Why not just grind them flat as far across as you can? Why the "ridge" on the one side of the TB butterfly plate? I remember you saying "These will flow more and help diffuse any turbulence going into the intake manifold." I guess I don't understand the concept.

<img src="http://pictureposter.audiworld.com/711/rxtb3.jpg">

but because our TB's are SOOOOOO difficult to disassemble then re-assemble this is easier and faster. Most people don't realize that while or TB's are very simple appearing and are anvil-like in their reliability they are composed of many, many parts and all of them have to come off during disassembly. Then when reassembled the springs have pre-loads that need to be followed very closely. Too much pre-load and they won't open all the way, Too little and they won't close all the way. I disassembled oneonce then re-assembled it. Thats all it took for me to know NEVER AGAIN!! It was VERY complex, complicated, tedious and painful.

By relieving the shafts I accomplish two goals; one is to allow more flow and the second is to diffuse and smooth any turbulence cased by the leading edges of the butterfly plates as they are not very aerodynamic. Look at the rear of many sports cars and you'll see diffusers under the rear of those cars. They are usually undulated and are called "diffusers." They are designed to help give the turbulent air coming from under the car a smooth/diffused exit. While I have no way of knowing empirically that it works or has any affect on the air entering the IM I have a strong gut hunch it certainly doesn't hurt. Also staggering them on both sides of the plates seems to be more effective than matching them. And I prefer small radii to large cuts taken in the butterfly shafts as I prefer to err on the side of conservatism.

And I never do these kinds of things on anyone elses TB's other than my own as there's so much sound theory but unproven reliability. Tho I do know the relieved/diffused shafts add over 18CFM on the RTB and 12CFM on the XTB.

the wall in between the venturis.

I may try to apply some of the tactics you've used on my S3 when I get a grinder (being careful not to ding the butterfly plates, of course). I know removing the center wall is not an option with the VS in place. Thanks. ;-)

the wall in between the venturis.

I may try to apply some of the techniques you've used on my S3 when I get a grinder (being careful not to ding the butterfly plate, of course). I know removing the center wall is not an option with the VS in place. Thanks. ;-)

the car last night I think I'm about at the end of the road performance wise. While it felt no worse, any improvements were subtle if real and nothing significant or dramatic.

I'll know more later when I put it back on the car and re-test.

I had to search to find your response because I can't see your deleted post.

the car last night I think I'm about at the end of the road performance wise. While it felt no worse, any improvements were subtle if real and nothing significant or dramatic.

I'll know more later when I put it back on the car and re-test.

do some other mods such as ported heads?

I bet this thread looks like déjà vu on your computer. ;-)

throttle, especially before the secondary opens. Maybe I'm off base here?

wall removed added a hair over 30CFM... 30.89 or 30.29 at WOT.

But I have to face the real possibility that I'll feel much less improvement than someone with less efficient intake or possibly feel nothing at all. If that turns out to be the case then it may be time to do cams and bigger valves.

then dial up the power slowly and watch for the first depression. Then repeat 2-3 times for consistency. It's really not a very sophisticated system but perfect for measuring gain even if that gain comes beyond the CFM we can generate.

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