I have read through most of the posts on swapping the 13b into the my 85 12A n/a. I will be ordering a rebuilt motor that will be ported before delivery. My question is should I stay with a 12A with stage 2 street port or go with a 13B. I have read that the 6 port 13B motors don't port as well as 12As. Would I still be able to get the 13B with a stage 2? And if so what year 13B should I order? Should I just stay with the 84-84 gsl-se motor or go with FC motor?

Thanks

 

Well most rebuilds require a core.. I would say go a very big street port with a nice size carb, and that should go very well. It is a pain in the butt and more expensive if you don't have to core to give the people to build your motor. Will save you some money if you just stick with the 12a. ANd it is true that the 13b 6-port doesn't port as well and the 4-port motors.

 

Just stick with a 12A. You can get the street porting done and keep all the other components stock for a while. Do you know what the Rat's Nest is? you'll find out soon enough.

Then you can start your upgrade procedures. The best place to start is with exhaust first. Then once you're satisfied with it, then you can upgrade the intake. After that, you'll have gained more knowledge in general and might take on an electric fan conversion as well as a direct fire ignition system. The list goes on and on... clutch etc.

The headaches involved with upgrading to a 13B at this time aren't worth the effort. Yeah, stick with the 12A. I would.

 

What headache is their to swap the 12a with the 13b?

I have done it and the only different thing you must do, is get a beater and beat the hell out of the motor mount that bolts to the front cover to straighten it out so everything lines up since the 13b is slightly longer than the 12a.

12a's take more abuse than the 13b, that is the only draw back. 13b's give more power though!

 

Oh yea, try to get a 4 port 13b if you go with the 13b.

If you cant get the older 4 port 13b, get the GSL-SE 84-85 13b, so in the future when you rebuild again you can change out th side plates with the 12a and create your own 4 port 13b! 6 ports SUCK ! ! !

 

When you go to the expense of having a new engine ported and built why not a 13b? What is the headache? There is no headache simply a modified mount which can be made in 15 to 20 minutes by welding not hammering. If you are not subject to emissions requirements, the easiest course is to start over and simply remove the entire old engine with all its attendant complex of carburettor, hoses, solenoids, and wires. Get an intake, carburettors, and headers for a 4-port 13b. None of those items removed with the old engine are required. In this way you save a great deal of aggravation and a have a very easy process. Also far simpler to do at once than in multiple instances.

 

You people keep mentioning 4 port 13B, yet they are almost impossible to find anymore. His best bet would be to have his 12A rebuilt with 13B stuff. Then of course he needs to upgrade everything else that is specific to the 13B he's getting, whether 4 port or 6 port.

He's obviously new here (1 post), and probably new to rotaries too. Like I said, I would stick with the 12A for now to learn about rotaries. Then when he's amassed more knowledge, he'll be able to rebuild his own engine with the proper 13B parts (like 13B stationary gears etc) and fit it to his 12A chassis by himself.

It;s still up to him, of course.

 

What's so bad about the 6port 13B? You get what 40 more hp out of the box? It seems like that would be worth any minor headaches or "quirks" associated with the 6-port.

Anyways, just my opinion, please educate me if I'm way off base here.

 

Thanks for the replies. This is actually my 3rd FB spanning 8 years. I just haven't had much conctact with 13B and noticed that finding the 4 port was difficult and that the 6 ports don't seem to be liked as much as the 12 A. My main objective is a streetable 260 to 300 rwhp. I have never attempted to rebuild my own though I have read alot over the years as well as checked out Bruce's 13B rebuild video. The only part of the rebuild which has me slightly hesitant is the porting. The main reason I was looking at getting a rebuilt motor is the warranty. So...as it stands I am still undecided but I will probably stick with a built 12A. Again thanks everyone.

 

The 13B gets the nod from me, if only because the little extra torque makes a world of difference.

BTW, 260hp from a streetport is being overly optimistic.

 

Sorry I guess I typed that a little too quickly. I don't expect 260 out of the street porting. I expect the 260 when I get around to running a blow through mild boost setup. By the way, if I were to try to find me a rebuildable 13B what would be some things I should try to check out before buying. Obviously they would have to be external checks, but any ideas would help. My baby needs a heart transplant.

 

Pineapple has 4-port 13b

 

kleinke: Welding? What exactly would you weld? You dont need to weld anything, all you need is to flatten the 12a stock mount that bolts to the front cover and BAM the 13b will easily fit! The 13b is what a .5" length difference? If that? Beleive me you dont need to weld anything and dont need to buy a 13b mount. If you plan on useing a 6 port all that is needed would be to swap front covers and use the 12a front cover with the 6 port 13b and like I said before flatten your stock 12a cover motor mount and will easily fit!

 

20mm difference. You shouldn't use the dumb system for measuring an obviously metric engine; especially when it comes to somethng as important as engine length and a modified front cover motormount.

By the way, flattening, cutting and welding worked for a 12A to 13B swap I helped on.

 

About 17 years ago when I did the swap the first time, I considered flattening the existing mount. But I was very particular about achieving exactly correct positioning, and did not want to re-bend the mount. The easiest and most straightforward solution was to simply extend the length of the mount by welding additional metal stock on the ends to allow extra holes drilled 20mm further back. The procedure took less than 30 minutes, and guaranteed that the geometry would be correct. We did this for all our race cars from that point on, and it got to be a no-brainer. Not saying it can't be flattened and made to work. You could model it in Autocad or build a mockup first.