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Why on earth do you have 38mm ports??

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, 200917 yr by Mybowlcut

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).

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.

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, 200917 yr by KE30_KE35_KE55

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.

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:

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.

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.......

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

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.

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.

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, 200917 yr by philbey