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Big Bore Engine - Part 2 - Head (Read 135 times)
DragBikeMike
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Big Bore Engine - Part 2 - Head
07/19/20 at 22:55:21
 
This is the second in a series of reports outlining my big bore engine project.  Part 1 covered the cylinder.  If you haven’t read Part 1 you can find it here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1593567475

Part 2 covers the cylinder head.  I am currently running my Stage II head on a 94mm bore.  It runs very good.  For the 97mm big bore, I took the cylinder head to the next level, Stage III.  Larger 34mm intake valves were installed, and the exhaust port was enlarged to a full 1.79” to match the Mac header.
 
The valves were setup to accommodate cams up to .420” lift.

Let’s get started.
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DragBikeMike
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Re: Big Bore Engine - Part 2 - Head
Reply #1 - 07/19/20 at 22:56:54
 
The core was a stock head removed from my 2016 LS650.  It has about 3000 miles on it.  This is the box-stock intake port, warts and all.
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Box_Stock_Int2.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #2 - 07/19/20 at 23:00:53
 
You might look at that cobby intake port and think a little cleanup with a die grinder will provide a huge increase in flow.  Well, it doesn’t.  Cleaning up all that ugly stuff helps a little (about a 3% increase if combined with back-cut valves), but it doesn’t amp up the flow like you might think.

On the Stage II head, I found the big flow increase (about 9%) came from reshaping the floor of the port to make the short-side radius more gradual, then widening the left and right port runners to compensate for the vertical reduction in area.  The cleanup combined with the epoxy/widening mods resulted in a 12% increase in flow.  The nitty-gritty details on those mods are in the report on the Stage II head.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1565076891

To improve the short-side radius you must build up the floor of the port with epoxy.  This is the third time I have done this epoxy mod to a LS650 head.  I flow tested each head and got almost identical results on all three.  

This port modification works.  It’s easy to do.  The improvement is substantial.
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Re: Big Bore Engine - Part 2 - Head
Reply #3 - 07/19/20 at 23:01:35
 
First, the port surface must be prepped for the epoxy.  I just use a very course carbide burr in a drill extension.  Use the extension as a handle and work the burr over the surfaces where the epoxy will be applied.  Don’t turn the burr with a drill or die grinder, just scrape away at the surfaces by hand to make it as rough as possible.  You want a good anchor for the epoxy.
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Epoxy_Surface_Prep_22.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #4 - 07/19/20 at 23:02:21
 
Start by washing the entire head in hot soapy water.  Get it super clean.  Then work on the port surfaces with the carbide burr.  When your done with the carbide burr you should have a surface finish like this.  Very rough, deep scratches, lots of burrs raised up.
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Epoxy_Surface_Prep_12.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #5 - 07/19/20 at 23:03:01
 
Once the port is roughed up in all the areas where epoxy will be applied, clean it with copious amounts of Brakleen and a small wire brush.  It has to be pristine, no oil or grease allowed.  After the Brakleen has dried, apply a thick layer of the epoxy (be generous, pile it on).   You want plenty of excess to allow shaping the floor of the port.  My go-to for this job is JB Weld HighHeat.
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High_Heat_Container_1_2_001.JPG
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Re: Big Bore Engine - Part 2 - Head
Reply #6 - 07/19/20 at 23:08:40
 
This should give you an idea where this is headed.  You can see the epoxy on the floor of the port.  I have started shaping and blending the epoxy with a Dremel tool and a small abrasive roll.  Note that the once-round right-hand runner is now starting to look oval.  It is bigger left and right than it is top to bottom.  That will naturally occur due to the epoxy build-up, but I also widen the port substantially with the Dremel tool.  Each runner ends up about .080” (2mm) wider than stock.  The widening also narrows the thick bridge in the center of the two runners.
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Epoxy_Buildup_22_001.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #7 - 07/19/20 at 23:09:48
 
Once the epoxy has been blended and shaped to the desired configuration, and the right & left runners widened .080”, I go through the stud hole and drill & tap the epoxy to prevent the cylinder head stud from pushing the epoxy off the port.
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Int_Port_Empty_Stud_Hole_3.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #8 - 07/19/20 at 23:10:37
 
I get 8mm exhaust manifold studs (Dorman 03411) from O’Reilly auto parts.  Then cut the small hex off with a hacksaw and file a nice radius on the end.  
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Studs_for_Intake_Side_2.JPG
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Re: Big Bore Engine - Part 2 - Head
Reply #9 - 07/19/20 at 23:11:22
 
The stud fits nice and provides a fairly smooth surface for the air to flow over.  It also serves as an additional anchor for the epoxy.
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Intake_Port_with_Stud_3.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #10 - 07/19/20 at 23:12:25
 
This is a cross section of the port with dimensions.  It’s pretty simple.  The epoxy on the floor of the port runs at an incline to the apex directly below the valve guide and then arcs into the throat of the port runner, right at the edge of the throat.  It’s a buildup of about .16” (4mm).  The runner is widened by about .08” (2mm) to help compensate.  You can see how the arc is much more gradual, so the airflow doesn’t have to make such a tight turn.  This sketch plus the photos in this report should be more than enough info to allow anyone to replicate the port.  As you will see from the flow curves, the configuration works great with the stock intake valves too (Stage II).
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Stage_III_Port_Sketch.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #11 - 07/19/20 at 23:13:23
 
It’s easy to measure the runners with a simple inside caliper.  The apex of the arc needs to be directly below the edge of each valve guide.  The vertical distance should be .95” from the top of the runner (aluminum) to the apex of the arc (epoxy).
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Port_Height_at_Guide__95_3.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #12 - 07/19/20 at 23:14:09
 
Since the runner is now oval, the horizontal distance will be larger.  The distance right to left will be 1.17”.
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Port_Width_at_Guide_1_17_3.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #13 - 07/19/20 at 23:15:24
 
The 34mm Kibblewhite valves are intended for an early Honda CB350 (1968-1973).  They are Kibblewhite part number 30-30361.  The Kibblewhites are only slightly larger (1mm) than the stock intake valves.  The stem diameter is reduced in way of the port.  That reduction effectively increases the port cross section.  It also reduces the weight of the valve.
 
The Kibblewhite stem is .06” (1.5mm) longer than stock so rocker geometry might be a problem.  I did a contact check to make sure that the rocker adjustment screw doesn’t get too close to the edges of the valve tip as the rocker swings through a full arc.  It was fine, but the longer stem could result in accelerated guide and stem wear due to side loads.  I guess we shall see.


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Rocker_Contact_34mm__340b2.jpg
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Re: Big Bore Engine - Part 2 - Head
Reply #14 - 07/19/20 at 23:16:28
 
I experimented with 35mm valves but there just doesn’t seem to be enough valve seat material to allow safe installation of 35mm valves.   I don’t have the equipment or skill necessary to install larger seats.  A typical 650cc single with a four-valve head uses intake valves around 38mm.  The 33mm intakes on the LS are ridiculously small.  Looks like 34mm is the best I can do.
 
This shows the Kibblewhite valve (on the left) next to a stock valve (on the right).  Both valves have a 30° back-cut which improves flow about 2%.  It’s worth doin the back-cut.  The undercut stem in way of the port (Kibblewhite) takes up a little less space, so there’s more room for air to flow through.
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KW_Stem_vs_Stock_Stem_2.JPG
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