So has anybody tried lathing down 13B housings to make 12A housings? Then use the FC irons and a 12A rotating assembly to make an engine?

Sounds crazy I know. But without new 12A stuff why not (other than "its not original equipment"). Well neither is an FC engine.

 

Not that crazy. There are several company that offer/sell milled 13b housing to suit 12a . Atkins and rec both do and I think goopy does as well. I know rec does it using gslse rotor housings and re machine water jacket seal groove but I think Atkins does not.




Edit Atkins does have a water seal groove .goopy does not.

 

been done for years, however it is not popular because no one seems to want to drop $2000+ to build an FB 12A carbed engine.

 

Ouch, $2k?

I'm not talking pro built with grooves and all that. I'm talking take some good housings off a junkyard FC and bring them over to a machine shop to get them decked (like a cylinder head). Then piece the FC engine back together with 12A guts.

I guess my question is answered... Yes, it can.

But I'm not even near and engine rebuild for my SA yet. Got a lotta other stuff first. Shoot I might be able to source some good housing in that time frame.


EDIT: Also, I'd love the strange look of having 13B stamped on the side of a smaller housing that contains 12a rotors. Make people look twice.

 

well, i was actually considering that

~$500 for a machine shop to cut your own housings
$400 new apex seals(why would you run used seals on a virtually new housing?)
$125 soft seals/gaskets
$40 oil seals
$25-100+ misc springs(at least run the flat spring corners)
$20 F+R main seals
$50 cleaners, sealants and lubes

however i figured in about $350 additional to CNC cut the rotor housings for coolant seals, some may have spare FC irons and some may not. maybe not $2k but it is close and that is if you do it yourself. for anyone who couldn't do the work and had a shop build it, then yeah. atkins charges $750 for each rotor housing, but that is a bit much....

some shops might charge less for the work on the rotor housings, but it is a bit of work for nearly perfect tolerance machining.

 

Shoot, I got a buddy in Charleston at the O.K. Machine shop that'll deck a head for $75. I suppose I'd toss him $200 for a pair of housings cause it would be the same work as 4 heads. (I love my math BTW)

And I'd just use the 6 port or whatever irons and make the carb situation work*.

$140 for the fel-pro gasket set (comes with oil rings and ft/rear seals) and RA or Atkins seals (come with springs), and I'm out the door for under $800.

Not a nostalgic pro built, but enjoyable none the less. But with all builds there is the possibility of needing other things bearings yada yada yada. Shoot if it works I'll build a few and blow them up and toss em in so fast it'll make your head spin.



*dunno about the compatibility of 13B intake bolt patterns and 12A patterns. Honestly I've got 0 experience with 12As, other than dumping some fuel in my SA and seeing if it runs (it does).



EDIT: I'm just thinking out loud at this point.

 

I think the bolt patterns will work after being milled evenly on both sides. I'm no expert but some
quick measurements of the 13B housings should verify it.

 

i don't really think the 4 port turbo 13B irons share the same intake bolt pattern or runner size as the 12A, but i don't have any 12A irons to check against. plus i dunno, the turbo irons are worth about $600 a set now where the 12A irons are literally almost scrap cost.

more than worth it to sell the irons and just have the additional work done on the rotor housings.

 

Good point. I was thinking the cheapest of the cheap 6 ports that nobody seems to want. Obiously it wouldn't flow too great, but I'd build it for DD abuse, not pro-track.

Eh, seems like hunting down parts is still the best option... we haven't gotten savage enough to go to these lengths

 

All rotor heads are savages, you know that James.

And Atkins has been savaging 13B rotor housings for years, with a nice product to show for their efforts.

I was tempted myself, back before the Rotary Gods showered me with 12A housings that meet spec.

79-85 12A Rx7 Re-Tooled Rotor Housing (ARE128)







Only $750 per housing, not a bad price when you think about it.

 

They don't the difference is big. At least bolt pattern wise.

 

is there a 6 port 12A intake manifold? i only recall the 13B from the 84-85 GSL-SE.

 

yes there is . I recall running into a hand full of aftermarket manifolds over the years and a few Jdm 12a 6port . I also seen a post jeff20b has where there is one pictures . Here a link https://www.rx7club.com/1st-generati...rt-12a-800835/

I was very tempted to purchase a manifold that went up for sale about a month ago . I still do a lot of work with 12a engines.

 

Yes Ben, there is. I have one, like he mentioned.

The plan is to build the 6 port 12A with GSL-SE end plates and a Y intermediate and throw some kind of modded Nikki on it. However the original Nikki looks promising. I'd like to see if I can make the aux ports work, but to do so, the carb would need to handle the change in secondary air flow. The stock 6 port one does using some kind of trick holes in the float bowl that communicate directly with the long slow air bleeds. Note these are the bleeds I fill with solder to reduce the nasty mech sec fuel flow delay I was getting under boost. However as the 6 port will remain NA, I think I can keep its different looking long slows stock. But only experimentation will bear this out.

 

Wire up the factory TPS+electronic power valve and machine the tang to it only turns on at WOT.

It wont be *exactly* when the secondaries come open, but it would be extra fuel for WOT and less fuel for below WOT which imo would be pretty fun.