Compressed to .950”

Check coil bind height by inserting the spring in a vice with soft jaws and closing the vice just enough to make the coils start to touch each other.  Don’t over do it or you will trash the spring.  Make sure to use soft jaws so that you don’t nick the spring wire.

Here’s the combustion chamber ready to measure.

Here’s a shot of the intake port all leveled out and ready to fill.

I hope you find the information in this post interesting and useful.  As usual, I invite any and all comments.  I had fun on this project, and I learned a lot.

Knowledge is power.

Best regards, Mike

Great series of posts. Thanks for taking the time to explain this in simple language.

Thanks for the Kudos.   I put a lot of work into this and I think that the info will be very helpful to the folks who are looking to increase their performance.

Good comment on the exhaust port Batz.  It surely is a challenge.  I've spent a lot of time pondering that ugly port and really haven't come up with any practical solution yet.  But hope rings eternal.  I didn't measure the port size at the valve, but it's a good idea, and I will do it and post the results.  Looking at the numbers you provided we can see that the stock port must fall short of 88% to 96% geometry.  It's not getting bigger as the flow moves away from the valves, it's getting smaller.  The stock exhaust valves combine for a cross section of 1.9 square inches.  The outlet of the exhaust port (1.34" diameter) is 1.4 square inches, or 74% of the valve cross section.  Then the gasses continue on to the inlet of the header (1.275" diameter) which is 1.28 square inches, or 67% of the valve cross section.  So the path is converging rather than diverging.  This might be a good thing.  The shape of the exhaust port might be fixed due to the thin wall on the top, but the outlet can be opened up to create a more divergent flow path.  When combined with a larger header ID the flow path would then be divergent and more on the lines of a conventional system.  The differential across the exhaust valve is very high, much greater than the intake, so it is more forgiving in terms of flow.  Simply clearing out some of the junk (like the protruding guides) and reshaping the outlet so that the flow path is divergent (or at least uniform and not convergent) and using a reasonably sized header, might unleash the beast.

I should have qualified my comment on raising the top of the port to improve the angle of attack.  My comment was intended for modification of the intake, not the exhaust.  I don't see any practical approach to raising the top of the exhaust port.  There just isnt sufficient material up there.  One possibility might be to come up with valve springs that are significantly shorter, but still provide ample force and travel.  I just finished installing a set of Kibblewhite springs on an old Honda CB350.  The Kibblewhite springs were about .125" shorter that stock, but could accomodate up to .465" lift and had more spring force.  If a spring similar to that could be found with correct dimensions for the LS650, then the spring pocket on top of the exhaust port could be welded up and machined to correct the spring height, which would then provide about 1/8" of material for removal from the roof of the exhaust port, while still maintaining the original wall thickness.  But 1/8" doesn't seem like it would be adequate.  It's just too ugly with the steps and such.

Another possibility might be to work the sides and leave the top and bottom alone.  But then you're faced with increased volume and the associated drop in velocity.

I have used a product similar to the one you describe.  It wouldn't surprise me if its exactly the same stuff but with a different label.  It's JB Weld Extreme Heat Metallic Repair Paste.  It's a one-part product (no catalyst), not an epoxy, and good to 2300F.  It contains silicic acid, sodium salt, and steel fines.  I imagine it probably has some other stuff in there too.  After it sets up, it is really hard and also seems to have good adhesion.  But I wouldn't feel comfy with it in a port unless it was captured (for instance the stud hole in the floor of the exhaust port).  Since the filler material is steel, it will have a significantly different coefficient of expansion from the aluminum, so the thermal cycling will torture the bond between the aluminum and filler.  Might be able to grind in an anchor tooth profile for the filler to grab.

I used the stuff to seal the joint between the flexible exhaust pipe and Mac header.  I applied it to about the top 1" of the flex pipe before I fed it down into the header.  I've only logged about 300 miles on it since I put it in, but I haven't noticed any funny business.  One of these days I intend to take the header off and pull out the flex pipe to see how it runs with the 1.79" ID pipe.  I'll let you know how the putty held up.  If I can't get the flex pipe out the putty gets an A+.

The exhaust port also has the unique problem of having unequal runners.  The left runner is a lot longer than the right runner.  Confining metal removal to the left side might be more beneficial than removing metal from both sides. Removing metal only on the left, thus increasing the radius on the left, and increasing the length on the left might force the gas to accelerate.

As far as filling in the intake port to compensate for material removed from the top, I'm pondering a Manley product specifically made for intake ports and manifolds.  I don't see welding as being an option because the port is so long.  I also imagine any significant amount of hot work will result in annealed base material, loose valve seats, etc.  I will probably confine my modifications to clean up, blending, tapered guides, possibly larger valves, a good three or five angle valve cut with back-cuts on the valves, stuff like that.  

With your discussion of the convergent exhaust port to header of the stock system, do you have thoughts on modest mod’s in the port of smoothing out sharp edges and opening the outer ring to 1.5” and then using a header of 1.5”ID OR 1.65”ID...which header size do you consider the most beneficial ?  And why ?