I was wondering what flywheel I should use in a 2nd gen transmission (not sure if I'm going to use a s4 or s5 yet) swap into my 85 GS 12a. I knew the answer at one time, but it has been a long time since I've read about this and can't find the answer for the life of me.
I know that the 83-88 clutch and pressure plates are the same 225mm, but would the difference between the 13B and 12A flywheels require a swap?
Thanks!
Justin

 

The rear counterweight for each engine is built into the flywheel, so you need to use the flywheel that was originally on the engine (or the same series/model). Or if you are using an aftermarket flywheel you have to get the rear counterweight that completes your balanced rotating assembaly.

 

Just use whatever flywheel came with the motor. Why would you change it? Get the s5... it has the lighter rotating assembly.

 

If your not going to run a rear counter weight and aftermarket might flywheel,then you MUST retain the stock flywheel that is correct for the ENGINE.
Transmission type isnt rule 1 when selecting a flywheel choice,correct engine balancing is what matters first.
After you select a flywheel or counterweight that will keep the engine balanced,then you look at what clutch setup is availible that will accept the tranmission you are planning to run.

 

The S5 does have the lighter rotating assembaly, and higher compression rotors. But at the same time you can put a lightweight flywheel on a S4 motor, and run more boost without worrying, you can also fit more air/fuel in the housing at once = more power.

Kind of a toss up, depends on what your looking for. If you are just going to be running a stock setup i'd go with the S5.

 

I apologize, I should have been more specific with my question. I was just wondering if the 2nd gen transmission would bolt up to the 12A with the 12A flywheel. I wasn't sure if the input shaft was longer/shorter. I'm assuming I would need to use a 13B starter as well..?

 

You can use the S4 trans with no problems. The splines and lenght of the transmissions are the same. What you need to do is swap out the tailshafts. Meaning you need to take the tailshaft off of your 1st gen trans and put it on the 2nd gen trans. This is so the shifters are in the same spot and so you can use your existing 1st gen transmission mount.

As far as the starters go, your 12a starter will go in and work.

Forgot to add. The S5 transmission will not accept the 1st gen tailshaft housing.

 

Thanks doc!

 

You don't "have" to swap the tailshafts. It's also not a simple swap. You would have to cut and redrill the shift rod.

You can just make the shifter hole in the body bigger. It will fit the extended shifter housing of the FC tranny. It changes the location of the shifter towards the rear slightly and looks and fits to the factory interior.

There is a post on this by "Ductape". Just search for posts by him and you will spot it. It explains the entire process.

Good luck.

 

What are you talking about?
It takes 15 minutes to swap out the tailshaft housings. There is no redrill of the shift rod whatsover. The housing comes right off of the S4 N/A trans and the 1st gen Fb housing goes right on with no modification.
I have done this swap many times over and am currently running a S4 N/A trans in my Se.

Maybe that other procedure is for the TII transmission swap which is completley different.
I forgot to ask if he was using a N/A Trans or a TII one.
If it is a TII then all of the info I posted is incorrect, if it is a N/A trans and using the S4 one then it applies.

 

I will more than likely use the S4 NA transmission.