How much Horsepower can the Dana 20 T case take, reliably?

[johnnybgood74]

just curious on how much a stock Dana20 t case can withstand and still be reliable. I know people are onstalling coyotes in their EB but curious on HP numbers? What upgrades are needed in the T case to handle 500 hp reliably? I'm not wanting to do huge burnouts and hammer off the line but I am wanting to install a S300 Borg Warner turbo with only about 3 to 5lbs of boost. Mainly for that extra push for passing and climbing hills. Thanks!
John

 

[Viperwolf1]

We have a D20 with the AA heavy duty rear output assembly in the racer. 408W with about 500 horsepower. It sees constant hard use but probably all of it in either 2wd or 4Hi. I think you would be fine with the AA output.

 

[sanndmann3]

In my opinion, low range is the weak point for the '20. Have you seen how skinny those spur gear teeth are? and the bushings that go between the idler gear and case aren't a very robust design.

 

[SteveL]

Dont have numbers but the original bigfoot ran a dana 20.

 

[johnnybgood74]

Viperwolf1, did you use the HD output shaft and the rear assembly with the 1350 series U joint? Thanks,
John

 

[Broncobowsher]

I don't think it is so much of a HP number, but a torque number. A 435 with a doubler in front of a D20 is real good at taking out the rear output shaft. And it is typically at low speed in a crawl that it goes.

Take the gearing out of the transmission and put it in the axles, typically with an overdrive transmission, and the torque levels through the transfer case drop off while still maintaining the same axle torque. You are spinning the transfer case faster, but not loading it as hard.

I am not aware of a speed limitation on the dana 20. I remember a long time ago there was a low gear set for some other transfer case (I think it was a planetary gearset) that had a warning about driving too fast and overspeeding the gears. But that was 15-20 years ago. I have done a lot of overdrive cruising in low range when I had the 4R70W and tera-lows.

 

[nvrstuk]

I've been saying what Broncobowsher said for years... 2 decades actually. TORQUE is the D20 killer... I went thru 28 spline axles like oil filters with my HP289 high rpm shifts and never had a D20 issue. The first trip out rock crawling with my 351W/ZF (5 spd)/NP203 (doubler)/D20 I stripped the teeth off the low range idler like mentioned above.

Couple wheeling trips later- output shaft (I put together BC Bronco's 300M mass buy)
then cases started cracking and snapping... then 9"rear ends started grenading and this was ALL at low crawling speed...

I'll see if I can find my post of the D20 and 205 teeth side by side as a comparison... like comparing a D25 axle to a D60... lol

Here ya go. Pg 2, post #24 on my suspension build.
https://classicbroncos.com/forums/showthread.php?t=278607&page=2



I think the D20 would be fine for street use. When it breaks, go 205. Bulletproof and you don't need low gears for street or mild trails.

 

[nvrstuk]

Here's a pic of a pic from my build post. D20 is the scrappy little straight cut gear on the left... the 205 is the 2.5X larger helical cut gears on the right...

You can see the little D20 is missing a few teeth.

 

[Viperwolf1]

Viperwolf1, did you use the HD output shaft and the rear assembly with the 1350 series U joint? Thanks,
John

Yes, 1350 flange.