K & KR Head Questions

Racing K Models

K & KR Head Questions

Postby LDB » Tue Sep 03, 2019 1:26 pm

What do you Harley experts think the reason is for the area above the intake valve being recessed, or deeper in other words, all across the transfer area from the intake valve to the shelf on the K and KR heads as compared to the exhaust side? Do you think that maybe the area works like a channel of sorts to better direct the air flow toward the cylinder when the intake valve opens? Or do you think it has something to do with helping the flow toward the exhaust valve on the exhaust stroke?

Also, what is the advantage of the shelf running at an angle on the KR head as compared to it being straight across on the K head?
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Re: K & KR Head Questions

Postby 55panman » Tue Sep 03, 2019 1:50 pm

LBD the main reason for a recess about the valves on a KR is to give more valve to head clearance room for a cam that has more lift.
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Re: K & KR Head Questions

Postby LDB » Tue Sep 03, 2019 2:04 pm

Thanks. So if that's the reason then why is it necessary to keep the recess so long and uniform all the way across to the shelf on the K head as well as the same design but angled farther across the slanted shelf on the KR?
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Re: K & KR Head Questions

Postby 55panman » Tue Sep 03, 2019 2:27 pm

Same thing as in a port. You don't want to tighten up an area and restrict the flow. Not sure about the effect of the angles.
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Re: K & KR Head Questions

Postby JohnF » Tue Sep 03, 2019 3:28 pm

It’s all about volumetric efficiencies. Getting the best/most charge into the cylinder, then getting as much of the spent gases out of cylinder in the time allotted. Since “flathead” engines have the valves/ports located to the side of the power cylinder, it is more difficult for the gases to enter and exit combustion chamber/power cylinders efficiently. Hence the development of “overhead” and “hemispheric” valve and combustion chambers where greater efficiencies are achieved. There have been many variations of shaping the combustion and flow characteristics of internal combustion engines to maximize volumetric efficiencies. The one you see on these components is one of those.

Back in the 1970’s, Honda was able to achieve an amazing 98% volumetric efficiency @ 18,000 RPM in the racing prepared six cylinder version of their motorcycle engine. That’s a lot of gases moving in and out of power cylinders! That was a naturally aspirated engine as well. Turbochargers? That’s a complete different design theory and another topic altogether.
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Re: K & KR Head Questions

Postby Ferrous_Head » Tue Sep 03, 2019 4:21 pm

Yeah, turned out overhead valves weren't just a passing fad.

Hemi heads ain't all that good ether. Pretty sure the Honda's at that time were pent roofed.

Mind you Taglioni tried 4 valve cylinders at one time and said they "weren't worth the bother"

And I'm the guy who told Wella that IBM PC's were a "useless toy".
"I know only too well the evil that I propose, but my inclinations get the better of me."
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Re: K & KR Head Questions

Postby LDB » Tue Sep 03, 2019 4:50 pm

JohnF wrote:It’s all about volumetric efficiencies. Getting the best/most charge into the cylinder, then getting as much of the spent gases out of cylinder in the time allotted. Since “flathead” engines have the valves/ports located to the side of the power cylinder, it is more difficult for the gases to enter and exit combustion chamber/power cylinders efficiently. Hence the development of “overhead” and “hemispheric” valve and combustion chambers where greater efficiencies are achieved. There have been many variations of shaping the combustion and flow characteristics of internal combustion engines to maximize volumetric efficiencies. The one you see on these components is one of those.

Back in the 1970’s, Honda was able to achieve an amazing 98% volumetric efficiency @ 18,000 RPM in the racing prepared six cylinder version of their motorcycle engine. That’s a lot of gases moving in and out of power cylinders! That was a naturally aspirated engine as well. Turbochargers? That’s a complete different design theory and another topic altogether.


Thanks but my question has not quite been answered. Naturally, it's all about volumetric efficiency as it is with the performance of any internal combustion engine. So let me ask this way:

If the combustion chamber did not have that long recess above the intake valve and the chamber was just uniform smooth across its width but with the same clearance above the intake valve as it has with the recess, would the engine still perform as well as it does now if the compression ratio was still the same?

Do you think that maybe the recessed area works like a channel of sorts to better direct the air flow toward the cylinder when the intake valve opens? I can see that the ridge of the recess is higher than the valve when it opens but I'm curious if the incoming air from the valve tends to hang on the edge of the recess as the air flows toward the cylinder to fill it.
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