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Old 10-07-2010, 08:47 AM   #1
Bad Noodle
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2007 SuperWagon
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Default Are motoman's head port ideas really that crazy?


and did some reading. This guys sounds like one of those crazy conspiracy people but does bring up some interesting points about reducing the size of the intake ports.


So what do you guys think?
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Old 10-07-2010, 09:06 AM   #2
Sammo Hung
Member#: 10613
Join Date: Sep 2001
Chapter/Region: South East
Location: S Ga / N Fla


those are na motorcycle engines not forced induction.
but i there is some merit to his method.

for na heads increase flow velocity would fill the cylinders in
lesser time than stock velocity. but there is a fine to this method.
yes the smaller port size increases velocity, but your dealing the vacuum
generated by the pistons plus atmospheric pressure.

but when you pressurize the intake, supercharger or turbo,
you have an increase pressure to fill the cylinders. so you
say that porting will allow more into the cylinders.

the smaller the ports, cross-sectional area less volume
that you could fill in a given period of time.

why do think motors with head work make more power
compared to stock ports on our turbo motors?

if this true for our motors then engines/motors without
head work should be make more power with the same set up.
and this is not true...let say a car with vf series turbo and
supporting mods.

my 2 cents..
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Old 10-07-2010, 10:01 AM   #3
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2006 Impreza WRX
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Have you ever seen WRC heads and its' ports. Guess not! Otherwise you would see that it's right on par with what Motoman says. However that doesn't mean making your ports smaller WILL give you more power.

The reason he makes the ports smaller is to increase the speeds of the intake charge. IF the flow of the ports is not limited due to it's size it makes sense to make them smaller UNTIL they start to restrict absolute flow. Higher intake charge velocity is also a way to actually get more air into the cylinder. It greatly increases response as the higher velocity air will atomize the fuel better and thus gives a better burn.

Engine like the WRC engines are limited on flow due to the restrictors they are running. So when that's the case you better get the most velocity you can out of the ports. Another trick most people don't know is to use SMALLER valves rather than larger valves to get more power and torque. However that's a whole other can of worms that I won't be opening today


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Old 10-07-2010, 10:40 AM   #4
FuJi K
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MY99 GF4 JDM 6spd
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humm.... here's my opinion.

The smaller ports allow that air and fuel to enter the cylinders at a higher rate. This allows for better air fuel mixing. This works well at lower mid RPM's. It can restrict flow as RPM's rise if the port is too small; choke.

The larger ports has less velocity. They can be a bit too big to where lower RPM driving isn't as good. However the benefit is seen more at higher RPMs where fuel mixing is still better because the port velocity is at a speed where it's most efficient. This is why the engine is kind of a dog at lower RPMs.

The smaller ports can be made larger to a medium so you still have good lower RPM and good mid. This also is depending on application and the engine setup.

Our Subaru heads are not big. I'm sure all of you, most if not all have seen how the JDM big ports are. They are NOT that big. If anything the F20C/F22C S2000 ports are bigger. Our port designs are actually pretty nice with the long splitter. You look at Honda heads and they are not the same. So if you haven't ported a USDM STi/WRX head to the size of a JDM STi big port head, then you don't have to worry about "Did I over port my heads?"

NA application you need good velocity. This you can leave a head stock because it matches what you're doing, or you can modify it to better suit what your application is. Force induction you can leave it stock because of your power level. You can modify if you need a wider powerband. Turbo size and RPM range are just a few things to determine if you need headwork.
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