AirSpeed VW Community Forums
Technical => Engine Tech Forum => Topic started by: Black-Back on July 30, 2004, 03:19:55 PM
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Surfin' again, and I came accross this link, click me (http://www.directmotion.com/head_porting/cnc_head_porting.htm), my ? is this, how much porting is too much? if you remove the valve guide boss don't you run the risk of dropping a valve? or maybe poping the guide out? I know you need flow but isn't blending the air/fuel just as important, doesn't the valve guide boss act kind of like a venturi inside the head to speed up the air/fuel around it and help mix it all up?
Mike the Brain picker.....
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I don't think flow is as important as velocity, my ports aren't overly big but I am getting decent power out of them.
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Ok so velocity is good, but how do you achieve that?is it like a venturi effect, how do you gain velocity, as well as flow?
Ohhhhh, wait a minute....does the intake manifold act as a venturi itself? if thats the case, as the mixture compresses at the bottom of the manifold
it speeds up like in the carb, but you need an area for it to open up, do you want the port in the head to start a certain size and then open up bigger through the port, to create that venturi effect, to gain velocity, or do you want the port to be the same size as the valve all the way so that the venturi effect is completed in the combustion chamber? or am I talking out of my ass?
Anybody else have any other imput??? have a look at the link I put up, obviously the valve guide boss has been removed, but is there a limit? I mean, does this much work reduce the strength or the cooling of the head? in any way shape or form? Or, wouldn't creating a small teerdrop shape above the guide itself allow the mixture to flow more smoothly around the guide?
Just picking your brains.....
Mike :wacko:
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So, whats your feeling on this James???? :blink: :blink: :blink: :blink:
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Best person to answer would be Darren - I'm just reguritating what I have heard. Hey Mike have you been on the STF? Lots of good info in the speed and drag forum.
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Whats this?????
What is STF??
Maybe offer a link.......
Mike
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www.shoptalkforums.com
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Wow , those CB heads are looking good. I talked to a guy in cal. that ran his car at dyno day. It made 180hp to the rear wheels. Here's what he told me was in it.
78.4 stroke
94 bore
k8 cam
cb 044 wedge port's untouched out of the box.
he also said he sent the heads to be cut for more compresion (he wanted 9.5 I think) but they screwed up and cut way to much so he ended up increasing the deck hieght way up to compensate. It still made 180hp.
I'm sure flow and veocity are equally important as is the nature of the air fuel mixture in the combustion chamber. Every thing from the carb to the tail pipe will have an effect on this. And it will never be perfect , just better and better combination of compromises. There are guys that can watch and study the combustion as it happens in a motor. Don't know if anyone's ever done it with our aircooled vw's but I just find all this stuff fascinating and allways wish I could have been closer to this kind of industry.
check out http://theoldone.com (http://theoldone.com)
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Cool link...will make for good reading on rainy days