Topic: Low Buck 750 Cylinder Head Project

[MRieck]

K/early F intake tracts 30mm.....F2 32mm

[TurboD]

The current F2 head that I am working on, they are measuring right at 1.22 which equals a 30.98mm.

[scottly]

I measured a K7 spigot at 28.4 mm today (1.118")
1.22" equals 30.988mm.

[TurboD]

I measured a K7 spigot at 28.4 mm today (1.118")
1.22" equals 30.988mm.

I corrected it. Thanks Scottly

[scottly]

the ol play do makes life fast and easy for guide shapes

Hey johno, I prefer modeling clay to play-doh. 

[HondaMan]

Although hard to test on a flow bench unless you can rig up a "valve operator" like the ones Jerry Branch Flowmetrics used to have in the 1970s: adding some pocket(s) above the intake valve also helps as speeds increase above 5000 RPM or so. This allows the incoming air mass to compress into a space, which both reduces the pulsing vacuum levels in the intake tract and provides a positive pressure available above the valve at the moment of opening. It significantly changes the way the carbs mix, which is the first clue: they run so rich that the needles have to become thicker to work at all between 4000 and 7000 RPM.

We never found the 'practical limit' to how big these pockets could be, until we ran out of head to remove. The biggest ones, used on the midget cars at 14k-16k RPM engines (sans trannys) were cut open so much above the intake valves that the open space resembled a mushroom shape. The tradeoff for this extreme seemed to be lost tractability in the ranges below 5k RPM, however, and hard starting.

[MRieck]

Side by side comparison. First pics Honda F2 OD spigots, second F1 OD. Obviously, F2 is much larger than F1, thus the need for different insulators.

[MRieck]

Although hard to test on a flow bench unless you can rig up a "valve operator" like the ones Jerry Branch Flowmetrics used to have in the 1970s:

What do you mean by "valve operator"?

[Roach Carver]

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[MRieck]

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Great!

[HondaMan]

Although hard to test on a flow bench unless you can rig up a "valve operator" like the ones Jerry Branch Flowmetrics used to have in the 1970s:

What do you mean by "valve operator"?

The article I read about this was named something like: "Discovering free turbocharging", and it was a combination engineering article and college (some college in CA in those days) science project. What they did: the made a cam rotator (electric motor, about 1.5 HP) that rotated the cam to open and close the valves on an OHV head, and measured the resulting flow through the intake valve, on the upstream side, and compared that to the measured flow on the downstream (chamber) side. The idea was to try to quantitatively measure the compression that was happening, due to air mass flow and its speed, and turn it into something Detroit engineers could use. The numbers were impressive, showing clearly that adding open volume above the intake valve (aka "pocket porting") caused a significantly lower suction moment in the chamber if:
1. The Pocket was increased in volume, and
2. the speed of the flow in the intake tract was kept higher, rather than lower (i.e., the cross-section of the throat should be smaller coming from the carb zone, leading into a larger pocket), and
3. the intake tract was made longer than the length of the venturi that was doing the mixing (i.e., longer than the length of the carb body), which plays right into the long intake runners of the SOHC4 designs.

In the article, Branch Flowmetrics was mentioned as being involved. They came up with interesting calcs and formulas from the work they did. It (the phenomenon) proved to be somewhat predictable by design, and was therefore heralded to become a help toward more efficient, smaller car engine designs in the future (which would have been the 1980s designs, leading to the 1990s engines).

(Sadly, when I went thru a divorce in the mid-1970s, she took that box of my 'stuff' with her, and I never noticed it for years afterward, so I don't have the article any more.   )

[johno]

Boys , that is exactly what this bike had when I had a look, Vance and Hines Pro 1. Kwaka
long narrow intake leading into a pocket that was the size and shape of an egg. It was the cool thing to do then.

Ironically it is not the most popular method now as it takes lots of dyno hours to get it right , carbs, manifols, port and exhaust..............lots of dyno time.

I feel a positive of that type of port combo is with the small port usually results in good mid torque,  the opposite to what is experienced by the TQ racers who just take it to an extreme .
johno

[johno]

This is a rough arsed drawing of what I think happens with the big googy egg pocket port.
The numbers were based on my senile memory from a Vizard book a long time back, just simple fluid dynamics.

ah grasshopper , if it is easy everyone would be doing it,  so begineth the challenge

[754]

Branch did do a lot of development work for GM, back in the eighties , give or take a decade.
 I visited their shop once, got the tour, it was very interesting..

 Back to the late 750K and F heads, the different style intake boot, is the same for both late style heads, ie all77/78.... Is that not correct?

[MRieck]

The 77/78K heads have the smaller spigot OD (but larger carb side ID for the different carbs). There are 4 types of insulators for the CB...the real early ones for the 69/70, 71/76 K & F, 77/78K and 77/78 F2

[Greg H]

Obviously we've moved on a fair bit from just cleaning up ports in the most cost effective way, but I'm just loving this . It's  got me rummaging through boxes looking for old books and magazine articles    . It's even got me down to the old shed at my mothers   looking in the old drawers and under the workbench  for the tools we used to use when me and a couple of my brothers used to play at hopping up  both four and two-stroke motors back in the day . Great stuff ,Keep up the good work guys     

[PeWe]

Although hard to test on a flow bench unless you can rig up a "valve operator" like the ones Jerry Branch Flowmetrics used to have in the 1970s:

What do you mean by "valve operator"?

