest on a sprag.. Plus have the most first gear drag..

What a bummer... My mind was set..

Now I don't know if I should go with the 1.77 or the 2.08.. Right now.. With the stock 2.48 first gear... 3.27 gears in the back (28 inch tire).. And a super tight converter.. The car turns 1.21 sixty foots without trying very hard (3800 rpm leave)..

That 2.48 gives me an overall ratio of an 8.11.. A 1.77 would be an overall ratio of a 5.79.. A huge, huge difference I'm not sure I could pull.. And the 2.08 doesn't seem like enough change..

BTW.. Who makes the 2.08 gear sets..

 

Who makes that 2.08/1.56 gear set?

 

I have them if you need them.


Hutch

 

Thanks for the PM with the price Hutch. They are not cheap, lol!

 

Budget starts at the flexplate!

 

I can buy a 1.86 or 1.66 Coan gear set for less money, so, yes, out of my budget!

 

Use the aluminum direct drum and the ratio that works best with your combo and let the anti-rotation rpms be what they will be IMO.

 

So you're saying I could probably rock an 8 element roller clutch with that gear set and 750whp? LOL

 

What if I told you done properly you probably already can even with 2.48 👀