TOPIC: Throttle body Dimples

So I thought I'd re-explore the idea of adding dimples on the bore wall surface of a throttle body. I'm doing this to invite thoughts from others here. My ideas of adding the dimple cuts are still murky. I did add them to the TB I'll show here, and the customer was very pleased with overall results of this job. It was on a VW Passat. Far as I know there has been no before/after testing of the dimples in our programs. It has been just something I thought might give a benefit. Another G-Man, Juan Reyes, did use them in his own Groove work, it was he who seemed to first "test the water" in a significant way here.

The dimples are of course used on golfballs. I've seen a picture or two online of another use on a spherical body- they were added to the surface of top-secret spherical bombs. These were the ones invented by British scientist Barnes Wallace, used by the RAF to destroy German dams, the famous Dam Busters of WW2. To see a video of one of these weird bombs look in this link at the 10:00 min. mark:

So the dimples were and are known to have a benefit, in other applications. Using imagination, I bought some small Dremel ball cutters, and added 'em to this TB Groove job. I realised that Gadgetman bits weren't the ones to use, just regular un-modified ball cutters. In case you read this and think you can cut the Groove with these regular Dremel ball cutters--No you Can't. You need the real Gadgetman ones to do that. Grooving and dimpling are separate operations. Here you will see them combined in this TB.

I'll add that I visualised the Groove and the Dimples working together. I thought that the dimples might intensify the Groove's effect by holding more air in the boundary layer on the bore wall. I also imagined that the "stregnthened" or "densified" bore wall boundary layer air- might act under some conditions like a dynamic "restriction" in the throttle body. This could be sort of like a weak Venturi effect to the more central main airflow, causing it to speed up. This, in turn, could improve cylinder filling and promote better air/fuel charge mixing. Over and above what the Groove does alone.

Ideas, anyone?


Tracy G

Thank you for coming back into the fold, Tracy! I have MISSED YOU!!!

As you say, there is a lot of research into "dimpling" the surfaces in a fluid flow system. Golf bvalls and airplanes are two primary markets (and in that order!) Strange, don't you think that people are more interested in how far a GOLF BALL flies, rather than how far a PLANE can go on a few THOUSAND gallons of fuel?

My theory is that the dimpling (shape notwithstanding) allows the air to create its own kind of "roller bearing" reducing drag in that fashion.

That's MY two cents worth!

OK, I've finally found videos that explain the actual math and physics of what's happening.

Physics 34 Fluid Dynamics (1 of 24) Viscosity & Fluid Flow: Introduction - YouTube touches on fluid (air) sticking to the boundary layer (bore wall of the intake tract). The Groove, post throttle plate, and the dimples before, free that air up into the stream that is measured by the MAF to calculate how much fuel to deliver at the injectors to come close to 14.7:1. (the O2 sensor fixes it after wards...)

Physics 34 Fluid Dynamics (3 of 24) Viscosity & Fluid Flow: Reynolds Number (Re) - YouTube gets into the math. Pay attention to how the units get cancelled out, and what remains. Remember that the ECU, our sworn enemy in modern cars, can only do what they're programmed to do. Our little groove and dimples mess that up - actually, we just show it how it thinks isn't quite right - and that can cause some computers to "lose their mind" and throw codes. Luckily, we know what to do to fix that.

I'll come back another time and explain how our groove (and the dimples) connect these 2 videos. For now, watch them with open minds and absorb what they have to say.

I must confess that math was my worst school subject- starting in first Grade.

Ron, your analogy with the golfball dimples- of the dimples making little "roller bearings" seems a good visualization. Each dimple creates a rolling vortex. The dimple shape makes a tight round ball of air that sticks into the depression of the dimple. The many dimples on the golfball in combination create a stronger boundary layer that "sticks" to the golfball surface. A key to why this makes the golfball fly further is a bit non-intuitive. The air "sticking" to the golfball is reducing the area of low pressure in the ball's wake. That reduces aerodynamic drag.

The dimples create a higher pressure zone, a layer of denser air clinging to the ball as it flies. Now- I'm not formally trained in this stuff, I'm simply groping and visualizing here. One uncertainty for me is- in the golfball's case it presents it's shape to the air it flies through such that the pressures should vary according to what part of the ball you look at. The front side is in tangental opposition to the air. The sides are parallell or close to, the airflow, etc. IT's a sphere.

But- would the dimples as I did in this TB, gather air like those on the golfball? I'm making a stretch, an assumption. I mean, in studying what Juan Reyes put up, he did give a link ( I Think it was) to some European website, showing what looked like research lab. There were pics of some cylinder heads or intake manifolds. I couldn't read any of the text, I'm not even sure what language it was. But in any case, somebody had spent time adding dimple shapes to the inner passages and ports, it looked like CNC work. Somebody thought it worthwhile to experiment with this, and spend some money on it. So I did Monkey See Monkey Do...

This example was a mail in Groove job, and the Customer was well pleased w/ results. I don't recall exact numbers, but he did report a substantial gain in both performance and economy. This is all anecdotal of course. I'm simply thinking the Dimples might be an addition to the Arsenal.

Yes, it it nice to be in here again, Ron! You and Greg both know how much I dig this stuff. You are both Brainiacs, I'm merely a humble Toilet Tuner and Lightbulb Faith Healer!

Tracy G

Earlier this week, I had Wendy's TB off, so I took the opportunity to put a few dimples in on the upstream side of the bore. I don't think I went anywhere near as deep as these, and I only did them so that whatever boundary layer air that gets thrown up into the more mobile part of the airstream hits the plate and is directed towards the groove. I also did some shaping of the plate's downstream edge, the one that passes over the groove- something I didn't do as confidently in the initial groove process, so I may have been a bit too gentle with it.
In the small amount of driving I've done since then, I can tell there is a difference in performance, but mileage numbers will have to wait a bit more. I'm hoping a slightly stronger groove effect makes for slightly better mileage.
...which reminds me that I haven't updated Wendy's megathread with EFIE numbers. Time to let the proverbial cat out of the bag:
when I started down this road a few years ago, I was looking to spend less at the pumps; since I achieved that, I've been looking to extend my range: I wanted to see if I could hit 1000km/68L (that's 600Miles/18USGallons) in combined city/hwy driving (originally pre-mods it was 550-650km, 3-400 miles give or take; post groove and ignition upgrades, I was fairly consistently 700-800km). Now, after the EFIE install, >900km fillups have become the norm.
Dimples may take me over my initial target.