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Discussion Starter · #1 ·
1050cc intake mods and thoughts:

If you open the throttle, you may notice a few things in the inlet track.
1. The throttle butterfly is 45.77mm, but directly behind the butterfly (throttle blade), there is a sharp ridge where the TB necks down slightly – approximately 1mm smaller. This is an obstruction to airflow that makes the air flow as if the TB was even smaller than it actually is.
2. The rubber venturi may have a slight ridge at the bottom where it meets the TB. If this ridge extends into the intake, it is an obstruction to flow.
3. The rubber mounts connecting the TB to the head may have ridges that intrude into the intake slightly. If so, this is an obstruction to air flow.
4. The throttle blades themselves are quite flat on their leading edges.
5. The throttle bar and blade retaining screws intrude into the airflow.

On my engine, these items were worse on some cylinders than on others. I took a small hand grinder with fine sanding rolls and Craytex rolls to smooth the airflow in the intake track and radius the leading edges of the throttle blades and bar. I also removed the blade screws and replaced them with fine counter sunk gun screws. On my flow bench, this work has shown a 3% increase in flow with a very slight gain in velocity. The flow to each of the three cylinders now is better matched than the way it was in stock form. Is this worth any performance gain? Only time on the dynamometer will tell.

Note: Cratex is rubber imbedded with diamond dust. The rolls are available in three textures and in various shapes and sizes for fine grinding/polishing.

I also took a long look at the rubber venturies in the air box. These are slightly curved and are 75mm long (approximate length due to the curve). They also have a very large taper that expands towards the opening. This looks like it can be improved to better match the power band and inlet pulse tuning. I will have to make three adjustable length venturies with a properly shaped bell mouth to test.

The rubber “snorkels” that allow air to enter the air box are greatly curved. This is done to fit inside the frame. This is not the best idea for air flow. A better approach needs to be found.

Heat: The hot air from the radiator, oil cooler, header, and block all combine to feed hotter than ambient air into the air box. I have measured air temps up to 50 degrees F over ambient in front of the air box. There is an old rule of thumb that says for each 10* F increase in intake air temps, you lose 1% of potential power. This means that making sure the air entering the air box is at ambient temperature can be quite an improvement in performance for these engines.

As a result, I have coated and wrapped my headers. I have also blocked the top of the radiator and block with a small sheet of thermal blanket material from the air box to the top of the radiator. Adding inlets to the air box that pull in air from outside the frame will be the next step. Measurements thus far have shown over a 20* F drop in inlet air temps. This should lead to a nice increase in power that will be measured on my upcoming visit to the dyno for additional tuning.

After studying the intake and exhaust ports, the heads will definitely be removed over the winter for port work.

Discussion Starter · #3 ·
Will do. I have the bike apart for custom paint - the reason why all of this was done now. I should be able to get it on the dyno next week.

In the throttle body, the inside ridge is caused when the TB is machined. It is not machined any deeper due to the change in shape below this point. I used a boring bar on my mill with the tooling set at 14 degrees off vertical. Air does not see changes in angle less than 15 degrees. But it DOES see the lip left by machining the TB bores - especially when the area is reduced. It only took a light "kiss" with the tooling to clean this up.

I am working on custom venturies for inside the airbox and on the outside of it this week. Removeable spacers will allow it to be tuned to length.

Only after all of this will I be able to work with cam timing.

Discussion Starter · #9 ·
There is one other place where air is disrupted - where the rubber adapter meets the head. There has been a WEAK atempt by the factory to clean up the intake port opening, but it is done very roughly and obviously very quickly with a sanding roll. This will have to wait until I pull the heads for more work this winter.

The big surprize is the throttle body bore diameter - 45.77mm+. The TB opening is actually larger than this. This is quite a bit bigger than in previous 955 engines. ;)

Discussion Starter · #17 ·
After cleaning up the intake and resetting the IACV with Tuneboy, the bike now starts VERY easily hot or cold without opening the throttle like in the past.
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