Cylinder Head Discussion
On The Tree
Joined: May 2004
Posts: 103
Likes: 0
From: TEA
For a full out nitrous engine make the exhaust port mostly match the header pipe, for most anything else, don't do it.
BTW, we can flow a square exhaust port with a round pipe and then flow it with the pipe that has been squashed down square to match the port and it flows less.
BTW, we can flow a square exhaust port with a round pipe and then flow it with the pipe that has been squashed down square to match the port and it flows less.
Don't mind me asking, but have you arrived at a conclusion of what would cause that?
I don't see how two ports that matched each other would flow less than two ports that did not-either way, in or out. I think if that was the case, flowing a head with a pipe would cause less flow, not more. I don't in any way consider myself a pro, or pioneer in the industry, but I'm not finding much sense it that.
The only thing that I can think of that could be the cause of such findings, would be the big miss-match of the angles at which the runners would be entering the header flange and primaries. Instead of a straight shot or smooth transition, the exhaust is haveing to hit a sharp agle where the primary begins. I think that's why 'D' ports flow more than the standard oval ports-it's a more obtuse angle, causing less back-pressure in the runner. A very easy transition between the head and primaries can be made out of aluminum.
If it is true, I guess I'll see it first hand. In any case, the results and information will be added to this thread to put out any future fires on the same subject.
I don't see how two ports that matched each other would flow less than two ports that did not-either way, in or out. I think if that was the case, flowing a head with a pipe would cause less flow, not more. I don't in any way consider myself a pro, or pioneer in the industry, but I'm not finding much sense it that.
The only thing that I can think of that could be the cause of such findings, would be the big miss-match of the angles at which the runners would be entering the header flange and primaries. Instead of a straight shot or smooth transition, the exhaust is haveing to hit a sharp agle where the primary begins. I think that's why 'D' ports flow more than the standard oval ports-it's a more obtuse angle, causing less back-pressure in the runner. A very easy transition between the head and primaries can be made out of aluminum.
If it is true, I guess I'll see it first hand. In any case, the results and information will be added to this thread to put out any future fires on the same subject.
Exhaust ports I do cylinder head development work on special projects as time permits.
An exhaust port will always flow better with a test pipe in place. Notice I said test pipe, not header. The pipe tends to straighten the flow and create a draft effect in the tract.
You generally want a mismatch at the exhaust face, the header should be larger than the head port, especially with a long duration high overlap cam. This to help reduce reversion - back flow of exhaust gases into the combustion chamber. Some ports may indeed flow slightly better with a smooth transition from head to pipe but you will loose power due to reversion.
If you look at the exhaust port from the side if it were cut down the middle you could plainly see that the short side (floor) of the port is considerably shorter in overall length than the long side (roof). Thus the exhaust gases need to travel further along the roof of the port than they do along the floor to reach the exhaust face of the head. One way to get the floor and roof exhaust gases to arrive at the port face at the same time is to reduce the cross section along the roof "D" shape thus increasing the velocity of the exhaust gases along the roof. Some heads respond better than others to the "D" shape which is why the shape is not universal for exhaust ports. That's why you need a good flow bench and a lot of time to experiment.
Steve Demirjian
An exhaust port will always flow better with a test pipe in place. Notice I said test pipe, not header. The pipe tends to straighten the flow and create a draft effect in the tract.
You generally want a mismatch at the exhaust face, the header should be larger than the head port, especially with a long duration high overlap cam. This to help reduce reversion - back flow of exhaust gases into the combustion chamber. Some ports may indeed flow slightly better with a smooth transition from head to pipe but you will loose power due to reversion.
If you look at the exhaust port from the side if it were cut down the middle you could plainly see that the short side (floor) of the port is considerably shorter in overall length than the long side (roof). Thus the exhaust gases need to travel further along the roof of the port than they do along the floor to reach the exhaust face of the head. One way to get the floor and roof exhaust gases to arrive at the port face at the same time is to reduce the cross section along the roof "D" shape thus increasing the velocity of the exhaust gases along the roof. Some heads respond better than others to the "D" shape which is why the shape is not universal for exhaust ports. That's why you need a good flow bench and a lot of time to experiment.
Steve Demirjian
Originally Posted by NoseUpChromeDown
Don't mind me asking, but have you arrived at a conclusion of what would cause that?
I don't see how two ports that matched each other would flow less than two ports that did not-either way, in or out. I think if that was the case, flowing a head with a pipe would cause less flow, not more. I don't in any way consider myself a pro, or pioneer in the industry, but I'm not finding much sense it that.
