<center><img src="http://pictureposter.audiworld.com/711/rxtb.jpg"></center><p>You can always tell when it takes gobs of work to net very small increases in flow. I've now got an "RXTB" that is flowing over 740CFM and if I can get it to 775-790CFM I'm going to have to set it down, walk away from it.

Can anyone tell from this pic exactly whats been done that set this apart from an ordinary XTB?

Hint: grinding/polishing has nothing to do with it.

Next I'm going to grind it's butterfly shaft screws and relieve the butterfly shafts like I did on the RTB. Then whatever it flows is all it's ever going to flow. This is VERY obsessive-compulsive work. And don't even ask... you can't afford it. Hell I can't afford it!

However, you state that you did not do any "grinding/polishing".

Regardless, 740 CFM, damn, Mance, you're good!

Theoretically, what kind of hp can an engine make with 740CFM air flow?

Other than that... no clue. Primary looks kinda oval shaped, but I think that's the angle that you took the pic at. You wax it up to make it flow better ;)

Nonetheless, you never cease to amaze me.

<center><img src="http://pictureposter.audiworld.com/711/rxtb2.jpg"></center><p>granted I did port a little but it was secondary to milling and only for dresing the sharp edges the milling left behind.

I don't know how or why this works but I knew the old 5 cylinder 20V cars had a TB with a center section missing and I use to see 20V Audis in 1989-1991 racing in the BTCC and there were people in England who did this type of work on those throttle bodies. I couldn't find them for reference so I just hunkered down and did one lightly then flowed it and it showed light gains so I got more aggressive. At this point I maxed-out... no additional gains showed up with the last .040" depth so I stopped.

In this pic you can see more clearly just how wide/deep I got. And I know it does work but for the life of me I can't understand how or why it works. And like the dog chasing a car what would I do with it if I caught it!?!

wow. that's all i gotta say.

I'm guessing you'd get the 795 CFM if you did this to the special TB then huh?

Good work mance... keep it up

<center><img src="http://pictureposter.audiworld.com/711/rxtb3.jpg"></center><p>
I now need to go back and apply more expoxy to the outside of the primary venturi as my latest grinding foray ate thru the walls and epoxy layer for the third time today. After I cure the epoxy, then hone it smooth inside I'll go for one last flow attempt to see what it's up to.

In this pic you can also see the shaft screws have been ground flush with the shafts and the reliefs/diffusers ground into the shafts. These will flow more and help diffuse any turbulence going into the intake manifold.

the deepened center wall I mean.

check yah later

incorporate all/some of this into their throttle body. But the ones I offer will remain unchanged from what they were before I started this.

I'm trying to wrap my mind around the magnitude of benefit when going from stock (~300cfm) all the way through this monster (~750cfm). I suppose it's the units that are getting to me. I know it's industry standard to measure the flow capability in CFM. I remember you saying in a previous post that the test is to ramp the flow until there's a knee in the pressure drop curve (the part becomes "restrictive"). I'm having trouble figuring out, though, what 700cfm means to our engines that will only flow something on the order of 300cfm at 5000rpm.

So tell me if this makes sense. If you think of the engine as a positive displacement pump, then at a given RPM, it's moving a given volume of air. Assuming that the air starts at ambient pressure outside the car, and ends at some lower pressure (vacuum) as it enters the cylinders due to the "pump" sucking the air through a number of restrictions (air filter, MAF, TB, etc..) in series. The final pressure will be a function of RPM, but for a given RPM the volume of air will always be the same. The mass of air (which is what we're really interested in) will be determined by the pressure and temperature as it enters the cylinders. The higher the pressure, the higher the mass, the more power the engine will make. By boring the TB, for example, what you're effectively doing is reducing the pressure drop through that component, and thus allowing the air to reach the cylinders at a higher pressure (closer to ambient, thus more mass flow, and more power. It seems that by measuring the pressure drop through the modified component over the range of volumetric flows corresponding to the engines operating range, and comparing that to the stock component, one would be able to calculate the increase of air mass flow and thus the power gain as a function of RPM.

I'll try to do the calculation tonight. Do you have any idea what the magnitude of delta P change is at the flow rates of interest for any of the components you've made?

I'm not, by the way, asking this to make any judgements regarding the value of your products. The engineer in me just likes to understand what's going on. I thought it would be an interesting topic to discuss.

