porting and polishing should be done if your looking to make more power. but if you do, do it yourself i would suggest being very careful and use a gasket as a guide. and in this case bigger is not always better but if your going with a turbo say like a KA85R(i believe this is the one my friend has on his pulsar gti-r) you want as big as possible. but say one not as big then a smaller port would be desired. if your not added anything to make a big difference then i would suggest just a polish, as porting is a time consumeing process. but thats just my opinion

 

what about intake porting, are there any kits for that too?

 

As far as intake porting you can use the same kit to increase the diameter size of the TB port, the same goes for the ends of the runners. I wouldn't worry to much about honing the KA runners, IMO I think the plenum and long runner combination sucks tobegin with, and actually causes about a 20~30 torque and HP drop off in the high end. Porting the TB port and and the ends of the runners should add a bit more kick in the high end.

 

What about increasing valve size, what would be an optium size increase to get peak performance without a major risk of cracking the head.

 

Well I wouldn't worry so much about cracking the head. What you should worry about is valve size diameter and how effective will it be in making swirl.
For an intake valve I wouldn't increase it any more than .010 over stock, the exhaust could be increased more to .020 overstock.
I would only have a proffesional do 3angle or 5angle valve work, it is a bit more complicated.

 

Are there any altenatives to porting the intake like a better aftermarket N/A intake?

 

if you increase the valve size you might cause more problems than you are trying to fix. if your valve goes to big you could cause a problem called valve shrouding. if your valve is too close to the cylindar wall by the increased diameter, the cylindar wall itself could block and disrupt incoming or outgoing gasses, decreasing flow in the process

 

I don't know why everyone worries so much about the damned port size. If you are running N/A and not boost then stock heads are more than enough that you need. You just need cams to move your power band around to where you want it.

Think about it this way: if you are running 2.4L displacement then your engine can only pump 2.4L of air per reveloution. Divide that by two because in one 360 degree rotation only 2 cylinder actually do any work. You are still physically limited to 2.4L of volume. Does it make any sense to make the ports flow any more air than the cylinders can draw in? I would worry about port design and making velocity as high as possible. Velocity is what is going to get you good numbers. It is responsible for creating the turblence that suspends the fuel in the mixture making sure you have a good mix. Lets take a look at some numbers.

first covert 2.4L to cubic inches: 2.4 X 60= 144 cubic inches
so if anyone has read Corky Bell's "Maximum Boost" you already know this equation: (cid*rpm*.5*ve)/1728 the ve is volumetric efficency, or how well your engine pumps air. Now it is wise to use a conservative number like .85 or 85%. If you have done some mods you could go up to .9 but I would go too much above that. For my example I will be using .85.
144*7200*.5*.85=440640
440640/1728=255
Now that means at 7200 rpm our engines only flow 255 cfm! divide that by 4 for your number of cylinders and you get just below 64 cfm!! why do you need a port that will flow200 cfm (for example) if the motor is limited by physics to only move 64 through that head? Lets use our heads (exuse the pun) and make better use of what we have instead of following the norm.

 

Beyond anything you just said... The KA engine is rated one of the most ineffecient, anemic engines for todays performance engines. Even by older standards an FJ24e was much more effecient in making power and used a Hemespherical dome head, instead of the more effecient pentroof design head that the KA uses.
There are other factors that are also figured beyond Cubic Feet Per Minute. You also need to calculate air density. The length of the intake runners actually heat the intake charge expanding and burning air before it even makes it to the cylinder chamber. Less air gives less power (obviously), this also allows for less air to be compressed during the compression stroke. So the main purpose of intake porting is to increase air VOLUME, not really what ever it's flow rate is. People misinterprete the 2 differences between air volume and flow rate. Proper porting is to optimize swirl for atomization, while increaseing air volume.

So would you rather be moving 10 o2 molecules at 64cfm, or would you rather move 4 o2 molecules at 64cfm. That my friend is the purpose of head porting. Honestly I would rather help people how to redesign the crappy plenum and build a new one with shorter runners, (obviously more than half the people here don't know how to weld).

