A week or two ago, I pulled out another set of spare 54mm throttle bodies to start modifying for my bike built from all the spares I had laying around.
I have made these modifications on several sets of SV1000 throttle bodies in the past, but have also made these types of modifications on other bikes too.
I figured while I was in the process of making these, I would take some pictures and show what can be done to improve flow in a set of stock bore throttle bodies. These modifications can be made on the 52 or the 54mm units and can also benefit bored throttle bodies too.
These modification will increase the total flow area at the main bore section of the throttle body.
The modifications will consist of the following:
- Smoothing and blending the inner bore of the casting prior to reaching the throttle plate.
- Removal of the STV plates, shafts and stepper motor
- Modification of the vacuum port tubes that extend into the flow area of the throttle body.
- Cutting and modifying the primary throttle shaft.
- Modifying the primary throttle plate to use counter sunk flat head screws and removing excess threads.
Lets start with item #1
I dismantle the throttle bodies completely down to the bare castings. I then hand finish the inner parts of the bore prior to the throttle plates. I don't think there is too much explanation needed here. The question does come up about up about surface finishes and boundary layers to assist in flow. The attached images show that the surfaces are smoothed but not polished.
Several people have removed the STV plates, but not too many have fully removed the STV system from the throttle bodies all together. Removal of the plates and shafts both increase the flow are into the throttle body. The four existing holes where the STV shafts used to then need to be plugged. In the past I have used some custom machined Delrin inserts I can press in and then smooth and blend from the inside of the bore. This particular time I used JB Weld to fill the holes and then smoothed them from the inner bore. If the system is completely eliminated, a STV eliminator unit should be purchased to prevent the FI light from coming on. Thanks to D'Ecosse (SVRider name) and RecoilRob, they got the eliminator unit working much better on the SV1000. Previous units like the ones I have currently, would still throw codes now and again. Several of my units are being sent in for modification. Thanks Guys! Please contact D'Ecosse for purchase of an eliminator unit.