In the field of metal work, isn't a mill a machine for grinding/cutting??? Doesn't "to mill" generally mean to grind or cut???

You obviously use the verbs "to mill" and "to grind" differently--Why?

See Definitions below.

__________________________________________________ ________
grind

\Grind\, v. t. [imp. &amp; p. p. Ground; p. pr. &amp; vb. n. Grinding.] [AS. grindan; perh. akin to L. frendere to gnash, grind. Cf. Grist.] 1. To reduce to powder by friction, as in a mill, or with the teeth; to crush into small fragments; to produce as by the action of millstones.

Take the millstones, and grind meal. --Is. xivii. 2.

2. To wear down, polish, or sharpen, by friction; to make smooth, sharp, or pointed; to whet, as a knife or drill; to rub against one another, as teeth, etc.

3. To oppress by severe exactions; to harass.

To grind the subject or defraud the prince. --Dryden.

4. To study hard for examination. [College Slang]

grind

\Grind\, v. i. 1. To perform the operation of grinding something; to turn the millstones.

Send thee Into the common prison, there to grind. --Milton.

2. To become ground or pulverized by friction; as, this corn grinds well.

3. To become polished or sharpened by friction; as, glass grinds smooth; steel grinds to a sharp edge.

4. To move with much difficulty or friction; to grate.

5. To perform hard aud distasteful service; to drudge; to study hard, as for an examination. --Farrar.
__________________________________________________ ________
mill

\Mill\, v. t. [imp. &amp; p. p. Milled; p. pr. &amp; vb. n. Milling.] [See Mill, n., and cf. Muller.] 1. To reduce to fine particles, or to small pieces, in a mill; to grind; to comminute.

2. To shape, finish, or transform by passing through a machine; specifically, to shape or dress, as metal, by means of a rotary cutter.

3. To make a raised border around the edges of, or to cut fine grooves or indentations across the edges of, as of a coin, or a screw head; also, to stamp in a coining press; to coin.

4. To pass through a fulling mill; to full, as cloth.

5. To beat with the fists. [Cant] --Thackeray.

6. To roll into bars, as steel.

To mill chocolate, to make it frothy, as by churning.

mill

\Mill\, n. [OE. mille, melle, mulle, milne, AS. myln, mylen; akin to D. molen, G. m["u]hle, OHG. mul[=i], mul[=i]n, Icel. mylna; all prob. from L. molina, fr. mola millstone; prop., that which grinds, akin to molere to grind, Goth. malan, G. mahlen, and to E. meal. [root]108. See Meal flour, and cf. Moline.] 1. A machine for grinding or comminuting any substance, as grain, by rubbing and crushing it between two hard, rough, or intented surfaces; as, a gristmill, a coffee mill; a bone mill.

2. A machine used for expelling the juice, sap, etc., from vegetable tissues by pressure, or by pressure in combination with a grinding, or cutting process; as, a cider mill; a cane mill.

3. A machine for grinding and polishing; as, a lapidary mill.

4. A common name for various machines which produce a manufactured product, or change the form of a raw material by the continuous repetition of some simple action; as, a sawmill; a stamping mill, etc.

5. A building or collection of buildings with machinery by which the processes of manufacturing are carried on; as, a cotton mill; a powder mill; a rolling mill.

6. (Die Sinking) A hardened steel roller having a design in relief, used for imprinting a reversed copy of the design in a softer metal, as copper.

7. (Mining) (a) An excavation in rock, transverse to the workings, from which material for filling is obtained. (b) A passage underground through which ore is shot.

8. A milling cutter. See Illust. under Milling.

9. A pugilistic. [Cant] --R. D. Blackmore.

No dust!

in wood a mill would be a knife and a grinder could be a rock or cinder block... anything abrasive.

And as the donut guy says a grinder creates dust like with sandpaper on wood. A mill produces shavings from wood like a knife. One cuts material the other abrades (rubs) material away.

You have a grinder you dont have a mill.


But I believe we're straying far wide of the subject today which isn't related to cutting/grinding tools but flow rates.

Theoretically speaking . . . we have more than doubled what we started out with. I am guessing that you could slap one of our TB's on a big ol' 400 hp V-8 and adequately feed it? Or not?

but I think the stock IM plenum would work well for one as it's a HUGE capacity probably capable of holding right at or over 1.5 gallons of liquid volume.

