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Cylinder Head Porting & Flow Test (Read 1120 times)
DragBikeMike
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Cylinder Head Porting & Flow Test
04/04/19 at 00:16:53
 
In late January I posted a report on a cylinder head I was testing.  I refer to it as the HammerHead.  It was the victim of a valve/piston collision that beat the ever lovin daylites out of the thing.  I salvaged the head for testing, and then did flow comparisons between the HammerHead and a good used head.  The heads flowed almost the same, so I deemed the HammerHead a valid test mule for trying various porting techniques.  Since January, I have done extensive testing on the heads.  Now it’s time to share some of that hard-earned information.

I will start with a correction.  In January, I stated that I would be using 10” H2O as my test pressure for all the tests.  I would either test at 10”, or test at the highest pressure I could achieve with my little bench, then convert the results to 10” using the DTec conversion tables.  After running numerous tests, and starting modifications on the intake port, it became apparent that 10” wasn’t gonna cut it.  I needed more oomph.  Also, I kept seeing results that led me to believe that at some point above 10” the forces acting on the air were causing it to naturally pull away from the bottom of the port and run along the top.  Apparently, that’s a well-known phenomenon and to be expected.  I needed to up the ante, so I switched to a double vacuum cleaner setup.  As it turns out, that still wasn’t enough juice, so I added in a third vacuum cleaner.  Now I was cookin.

This is the three-vacuum setup for intake tests.
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3_Vac_Int_2_2.JPG

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Re: Cylinder Head Porting & Flow Test
Reply #1 - 04/04/19 at 00:17:51
 
This is the three-vacuum setup for exhaust testing.
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3_vac_Exh_1_3.JPG

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Re: Cylinder Head Porting & Flow Test
Reply #2 - 04/04/19 at 00:19:25
 
The three-vacuum setup allowed me to test the intake at 15” H2O all the way up to .400” lift, and it allowed me to test the exhaust at 28” H2O all the way up to .400” lift.  I could get some serious test data now.

I knew all my test data on the intake would be taken at a maximum test pressure of 15” H2O; the rig didn’t have enough reserve to test the intake at higher pressures.  I also knew I had 28” H2O available to test the exhaust, but also had the option to test the exhaust at 15”.   I could test the exhaust at the higher pressure to evaluate changes, and then test again at 15” to compare the two ports at the same test pressure.  Sweet!  To provide a little reassurance, I tested the stock exhaust port at both pressures, converted the 28” data to 15”, and it came out essentially the same as the data I actually recorded at 15”.  That’s gonna work.

I was able to make big improvements to both ports, but the exhaust port really responded well.  The intake flow was improved by 17.5%, from a maximum 167.6 CFM to a maximum 196.9 CFM.  The exhaust was improved by 43.1%, from a maximum of 114.2 CFM to a maximum of 163.4 CFM.  The flow bias is now 83%.  The final numbers are actual 15” flow values (no data was converted).

I took flow readings at .025” lift increments (16 readings).  So, a more realistic way to look at the data is to add up the flow readings and divide by 16.  That gives you an average flow for the configuration.  If you use average flow to evaluate the modifications, the intake has improved about 15% (121 stock vs 139 ported), and the exhaust has improved about 34% (90 stock vs 121 ported).  I believe this is a more realistic way to view the results.
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Re: Cylinder Head Porting & Flow Test
Reply #3 - 04/04/19 at 00:20:13
 
Here’s a look at the intake graph for 15” H2O test pressure.
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Intake_Flow_Graph_Final.jpg

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Re: Cylinder Head Porting & Flow Test
Reply #4 - 04/04/19 at 00:20:55
 
Here’s a look at the exhaust graph for 15” H2O test pressure.
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Exhaust_Flow_Graph_Final.jpg

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Re: Cylinder Head Porting & Flow Test
Reply #5 - 04/04/19 at 00:21:40
 
These flow improvements were achieved without increasing port volume.  In fact, the intake port volume was decreased by 2cc, from 112 to 110, and the exhaust port volume was decreased by 1cc, from 66 to 65.  I think that’s a big plus.  These should not be lazy ports.

Except for flush exhaust valve guides, every modification I list results in a measurable gain in flow.
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Re: Cylinder Head Porting & Flow Test
Reply #6 - 04/04/19 at 00:23:09
 
Modifications to the intake port included:

A general clean-up of the port by removing rough cast areas, blending the valve seats into the aluminum port wall, and attempting to blend and increase the short side radius.

