... As an old school machinist, I'm curious about how these tests are performed ....
The entry and exit from the port can be "simulated" many different ways.
The saavy guys use an intake manifold set-up, complete with throttle body, that is similiar (if not exactly the same) as what that particular head will be running, to ensure thay are not going to get a biased set-up in service.
They also use an exhaust manifold that is representative of the type and style that will be used on that particular engine.
Back in our racing days, we saw a lot of heads that had awesome laboratory flow numbers perform very poorly in the real world when intake and exhaust mani's were bolted up.
It's also helpfull to remember most of these numbers in the chart Curis posted are being presented by the shops that did the work, or a facility that *may* have a vested interest in how the product performs.
While I can't blame a shop for presenting the best possible scenerio for their products, I think it creates an unrealistic basis for comparison. Going thru a bunch of cores and cherry picking the best one is just good business, but it leads to results that will be hard to duplicate in the real world.
(Most) Magazines also flat suck at presenting unbiased information (ever notice how people that advertise heavily in a certain rag always do really well, while competitors that don't advertise have a poor performance index?... /ubbthreads/images/graemlins/idea.gif )
Bias, baby, bias... /ubbthreads/images/graemlins/banghead.gif
In addition, there's a whole slew of other factors that will seriously affect the numbers.
Core shift is a bitch.
Mitsubishi's 4g63 castings are better than some, but there's some pretty sizable variations in port centers from head to head and mani to mani. (we're not talking about a thou or two, we're talking sizable variations up to 60 thou or more)
Something as simple just swapping intake manifolds ("stock for stock") can make a port's numbers go from dog to super hero status, if the core shift of the mani compliments the core shift of the head.
If the as tested combo is port matched (just common sense!), then the variations really show when compared to a combo that has not been matched.
So, always take flow numbers with a grain of salt!!!
Most shops production pieces won't get anywhere near the "test" numbers...
I played with this stuff when I was a kid, and I learned a whole sh*t ton about reality... (and my limitations ! )
Many heads show a bias, and/or favor certain cylinders based on the basic engine design/manifold layout.
It's just simple physics.
Mitsubishi's heads and mani's are no exception.
Entry and exit areas of the intake/exhaust manifolds can be just as important as the work done to the ports in the head.
Minimising the bias (unequal flow to each individual cylinder) is mission critical to putting a package together that will live a long life and be tunable.
> remember, your wideband is reading the average of all four cylinders <
(and your egt is probably only reading one cylinder...)
A good "average" tune will lead to melt down/crushed ring lands on the weak cylinder when you turn things up. /ubbthreads/images/graemlins/wink.gif
The closer you get to the edge, the more this matters. /ubbthreads/images/graemlins/wink.gif
You can only tune to the weakest cylinder
All that said, I've seen a buncha "worked" 4g63 heads as a machinist...
...and I haven't been all that impressed with many of them...
...The old adage of "hog that baby out"... "lets get things flowing" is simply retarded when it comes to ports the size of the 90-94 ports...
It's my opinion that 90% of the benefits of a professional port job can be done at home, using standard tooling.
Just focus on the seat/bowl area.
Smooth the seat/bowl transition, and you're most of the way there.
Clean up the match between the mani's and the ports, and for all intents and purposes (for a street car), you're golden.
Sure, more *could* be gained, but there's a lot of other areas that could benefit from your attention before trying to squeeze that last lil bit out of the head.
If you are building an all out set-up, then it's best to let a professional handle the head work.