 

i agree with you on the runner/intake idea, but that is a totally different topic than the heads. The cfm rating is the volume rating. That is a volumetric measurement of how much air you can physically fit into or through that space in a given amount of time. The air density matters, but is not an issue once air reaches the port on the head. At the port opening there is nothing you can do to improve air density, but you do have control over how much air you can move and how fast you can move it. Or flow rate vs. velocity.
I do agree that the stock KA motor is very asthmatic. Going off of your example of the 200 hp for under 1K it is easy to see that a good portion of that is made up through moving air in and out of the head more efficiently with intake and exhaust componets. I am willing to bet you could get another 10 or more out of a ITB setup that was tuned right all on stock cams. But what about having a nice tapered system all the way to the choke point right before the valve to increase air velocities to near supersonic speeds. Wouldn't that help with atomization more that increases the flow rate 100cfm over stock. I am sure everyone has seen the break in secrets thing from motoman, but he also did a special on high velocity intake ports that actually makes more power with stock head configs. obviously if you turbo it is different. What it boils down to is that there is a ton of dead space in your port runners that causes air to become stagnant and lose velocity. By decreasing the size of the runners a certain amount you are increasing air velocity without sacrificing any of your volume or cfm. i want to try it as soon as my business gets off the ground and I can afford some side projects.

 

You just answered what I told you. You and I both agree that runner length is much too long. The air that could of measured @64cfm is burned in the intake runner, (air becomes less dense therefore isn't taking what you think is volume matched to 64cfm), (you still don't have what are flow bench numbers for the KA head either).
An easy way to prove this theory correct is by increasing the diameter size of the TB which is equally matched to it's CFM rating.
It has been noted that increasing TB size by 2mm will increase HP across the board by 4% (and this is even after people say that the TB size does not need to be increased for the KA).
Beyond any debating porting is good by any means that you have chosen to disagree upon. Casted heads (Iron or Aluminum) come with many imperfections that decrease flow. It has been proven numerous times that shaving these imperfections increase swirl and atomization (this is all considered part of the porting process). Hey but then again this debate means nothing without dyno results. Many reputable shops such as Rebello Racing back up head porting for the KA engine. They have pioneered it for over 15years. Any one can come to these boards and bring up a calculation for CFM ratings. But then you deal with bolt on devices that work to enhance the improvement to smog emissions, and restrict what you think are those flow numbers you calculated, and how well they perform when sucking up hot exhaust gasses..
Like I say "don't knock it until you try it......."

 

Well not really. Ferrea has flow benched the DOHC head and has calculated the following information for the DE head. This information is quoted directly from www.240sxmotoring.com.

Since your name is KAsingle C I am assuming that you have a sohc. In this particullar instance I would actually increase the valve diameter of the exhaust valve with the SOHC to a .040 increase in size (equal to 2mm ) Shure there are instances of valve shrouding if a valve becomes to large. Curtain space can become to large to maintain any type of swirl especially when it comes to using a 16valve DOHC. But in the instance of the KA SOHC there is alot more room for one single exhaust valve. Even due to the fact that there is NO curtain on the exhaust port side. Due to the pitch and angle that comes with the sohc head being hemispherical.
For the DOHC engine using natural aspiration I would only increase the diameter size of the exhaust valves and I would leave the intake valves alone.

 

BigVinnie, if you could come up with a good design for a better intake for the N/A DOHC KA24 I could get somebody to weld one up custom, I've been searching for a better N/A intake but have yet to find one it would be awesome to get one bc the stock one is kinda of the poor design. Get back to me on this bc I'm really interested.

 

here is a link for DIY 9000 RPM SR20DET Head I havnt done this but i know someone that has and it worked wonders.

http://www.nico club.com/articles.php?id=238409
take the space out from between o and c and it will work. this forum must not like competition it wont let me post about other forums.

 

If you need template you can use the gaskets from the exhaust and intake for port maching. The best way is to p&p your intake and exhaust (if factory) for the best flow.