head porting how much and how far

[jdmawd]

the time has come to knock the cob webs of this stock head i have in my basement, and send it out to be ported. from doing some semi in-depth research on head porting. i have found that a slight clean up, and port match is the best idea for my current setup and needs. the head will include, most likely hks 264/272 cams 1 mm oversized valves, and at some point a sheet metal intake manifold from polk. my ultimate question, is a slight clean up and port match and valve job enough for my setup. or is more head work needed or recommended that im overlooking. Any help would be appreciated. also who have you guys done business with, for head porting and who has good prices?

 

[NosLaser]

...the head will include, most likely hks 264/272 cams 1 mm oversized valves, and at some point a sheet metal intake manifold from polk. my ultimate question, is a slight clean up and port match and valve job enough for my setup. or is more head work needed or recommended that im overlooking. Any help would be appreciated. also who have you guys done business with, for head porting and who has good prices?...

I am going to make some recommendations here that some people may or may not agree with. When it comes to head porting, the following is the work I like to perform, and also some of the things I like to avoid. First things first, you want to pay your MOST attention to the bowls and the combustion chambers. The ports flow quite a bit as it is, so not much work at all needs to be done there. Make sure the machinist pays special attention to the bowls and the combustion chambers, because that is where all of your power is. Have the combustion chambers polished polished polished. Remove all hot spots, and just SLIGHTLY smooth the step on the edge of the quench area. Do NOT grind down the step at all as you will lose combustion efficiency, just simply smooth any sharp edges to alleviate any hot spots. On the intake side, simply remove the casting marks, and slightly enlarge the ports. On the exhaust side, I like to do a nice D port for maximum velocity, and to help negate reversion. There is a brief moment when the intake and exhaust valves will be open at the same time, and it's going to want to suck the exhaust gases back into the cylinders/combustion chambers. This phenomenon is called reversion. (That is VERY basic explanation, as entire books have been written on reversion.) The idea behind a 'D' port is this. The top of the port is going to have the highest flow area, so that is where you want the port to be most free-flowing. The bottom is a lower flow area, so by leaving that 'step' on the bottom of the port (the bottom of the 'D' shape, picture the D laying on it's side) isn't going to hurt flow as much, but it WILL help stop exhaust gas from creeping back into the combustion chamber. This is also why I like the port the exhaust manifold slightly larger than the exhaust port because that extra 'step' will block those exhaust gases. Ever heard of 'stepped' headers? This is what they are, and what they do.

Now on to the oversized valves. The idea behind oversized valves is to create a bigger door and therefore, increase overall flow capacity. Great on paper. However, unless appropriate work is done on the combustion chamber, you could be simply cutting off your nose to spite your face. Most jobs I have seen done with oversize valves came out with the valves being even more shrouded than before, thus losing quench efficiency, thus, losing power. The trick is to re-work the combustion chamber so that the two theories work WITH eachother instead of against eachother, which is a very precise science. Let's talk a second about quench area, burn efficiency, and flame travel. Basically, with the dished pistons in the 4G63, you have this big volatile ball of stored energy in the form of compressed air and fuel. (Once you can picture in your mind that this ball of energy actually takes up space, and is not just 'air' then you will better understand what is going on inside of your combustion chambers.) The piston starts to make it's way up the cylinder, carrying this ball of energy. You want a nice tight quench area (read: a smaller combustion chamber) to keep the energy tight and compacted, and ready to explode. The farther you get that ball of energy from the spark plug (flame) the less powerful that part of the explosion will be. When the plug fires, the flame is only going to travel so far, so you want to make as good of use of that small flame as possible to light off that entire ball of energy. (And there you have burn efficiency.) Back to the valves. With shrouded valves, and an improperly shaped combustion chamber, you are going to lose a lot of that burn efficiency. The explosion will be less powerful, and leave behind more unburnt fuel and exhaust gases, which aggrevates the reversion process even more, which causes crappy old exhaust gas to try and be burned again, and you can see the snowball effect from here. Now, which one do you think is worth more power? A huge powerful explosion lighting off the cylinder, or 1mm more of air flow? See the point here? To properly install larger valves, you must re-shape the combustion chamber and properly unshroud the exhaust valves without compromising combustion chamber efficiency and quench area.

This right here is why it BOILS MY BLOOD when people cheap out on building their motors. Your typical guy has no clue how much power there is to be had with a properly built motor, and attention to things inside of the motor like I just described. Perhaps people contemplating a motor rebuild will benefit from this post, and understand just how much science is going on inside an engine from the very moment you twist that key. Sorry this post got so long, but good luck.

Regards,

 

[jdmawd]

you want to pay your MOST attention to the bowls and the combustion chambers. The ports flow quite a bit as it is, so not much work at all needs to be done there. Make sure the machinist pays special attention to the bowls and the combustion chambers, because that is where all of your power is. Have the combustion chambers polished polished polished. Remove all hot spots, and just SLIGHTLY smooth the step on the edge of the quench area.

So the above and have the exhaust side ported in a d shape, is what im looking for. you suggest skipping the oversized valves, just do what you stated above with cams and that should be fine?

 

[NosLaser]

That is correct sir.

Regards,

 

[L2RTSiAWD]

Wow. I love all this info. I guess I will not be getting oversized valves. That just save me 300 bucks. I don't know anyone will will be as careful and through as you suggested they need to be. I just copied that whole post into a word doc for future reference.

 

[jdmawd]

Originally posted by NosLaser
That is correct sir.

Regards,

cool, you are the man thanks.

You must be logged in to view this image or video.

 

[L2RTSiAWD]

Do you recommend that for a 2g head also?

 

[NosLaser]

Absolutely. The 2G heads actually flow better than the 1G's when ported properly. A little bit better combustion chamber design, and slightly reshaped ports.

Regards,