Back-cutting the valves 30°.

Replacing the stock 33mm valves with Kibblewhite 34mm valves.   The Kibblewhite valves have undercut stems that increase the port cross section slightly and reduce weight.  They are 1mm larger than stock, but are 3 grams lighter.
                                   
Raising the bottom of the intake port to increase to the short side radius.

Widening the individual port runners by .050”.
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Re: Cylinder Head Porting & Flow Test
Reply #7 - 04/04/19 at 00:27:41
 
Let’s look at the various modifications to the intake and discuss the pros & cons.

The general clean-up of the port provides about a 1.5% increase in flow.  It is straight-forward and relatively low risk.  Pretty much anyone with a Dremel tool and steady hand can pull it off.  Be careful around those valve seats.

Back-cutting the intake valves 30° provides about 1.0% increase in flow.  Gains are realized for lifts up to about .250”.  If you have the tools, it’s easy to do and seems low risk.  You will need a lathe or Neway Gizmatic to do it.  If you don’t have the tools, a trip to your local engine rebuilder and a few bucks should get it done.

Replacing the 33mm valves with 34mm valves requires a higher level of skill and tools.   The seat inserts must be enlarged by cutting the throats with 60° and 75° cutters.  The valve seating surface must be re-established with a 46° cutter, and the new seat must be blended to the combustion chamber with a 31° cutter.

You will need all the various cutters, and of course the valves (about $120).  The valve seats are hard as diamonds.  It takes a while.  You can expect about 3.5% improvement in flow.  Also, the valves I have procured are for a 1972 Honda CB350.  They are not an “exact” replacement.  I still have a bit of work in front of me to make those valves work in the LS650.  

You can order custom valves that will fit exactly, but it will cost more.  I don’t know what that additional cost is.  More to come as I start doing the official mods to my good head.  

Another option is a junk Honda CB350 engine.  If it suffered infant mortality, you might be able to score pristine valves and the associated spring retainers and cotters.

Raising the bottom of the intake port is inexpensive and highly effective.  My early declining pressure tests show that the raised floor with increased radius is good for a whopping 6.6% increase.  That’s with stock valves.  With the 34mm Kibblewhites, the raised floor provided a phenomenal 11.6% increase in flow.  Both these tests used back-cut valves.
 
This raised floor modification really seems to do the trick.  It reduces the port volume while increasing flow substantially.  Believe me, I spent many hours of testing this.  It defies logic.  But after testing this configuration over and over, I am convinced it works.  Fill in the floor of the port, blend it in just right, Baaaammmm!  Instant gratification.  I did this like ten times and always got identical results.  The trick is the blend into the bowl (the area just above the seat insert) on the lower side of the runner (short side).  You really don’t want any filler in that area.  You should be able to run your finger over the bottom of the port through the bowl area and feel a nice, generous radius, with no abrupt changes in direction.

How do you raise the bottom of the port?  Epoxy.  If you fish around on the web, you will see that there are folks using this technique.  It’s also discussed in various performance publications.  Manley and Goodson both offer epoxy putty specifically intended for intake port modification.  I am currently performing some tests to determine what might be the best product and surface prep for me.  I really like JB Weld products.  Stay tuned for a full report.
 
Widening the port runners by .050” helps to compensate for the loss in cross section due to the epoxy filler on the bottom.  It’s good for about a 1% improvement.  It’s simple and low impact.  However, when I tried opening it up another .030” I started running out of go power.  I was having trouble maintaining 15” H2O.  I am not sure what will happen if the runners are widened more that .050”.  My flow graph reflects the .050” wider port runners.  If you want to go past that, you are on your own.
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Re: Cylinder Head Porting & Flow Test
Reply #8 - 04/04/19 at 00:31:00
 
Let’s take a look at some of the intake port mods.

