snot35 Posted January 28, 2009 Report Posted January 28, 2009 Why on earth do you have 38mm ports?? Quote
Mybowlcut Posted January 28, 2009 Author Report Posted January 28, 2009 (edited) Why on earth do you have 38mm ports??I bought the engine off someone who bought it off someone else who ported and shaved the head. Is 38 a bit much? Edited January 28, 2009 by Mybowlcut Quote
Mybowlcut Posted January 28, 2009 Author Report Posted January 28, 2009 I just rang up a local parts store and they said the size of the 3K gasket intake ports is ~23mm... I probably should have phrased my question better... I want to know that if I enlarge the 4K gasket intake ports in the same way as the picture I posted in my first post, that it won't overlap the intake port on the head and restrict it (the flow). Quote
snot35 Posted January 29, 2009 Report Posted January 29, 2009 Considering the valve is probably 38mm at the most then it probably is too big. All the texts that I can find on porting, and any work I've done seem to indicate around 30-32mm wide. Are you talking width or height? 3K gasket should be around 25mm. 4K would probably be larger, but still possibly around 27mm. Different manufacturers appear to have different sizes. If you want to use that head, you're probably going to have to trim the gasket yourself and match it to your manifold and ports. Quote
KE30_KE35_KE55 Posted January 30, 2009 Report Posted January 30, 2009 (edited) Considering the valve is probably 38mm at the most then it probably is too big. All the texts that I can find on porting, and any work I've done seem to indicate around 30-32mm wide. The bigger port the better flow its that simple, just because a exhaust valve is say 27mm you wouldn't run a 27 mm exhaust system. I have a standard big port head I can measure for you. in pic standard big port at bottom Edited January 30, 2009 by KE30_KE35_KE55 Quote
snot35 Posted January 30, 2009 Report Posted January 30, 2009 The bigger port the better flow its that simple, just because a exhaust valve is say 27mm you wouldn't run a 27 mm exhaust system.I have a standard big port head I can measure for you. in pic standard big port at bottom It's not even nearly that simple. Define better flow. Quote
Taz_Rx Posted January 31, 2009 Report Posted January 31, 2009 You don't reall get any more flow from a big port head just because they have bigger ports. They've still got the same small valves below them. :y: Quote
philbey Posted January 31, 2009 Report Posted January 31, 2009 Possibly a bit better. Has anyone dealt much with bigger valves in a K head, I asked my builder about the 5K and he said there wasn't enough room in there. Quote
Redwarf Posted January 31, 2009 Report Posted January 31, 2009 Possibly a bit better. Has anyone dealt much with bigger valves in a K head, I asked my builder about the 5K and he said there wasn't enough room in there. Yes. I have a K head (K, not 3K bp) which had the big ports but small valves. (AFAIK, Doug will come in shortly to correct me. :y:) We put in valves from a later head and also changed the valve stem seals to the later variety as well due to the earlies being.... lets say a bit substandard for the application it was being used for. I've just re-read your post, we're you talking about a K head or a 5K head? You can also fit Gemini valves in at a pinch....... Quote
KEI069 Posted January 31, 2009 Report Posted January 31, 2009 You don't reall get any more flow from a big port head just because they have bigger ports. They've still got the same small valves below them. :y: the whole point of having bigger ports is to flow more air/gas, so you put a bigger cam in to hold the 'same size' valve open longer and TA DA , more flow Quote
Felix Posted January 31, 2009 Report Posted January 31, 2009 Rob :y: Bigger ain't necessarily better when it comes to getting performance out of a motor. This applies to exhaust selection, cam, carbs, portwork, etc.. A properly matched package suited to the intended application is what it is all about to get the best allround performance. Peak HP means shit all. Area under the powercurve is where it's at. Hogging out the ports on a 5k is going to kill all it's low-mid torque. It won't really affect the top end as the valve size is the governing factor for flow. As stated there isn't much meat between the valve seats to fit in larger seats and valves. Offset valve guides is the go to fit in larger valves if you have a few bucks. Check out the attached image showing flow in various sections of a mini engine intake port. Quote
KE30_KE35_KE55 Posted January 31, 2009 Report Posted January 31, 2009 You don't reall get any more flow from a big port head just because they have bigger ports. They've still got the same small valves below them. :y: You are correct it is unfortunate that the valve size can't be changed by much, so we look to improve swept volume by other factors such as porting, aspiration or a cam to hold the valves open longer. Every little bit helps. Quote
philbey Posted February 2, 2009 Report Posted February 2, 2009 (edited) I've just re-read your post, we're you talking about a K head or a 5K head? You can also fit Gemini valves in at a pinch....... Bit of both really - I know 5K's are difficult to do, I was just wondering what the various valve changes people have made to various different generation K motors? Edited February 2, 2009 by philbey Quote
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