Finished my first build of the RX3. Looking into a NA 20b.

Motor and tranny need to be pushed back into the trans tunnel and still have shifter in proper location.

Anybody have a suggestion

 

I would probably go with RX-8 6 speed.

I believe its about ~4" shorter to the shifter than TII/FD trans, it is designed to shift well at higher rpm, it has good ratios and an easier to deal with push clutch (easier to switch to serious low inertia multiplate set-up).

If you are worried about its durability use the '09-'11 spec one (~ $2,000 brand new through Mazdaspeed).

Fast shifting and good ratios are going to mean a lot with the relatively low torque high revving NA.
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I hear you could modify an FD trans to use the forward shifter box and get it about the same length from shifter to bell housing, but its more work, balkier high rpm shifting, pull type clutch (have to convert for serious low inertia clutch) and worse ratios.

 

Thanks that's a good starting point. Now to get some measurements.

I'm currently doing the 4 inch shifter relocation to a 87 RX7 trans to replace the original RX3 ribcage 4 speed.

The 20b needs to sit back in the trans tunnel farther yet.

 

+1 for the RX-8 transmission.
I've heard the T-56 or the Ford C6 as being pretty capable as well. These are just options, not sure what you're doing with it

 

How far back are you pushing the engine? I just picked up an M12 T56 from a Cadillac CTS-V. It has linkage style rear housing mechanism to mount the shifter. So you can virtually mount the shifter anywhere you want. I bought it so I could mount it on my NA 20b Fd (which is moved mack 5-1/2"). The gear ratios are also perfect for a NA rotary.

I'll get some picks here in a little bit.

 

These T56 can shift at high rpm? Do they last running at high rpm?

EDARX3, have you also considered moving the driver's seat as far back as possible? That would give you more length from bellhousing to the shifter and get some weight further back.

 

That's about how far I'd like to go.

Have you found an adapter for bell housing match?

What are you doing for fuel and spark?

 

Well OP never said anything about racing so I'm assuming street setup. Howard Coleman had no problem shifting his at 8,500.

 

I have a Howard Coleman adapter plate to use an Fd auto tranny bellhousing.

https://www.rx7club.com/3rd-generati...500-hp-905977/


I just run regular gas 87-91 octane as I have a pure street car. Right now I have LS1 coils with an old Haltech E11. Works fine for now.

 

Well OP never said anything about racing so I'm assuming street setup.

I see. Its strange guys like you that put bad *** engine in and cut firewall to push it back in a street car that was confusing me

Fair enough though, I guess we both viewed the question from our own perspective.

Also, I really don't know much about the T56- that is why I was asking.

Well, I have heard the V8 owners complain that though they hold up to torque they are slow to shift at any rpm which doesn't seem like what you want in a low torque NA car that will be slamming gears.

 

Who said anything about me cutting firewall?

https://www.rx7club.com/20b-forum-95...s-info-937928/

I pushed mine back because I didn't want to deal with bumpsteer issues by moving the rack and not have to deal with putting more weight towards the front end. I felt that's the way Mazda would have done it had they ever built a 20b fd. That forward compartment in front of the fd shifter kinda tells me that Mazda thought about it at one point. Mazda likes put as much weight towards the center of the vehicle as possible but you knew that already.

 

Here's those pics.

 

Impressive you were able to get the bigger T56 that much further back without altering the firewall!

 

No I haven't installed the t56 just yet as I just got it a month ago. I took that pic yesterday. That's a busted fd tranny I put beside it for length reference and to show were I would have to mount the shifter. Right now my shifter is in that forward compartment of the fd tranny. My firewall will clear the bulkier auto bellhousing. I just have to make sure the added tranny bulk will clear the tunnel. We'll see early next year when I pull the engine to install it.

 

I kind of figured the tranny selection would be my first big challenge.

The RX3 is mint, so there will be no cutting of original bodywork. It's a street car with hopefully a little track time every now and then to get objective numbers for performance.

The car originally had an auto tranny, so its supposed to have the larger tranny tunnel for more room.

I've barely got the bugs worked out of this build (12a 1/2 bridge), yet I'm already looking for more kick.

I think I'll just keep an eye the 20b forum for ideas and watch you guys have fun. I'm on at least a 3 year plan before I'd expect to hear my 20b start up.

Thanks for the info

 

+2 on rx8 trans. The series 1 trans has issues with the crown on 2nd. The series 2 trans is a much better unit with reverse in the right place hehe

 

I'd use a TII transmission personally. You can relocate the shifter forward if necessary.

Having been inside a TII transmission and an RX8 transmission, I am not a fan of the Aisin (RX8) design. Mostly that is because it is such a pain to work on, but also not as well built as the TII unit.

 

I'm leaning toward the TII, especially after finishing the 5 speed transplant into the RX3.

Turned out the 5 speed I have is an 84 or 85. The rear tranny mount fab. was easy. I can see a modification that would relocate the shifter another 3 to 4 inches on the tranny.

Setting the tranny deeper into the tranny tunnel will require eliminating the clutch fork and dropping the tail shaft lower(that will lift the front of the longer 20b).

 

PM'd you. I have all you need for sale. Let me know if you're interested.

 

There is a 5 spd RX8 option for JDM & Euro that is essentially the FD trans with RX8 bolt-on bell/tail housings. So switching the FD trans to a push clutch setup is fairly simple. However, for NA the SII RX8 6-spd ratios are probably a better choice. Just making sure that you understand that the SII RX8 trans is not the same as the SI Aisin model.