I need to rebuild the engine in my rotary truck because it was built wrong before I got it. Whoever rebuilt it used an intermediate housing with extremely small ports. It was also gas nitrided so it obviously came from an RX-7. Can you believe it?

You may be asking, "So isn't that a good thing, the gas nitrided housing?" Well, normaly yes. It's got better wear resistance than the older housings, but in this particular engine, it's not worth it since the ports are tiny. It contains an EGR vent in the top, and would not allow very much of a streetport due to the casting itself. I think the port timing is very similar to that of a GSL-SE's intermediate housing. I recently found out it came from a Jspec engine. Hmm...

If any of you guys know how small the ports are on that type of housing, you will understand why I need to rebuild my engine with the correct housing soon. For those who don't know, the ports are only half the size that they should be for a normal '74. My primary intake flow is even less than a 12A! (untill I installed my Cosmo's reversed runner intake manifold, that is).

I don't know if my engine's original intermediate housing was bad, or maybe misplaced, or maybe the engine builder had a weird idea to try to increase low end torque by using tiny ports?

Well, whatever the builder's intentions, my engine is still really weak. Any torque possibly gained by the small ports is simply not worth it. I still have a limited rev range which peaks at 6000RPM and vibrates the shifter quite a bit. I don't know if the tranny is going bad or what.

My engine used to only rev up to around 4500RPM and had no power above that. The secondaries would only open in a very narrow RPM range somewhere between 2500 and 3800RPM. They also almost never opened in first gear (not too great for accelerating from a traffic light).

The problem turned out to be an intake manifold that had been die grinded by some idiot mechanic. He thought it was cool to remove the old gasket really fast with a power tool instead of taking his time and doing it right. He ended up grinding the little bridge in between the two intermediate ports to the point where it is lower than the surounding material and caused the gasket to come out which allowed comunication between the two ports. What a bad running condition that was! No wonder it had so many problems! This happened back in '95 which was a few years before I got the engine.

I have since temporarily fixed the problem by installing an intake manifold from my Cosmo which has reversed runners. This means that the primaries from the carb now flow into the (big!) secondary ports on the engine (genuine '74 end housings). However, the secondaries now flow into the tiny intermediate ports.

Why would I want to sacrifice my secondaries by flowing them into my tiny ported intermediate housing? A compromise to have good primaries perhaps? Well, the actuall loss in secondary performance is not noticable. Seriously! Infact the secondaries seem to flow better now, despite a port mismatch on the intermediate housing. The intake manifold has the really tall outlets (around 2 inches) found on '76 and '83-'85 engines, but the intakes on my intermediate housing are the normal height found on most engines from '74 up to '82ish. At least the manifold outlets/intakes on the end housings are the same size. Good thing I don't need to run on the secondaries 100% of the time either (a carb with faulty primaries, but a good idle circuit, and good secondaries is not as fun to drive as you might think; just ask Tom).

This quick fix solution is fine for the time being. I now have more power, the engine revs higher and quicker, the secondaries actually open in first gear, and I now know that I need to rebuild my engine with the correct intermediate housing.

It would also be nice to install a high volume oil pump, shim the rear oil pressure regulator to 90psi or so, possibly streetport the housings, and paint it all before reassembly. That would be cool.

Then I could install a supercharger and it would flow really well!

This sounds like a great project so far.

I also need to get my Cosmo running because if my truck is apart, I won't have anything to drive. My MG still needs some more work too.

FUN!