Shadohh

I stole this information from a site I pay for so you all can read.

Now you all can know what to ask for from a shop and what to look for on what is a godo job done.

Course are head will always suck.. sad.gif


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Headwork entails enlarging the intake and exhaust passages in a head to allow for more flow. Good headwork entails subtle reshaping, not just hogging the whole port out bigger. Generally, good headwork leaves the floors of the port alone since most of the flow activity in a port is near the roof of the port. The roof is the outside radius of the bend going to and from the combustion chamber and by inertia, most of the air wants to flow up there. Good headwork usually rounds the floor hump which is the transition from the valve seat to the floor of the port. Stock, this is usually a sharp edge which causes non-laminar (turbulent) flow separation.

The object of good porting is to increase flow as much as possible while keeping the port volume as low as possible to maintain as high of a flow velocity as possible. Big ports have low velocity at low rpm. This results in a loss of bottom end power due to the lack of energy available in the moving gas column behind the valve. The gas column has inertia which helps fill the cylinder, especially at low RPM. Generally porting your head will cause some loss of bottom end power. Good head porters might be able to increase flow in the head up to 40 percent with no loss in bottom end but that is usually for American Iron heads which are terrible to start with. Modern Japanese engines don’t usually see as big gains as their design is much better to begin with. Gains of 10-20 percent are typical with a modern Japanese motor.

The other major area of headwork flow gain is in the valve job. A large percentage of gain can be in the valve job alone. The best valve jobs are called multi angle valve jobs with three or more distinct angles. The main angles are the throat cut, which is a 60-70 degree cut that blends the port wall to the seating cut. The seating cut is a 45 degree cut which is the sealing surface for the valve. This critical cut should be 0.040-0.060 wide for a multi valve engine like an SR20. Finally there is the top cut which is a 30 degree cut which blends the seating cut to the combustion chamber. The purpose of these cuts is to help the air flow smoothly around the valve, especially when the valve is starting to open or close.

Another valve job trick is to place a 30 degree back cut above the 45 degree seating cut on the valve itself. This helps the air get around the valve better especially at low lifts. A five angle valve job uses two extra cuts to make the transition even smoother. The best valve jobs are radius valve jobs which are a 3 or 5 angle valve job which is hand blended after cutting for a perfectly smooth transition. The quality of a valve job is very important because it can contribute up to 50% of the flow gains that headwork will get you.

The best valve jobs are done on a Serdi machine. The Serdi is very high precision which insures that all the valve angles and depths come out equal. Most low price shops use stones. Stones can give a good valve job but the stones must be dressed frequently and dial indicators must be used to insure that the seating surface remains concentric. Stones require a highly skilled person who is conscientious of doing a good job. A butcher can make a big mess with stones.

Unshrouding the valves is an operation where the edge of the combustion chamber is cut back by about 25% of the valve diameter so that the wall of the combustion chamber does not block the air going past the valve into the cylinder.

Polishing the combustion chamber removes sharp edges that can glow red hot and trigger detonation. It also makes it harder for carbon to stick. Polishing should be limited to the combustion chamber and exhaust port. The intake port should be no smoother than 220 grit as maintaining some boundary layer turbulence is good for good bottom end. This turbulence makes the port virtually a little smaller at low flow velocities.

2 UNIQ

This article is very informative BUT i DISAGREE on a 3 angle or MULTIPLE valve job being MORE effective.YES Working on your valve porting IS the MOST concentrated AREA of the HEAD but from my radius cut i have gained MORE WHP from others taht have ported their Tiburon heads.The shop i took it to STRICKLY does MUSCLE cars at over 1000HP and he has been in business for over 30 years.People from the U.S Deliver their RAce cars or daily drivers to his shop on a daily basis and HAVE seen this with my own two eyes.Their are cars from Florida,California and the list goes on as he is VERY WELL known!
I say the RAdius cut is DEFENTLY more effective! smile.gif smile.gif smile.gif

Shadohh

Maybe you should reread it...

I qoute from above

" The best valve jobs are radius valve jobs which are a 3 or 5 angle valve job which is hand blended after cutting for a perfectly smooth transition"

Sounds like hes agreeing ^^

2 UNIQ

IM sorry if im reading it wrong BUT to my understanding a RADIUS Cut has NO 3 or 5 angle in it.Its just a smooth round cut with no Grooves cut into the valve hole smile.gif

[ March 20, 2003, 12:13 PM: Message edited by: 2 UNIQ ]

Jon

Yep thats what he said.

2 UNIQ

Oops my bad sorry suicide suicide

But Like Shadohh said its not worth it on the Hyundai Head.I must of gained ablout 6-7WHP from this mod and not worth the money if you ask me! sad.gif frown

turbulence

i disagree with you on that. it's certainly worth it on a hyundai head, especially since it doesn't flow well. i mean, if you're going fi, why not get the head p&p'd?

KillerShark68

If yall want that Onpol is selling Ported Heads and TB ,amd Intake Manifold. Email him for info