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Post by justboosted on May 21, 2016 1:41:51 GMT -5
I am porting the d port head off of my svo and need some help from people who have done it. Obviously, we are humans and not cnc machines. My question is, when smoothing out the bowl/throat area is it a huge detriment to not get every bowl exactly the same (I mean like mirror images of each other)? I have been cutting on this thing for two weeks trying to get every single turn and transition the exact same and I think, to a degree, I am being too anal. I have read many threads and the like that of people that have ported their heads in 40 or so hours. I have gotten them all pretty close, but not perfect. Can anyone say anything about flow number difference with minor port shape mismatches and how this effects power? Thanks for the help.
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Post by Stinger on May 21, 2016 1:55:54 GMT -5
If you're not a pro that's being paid to do this then it certainly doesn't have to be perfect. Obviously you don't want it to be WAY off (like so far off we could see it in pics) but you're never going to get it perfectly flowing the same in every port (even with a flow bench) since there are two different port designs, and the intake manifold that's bolted to it is not going to flow the same in every port either so even if the head was perfect, flow through the engine would not be perfectly even.
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Post by justboosted on May 21, 2016 12:31:05 GMT -5
Alright thanks. How far off can the flow numbers be between cylinders ? I don't want one cylinder making like 10 hp more than another and beating the hell out of the main bearings because of it.
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Post by Stinger on May 21, 2016 21:48:55 GMT -5
Well, the head is only part of the flow equation. For it to make 10 more hp you've got to have that much more flow through the intake manifold/intake port, exhaust port, and header/manifold. For this to happen you'd have to line up the best flowing of each of those items all on the same cylinder which is highly unlikely to happen. The other thing is cylinders "share" some of the airflow (especially with a gutted upper intake) which helps to even out flow cylinder to cylinder.
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Post by justboosted on May 22, 2016 20:19:13 GMT -5
Am I correct in thinking that the middle intake ports on the head don't flow quite as well as the outer ports? I just ran some area calculations (using area of an oval) and the middles came out to approximately 1.635 sq in and the outers are approximately 1.792 sq in. I'm just curious on how to cut these. I figured, apart from taking the casting off, I will not work the floor of the port. I will cut the roof and the wall adjacent to were the air enters from the lower manifold. These should be the high flow areas, correct?
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Post by Stinger on May 22, 2016 20:31:00 GMT -5
Straight ports (in the middle) are slightly better than curved ports (on the ends) since the air doesn't have to turn to get to the valve.
The ports don't need to be enlarged much at all (or none at all) at the manifold to head interface. Just whatever minimal work is needed to match the port shape/size. All the "magic" is in the short turn radius, around the valve stem, in the bowl area right near the seat, and in the chamber to unshroud the valve when it opens.
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Post by justboosted on May 22, 2016 23:04:18 GMT -5
When you say to match the port shape size do you mean match the size of the middle ports to ones at the end?
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Post by justboosted on May 22, 2016 23:06:53 GMT -5
Or do you mean to match the lower to the ports on the head?
Thanks for all the help
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Post by Stinger on May 22, 2016 23:55:44 GMT -5
I just mean to make the ports the same between the intake and head so there is no obstruction between the two...a smooth transition. Like gasket matching but using the head as the "gasket" shape you're matching the intake to. Do not under any circumstances actually use a gasket to port the openings as it's much too large.
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