Head porting

[Brandon]

Explain how much, porting a boosted cars cyclinder head really helps, and or what to do to make it help. Will porting a turbo head for a larger CFM truely be more benefical unlike say porting a NA head where more CFM often means less power?

 

This article is interesting.http://mototuneusa.com/think_fast.htm

[evan9381]

i know a guy out in CO who had his head ported and had a 3 angle valve job on his 2003 turbo tiburon and picked up about 20WHP. theres dyno sheets somewhere, i just gotta find em. i think he paid about 600 total for labor/porting/etc

[Brandon]

What else did he change? Did he really pick up 20 hp from just the porting, or did he get some power from another bolt on, or more boost. Point it how differnt is NA porting then boosted, because the goal is to try and get 760 torr into and engine with NA, and if the head is ported properly you often can get slightly better, mabye like 780 torr. But with a boosted car your forceing in 760 torr in reguardless, so wouldnt opening up more flow help? The there is exhuast gas pressure, which affects teh turbos response rate...So many more things to talk about.

[Brandon]

Wow I usually thought bigger was better until I read all that..

It makes a lot of sense. Bigger can be better, but you need to make the motor more efficent to use the better or larger intake charge, but just like that says, raise the port volumes, you lower the intake velocity, which means you really are sucking in to much at the wrong time, and speed. So it can change the effiecny of the suck, squish, bang, and blow, which is also why we adjust timing in a sense. I want some more ideas!!!!

[Mensan]

You want port velocity to be high. If your port is too large, you lose velocity. Try and blow out birthday candles through a snorkel. This is similar to a large port on a low revving engine. Try and breathe deeply through a drinking straw. This is similar to a small port on a high revving engine. Velocity decreases tremendously. You want to match the port velocity with the cars RPM band.

[Brandon]

You want port velocity to be high. If your port is too large, you lose velocity. Try and blow out birthday candles through a snorkel. This is similar to a large port on a low revving engine. Try and breathe deeply through a drinking straw. This is similar to a small port on a high revving engine. Velocity decreases tremendously. You want to match the port velocity with the cars RPM band.

 

Which is why your going to have to make a sacrifice, somewhere in your intake track. Because if you go for top end, higher power, you certainly will have lower rpm intake ommisson, and lower power. But if done right you can record more HP throughout, with larger gains in the higher rpm range.

[Buck531]

Not that it helps much since my car was NA when I had this done, but oh well.

 

 

I had my heads milled .030, 9 angle valve job, gasket matched the ports and so on. I also put on a much thinner head gasket and added small headers. Went to the dyno and gained 35 hp.

 

http://bucky.kicks-ass.net/pics/enginemods/heads1.jpg

 

http://bucky.kicks-ass.net/pics/enginemods/heads2.jpg

[Brandon]

Not that it helps much since my car was NA when I had this done, but oh well.

 

 

I had my heads milled .030, 9 angle valve job, gasket matched the ports and so on. I also put on a much thinner head gasket and added small headers. Went to the dyno and gained 35 hp.

 

http://bucky.kicks-ass.net/pics/enginemods/heads1.jpg

 

http://bucky.kicks-ass.net/pics/enginemods/heads2.jpg

 

Then thinner head gasket and milling raised the compression I assume? 9 angle valve job.wow. Thats awesome for an NA head, but that dosent leave you much of a valve seat for a boosted car. Are you still using this head on your car now?

 

Who ever said americans with muscle cars are dumb

http://www.highperformancepontiac.com/tech/0211hpp_part2flow/

discuss

[Buck531]

Then thinner head gasket and milling raised the compression I assume? 9 angle valve job.wow. Thats awesome for an NA head, but that dosent leave you much of a valve seat for a boosted car. Are you still using this head on your car now?

 

"

Stock L36 and L67 head gasket thickness is .062". Running a thicker gasket will decrease compression, while running a thinner gasket will increase compression. For every .006" change in gasket thickness you will add or subtract approx .1 points of compression. " - Taken from a site that does 3800 stuff.

 

I'm guessing with the thinner gasket, and the milling of the heads, I was somewhere around 10.3ish:1 compression. Stock on my old NA motor was 9.4:1.

 

As for still using those heads, nope. I sold them along with every other mod I had on the car to a guy in Alabama.

[Guest powers]

Often times on NA heads they will add material and reshape the port for velocity.

On a boosted app the idea is completely different. You now need flow as the velocity of the air is dictated by back pressure and the CFM that your blower/turbo can move.

 

You can port the living crap out of a head and turn a motor into a dawg if the rest of the motor does not have deep enough lungs to fill that huge tunnel you just made.

 

Brandon also mentioned another thing about valve seat surface. This is something you need in order to seat that valve properly and able to hold back 30 psi of pressure.

[SPLN SUX]

I have yet to see a port job that didnt add power. However, i have seen polishing jobs that have reduced power.

 

When you do a polish job, you want to polish like the first 60% of the port. If you polish the port too much, fuel can actully collect and condensate inside the port cause puddling backfires, and erratic lean/rich conditions. Ive only seen this happen a couple of times, but they were all engines that the fuel is injected into the air stream as opposed to directly into the combustion chamber.

[SPLN SUX]

I've never heard of fuel puddling problems on a polish job, just some jibberish how incoming air won't turbulate (is that a word?) off the smooth surface and mix with the fuel in the chamber as well..

 

Yea that can happen too. The air wont be turbulant enough to atomize the fuel properly before the burn.

