After doing a number of grooves and seeing improvements on the emission side but not what I want on the performance/mpg side, I began to question the angle I have been cutting the groove. I believe the important angle is between the shaft and the throttle body plain. I noticed my large bit has a shiny mark close to the actual cutting portion. I think I am holding the bit to high, causing the bit to also cut into the back of the throttle plate itself. I know we are not looking for perfection here, but if I am close but not close enough - room for improvement.
Just a thought. I'm thinking of making some sort of "gauge" to check on the angle of the groove once made. I would hold this "gauge" across the groove, with the throttle plate wide open and look for gross imperfections.
Also - Dan Merrick mentioned cleaning the forward edge of possible burs and spurs. Would cleaning more of the groove itself and the trailing edge help or hinder. Are we looking for a sharp forward and trailing edge?
Thank you all for your help. I want to make sure my grooves DO make a big difference, not just a small change.
Well, I watched the training dvd again. The most important angle is the taper on the shaft to the body of the throttle body - keep it parallel. I will probably start by re-grooving our 2002 Olds Silhouette this weekend, paying close attention to angles. This will be a test of my theory - if performance changes. I will also double check all vacuum connections and seal problems.
A ditto to what Ron said. Little things can mean a lot, but vacuum is the key. Providing your engine is healthy, if you can get the vacuum system leak free and plug that pcv at the intake you are going to see your desired results. Vacuum, vacuum, vacuum.
I'm posting to this old thread to get it in front of us again. Notice what Scott says about the bit angle. To restate it again--the bit front flat side is held against the throttle plate in the initial cut. You hold the Dremel flex shaft so the bit remains steady in all directions, and use moderate pressure to begin cutting straight down against the plate. Using the plate as a backstop, cutting straight down into the bore wall material. You keep going, until the TAPER of the shaft directly behind the cutter head touches the TB bore wall. Strive to hold the tool so the TAPER of the shaft is parallel to the bore wall. This might mean the flat bit end will not be exactly flush to the plate.
I will take the bit itself and hold it in the TB to get an idea of the angle position needed- so that the taper is as close to parallel w/ the bore wall, then see how close to directly against the plate this is.
The next cut, is a half-cutter ball width to the right. Keep repeating this way from left to right.
I'm just restating what was already said here, with a bit more detail.
Gadgetman Reno, NV