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rb20 vs rb25 trans

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11K views 11 replies 5 participants last post by  Veetak  
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#1 ·
I've seen a few guys switch the rb25 trans for a rb20 trans on the rb25det's and was curious if there is any advantage to his? I have a full rb25det swap that came with an rb20 trans so i'd like to know what the differences are if any.
 
#2 ·
I've never heard of someone going from 25 to 20 on tranny. Most of the time its just that shady importers put 20 trannys on a 25. The 20 is a weaker transmission. I guess going to a 20 you could use the stock KA driveshaft yoke but I wouldn't ever want to downgrade just for the driveshaft.
 
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#4 ·
By cut tranny hole do you mean bang in the firewall? I didn't have to cut the tranny hole, but I had to bang in the firewall where the starter goes.
 
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#5 · (Edited)
Hmm, damn kinda wish i didn't have that trans. I'm not planning on anything more than 500hp for final numbers so i think the rb20 trans can hold it, i mean if my old borg warner T5 trans with a failing bearing held up to 350hp i think a good rb20 trans should hold up to 500hp as long as i dont shift like an ass. Damn was hoping there was some advantage.


So how much weaker are we talking? Is it worth waiting to do the swap to get the Rb25 trans? I'll be pulling the motor again over winter to do head work and a full gasket set and upgrade the turbo
 
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#6 ·
Rb20 tranny...

ALOT of rb25 do it to save money one the driveshaft. Rb25 with rb20 tranny = no need to make a custom driveshaft. I have done this before.

The rb20 tranys has held good numbers before, many of times. Its about the same as a ka tranny, and sr tranny.
 
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#7 ·
Well hell that's a good deal I suppose, I'm not shooting for crazy HP numbers anyhow, and it's good to know i can save $400, building this on a budget to get it going before summer is out, over winter will be some more mods and power. I would assume then if you could find the right trans shop you could upgrade the rb20 trans to hold a lot more power if you wanted to make the investment in that rather than the rb25trans and new driveshaft.

Thanks for all the info, I just wanted to know if i got shafted or not because the whole swap was pretty cheap in the grand scheme of things. As a side note I'll be posting all the pics i have as soon as the build gets underway.
 
#8 ·
Eh, it wasn't a big deal to me. I had a custom driveshaft made in town for 80 bucks. 1 piece too.
 
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#9 ·
I really didn't research any driveshaft shops so i was just thinking of the mckinney driveshaft for $424, like i said i'll be changing the set up later on down the road, might upgrade the entire drive line ro rb25 trans. custom driveshaft, and possibly a skyline diff as well
 
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#10 ·
if you blow up a RB25 tranny, you have to shell out close to $1000 for a new one, if you blow up a RB20 tranny, you just find a KA tranny and swap the bell housings, a KA tranny goes for $150, and you can find them alot cheaper if you look hard enough. and they are alot lighter.
 
#11 ·
If you're blowing up a RB25 tranny than you're making way more power than a KA tranny will handle.
 
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