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Gasket matching cylinder head exhaust ports

I'm trying to decide if I'm going to run a head I bought. It was a great deal and I got it for less than the parts alone would have cost. But, the exhaust ports were matched to the size of the gasket.

In some of the reading I've done it seems it's best to leave the port floor alone. But, I have found a few threads where people opened up the exhaust ports on 4g63s. Unfortunately, no before and after results were available.

Any thoughts? Should I gasket match the exhaust manifold and run the cylinder head? Or grab a spare head I have, clean the ports a bit, and have everything installed in it? Any experiences, theory, and opinions would be great.
 
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rmontalvo23

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A potted heat is a good thing if you have other mods to support the difference in exhaust flow. If your car is stock besides the head then I wouldn't run it. But if you have full exhaust, bigger turbo, fuel management, etc then you should benefit from port matching the exhaust manifold to the head.
 

dmj

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^^ A potted Heat /ubbthreads/images/graemlins/dunno.gif do you mean a ported head?
 

alansupra94

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I can't see how port matching could be a bad thing /ubbthreads/images/graemlins/dunno.gif
 

cheekychimp

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He's talking about having to start hacking away at the port floor in order to get the port to match the existing gasket/manifold. A lot of people have stated that once you port the floor of the head side, the head is essentially junk.

Edit: Actually I just realized he is talking about exhaust side ports in which case I concur, I can't really see any negatives here. Arguably some loss of velocity which might affect spool up and bottom end but more flow equals better top end. Depends what you are looking for I guess.
 
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Just to be clear, I am talking about if the gasket matched exhaust ports in the cylinder head will affect anything. The cylinder port floors had to have material removed to match the gasket.

I mentioned the exhaust manifold because I will need to gasket match it, so it won't block the ports in the head.

As far as mods go, there are a few. Click the link in my sig for modifications.
 
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Andy_S

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Having the manifold larger than the exhaust ports creates a step to prevent reversion. I would personally gasket match the exhaust manifold but not run a head that has the floor ported.

You can refer to Corky Bell's "Maximum Boost" for more on the topic of reversion.
 

RayH

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There was one shop I talked to a while back that added dowel pins to align the head and exhaust manifold better after port matching. I guess it depends on how much slop you have between the studs and manifold bolt holes.
 

Well, I've found that gasket matching is a bad thing.

Here's the head I'm going to run now. I didn't even use a cutter on it. Just cleaned things up with some sanding cartridges. I left alone any surface that was fairly smooth and didn't have any casting goobers on it.







I also opened up the exhaust manifold to be about 2mm bigger than the head ports.



And the beautiful stainless valves from the overly ported head.



I've got some brass valve guides from another spare head that I'm hoping can be reused in this one. Hopefully all this turns into a functional head. /ubbthreads/images/graemlins/smile.gif
 

curtis

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You can port the floor on either side just not the short turn radius. I always paint the surface with dykem use a crushed used gasket, center it up and scribe and take it right to the edge on the intake and exhaust side of the head and do the same to the intake and exhaust manifolds. The thing is is to do it gradually at an angle and not all the way to the valve seats. Hogging one out kills velocity but doing it properly keeps the air from having turbulence which is as bad as a hogged out port. I read an article in a mustang magazine once and all they did was pull the intake and gasket match to dispel all the myths. They dyno'd the car, pulled it, gasket matched within about an inch of the head mating surface not going up in the runner washed it up and centered the gaskets so they weren't hanging into the port and re dyno'd . 302 picked up 38hp and can't remember the torque but it went up as well. Only thing I ever ported that had a before and after dyno number report was a buddies old supra with a 7m and Na power. I gasket matched the intake to the head, cut out a phenolic spacer, removed all the casting flash first, then ported with a cutter, then cartridge rolled it smooth until all the ports matched with the spring gauges then went back through it with a rough cartridge roll roughen it up to help atomize the fuel. Car picked up 68hp and I believe 48ft lbs of torque but part of that torque was the 1 inch spacer keeping things cooler and adding an inch of runner.

Having a step around a mating surface creates turbulence on the edges and what it does is change the flow characteristics and gives the misconception of a smaller physically sized port which on a bench might skew the numbers flow numbers. Its like myths of the polished mirror port yea looks damn good and flow bench proves it with big numbers but you can run that port then pull it down to roughen it up some and the car will go faster because not only does air pass in the runner but so does fuel.


Here's an example. My pool has a 4K gallon per hour pump. (BS but thats what its rated at) Anyway goes into a valve turns 90 degrees into a shower head looking sprayer. It also has a screw on attachment for a hose. So one day I took a radiator hose and cut a 90 and attached it then started gluing up PVC pipe pieces. then the last is a piece of aluminum thin wall thats about 1/2 inch and a foot or so long. Sprayed up in the air but was ugly, Kids liked it but not what I wanted it only went up about 12 ft or so. I then took it back off and took a honeycomb piece out of an air meter. Yes hacked a 2nd gen meter for my pool. Took a razor blade and cut the honeycomb to the correct dia and inserted it in to the largest tube and put it all back together. Now the water is almost transparent and goes to about the gutter on the upstairs so about 20 ft as long as the filter is clean and new . Have to redo it or clean out bugs ever so often but still works great. Proof with pressure being constant velocity can improve with laminar flow.


sh*t can't talk anymore this is turning into fluid dynamics and Barnes doesn't allow it. /ubbthreads/images/graemlins/grin.gif
 

mitsuturbo

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Nice work, bkatter. That's the way i know (from working in a machine shop) to do a head properly in order to help and make sure you will not hurt things. That looks good.

