I've decided that as much as I'd love a bridged 12A and big Mikuni (I found both recently), I'm not gonna be happy until I've built a streetported 4-port 13B with a sidedraft. I'll likely go with a Dellorto DHLA 48, but where would I find a 4-port 13B? Junkyards around here don't have any old 13B trucks or anything. Just looking to get it all together so I can rebuild it at my leisure before the 12A ***** the bed. Where should I look? Also, will 6-port intake manifolds work okay on a 4-port? Running a 6-port with the 5th and 6th open is a possibility if 4-ports can't be found... Thoughts?

 

The easiest way to get a 4 port 13b is take the 4 port side housings from a 12a and the rotors and rotor housings from a 13b and reassemble the motor.

Why do you want the delorto? The weber or the mikuni carb is a much better way to go or even the holley but not the delorto junk in my opinion.

No cant use a 6 port intake on a 4 port motor.

 

The Dell'orto "junk"?
Hardly. Their major advantage is their having a choke, which the Webers lack.

 

Been running rx7 since 1991 and havent yet needed to have a choke on my webers yet IDA or DCOE. 3 1/2 years in Japan and never seen a nice rx use a delorto.

 

If youre referring to the IDA, proper tuning will cure that problem.

 

get manifolds from a pre rx7 13b, or use aftermarket
12a or pre rx-7 13b side housings
and 13b rotor houseing from a gsl-se or earlier 13b

or if you have too you can use turbo 2 side plates and 86-up 13b housings

 

why's a four port more desirable than a six?

 

I know there are a couple ways to do it, and I'm considering stripping a dead TurboII, but I've got time enough to take my time with it. I know the epitrochal size of the endplates is the same from 12A to 13B, but I didn't realize they're interchangable. I found a bridged 12A for sale - I could use those plates without any trouble then, right? Just gotta find some 13B rotors, housings, and springs and seals? When sticking N/A, would my best bet be to use N/A FC rotors, then? I'm sure this has been discussed before and I've followed along, it's just that you never really understand things until you try to plan them for yourself. So yeah, treat me like the noob I am. What I really want is advice on the right way to do it without spending unnecessary money since it's not a rush job or anything.

 

Sorry to repost, but the SE that I snagged my suspension from is still around with a blown rear rotor. If it's salvageable, can I use SE rotors, e-shaft, housings, and engine mount (crosses under the water pump, right?) with 12A plates? How does SE rotor compression compare to FC N/A compression?

Looks like I need to gut that SE motor and see what's left.....

 

yes, you can use everything from the SE motor except the plates. while youre at it, be sure to modify the e-shaft for better oil flow, shim the front cover and modify the oil pressure regulator (or you can buy a hp regulator).

 

I, too, have always been curious... i am in the midst of going from 6 port (SE 13b) to the S5 13bt 4 port and it would be nice to know what all the beneficiaries are...

Zachstylez

 

Well, as far as porting goes you can always port a 4-port to include the swept area of a 6-port. Thing is, you don't have to worry about actuators and crap with the manifold (I'm going to a side-draft with a simple RB header, so no actuators). Besides, if I wanted to keep the actuators, I'd need a new exhaust. There's more flow available in a 4-port because you can open up as much as you want and it's much simpler.

 

SE compression 9.2:1... REPU 9.0:1... Not sure on the FC off hand will look around

 

sorry to reserect this week old thread, but this is interesting me,
so you guys say you canbuild a 13b 4 port?,
ok, can you use FC rotors and housings etc, with the 12a side plates? or do you have to use FB, or pre-rx7 housings etc.?
once you have allthis sorted out can you use 12a headers and such?

 

You have to use 13B headers since the flanges are gonna be spread 10mm more since you essentially have a longer motor. 13B and 12A plates are more or less interchangable except for the front plate. I think the water pump is different, but I'm not sure. Can anyone tell me why I need to retain the front plate from the 12A in order to work in the car? I've got the SE radiator, if it makes a difference.

 

By the way, I picked up an SE block today with a puked rear rotor. Any info on building the 4-port would be verrrrrrry helpful. Pointers?

 

You can't mix and match FC housings with earlier ones because the water seal groove location is different.

Basically, it's like this... if you want to build an n/a late model 4-port use a T2 block with n/a FC rotors. You then have to do the usual sump and front cover mods but this engine would be the best starting point for making power especially if you use S5 high-comp. rotors.

The other option is to find a 13B from an Rx-4 or 5 or build a 13B using using Rx-7 12A end plates and SE rotor housings and rotors.

 

my $0.02. shall you decide to use a 12-A, use the earlier RX-7 12-A engine due to long or tall primary ports. the later ones have short runners.

 

I have a 4 port out of a cosmo, look forward to finding an oil pan.
12As won't work
13Bs with the side mount won't work without the right engine slices (whatever you call the layers that form the engine)

I am having difficulty finding an oil pan for a 13b WITHOUT the side motor mounts.

on waterpumps - so far I have seen two different setups.
one uses a steel housing, the other uses a aluminium housing. (the housing is the bit the pump bolts to, that bolts to the engine.)

the aluminium housing uses an additional mounting stud that the iron one does not have.
the stud screws into the engine, so to use the aluminium housing you have to have the engine slice that has the stud.

the water pumps have a bolt hole that is different, stud, or no stud.

steel and aluminium housings


I have read about grinding being needed to put certain housings or pumps on certain engine slices, but I have not yet seen exactly what that is all about.

 

79-85 12A 9.4:1 compression ratio rotors
84-85 13B 9.4:1 compression ratio rotors

86-88 13B n/a 9.4:1 cr rotors
87-88 13B turboII 8.5:1 cr rotors.

89-91 13B n/a 9.7:1 cr rotors
89-91 13B turboII 9.0:1 cr rotors

93-95 13B had 9.0:1

facts taken from here

 

Okay, so this is a lot more complex than I originally thought. I can't rebuild my SE motor anyway because the rear rotor and housing are shot. Looks like I'll just have to keep looking to find a good combo of parts. Dammit.