Modifications to the Henning Honda CB500

What exactly did Kenny Augustine do to a mild-mannered Honda CB450 engine to turn it in to the Daytona-winning Henning Honda CB500?

"We started out with a 2- item Honda CB450 wish list that I made up," says Augustine. "From that, Todd picked four areas that we would work on before Daytona."

"Out of those four areas, a 16 step to-do-list was generated. All of these steps were specialized changes to the Henning Honda above and beyond the basic blueprinting which gets done to every motor that comes into Augustine's shop.

First Things First:  

Augustine didn't like the 450 cylinder head, so a decision was made to swap it with a 500T, which would be fitted on top of the 450 cylinders. Then the process of modifying the top end began...

A Quick Reference List of Steps A 500T head ready for Augustine's magic touch

Step 1: A Special Valve Job Step 2: Porting Step 3: New Valve Springs Step 4: Smaller Exhaust Valves Step 5: Custom Valve guides Step 6: Fill in Around the Exhaust Valve Guides Step 7: Fill in the Exhaust Port Floors Step 8: Raise the Exhaust Flanges Step 9: Fill in the Intake Port Floors Step 10: Move the Intake Flanges Forward Step 11: Design Custom Pistons Step 12: Re-sleeve the Cylinders Step 13: Re-true the Combustion Chamber Step 14: Add a Second Plug
Step 15: Install Custom Valves Step 16: New Cams 

Step 1: A Special Valve Job

From left to right: stock valves, some early prototype valves, final prototypes, and finished custom valves. "Step one on the list was a special valve job," says Augustine. "Anybody can walk in [to Kinetic Analysis] and ask for a special valve job. It isn't a radius cut -- it has a lot of different angles than everybody else uses, and a lot of different widths and it is really precise. Everything is measured with precision instruments. Nothing is left to chance." This kind of tuning is more commonly known as blueprinting (though blueprinting can mean any amount of accuracy, and Augustine's accuracy is very high), and allows the engine to run with a higher tolerance for stress.

Step 2: Porting

Intake ports on a 500T head. The one on the right is ported, the other has a custom valve guide installed, but no porting done yet.

The second step is a fairly typical porting job. This allows greater flow of uncombusted mixture into the chamber, and greater flow of combusted gases to the exhausts. This both increases the amount of mixture that enters the chamber on the intake stroke (giving higher compression), and allows the engine to flow spent and unspent gases more quickly (allowing higher rpm's). Kenny describes this modification as "Smooth raii, mmore cross-sectional area where it needs it, but leaving it alone where it doesn't need modification." Some tuners now do this process using a extrusion hone, which forces an abrasive substance (king of like gritty silly putty) through the ports, but Kenny prefers the control of a hand grinder.

"Many areas need to be filled rather than extruded. You want to leave those areas alone. Knowing what can be left alone is a discipline in itself."

Step 3: New Valve Springs

The third step was to put in a new coil valve spring kit developed for Augustine's work on the Henning Honda by R.D. Spring. Coil valve springs made with modern steel allow the valves to lift faster and close faster (actually, they're accelerating from the stopped seated position to fully "open" where they are again immobile, and then they accelerate back "down" to close -- it is these smashing accelerations that breaks valve springs), preventing them from `floating', and crashing into the piston dome at increased rpms. "A standard coil valve spring kit from R.D. Spring could have been used," says Augustine, "but it required some head machining and I didn't want to weaken the already thin head, so I designed around the problem and R.D. Spring provided special parts and advice."

Step 4: Smaller Exhaust Valves

Step four was smaller diameter exhaust valves with smaller diameter stems. This may seem like it would restrict gas flow and overall engine breathing,, but Augustine felt that the diameter of the exhaust valve was too big relative to the diameter of the intake valve (remember, the exhaust gas is pressurized so it's easier to get out than it is to suck intake mixture in -- hence, exhaust valves are always smaller than intake valves). By making this valve smaller the mass which the cam must operate on is reduced and the chances of the exhaust valve `floating' are decreased.

Step 5: Custom Valve guides

On the left, a set of custom valve guides. On the right, a stock one. The smaller exhaust valve stems necessitated the creation and installation of custom valve guides to match the smaller diameter intake and exhaust stems, which was the fifth step. These stems were made longer than the stock stems to give better control and longevity. They were all made with a different material to make them compatible with the new titanium valves. These stems were made longer than the stock stems to give better control and longevity. 

Step 6: Fill in Around the Exhaust Valve Guides

Step six was to fill in dead area between the valve guides and the roofs of the ports to allow the smoothest possible flow around the valve guides. This seems simple enough to do, but only an experienced tuner can do it properly.

"Do it. I dare you. You can't do it with clay and you can't do it with putty; it's got to be metal, and I like to weld it in there. But that's a pain and usually the arc wonders and eventually melts the valve guide, and heaven forbid if it hits the seats." A close up of a partially raised exhaust port (Click here to see the entire head).

Step 7: Fill in the Exhaust Port Floors

Step seven was to fill in the exhaust port floor and raise the roof just like you would do in any drag racing hot-rod engine. Augustine emphasizes that the key to doing this step properly is to go all out, and give the port the shape it needs rather than one that can be done where access is easy. In places on the head you can see that Kenny has actually ground a hole right through, and then welded things back up, just to make sure that he went as far as he could in the direction that he wanted to go.

"You can make air go fast, or you can make it go around a corner, but you cannot do both."