Here is a shot of the general cleanup on the intake.
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Int_Port_Cleanup.JPG

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Re: Cylinder Head Porting & Flow Test
Reply #9 - 04/04/19 at 00:32:16
 
Let’s have a look at the 34mm Kibblewhite next to the stock 33mm valve.  Kibblewhite on left.
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Re: Cylinder Head Porting & Flow Test
Reply #10 - 04/04/19 at 00:33:05
 
This is what the raised intake port looks like.  Note the shape and blending of the epoxy filler.
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Finished_Intake_6_2_upright.jpg

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Re: Cylinder Head Porting & Flow Test
Reply #11 - 04/04/19 at 00:33:55
 
Here is a detailed map of the finished intake port.
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Modified_Int_Port_04_01_19.jpg

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Re: Cylinder Head Porting & Flow Test
Reply #12 - 04/04/19 at 00:38:12
 
Modifications to the exhaust port included:

A general clean-up of the port by removing rough cast areas, blending the valve seats into the aluminum port wall, and attempting to blend and increase the short side radius.

Back-cutting the valves 30°.

Cutting back the valve guides until they are flush with the roof of the port.

Filling in the step in the roof of the port to provide a smoother flow path.  I refer to the step as the “Dipsy-Doodle” (DD).

Enlarging the port opening (location “D”, see sketch) from 1.3” to 1.5” diameter and blending the adjacent wall to provide as straight a flow path as possible.  Material removed from top and sides of port, floor of port left as-is.  This is a “D” shaped port.

Note: I used a 1.5” ID test adapter to connect the test bench to the exhaust port.  When I tested with adapters smaller than 1.5” ID, flow dropped dramatically.

Let’s look at the various modifications to the exhaust and discuss the pros & cons.

The general clean-up of the port provides about a 1.5% increase in flow.  It is straight-forward and relatively low risk.  Just like the intake, pretty much anyone with a Dremel tool and steady hand can pull it off.  However, the opening is a lot smaller and there are lots of nooks & crannies that are hard to get at.  Be careful around those valve seats so you don’t end up with any rat bites in the seating surface.

Back-cutting the exhaust valves 30° provides about 1.0% increase in flow, with gains mostly at lifts up to about .250”.  If you have the tools, it’s easy to do and seems low risk.  Like the intake valves, you will need a lathe or Neway Gizmatic to do it.  If you don’t have the tools, a trip to your local engine rebuilder and a few bucks should get it done.

Cutting back the valve guides until they are flush with the port didn’t seem to improve flow very much.  I found that odd.  However, with various combinations the flush guides appeared to have a positive effect.  Removing the guides, cutting them, and reinstalling is not an option as the interference fit is reduced dramatically when the guides are pushed out.  You must install oversize guides.  It is possible to grind or machine the guides in-place, but it just doesn’t seem to be worth the effort.  I’m gonna leave the exhaust guides alone.

Filling in the Dipsy-Doodle improved flow by 4.5%.  It worked well.  It should be inexpensive and relatively low risk.  In the event of a failure, flow should carry the filler material away from the valves.  Fishing chunks of filler material out of the muffler shouldn’t be too hard.  The trick will be coming up with a product that can live in the extreme operating environment.

A good anchor profile will have to be cut in the surfaces of the DD.  That should be easy with a Dremel along with number 113 & 199 high speed cutters.  

JB Weld “Extreme Heat” paste is rated to 2300°F, but it’s single-component water-based.  That means it shrinks as it sets up.  I currently have a test specimen filled with the product.  Stay tuned for the results.

As expected, enlarging the port opening from 1.3” to 1.5” was a grand slam.  It resulted in a 25.3% improvement.  Except for some minor cleanup, all material was removed from the sides and top of the port.  There’s not much flow across the bottom so leave it alone.  You end up with a “D” shaped port.
 
It should be noted that this modification’s effectiveness can only be realized if a proper 1.5” or larger exhaust pipe is used.  Using the stock header kills the effectiveness of this modification.  More on this later in the report.
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Re: Cylinder Head Porting & Flow Test
Reply #13 - 04/04/19 at 00:39:25
 
Let’s look at some of the exhaust port mods.

Here is a shot of the general cleanup on the exhaust.  Note the crack.  There are two cracks in this port.  They run all the way up through the guide boss into the spring seat above.   It’s the sort of thing you would expect when an irresistible force meets an immovable object.  Snapped the valve off too.
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Typical_Exh_Port_Cleanup_2.JPG

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Re: Cylinder Head Porting & Flow Test
Reply #14 - 04/04/19 at 00:40:25
 
Typical backcut valve.  I used Honda valves for the testing so as not to risk the stock valves.  Backcut Honda on left, stock valve on right.
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Stock_Exh_vs_Backcut.JPG

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