Good guides are cheap. Check out engnbldr on ebay. He's well known to provide good head parts. What valves are those? The intakes look to be backcut, but not the exhaust. Is this correct?
 
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Barnes

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Quoting curtis:
sh*t can't talk anymore this is turning into fluid dynamics and Barnes doesn't allow it. /ubbthreads/images/graemlins/grin.gif



Wayyyy ahead of you.

You got any pics of this pool setup? I've got some issues with this sentence: "Proof with pressure being constant velocity can improve with laminar flow. "
 

curtis

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I'll have to do it after the pool is cleaned out, looks like antifreeze right now because I waited to late in the summer to top off the salt and is full of those damn sweet gum seed pod MF's but yea, Later in the spring I'll get my buddy over here with his street race video camera and I'll do a before and after with the honeycomb and put it on you tube.
 

Quoting mitsuturbo:
Nice work, bkatter. That's the way i know (from working in a machine shop) to do a head properly in order to help and make sure you will not hurt things. That looks good.

Good guides are cheap. Check out engnbldr on ebay. He's well known to provide good head parts. What valves are those? The intakes look to be backcut, but not the exhaust. Is this correct?



Thanks man.

I definately was trying to help without hurting anything. I think the other head would have hurt the low end a lot. Hopefully I'll get some new found efficiency without hurting my powerband at all.

I didn't know engbldr did guides. Looks like around $60 for bronze ones. Not bad at all. The valves are Ferrea and they are backcut on the intake side.
 

curtis

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Man it isn't that hard to grasp. I've learned alot working on aircraft, fluid classes in school, reading on my own but one of the biggest thing I learned was from an old gearhead almost 2 decades ago. He told me this and I take it to heart and think of it every time I start cutting on a intake head etc. "Air has mass and volume just like water yes compressible but if you treat this like your flowing water through it you'll go fast". I sometimes even get out a waterhose and see what the port acts like with water exiting around the valve seat. or how it acts in a header or manifold as it exits.

I ported my buddies weld bend header flange just the other day. The header was built with the small sized T3 flange not the bigger sized gasket. The collector looks as if it was for the larger. This left a step on the inside around a 1/4 inch on the front and rear. We angled the inside and blended it in and gasket matched it. After I finished the first one I blew out the shavings with a air nozzle and as I went from port to port the sound was a very noticeable change between the first and the other 3. This continued to change from port to port as I did the steps for the other runners. Car will pick up but it also got a rebuilt turbo now, bigger gate and other changes so I'll never know exactly how much.
 

Barnes

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I gotta be honest Curtis. I think your comparison to the laminar water flow in fountains is not applicable to this situation. My biggest problem is your comparison of an unconstrained external flow to a constrained internal flow. Also, I'm not entirely sure the reason your personal fountain example goes higher is due to laminar flow being 'better flowing'. I think it has more to do with the interaction of the laminar water column with the surrounding air. Essentially the laminar flowing liquid does not disintegrate because there is no internal turbulence causing water molecules to break free from the stream. This keeps the water column cohesive. From some other videos I watched, it would seem that since the water is not turbulent, the actual surface tension of the water helps keep it together as well. Since the water stream does not disintegrate, it does not disassociate in to smaller, and independent bits of water that will incur much more aerodynamic drag per unit of volume than a cohesive stream. Effectively, the more cohesive stream is more aerodynamic, and thus can go higher and/or farther. It does not mean it has more hydrodynamic head, I.E. more pressure backing it up.

As for the cylinder head discussion, I would bet lots of money that the flow exiting the combustion chamber is turbulent long before it enters the valves and exits through the ports. I would also bet that the velocity of the gas in the port is high enough to induce turbulent flow on its own. I would also assume that any laminar flow would be transformed into a turbulent flow by many of the sharp edges and turns the flow encounters on its way into the exhaust port. Namely the exhaust valves. Generally in fluid flows, a flow that has induced turbulence will remain so unless the Reynolds number falls to a very small number. And in this situation, I doubt it happens. Also, turbulent flow on it's own does not cause great pumping loses. The velocity of the gas flow is much more important. In fact, the relative roughness of a pipe in an internal flow reduces as a flow goes from laminar to turbulent. Since in a turbulent flow so much mixing occurs near the surface of the pipe, actual pipe roughness becomes much less relevant than in the case of a laminar flow where water is near the edge of the pipe for a very long time.

The thing to remember with fluid flows is that turbulent flow is not what you should be concerned about, especially in engines. You should pretty much assume you are dealing an a turbulent flow. That's okay. The thing you want to avoid is unnecessary steps, edges, contractions, and expansions. ALL of those features will cause a flow, in this case gas exiting the exhaust valves, to lose dynamic head(energy), and thus velocity. This lose of dynamic head is basically an increase in pumping resistance. By avoiding these features, you reduce your pumping resistance, and increase horsepower by allowing the exhaust gas to leave more freely.

With this in mind, I'm very skeptical about the exhaust side port work that I see. Mostly because of the exhaust manifolds that will be bolted to these heads. I'd have to measure, but it seems to me that on a 2g exhaust manifold the pathway leading away from the cylinder head decreases in cross sectional area as it approaches the collector. So it makes very little sense to me to expand the exhaust port, and expand the entrance of the exhaust manifold, only to have it decrease again. Keep in mind, that it has been a LONG time since I've seen a bare cylinder head next to an unported 2g exhaust manifold. IF there is a step between the two, it would be beneficial to remove this step. Even if the cross section area expands, and then reduces again. A smooth expansion/contract is still superior to a sharp step. Especially if it is unavoidable due to inherent geometry.
 
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