The only thing that I can think of that could be the cause of such findings, would be the big miss-match of the angles at which the runners would be entering the header flange and primaries. Instead of a straight shot or smooth transition, the exhaust is haveing to hit a sharp agle where the primary begins. I think that's why 'D' ports flow more than the standard oval ports-it's a more obtuse angle, causing less back-pressure in the runner. A very easy transition between the head and primaries can be made out of aluminum.
If it is true, I guess I'll see it first hand. In any case, the results and information will be added to this thread to put out any future fires on the same subject.
I don't see how two ports that matched each other would flow less than two ports that did not-either way, in or out. I think if that was the case, flowing a head with a pipe would cause less flow, not more. I don't in any way consider myself a pro, or pioneer in the industry, but I'm not finding much sense it that.
The only thing that I can think of that could be the cause of such findings, would be the big miss-match of the angles at which the runners would be entering the header flange and primaries. Instead of a straight shot or smooth transition, the exhaust is haveing to hit a sharp agle where the primary begins. I think that's why 'D' ports flow more than the standard oval ports-it's a more obtuse angle, causing less back-pressure in the runner. A very easy transition between the head and primaries can be made out of aluminum.
If it is true, I guess I'll see it first hand. In any case, the results and information will be added to this thread to put out any future fires on the same subject.
__________________
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Steve Demirjian
Race Engine Development
Oceanside, Ca.
760-630-0450
web: www.raceenginedevelopment.com/
e-mail: race-engine-development@***.net
Well explained. Thanks Steve.
I'm not after some crazy flow numbers here, hence the reason I said header and not test pipe. I'm looking for real world. I'm going to try and have my heads benched with not only the header, but also half of the exhaust system in place. I dont' see how you could get closer to real than that with a flow bench. I'm doing this prior to the designing/grinding of the cam for obvious reasons. If there's another 5rw right there at the flange, I will find it...It's just a terrible disease I guess...
Again, thanks for your input-much appreciated.
I'm not after some crazy flow numbers here, hence the reason I said header and not test pipe. I'm looking for real world. I'm going to try and have my heads benched with not only the header, but also half of the exhaust system in place. I dont' see how you could get closer to real than that with a flow bench. I'm doing this prior to the designing/grinding of the cam for obvious reasons. If there's another 5rw right there at the flange, I will find it...It's just a terrible disease I guess...
Again, thanks for your input-much appreciated.
Staging Lane
Joined: Sep 2004
Posts: 73
Likes: 0
With a turbocharged application, what is your opinion on the "step" for reversion? I would think that you would want to do all you could to keep the velocity up, so you would want to have the transistion as smooth as possible, but at the same time, the backpressure in the header for a turbocharged car will be much higher. Also, turbo cams tend to have less overlap. What do you guys think?
--Bryson
--Bryson
Teching In
Joined: Oct 2004
Posts: 3
Likes: 0
So in review:
1. Don't trust internet flow numbers.
2. Inspect the parts list on the heads chosen to make sure they are up to spec.
3. Consult a reputabl head porter for recommendations, and expext to have to have them finished by him/her.
4. The intake manifold should not be a hindrance, but may not be an asset.
5. The right heads with the wrong valves is still the wrong head.
6. You an have the right runner velocity or the right flow, but it is very rare to get the velocity and the flow to match.
7. CNC is good, but porters are better.
What is the check for the porter who sells a cheapy head knowing he can port it to where the "good" head is? Don't you gain something by just going with the quality head in the first place? The porter is able to show you big delta, but relative to the cost of the better head there's no corresponding delta in value?
1. Don't trust internet flow numbers.
2. Inspect the parts list on the heads chosen to make sure they are up to spec.
3. Consult a reputabl head porter for recommendations, and expext to have to have them finished by him/her.
4. The intake manifold should not be a hindrance, but may not be an asset.
5. The right heads with the wrong valves is still the wrong head.
6. You an have the right runner velocity or the right flow, but it is very rare to get the velocity and the flow to match.
7. CNC is good, but porters are better.
What is the check for the porter who sells a cheapy head knowing he can port it to where the "good" head is? Don't you gain something by just going with the quality head in the first place? The porter is able to show you big delta, but relative to the cost of the better head there's no corresponding delta in value?
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On The Tree
Joined: Jun 2010
Posts: 120
Likes: 2
The better the fuel automization the more power you will have (without fuel vaporization) . So the porter need to be careful when porting . porter may improve the CFM but he may hurt the fuel mix which will lead to lower power. it is called wet flow testing .
sorry, english is my second language.
sorry, english is my second language.