[Guest powers]

I've never heard of fuel puddling problems on a polish job, just some jibberish how incoming air won't turbulate (is that a word?) off the smooth surface and mix with the fuel in the chamber as well..

You never polish a surface thay a fuel air mix will flow over. The smooth surface will collect the fuel and seperate it from the air casing puddling and possible backfire.

[Guest powers]

I have yet to see a port job that didnt add power. However, i have seen polishing jobs that have reduced power.

It has happen on a few mustang heads I have seen. Bigger is not always better.

[Brandon]

As far as polishing goes, there is a static field on the intake side that is formed when the air travels through, so a polish wont help, and you also want some surface roughness, because you want to try and dictate the "swirl" of the air, to lessen the turbulence, and creat a better air pump. And you want to polish the combustion chamber and the exhuast ports to a mirror finish if possible this will help reduce the chances of detonation, and poor exhuast flow, because the polish will lessen the amounts of carbon build up, which are detonation catalysts.

 

Thinking in terms of a boosted car, I am still skeptical of just opening it up, It seems to make sense because I am not stricken with velocity as much as an NA person would be. What I am trying to get at is, I think that more focus should be done on the exhuast side of a turbo head then the intake. Any one else (I have some theories, just amuse me)?

 

And also what about sharpe edges in the combustion chamber on a boosted car? That screams pre ignigition, but how much do you really want to change the shape of the chamber? Do you mainly want to just smooth the edges or take them back to no mans land?

[Guest powers]

Thinking in terms of a boosted car, I am still skeptical of just opening it up, It seems to make sense because I am not stricken with velocity as much as an NA person would be. What I am trying to get at is, I think that more focus should be done on the exhuast side of a turbo head then the intake. Any one else (I have some theories, just amuse me)?

 

And also what about sharpe edges in the combustion chamber on a boosted car? That screams pre ignigition, but how much do you really want to change the shape of the chamber? Do you mainly want to just smooth the edges or take them back to no mans land?

 

As to the first part on a forceed induction car you port the head in reverse of what you would on an NA car. On an NA you shoudl clean up the intake path to clear an obstructions and to make transitions easier including the short side radius of the port. On the exhaust side you open it up pretty far to make it draw the spent gasses out of the chamber. On an forced induction car you do the reverse. You open up the intake side to allow more flow becasue volicity is no longer dicated by the port rather the device being use to force the air in. On the exhaust side you want to keep velocity up so you want to work the port and polish it as smoothly as you can to reduce carbon build up. On a SC car you open the exhaust port up more than you would on a turbo's car. So there differences to each set up. Most of the the stock castings are so bad all the gains are just from the clean up.

 

On the combustion chamber you should be removing any sharp edge in the chamber. Many people remove any pre ignitors that are cast into the head. You should open the head to match the gasket or unshroud the valves and smooth it out to a mirror finish to reduce carbon bulid up which can casue hot spots.

[Trouble Maker]

And you want to polish the combustion chamber ….to a mirror finish if possible this will help reduce the chances of detonation…

 

AFAIK polishing any metal will reduce its coefficient of thermal conductivity. This means that during any combustion process less heat will be absorbed by the metal, and it will also give off less heat. This will also lead to a more efficient process overall, as far as energy in/energy out. Whether this is a good thing or not, I'm not sure. I would venture to say that your EGT's would rise, but this is just a by-product. I would want to say yes because heat not absorbed into the combustion chamber should be more heat to expand the combustion chamber. Just mainly trying to explain why polishing stuff on the inside can reduce the propensity for detonation. I say ‘can’ because it depends on why you were detonation in the first place.

 

Reason polishing metal will reduces it’s coefficient of thermal expansion.

 

Think about it just like friction. Before, at a microscopic level, the surface might have looked like this

 

/\/\/\/\/\/\/\/\/\/\

 

Now it might look something like this.

 

/\------------/\----------

 

A lot less surface area in the second one.

[Guest powers]

The polishing is to remove high/hot spots and reduce for carbon build up. The effect you speak of Jesse is not the reason why the detonation is occuring but is true non the less.

[Mensan]

the surface might have looked like this

 

/\/\/\/\/\/\/\/\/\/\

 

Now it might look something like this.

 

/\------------/\----------

 

A lot less surface area in the second one.

 

 

Even less in this one:

 

^___^

 

KEKEKEKEKEKEKEKEKE

[Brandon]

Eli I saw you at winking lizards monday night. True story.

 

Back on topic, Powers makes an interesting idea, of opening the intake much more, so that more air can be forced, since we do not have to guide it in like a NA car. Are there some equations out there that can help you get an idea of how far to go, or is it more or less trial an error. Because to have an effective air pump, you need to suck in a much as you can, without forceing any back out, and this is really impossible in a real situation, but the idea is to get as close to this ideal value as possible. Here is another thing I keep reading about, and many people here it all the time, import head porting really isnt all that hyped up, this is mainly due to better desgins then most domestic stuff, I mean there is a reason imports are easy on fuel, they are more efficent, less energy wasted. So really with import heads there isnt as much changes that should be made? I guess for a mild *street* port you really just need to port match, and do minute abouts of porting to the intake, and a little more aggressive on the exhuast, and some polishing thrown in there. But for say a race port, do you go as far to start looking at cut aways of intake ports and figure out how they can be reshaped? What would be an ideal shape? Why? What would be an ideal exhuast port shape? Each motor is slightly differnt, but similar at the same time.