High Flow, Low Cost, 8V Cylinder Head Project
11-03-2013, 01:29 PM
#106
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Thread Starter
It depends. Smooth ports are great if the air doesn't need to turn. If it has to turn, it can separate very easily, creating a vena contracta (essentially a choke point from stagnant air) A rough port will disrupt the boundary layer, and prevent the air from separating as easily.
So if the port is tight and has a small radius, you don't want it to be very smooth. If it is darn near upright, and the air has to turn very little, smooth is probably better.
While the 951 has some of the best ports ever because of the shape of the head, it is best to err on the side of keeping it a tad rough. The extra flow from a perfect surface is minimal, but the penalty for separation is HUGE.
So if the port is tight and has a small radius, you don't want it to be very smooth. If it is darn near upright, and the air has to turn very little, smooth is probably better.
While the 951 has some of the best ports ever because of the shape of the head, it is best to err on the side of keeping it a tad rough. The extra flow from a perfect surface is minimal, but the penalty for separation is HUGE.
11-03-2013, 01:43 PM
#107
Drifting
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I am hopeful that you are able to dyno test the extrude honed intake to let me see how much money I wasted after reading Harry's post. 
However, all the new composite intakes are very smooth bore on the inside and have many curves, so I am still hopeful as to positive results.
However, all the new composite intakes are very smooth bore on the inside and have many curves, so I am still hopeful as to positive results.
11-04-2013, 06:06 PM
#108
Race Car
I am hopeful that you are able to dyno test the extrude honed intake to let me see how much money I wasted after reading Harry's post.
However, all the new composite intakes are very smooth bore on the inside and have many curves, so I am still hopeful as to positive results.
However, all the new composite intakes are very smooth bore on the inside and have many curves, so I am still hopeful as to positive results.
11-05-2013, 12:02 PM
#110
Race Car
Eric, I think you'll be fine. Had to go back and re-read for the context. Extrude honing from my experience (which is minimal with it) is great for cleaning up cashing flash and stuff. It generally doesn't give a polished like finish. I think to get a really, really polished surface, you'd have to run multiple passes, which would remove more material at turns, and make the resutls bad. But overall, I think you'll probably see a small improvement. My "too smooth" caution was really that some folks will port and polish the heck out of intake ports, and if the short side is too tight, air will separate.
11-05-2013, 12:53 PM
#111
Drifting
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Whew!!! Thanks Harry, guess we will find out soon, Shawn has it for testing. I put the most likely too smooth LR intake on the FL car and took this one off. I just liked the way it looked, really no other reason. If the EH intake really has any benefits, I might through it on the CA car later.
11-06-2013, 11:07 PM
#112
Rennlist Member
What you'll find, with enough flow bench testing, is that it's all about the shape of the port rather than the surface texture. Work on the shape!
Keep in mind that head porting is really 2nd semester stuff because it's not intuitive. There are people that do nothing but cylinder heads and some of them can really boost the power. Sometimes you're way ahead if you farm some of the work out. Cylinder heads, in my opinion, fall into this category because it's so easy to go backwards.
Keep in mind that head porting is really 2nd semester stuff because it's not intuitive. There are people that do nothing but cylinder heads and some of them can really boost the power. Sometimes you're way ahead if you farm some of the work out. Cylinder heads, in my opinion, fall into this category because it's so easy to go backwards.
11-06-2013, 11:28 PM
#113
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Thread Starter
What you'll find, with enough flow bench testing, is that it's all about the shape of the port rather than the surface texture. Work on the shape!
Keep in mind that head porting is really 2nd semester stuff because it's not intuitive. There are people that do nothing but cylinder heads and some of them can really boost the power. Sometimes you're way ahead if you farm some of the work out. Cylinder heads, in my opinion, fall into this category because it's so easy to go backwards.
Keep in mind that head porting is really 2nd semester stuff because it's not intuitive. There are people that do nothing but cylinder heads and some of them can really boost the power. Sometimes you're way ahead if you farm some of the work out. Cylinder heads, in my opinion, fall into this category because it's so easy to go backwards.
I think I am going to spend a bit of time on this and see what I can do. No matter the outcome, I am sure I will learn a lot and to me that is the fun of it.
11-07-2013, 02:48 AM
#114
Rennlist Member
What you'll find, with enough flow bench testing, is that it's all about the shape of the port rather than the surface texture. Work on the shape!
Keep in mind that head porting is really 2nd semester stuff because it's not intuitive. There are people that do nothing but cylinder heads and some of them can really boost the power. Sometimes you're way ahead if you farm some of the work out. Cylinder heads, in my opinion, fall into this category because it's so easy to go backwards.
Keep in mind that head porting is really 2nd semester stuff because it's not intuitive. There are people that do nothing but cylinder heads and some of them can really boost the power. Sometimes you're way ahead if you farm some of the work out. Cylinder heads, in my opinion, fall into this category because it's so easy to go backwards.
11-07-2013, 07:14 AM
#115
Race Car
Shawn, if you can section some heads, you'd learn a whole lot. Was able to do that with some old Ford 2.3L heads several years ago. Also, to Michael's point, he is absolutely right. There are some exceptions, basically older cast iron heads such as older American V8's. But for anything resembling a modern head (and that includes ours), tread very carefully!
03-24-2014, 10:06 PM
#116
1st Gear
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Stock 2.7l head
Hey...since your original intention was a 2.7l head, do you know if the company mentioned (SI) makes valves that will work in stock 944 2.7l heads? I need 3 exhaust valves (40mm, 944 105 418 00) and 1 intake valve (48mm, 944 105 409 03). Looking for options here so I don't have to spend over $700 on 4 valves...
Thanks,
Bob
Thanks,
Bob
03-25-2014, 12:22 AM
#117
Rennlist Member
Thread Starter
Hey...since your original intention was a 2.7l head, do you know if the company mentioned (SI) makes valves that will work in stock 944 2.7l heads? I need 3 exhaust valves (40mm, 944 105 418 00) and 1 intake valve (48mm, 944 105 409 03). Looking for options here so I don't have to spend over $700 on 4 valves...
Thanks,
Bob
Thanks,
Bob
03-20-2015, 02:00 PM
#118
Three Wheelin'
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Has anyone run any valves this large? I am looking into doing 50mm valves on my 2.7 head, which with the increased bore size, leaves some room to play.
03-21-2015, 07:28 PM
#120
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Thread Starter