The article I read about this was named something like: "Discovering free turbocharging", and it was a combination engineering article and college (some college in CA in those days) science project. What they did: the made a cam rotator (electric motor, about 1.5 HP) that rotated the cam to open and close the valves on an OHV head, and measured the resulting flow through the intake valve, on the upstream side, and compared that to the measured flow on the downstream (chamber) side. The idea was to try to quantitatively measure the compression that was happening, due to air mass flow and its speed, and turn it into something Detroit engineers could use. The numbers were impressive, showing clearly that adding open volume above the intake valve (aka "pocket porting") caused a significantly lower suction moment in the chamber if:
1. The Pocket was increased in volume, and
2. the speed of the flow in the intake tract was kept higher, rather than lower (i.e., the cross-section of the throat should be smaller coming from the carb zone, leading into a larger pocket), and
3. the intake tract was made longer than the length of the venturi that was doing the mixing (i.e., longer than the length of the carb body), which plays right into the long intake runners of the SOHC4 designs.

In the article, Branch Flowmetrics was mentioned as being involved. They came up with interesting calcs and formulas from the work they did. It (the phenomenon) proved to be somewhat predictable by design, and was therefore heralded to become a help toward more efficient, smaller car engine designs in the future (which would have been the 1980s designs, leading to the 1990s engines).

(Sadly, when I went thru a divorce in the mid-1970s, she took that box of my 'stuff' with her, and I never noticed it for years afterward, so I don't have the article any more.   )

I could not resist to use Google: Branch Flowmetrics + pocket porting
Several hits 2 of them here
http://cb750k2.honda4.nl/Technical/porting/Porting_the_Honda_Head.htm

http://books.google.se/books?id=aSKzZIqCk54C&pg=PA108&lpg=PA108&dq=Branch+Flowmetrics+%2B+pocket+porting&source=bl&ots=P3g9yQqltr&sig=7hIE_wQ74UEqRaL3EwFjozSYrVs&hl=sv&sa=X&ei=RTvBUs7sFuvV4QSOl4CQDQ&ved=0CDcQ6AEwAQ#v=onepage&q=Branch%20Flowmetrics%20%2B%20pocket%20porting&f=false

[LArzFroMArz]

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[TurboD]

Its great to see the continuing interest, as well as the added discussion and information on this topic.

After multiple trips to home improvement stores to find parts that I could use to perform a test on spigot sizing, I finally found what I was looking for and modified them as closely as possible for testing.

This test is purely for reference. I managed to replicate the spigots in two sizes, one the K7 size (thanks Scottly) and the second my 77 F2 head. This test was solely to give an idea as to possibly when the spigot itself would become a restriction. I view these numbers as a guideline and not 100% dinfinitive, because other factors before and after the spigot have some effect in actual operation.

K7 measuring 28.4mm and 1.118"  flowed 76 CFM @10 inches
F2 measuring 30.98mm and 1.22"  flowed 87 CFM @10 inches

I have some more testing for the Low Buck head in the works, I will post more when it is completed.

[TurboD]

Work has started on the exhaust port. The old SOHC honda exhaust port is pretty straight forward in design, like many motorcycles and auto heads, for most performance uses it mainly only needs a good blending along with slight enlarging.

Below are before and after pictures of the exhaust, I have intentionally left the port dirty and black to help show just where material is removed, at this point all grinding has been done to blend everything and just remove the high spots. It is hard to see, but a little work was done to slightly widen the floor and streamline around the guide like I did on the intake side. This will be followed up with the sanding drums for a good smooth surface, that will also increase the port size a small amount. There is no need to "hog" out the exhaust port, because the valve size will most always be the limiting factor on ultimately how much it will flow.
 
Before

[TurboD]

After

[Greg H]

I've been waiting for this bit  . How do you propose to establish whether your re-worked exhaust port will flow better than stock ?. 

[EnginebyAdam]

I've been waiting for this bit  . How do you propose to establish whether your re-worked exhaust port will flow better than stock ?.

Flow bench should confirm that I guess. Shouldn't a port that is only being smoothed out flow better than stock seeing as the port shape only varies slightly?

[MRieck]

I've been waiting for this bit  . How do you propose to establish whether your re-worked exhaust port will flow better than stock ?.

Flow bench should confirm that I guess.

A very good guess brother. That F2 exhaust doesn't need very much at all......a good size valve in there.

[EnginebyAdam]

I've been waiting for this bit  . How do you propose to establish whether your re-worked exhaust port will flow better than stock ?.

Flow bench should confirm that I guess.

A very good guess brother. That F2 exhaust doesn't need very much at all......a good size valve in there.

I went back and added a thought to the post but good to know some of this stuff is sinking in Sorry about adding to my posts after the fact. The power was out and I was trying to use my wife's android My phone is text and calling only, and the text part is VERY limited

TurboD you are getting me pretty pumped about getting my head porting equipment. Between this post and following MReick's work I have enough to go by for the F3 head I want to use. I'll be sure to post a thread when I get into the porting side of things. I'm pretty sure the K6 head is a practice piece

TurboD this thread is very well put together and the knowledgeable are helping it along nicely. Thank you for your time, I'm feeling mighty edgamakated