Here is some info on head porting for you girls and guys.
Maybe it will help you understand what to ask for and what to look for in a port job.
Course untill hyundai makes a better head it will always flow crappy.
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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?ft 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.
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hey mods, im bumping this so maybe you guys can make this a sticky. i've been looking for a machine shop to do me a head porting and valve job, but its been a lot easier with this information.
Head work is expensive in the fact its very percise, and without proper machines and work tables i wouldn't recommend doing it yourself, but then i'm picky about that kinda stuff and i like have a guarantee....you could spend from 500 to god knows what if you get them angled, honed, bored it could get expensive....
Shadohh bye the way nice report...most people i see with imports forget about head work....i'm glad somebody made mention of it since you can gain a lot of power out of headwork....do you have any ideas were i could find good valves and components for our cars? 03 gtv6 5spd - thanx
Good information for the most part. The serdi is good but the sunnen VGS-20 is pretty much the standard in the racing industry. I wouldn't advise home porting on a head that you will actually run on your street car. You can easily do huge amounts of harm (not only power wise but reliability too) Headwork is the most expensive part of building an engine. The cylinder head is also most responsible for power gains (or losses) and RPM capability. Whether it's actually worth it, dunno but supply and demand.
As far as what valve jobs to run and whether the valve job is 'radiused,' combustion chamber polishing. All of that: where to remove material, where not to,swirl and tumble, runner surface finish. The smartest people in the world argue about that crap.
Quote:
[body]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.[/body]
This isn't exactly true. Theoretically, yes this supposed to happen in a specific application, but even in that one example in an actual running state and varying rpms with a valve opening and slamming down 3000 times/minute who knows what the air does? How a port is designed results from induction type and efficiency, application, rpm range, camshaft specs, etc. Someday, someone will develop a flow device rigged to a spintron. That will be much closer but still not 100%. What i've said probably sounds like mindless rambling. alls i'm saying is that 90% of what you hear about how an engine should be is wrong. Anybody (short of a few) that writes books wouldn't be writing books if they really knew what they were talking about and the people that really know wouldn't sell their information. I'll try to compile a list for you guys when searching for a machine shop to do headwork and whatever else.
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Info about Head porting
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