12a BP vs 13B 6port SP?
 

heres the dilemma I need a motor for my rx2.
I have a 12a that needs tear down and a rebuild, and a 13b SE motor that also needs a refresh oil control seals are gone on the rear rotor.
So heres the question witch one should i go with.
do a 12a bridge port with a holley 650 on it or 13b 6 port large street port with the same carb. witch would be faster and what all should i worry about other than the standard list of stuff.

Well since the engine will be a bridgeport either way, obviously the 13B. It will give you more power and torque, at a very slight weight penalty. Or you could use the plates from the 12A and the housings/rotors/e-shaft from the 13B and build a 4 port 13B. Racing Beat has a Holley manifold for a 4 port 13B as well. This will give you more porting area on the secondaries. The downside is if both engines need a rebuild, you may end up shopping for new housings. I had one of each like you and both had housings with massive amounts of flaking. Wound up using a set of like new used REW housings. Good luck.

since its an rx2 id be tempted by the BP 12A, but plan B is to use the 12A irons and make a 4 port 13B.

i agree, 4 port 13b. but it's all dependent on which rotor housings u end up being able to reuse.

well I know the 12a locket up on me if you turned it over it would start and as long as it was warm it would but as soon as it cooled off it would seize up. The 13b came out of my SE it ran decent considering the amount of oil it was going throe has about 160k on that one it is rather amazing when you pull the motor out what you can find like a broken motor mount and tranny mount makes sense as to why there was so much drive train movement.
I was wondering if you could use the 12a irons on a 13b. is there enough porting material that you can take out to make it flow enough to where you would not be starving the of air. There is also a very remote possibility of doing a 13b PP but that would require a new carb most likely a webber 48 or a 51 IDA witch the 51 aren't cheap even used. Plus the cost of getting the rotating assy balanced and everything else.

12A Bridgy. Depending on how it's all done.

with the pre gsl-se engines, they use the same irons for a 12A and 13B, so like a 74 13B uses the same irons as a 74 12A, so yes it works.

PP is awesome do it!

you do need a 2 barrel carb, or go EFI. by the time you buy the carb ($500 new) and all the jets and e tubes and air filters and stuff, you will probably spend another $500, and this puts you in the EFI ball park.

with EFI p port, i think you need an ecu that can do sequential injection (with 2 injectors just about anything can), and i think you also need to be able to play with the injection timing, which narrows it down.

what would be a difference in performance between a 6 port 13b or a 4 port then. Has anyone ever tried on porting away the part that actually separates the 5-6 ports form the rest.

I haven't actually done it, but I have a friend that is. I'm fond of the idea. I like big ports, throw velocity out the window. :nod:

Good question! I am wondering the same thing...I have a 12A and may consider trying the 4port 13B...

yes. some of the E production guys have done it. the ports becomes GIGANTIC. the tq peak moves from 3500rpm-4000rpm stock to over 10k.

ive heard some pretty outrageous hp claims from an engine like this (over 290), but ive also seen the car run, and it looked like it had more like 90 instead of 290. so maybe the big motor moved to another car, or died or something, or maybe they are full of it...

in e prod, they have to run either a 48IDA weber, or the stock EFI intake, but on the street a 4 barrel with vacuum secondaries might be better, that way the giant ports arent open when you don't need em

that was going to be my next question how high you would need ot rev the dam thing to get power. What i have for a carb is a Holley Double pumper 650 with mechanical secondaries. Trying to keep the budget fairly reasonable because i need a bunch of cash for the rest of the car.

I think what i will do is I have a junk 6 port motor sitting around that needs a tear down. I will take of the irons out of it and take it to work cut the mass out with the bridge port and see how it looks.

:nod:
Yupp. The only reason they're not as quick as most of the Mi-Otter guys is simply because of weight, and, the FC is quite a big car IMO.

But yeah, give that six port a healthy port job and put a four barrell on it. I'm a fan of that idea.

