amateur porter, porting my head

[SlowSpyder]

The surface has to be some what smooth but with a rough finish to it. Its purpose is to help with atomization of fuel. Polishing the metal to a some what mirror finish may look nice but makes the fuel atomize like crap and creates alot turbulance which decrease flow. Your right when it you said that polishing will prevent the fuel from grabing the metal but that allows the fuel molecules to accumulate and not properly atomize to make fuel become potential "droplets" instead of the very fine mist. 60 grit is about right, 80 grit is about the max I would go on an intake port. 80 grit is good for an exhaust port but ive seen people go all out on the exhaust ports to almost a mirror finish(makes the engine's shit come out faster )

 

[compression]

and thats exactly what we used, 1" 60 grit flapper wheel for the intake side, and a 1" 80 grit flapper wheel for the exhaust ( to smooth it) to port it we used a dremel

 

[SlowSpyder]

and thats exactly what we used, 1" 60 grit flapper wheel for the intake side, and a 1" 80 grit flapper wheel for the exhaust ( to smooth it) to port it we used a dremel

Thats the best way to smooth out the port is with the flapper wheel the only problem is the flapper or flap wheels are kind of expensive. The other alternative is to use the flapper stick with flapper paper(emery cloth)

 

[1fast97gsx]

Without a flowbench nobody knows if you made your car faster or slower. Bigger is not always better. Remember, bigger = less velocity, smaller = more velocity. What would you rather have? Exactly, depends on everyones individual setup.

 

[rob99eclipse]

alright, now let me ask this. i'm about to rebuild the motor in my girl's 98 spyder gs. I'm doing a head swap from a 1G 4g63 and want to just improve flow and maybe give her a little better flow. I already opened the exhaust ports to within about 1mm of the exhaust all the way back to the individual exhaust chambers after the valves. I used 80 grit sandpaper to smooth out where i ported out the chamber. My question is should I leave the intake side alone since this is going to be a daily driver or polish those chambers also?

 

[MrPikolo]

You would want your intake ports decently smooth, not rough. Remember, not only are we dealing with multi port injection, but a turbo charged engine, so atomization is NOT a problem. As far as how much to port, I wouldn't take to much off judging by your mods. People run 10s in the 1/4 on stock heads. I would just gasket match and smooth them out a little.

 

[sonicnofadz]

I would just like to add that BIGGER is always better in terms of top end horsepower, as long as you have an engine and turbo capable of flowing enough air to utilitize the extra volume + area. If you do not plan on making booku power (300-400 whp) maybe smaller ports will be a better choice. Enlarging the intake and exhaust ports will allow higher flow, but at the same time it will slow down the velocity of the intake and exhaust streams. The same kind of theory applies to turbine housing A/R numbers (smaller = faster spool and lower total power output, larger = slow spool and higher total power output). Small intake and exhaust ports are actually BETTER for low power engines, since the smaller ports actually inject the air into and out of the engine at higher velocities. If you try to use the same dinky head on a high horsepower engine, those smaller ports become a restriction, at which point it would be advantageous to do some enlarging of the ports (resulting in higher horsepower numbers).

 

[92awddsm]

I would just like to add that BIGGER is always better in terms of top end horsepower, as long as you have an engine and turbo capable of flowing enough air to utilitize the extra volume + area. If you do not plan on making booku power (300-400 whp) maybe smaller ports will be a better choice. Enlarging the intake and exhaust ports will allow higher flow, but at the same time it will slow down the velocity of the intake and exhaust streams. Small intake and exhaust ports are actually BETTER for low power engines, since the smaller ports actually inject the air into and out of the engine at higher velocities. If you try to use the same dinky head on a high horsepower engine, those smaller ports become a restriction, at which point it would be advantageous to do some enlarging of the ports (resulting in higher horsepower numbers).

Almost all of what you said is wrong. You spend 7 yrs standing in front of a porting bench grinding and then flowing using a depression probe and you will understand what I mean. Until then, dont answer unless you know for fact.

In short, your post is misinformation.

 

[sonicnofadz]

My machine shop has a flow bench (JAM)? I have always been told once an engine reaches a certain power level, that it needs to have larger ports (smaller ports act as a bottle-neck in the flow) Is this incorrect?

 

[92awddsm]

My machine shop has a flow bench (JAM)? I have always been told once an engine reaches a certain power level, that it needs to have larger ports (smaller ports act as a bottle-neck in the flow) Is this incorrect?

Increasing the cc's of a port can either help or hurt performance. If done properly by someone experienced, usually you will see some increase in performance. For the most part on a dsm head, you can smoothe the short turn radius, blend the bowls, and gasket matchhead and manifolds, and it should support well over 500 whp without making it big. This applies to both 1g and 2g heads. The smaller ports on the 2g head actually flow almost as much as the 1g. The difference in flow characteristics comes from entry angle, not port size.

 

[sonicnofadz]

Angle of entry is important, but according to the laws of fluid dynamics, volume (cross sectional area)is also very important. Perhaps someone would like to go above 500hp, maybe 1200hp? The shear amount of fluid flowing through the head (at this power level) would almost require enlarging the ports (and perhaps the valves + seats themselves). It is too bad no one has any before and after flow bench numbers with their work?

 

[92awddsm]

Angle of entry is important, but according to the laws of fluid dynamics, volume (cross sectional area)is also very important. Perhaps someone would like to go above 500hp, maybe 1200hp? The shear amount of fluid flowing through the head (at this power level) would almost require enlarging the ports (and perhaps the valves + seats themselves). It is too bad no one has any before and after flow bench numbers with their work?

You make a good point but unfortunately, it doesnt apply to what the op is aiming for.

And before we spend gobs of time battling back and forth, you do realize how old this thread is, right?

 

[GVR4592]

Angle of entry is important, but according to the laws of fluid dynamics, volume (cross sectional area)is also very important. Perhaps someone would like to go above 500hp, maybe 1200hp? The shear amount of fluid flowing through the head (at this power level) would almost require enlarging the ports (and perhaps the valves + seats themselves). It is too bad no one has any before and after flow bench numbers with their work?

Velocity is more important than overall flow, if the port is too large velocity will suffer. I think most shops do before and after flow bench work, but there is no way they'll disclose that info. I know Polk did flowbecn testing on the stock head and posted it on here a couple years ago.

 

[Street Surgeon]

Cutting the guides in the port will not hurt anything at all. Most full race port jobs include removing the bottom of the valve guide. It has been done for ever and never caused any issues. It does, however, increase flow in and out of the combustion chamber. Someone else stated that it creates some oiling issues but that was more of an uneducated guess than anything based on fact. The valve seal is still intact and in the same location so nothing has changed there. Just make sure the bottom of the guide has been deburred before reassembly. If not, you run the risk of hanging a valve open.

Exactly.

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