My MR2 4AGE cylinder head page
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This page is supplementary info to my mid-port build page. Hopefully the info here will help
clear up my ideas and opinions so that the mid-port idea doesn't seem quite so crazy.
Toyota added this fitting to the left rear (drivers side) corner of the small port head. The
Toyota parts book and service manuals clearly call it a "crankcase vent" and NOT an oil
drain back as it is commonly called. Since the engine tilts forward a little bit, I can see
where the front of the head could "flood" the drain holes and cause a circulation problem.
The only way I could see this port draining oil back into the crankcase is on a steep uphill
right hand turn. I just makes sense that this is what toyota calls it - a crankcase vent.
clear up my ideas and opinions so that the mid-port idea doesn't seem quite so crazy.
Toyota added this fitting to the left rear (drivers side) corner of the small port head. The
Toyota parts book and service manuals clearly call it a "crankcase vent" and NOT an oil
drain back as it is commonly called. Since the engine tilts forward a little bit, I can see
where the front of the head could "flood" the drain holes and cause a circulation problem.
The only way I could see this port draining oil back into the crankcase is on a steep uphill
right hand turn. I just makes sense that this is what toyota calls it - a crankcase vent.
Next up are the port comparison pics. The first two have lines added to show
the general port layout. You can see the small port head enters very small
and then has to get very large to line up with the valves. The big port has a
much straighter shot at the pockets. I measured the port height and was
surprised - they are the same top to bottom - after you get past the chamfer.
Also, I was wrong about the small port having a raised shape - when I
measured it with a T square, they were equal. The chamfer on both heads is
pretty screwy. The big port head (as deep as I could go with my dial caliper)
is 2.375" wide about 1/2" into the port, but the chamfer is a little over 2.530 -
more than an 1/8" of chamfer. I'm thinking that it needs to be filled in, and the
go with that port shape for the intake manifold. I'm pretty convinced that a
single runner intake with a properly sized (diameter and length) runner would
be a significant improvement. Fuel distribution patterns are pretty interesting
too I think.
the general port layout. You can see the small port head enters very small
and then has to get very large to line up with the valves. The big port has a
much straighter shot at the pockets. I measured the port height and was
surprised - they are the same top to bottom - after you get past the chamfer.
Also, I was wrong about the small port having a raised shape - when I
measured it with a T square, they were equal. The chamfer on both heads is
pretty screwy. The big port head (as deep as I could go with my dial caliper)
is 2.375" wide about 1/2" into the port, but the chamfer is a little over 2.530 -
more than an 1/8" of chamfer. I'm thinking that it needs to be filled in, and the
go with that port shape for the intake manifold. I'm pretty convinced that a
single runner intake with a properly sized (diameter and length) runner would
be a significant improvement. Fuel distribution patterns are pretty interesting
too I think.
These 3 pics have the rough port shapes outlined in red. You can see how
much of a straight shot the big port has compared to the small port.
much of a straight shot the big port has compared to the small port.