Will FC rotor housings work with 12a irons?? Seems like there is a problem with the way the water seals work or something? Please enlighten me!!

Depends on the year of 12A housings you use, I'm not completely sure.

Anything 85' or older bolts together, or 86 and newer. You can't mix and match new with old due to the coolant seal moving from the housing to the iron.

I vote for a 4-port 13b(-se bits, inside 12a irons). I have one with a very large SP and it is a beast. Throw in an rx4 intake and you can use a modded nikki.

Isaac

nah last time they came up here, they were running lap times that you could run on foot.... or like the same laptimes that my friends wife's FC runs, and it dynos @112rwhp and is 2800lbs!

Lol. Well, Dave Lemons E-Prod car is fairly quick. (Certainly not up to par with Jesse Prathers Miata, also E-Prod) but, you know what I mean. Not sure you're familiar with either names. Speaking of which, I didn't see Dave at the Runoffs this year. :scratch:
That's right, he drifts with Kyle now.

yeah i know dave's car is fast, although he spend a lot of time/money getting it to stay together!

Yeah, but money doesn't win you races. And that's obvious,

This is my engine. My builder had the coolant seal groove machined into the REW housings so everything would bolt up nicely. RX-4 manifold with the studs moved to match the Nikki throttle body pattern. Just broken in last year, haven't tuned it, taken it over 6Krpm or dyno'd it, but it pulls fantastically.

If the GSL-SE housings and internals are still good, there is no reason at all not to go with the 4-port 13B. You can still go bridge with that and make even more power than the streetport or 12A bridgeport.

OK, OK.... so will this work???

12a irons, 85 and older 13b housing, any 13b E-shaft, S-5 high compression rotors???? Will this work??

Then do I use a 4 port 13b manifold for a side draft weber???

As you can see.... I am trying to build my dream motor!!!

Also.... please advise from folks who have done this.... Not just dreamers and guessers!!!

yes it will work..:icon_tup: make sure to get the right counter weights.or matching rotation assembly from a automatic so that you can use a lightweight flywheel..

would the stock intake manifold from an rx4 flow enough air to not starve a large port motor off air like that?

The best (and still somewhat affordable) way to do it is as follows.

S4/S5 turbo rotor housings
S5 NA rotating assembly (have to find a rear counterweight from an automatic turbo model)
S4/S5 turbo front and rear faceplates
12A tall port centre plate
S4/S5 turbo to IDA downdraft manifold
55mm twin tapered bore bodies (efihardware.com sell them)
S4/S5 crank sensor in the front cover.
FD oil pressure regulator (rear).
New FC turbo oil pump

If you use an early gearbox you can just use a 8.5" lightweight steel flywheel. 4 puck unsprung button clutch. Match that with the right rear end ratio and a LSD and you'll be keeping up with poorly setup turbo cars (which is most of them :lol:)

Have the intake ports all matched up. The only non standard thing about that build is the missing water seal groves on the 12A centre iron which is machine time.

If he has a 12a for irons and an -se for housings, there is no point in going with all those 2nd gen parts.

Yes, 80's OC, what you posted will work, and work quite well. The older style 4-port weber intake is fine, or the rx4 intake. The rx4 intake will flow just fine for what you want to do, I have been running one for years.

Isaac

well i guess i need to try and track down someone that has a rx4 mani then if not i guess the rb bridge port one will have to do but dam things are like 315 bucks.

^ Gotta pay to play. This isn't a cheap game. RX-4 mani's are going to be hard to find, and especially for a good price. I got lucky. 84stock got a hold of one and was willing to sell it to me for a fair price. Getting my hands on it is actually what decided the direction of my build for me.

I have seen several for sale on the boards here in the last few months. Ask in the Other rotary section.

Isaac

Being a parts hoarder I am still kicking myself for selling it, lol. It's like seeing the clean bare spot on the wall of a museum where the Mona Lisa used to hang. :blush: