Don Terrill’s Speed-Talk

There are a few old 4V port divider related threads.. but decided to open a new thread anyways..
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I've seen many different design 4 valve port dividers.
Most are quite short, and ports are oval shaped. On some heads the ports turn to round shape after dividers.

Is there any reason to not have 'long' port dividers, and keeping the ports in round shape untill the end of divider?
Example: instead of 30mm dividers there would be 90mm dividers, when the ports are 100mm length.

Some older BMW S -serie engines, like the S14 have that kind of port dividers.

Major changes in any Intake port shape need to be done where the port area is expanding as in the approach to ,and thru the valve bowl.
The reason why you might ask!

High flow rates go hand in hand with high velocity, and high speed air will not follow any change in direction of greater than some 15 degrees with out a flow loss Dependant on the velocity seen.

To get a air mass around a bend of more then 15 degrees you need to slow it down which means letting it expand into a larger port area.

Here's a picture of a set of sb Mopar heads I ported last month.
Notice that besides the increase in port area on the reworked port but also notice the far more rectangular port shape now in place as compared to the stock Oval!

Had I not changed the port shape to get better control of the larger air mass now moving thru the port I would have never achieved the 25% flow gain that I did at such low valve lifts like I did.

In regards to the port divider wall I like there leading edge to be round , not knife edged , and as to there overall lenght I find that if I need to even up the velocity better between the roof and the floor then I will grind back the floor of the divider shorter if I feel the ports have enough lenght to work with from the start.

The old 4v rotex singles had 2 carbs and 2 exhausts, so completely divided and were very fast. I think the added weight and packaging problems add up fast so it doesn't make sense to do that on multicylinder setups.

When I port 4v heads I always end up shortening the divider just because opening up the port ID means less wall is left between. It's got nothing to do with what might be the optimal length for the separator, at least not on the stuff I do.

Yes, those single cylinder / twin carb and / or headers engines are quite interesting.
Haven't seen or heard of many of them.

The cylinder head, what I'm planning has originally quite short dividers on intake side. Divider is wide and is rounded well.
Ports aren't very big, and the 'upper floor' is almost completly flat.

What I'm going to use the cylinder head, is to use it as a "test cylinder head".
Idea is to get rid off all possible compromises. No need of being built compact size, or emissions need to be taken account.
Only power, or BMEP to be precise. The engine is for me mostly just for testing, or developing as I like to say.

How I see "ideal" (though, in reality there's no such as thing as "ideal" - but I hope you understand what I mean) intake ports, including the divider, is two pipes and smooth short turn before valve. The pipes form the divider between them.
The start of the port should be made round, to fit the throttle body (invidual throttle bodies).
So, the divider would also be quite long compared to what most cylinder heads have.
I do not think it's a bad thing, but it is not all about the flow as I've understood. Two very different heads can flow the same amount on a flow bench but produce very different power curves and peak power / torque.

@mag2555 -

Here's a picture of a set of sb Mopar heads I ported last month.
Notice that besides the increase in port area on the reworked port but also notice the far more rectangular port shape now in place as compared to the stock Oval!

Interesting.

I would have made it more rounded, but those kind of cylinder heads would probably need a lot work on ports, so there would be any benefit on doing more rounded intake ports.

Ehhh.. this all would depend the design of the particular port;some you have to make all available port area and others just make nice entry to valve seat.
If doing the sharp divider you must be careful to make it equal (unless intentionally making port bias to make swirl)
Round divider is easier to make but for maximum flow the sharp is the way to go..
Have a flowbench,many heads to try with and finally have someone pay for the flowbench/dynotime to decide what design is best compromise.
Customer always ask for "as much power as possible!!"

They are called the charge point Interesting on fuel injection system the noodle is pointed the charge point

sbcharlie wrote: ↑Wed Nov 08, 2017 5:03 pm They are called the charge point Interesting on fuel injection system the noodle is pointed the charge point

What would that be in understandable English?

I’m the injection noozle

Sorry about my spelling I’m in Mexico and trying to use my phone. I was trying to say the injectors are directed to the charge point. It interesting to see how manufacturers alter the length. A very interesting cylinder head is the 4 valve Yamaha 250 they have very long port runner.