fbse7en

I pulled this mani. Any further info? Thx guys.

.::evil inside::.

It's an rx4/5 Hitachi carburetor manifold that's been modified because the motor it was attached to was no doubt rebuilt with a tallport center plate from a 12a. I'm not sure exactly which year the manifold is though.

Jeff20B

iTrader: (13)

J-spec 13B manifold likely from 78-82 with nitrided irons and probably an NO intermediate plate originally (short runners and small ports). Stock channels indicating it is not from a US-spec RX-4/5. I have a couple of genuine 74-75 REPU manifolds and 76 Cosmo manifolds and they look different from yours - they lack channels for one, and the REPU ones have an actual ACV port cover area of the casting, not something welded on. I also have a couple of NO J-spec manifolds and they look very similar to yours with some slight differences, with nothing covering the ACV port on the engine so I had to fill mine in with quicksteel.

What you have there is a great candidate for drilling/tapping the Nikki stud pattern and going blow through nikki like I did (or just NA which is also excellent). The carb should be hogged out though due to the 13B's larger displacement. Don't port the engine larger than a mild streetport, or better yet go for 74 spec ports, which are perfect on the street with a manifold like this. Also you can grind off the ACV mounting flange area for the turbo to fit.

In the end, it should look something like this. https://www.rx7club.com/build-thread...build-1072467/

fbse7en

Thanks for the extra info. Goin' from memory the "13B" does have tall center ports...you can also just barely see the impression they made in the gasket. I was think it might be the fusion of 12A plates and 13B housings. Is there anyway to tell if they're SE housings vs earlier 13B housings?

Love that turbo set-up Jeff!

Here's the carb that was on it:

Jeff20B

iTrader: (13)

What you have there is a fairly modern Hitachi carb from a nitrided R5 13B. Not the newest/latest/last model but towards the end of their run in the early 80s or very late 70s from Japan. It does have an air screw, which is good, not a fixed orifice like the newest model I had, which I could never get to idle right (even after swapping in a real air screw from a parts carb). Your carb has another more recent feature; it has a float bowl vent solenoid, not four slant cut tubes of the earlier 22mm carbs. By 22mm I'm talking about the primary venturi size. If you get a chance to clean that carb of yours, look down at the primary venturis. You'll see a 20. It was Mazda's attempt at saving gas. They have small primary jets too.

I'm half tempted to try a venturi swap in my early 80s Hitachi from a stock 20mm to possibly a 22, or maybe like a 23 or 24mm if there is enough casting to hog it out. These appear smaller than the Nikki ones so not sure you can hog them out very far.

These carbs have full size floats and tend to run at 5psi. They don't really slosh, or at least the old schools I've driven them in, don't pull as many Gs around corners as a 1st gen so I haven't noticed much if any slosh.

If you can get this carb up and working, I'm sure you'll enjoy it. The plunger style accel pump, for example, is a pretty good design and seems to pump in the right amount of fuel to give these carbs excellent driving manners.