What I'm trying to do, vague and ambiguous as it is, is to hit the wall. That is to say keep making the throttle body capable of more/greater flow until I hit a feelable no performance increase on the butt dyno or 15-60mph timed runs. It's got to happen sooner or later as I'm 250% above what Audi engineers deemed our engines require. But even if the result is purely enhanced throttle response with no accompanying HP/TQ that has worth, value and merit.

But I'm also rapidly approaching the point of diminished-to-zero return even on the TB this time and what I end up with is all I can get. But someone had to take it there as the logical conclusion.

Surely somewhere behind me is the stopping point. The last CFM that yields any true, measureable power. I don't know what that number is/was and minus the equipment to measure I'm doing the only thing available to me. Flying by SOP and hoping for the best. And the fact that I havent done anything yet that makes the car the same or slower is powerful incentive to keep scraping away in this direction.

And I'd love to know, even if only theoretically, how/why some of this works. But I have no deltas or anything beyond CFM to help you. But while you're at it wouldn't break my heart to hear some reasons why a common wall between two venturis would be/could be restrictive. Or more aptly why removing that wall increases CFM?

your number of 400 is likely very very close.

like is it really worth my effort to grind down the center, in terms of flow gains?

check yah later

and maybe it's over-kill. Might never feel it. But I see at least as much of me in you to know you'll never be satified wondering. 30CFM no matter how ya slice it is still 30CFM after all, right?

I know you're gonna. When are you gonna know yer gonna? Aint obsessive-compulsive grand!?!

I think you may have misunderstood what I meant. You should be able to use the differential pressure gauge that you used for the ram-air development to measure the differential pressure through the component on test. What I envision, without actually seeing your flow bench, is mounting an entire stock intake system, intake manifold through air box, and measuring the pressure differential between ambient (outside the airbox) and the inside of the manifold plenum at different flow rates up to the max you expect the engine to flow. Then, by replacing any or all of the stock components with modified ones, you can evaluate the change in the differential pressure. Knowing those numbers, I think I can calculate the change in air mass, and therefore the power increase. Does this make sense yet?

On the subject of removing the connecting wall.... Intuition tells me that your basically eliminating some of the skin effect. For example, one 1"x2" square tube would flow better than two 1"x1" tubes because there are less walls to cause drag. I think you're just eliminating the drag of one wall.

I just got back from a run and came to the same conclusion--by eliminating the center wall, you turn the entire TB into one large velocity stack versus two smaller ones.

Additionally, I speculate the divider-less design allows for much better throttle response, because each valve opens from the center outward allowing the air to more quickly get through the valve at partial throttle. Regardless of how quickly we slam the pedal with our foot, the air flow starts from the center wall. Decrease the center wall and you increase the air volume near the inlets. Reasonable explanation?

I was looking on ebay for thottle bodies(core to send you) and came across this. I was going to make a new post with a link to it. Not to give you pointers but rather to ask if you were thinking of doing this on any future TB's. Almost exactly like the new prototype you have come up with but more restrictive....

Also, I recall you mentioning that the RTB(I think that was the name) caused you to loose a little bottom end because of it's flow property's. What will this likely do? I am most concerned about low-end power.<ul><li><a href="http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&amp;category=33558&amp;item=2464414 973">NEUSPEED THROTTLE BODY</a></li></ul>

"if you're gonna be a dog, why be a toy poddle?" -woof

check yah later

anything more than -10inHg or +10psi will rupture the diaphram. I'd need to buy a slightly heavier duty unit but thats a pretty big-ticket item hovering near $500.

Just connect it backwards to read the differential as a positive pressure, i.e.the high side at ambient and the low side in the plenum. At 300-350cfm I wouldn't think there should be more than 10psi (20in Hg) of vacuum.

BTW, I'm not trying to make more work for you. I'm just having a dialog around measuring and benchmarking performance improvements.

and void the warranty. This is their lowest reading digital manometer. 11psi/inHg is instantly fatal. Even a blip of higher than that and this instrument is toast on the spot. I wouldn't feel very comfortable using it. There are higher pressure units but this one was the most accurate for airbox differentials going down to .001psi. The higher you go in pressure/vacuum the more coarse the values.