Mid Port Engine Build
reasons. Right now I have a nice shop available to do the work and also have another vehicle to drive while the project is in process. I've learned that it's a lot easier to do this sort of job on terms like this
rather than waiting for something to break. Also, after putting almost 60K miles on the car (including almost a year of commuting 125 miles a day in traffic to San Francisco), my clutch has been chattering
when cold lately. Obviously, I would like to get some more performance out of it as well.

package. This gives me a stronger crank, a stronger block with a knock sensor, and I'll be replacing the heavy small port rods with a set of lightweight 20V Blacktop rods. The block is being bored .5mm
oversize so that everything is tight and fresh. I'm also using Total Seal gapless rings to insure that I get the most out of my combustion. The replacement pistons are 10.3:1 compression and I'll be using a
TRD .8mm head gasket along with a compression cut on the head to get my effective compression ratio up to about 11:1

I'll be re-using my low-drag water pump and overdrive pulley, as well as the under drive pulley for my alternator. I also bought a light crank pulley from TechnoToyTuning to drop another couple of pounds of
rotating mass.

The entire rotating assembly will be balanced for smooth operation.
The cylinder head and intake is what will set this build apart. I'm building a "mid-port" engine. This will eliminate the TVIS setup but also should work better than either the original large port head or
the later small port head.

To me, the TVIS system was a good idea to mask on overly large intake port design error and help to make it more streetable for the average driver. It does a good job of that, and for a high RPM,
high output race engine it is a very good head - typical of the Yamaha designers who created it. The small port head was (to me) a cost saving way to continue producing an existing engine. By
eliminating the TVIS setup and reducing the port size, the same basic function was achieved. The good news is that the small port intake manifold is far superior to the TVIS intake in terms of flow
and RPM range.

So, to me the best thing is to build a mid port engine that combines the best of both worlds. Since the small port head can't be ported out enough to do this without breaking into the water jackets, I'm
taking my original big port head and using Devcon Aluminum Putty (an epoxy) to reduce the size of the intake ports.

I've roughed up the surface of the ports so that the Devcon has a better surface to stick to, and also added some deeper grooves to help anchor the epoxy. I've also made individual styrofoam
"interior" molds that should be the final shape of the port. Each foam insert was shaped to fit a specific port, as each one is slightly different (this IS a production part after all...). Each one was labeled
and marked for easy identification. I used clay to fill in the injector bosses since I don't want to change those areas at all.

Here are some pictures so that things make more sense:
I had to make the inside
end of the cores pointed
so that I got a tight fit.
Here are four shots of the intake manifold machine work in progress. You can see that
to build the manifold correctly I had to mill through the aluminum casting and into the
epoxy I had used to block off the center sections of the manifold from my "try a small
port intake on a big port head" experiment.
Pics below are the work in color differences how much material is being added to the injector
ports was important. The styrofoam cores dragged epoxy down farther than I thought they would,
but nothing I can't fix.
I also started to pocket port the head, just to
smooth out the transitions from the head casting
to the seats. You can see the factory machined
area and also some of the core shift that leaves
material hanging out into the port.
On the left is a stock small port gasket laid over the mid port manifold. The next two are a stock big port gasket laid
over the mid port manifold.

You can see from this that the mid port floor is raised quite a bit, wider than a small port, but not as wide as a big port.
This is the chamber after porting away the
casting humps shown in the top photos.
One of the small port head "features" is what most people think is an oil drain in the drivers side rear of the head with a matching hose and fitting in the engine block. Supposedly this addressed a
problem of oil pooling up in the head on hard cornering. The problem with that idea is that this area is much higher than the existing oil drain ports in the head.

In the Toyota parts book this "drain" is clearly called a "crankcase vent". Since the description sounds like it's part of the pollution control system, I made sure to add it in as part of the build. I used the
same Devcon aluminum putty to fill in the exterior corner of the head, then pushed in the metal fitting that I had intended to thread in after it had set. While I was doing this I realized it would be much
easier to just sink the fitting into the putty and let it harden. It sat overnight, and then I just carefully drilled through from the backside. It was much easier and quicker doing it that way.  
The OBX cam gears are machined 1 tooth off - that explains the problems I had last year!

Also pictured are the oil squirters, the really cool Blacktop rods, the small port pistons with
the cutouts for the squirters, the engine just before re-installation and the Dynamat
Extreme sound deadener.