"So opening the corner up in the short side radius is what makes it work. No amount of magic shape that you can see with your eye as you look into it makes a difference.""So opening the corner up in the short side radius is what makes it work. No amount of magic shape that you can see with your eye as you look into it makes a difference. It's the shape if you saw the head in half from front to back; it's the cross section in that direction rather than the cross section in the transverse view. Everybody looks at it and thinks that it has to be this magic oval or this magic `D'. That's total, absolute bullshit. You could make the thing look like a `W', or a frog, or anything you wanted as long as in the other view it was a very large radius frog, and that would work."

Step 8: Raise the Exhaust Flanges

Step eight was to raise the exhaust flanges five millimeters so that straightest possible flow of exhaust in to the pipe can be attained even though the exhaust ports have been raised (in step seven). This meant removing the existing bolts for the exhaust, welding up the existing flanges, machining a new flange at the raised position, and re-drilling and tapping for the exhaust bolts. All of this is accomplished with the help of a computer controlled milling machine, but as you can imagine, it's still a complicated process.

Step 9: Fill in the Intake Port Floors

Step nine was to fill the intake floors with epoxy. This operation is similar to step six, but in this case epoxy can be used because the intake ports are not exposed to high amounts of heat like the exhaust ports. Keeping the epoxy in the ports has always been a problem, and Augustine uses a special epoxy and technique.

So what's the magic formula? Augustine didn't want to tell us. "It's a trade secret."

Step 10: Move the Intake Flanges Forward

Step 10 was to move the intake flanges forward. This reduces the length of the intake, and it's resistance to flow of incoming charge. It's simple to describe, but again requires some complicated and delicate welding and milling on the cylinder head.

Step 11: Design Custom Pistons

Step 11 was to design a custom set of pistons for the motor. To do this Augustine started with a stock piston and added a layer of epoxy to the top. Then precise measurements of the new dome and valves were taken. The epoxy was cut away to match the dome radius, squish anFrom left to right: A stock piston (used), a prototype ready for blueprinting, a Wiseco blank, a finished custom piston. gle and to accommodate for it's larger size. Preliminary pockets were cut to fit the new valves, and the motor was test assembled. Measurements were taken to show the exact travel of the new valves, and the pistons' valve pockets were cut to a finished depth and radius matching the motor's new head. After the compression was measured and adjusted with the mock-up, the piston was sent to Wiseco for blueprinting and reproduction.

Step 12: Re-sleeve the Cylinders

A pair of 500T sleeves. Pressing in the 500T sleeves





Step 12 was to re-sleeve the stock CB450 cylinders with larger diameter sleeves from L.A.  The CB450 could have been bored to 500cc to accommodate the custom pistons, but this would have left the walls of the cylinder too thin, resulting in performance-robbing distortion along the cylinder walls at the engine's increased pressure and temperature. Once the sleeves were installed in the cylinder block, the top of the cylinders were milled so that the head would sit perfectly perpendicular to the bores of the cylinders.

Truing the 500T sleeves.

Step 13: Reshape the Head

Step 13 was to fill the entire inside of the head with aluminum weld and re-machine it to give it high compression and a squish band which precisely matches the top of the custom pistons.

Step 14: Add a Second Plug

Step 14 was to add a second spark plug.

This in conjunction with the previous two steps gives the motor very even flame propagation, and less chance of detonation.

This allows the ignition to be run with less advance and/or at higher rpms, and ensures that the maximum amount of mixture possible is combusted, both of which are crucial elements in making more horsepower.

Step 15: Install Custom Valves

A close up of a beryllium-copper valve seatStep 15 was to install a set of custom manufactured titanium valves. Like using smaller exhaust valves, this lightens the total mass the cam must operate on, and reduces the chance that the valves will float. A problem with using titanium is that it is metallurgically incompatible with steel, so a set of beryllium-copper valve seats replaced the stock ones.

Step 16: New Cams

On the left a Custom designed cam with an adjustable sprocket, produced at Megacycle. On the right a stock cam. The final step was a redesigned cam geometry. Augustine points out that: "this has been the Achilles' heel of th Honda 450 motor all along. There are some pressure angle problems in the geometry, which is why the valve train rockers wear out, especially the short side radius on the exhausts. People think that they just plain wear out, but there's more to it than that. It wears out on the closing side of the exhaust valve because the pressure angle is so rotten. Nobody can tell you what the pressure angle is except somebody who designs cam-shafts."

The final step was a redesigned cam geometry. Augustine points out that: "this has been the Achilles' heel of th Honda 450 motor all along."

Augustine spent hours on a CAD system with master cam builders from Megacycle Cams designing and perfecting the cams for the Henning Honda. While fitting of the final cam shafts required no major matching be done to the head, Augustine is quick to point out that without all of the other work he had done to the engine the new cams would be worthless.

When the top end was complete it was returned to Todd Henning to be installed on his specially designed and blueprinted close-ratio bottom end. With all this complete and a big win at the Daytona season opener you would probably expect to find Augustine taking a vacation, but that's just not his style. For more years that anybody cares to count Augustine has worked seven days a week, and often 24 hour days.

"On Christmas I work half a day, and by the way, I won't, 'see you at the races.' I'll be in my shop working on my next project."

Plans are already in the works for next year's bike: "Next time around we're going to re-angle the valve guides, re-sphere the head, and change the rocker geometry some more. We're going to have new rod ratios, better carburetors, lots of flow development, lots of dyno development, automatic data acquisition, and a specially developed oiling system which didn't make it on to this year's bike."

Stay tuned.

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