Penny-pinching car geek's guide to racing, track days, and car build. DIY projects, product reviews, and interviews.

Thursday, March 31, 2011



Of course, my original post is untrue. My car does not have all those cool mods, I made no money on this blog, and of course I don't have substantial savings.  I'm what you call "Judgement-proof" right now.  Also, I haven't been notified of any sort of intellectual property infringement.


Click on photo to see original April fools post.  You shoulda seen my facebook.  People were even talking about NSX performance. Oh man I love pranks.

Flow visualization Techniques - Vortex Generators Part 2

We know that a typical hardtop will see flow separation a few inches below the roofline.  I wanted to see what the Airtab® vortex generators did to help delay separation.  One simple flow visualization technique is tufts testing.  I did the testing on the rear surface of my car.  My wife really didn't want to help, but she did.  Bless her.

Tufts testing is really easy.  Stick on a bunch of strings onto the surfaces that you want to test at.  Now, a lot of people use yarn.  Yarn might be good enough for these purposes but it really isn't ideal because it is too heavy.  A good choice is a lightweight monafilament string, such as fishing line.  The compromise you have to find is visibility, weight, and cross section of the string.  I think a florescent colored fishing line would work well.

I just used very lightweight nylon strings for this experiment.  The strings should be 4-5 inches, not too long and not too close together to tangle themselves.  I used varying lengths from 4-20 inches just to see what it does.

What you are shooting for is turbulent but attached airflow.  This means a gyration of 20-30 degrees or so is acceptable.  What you don't want to see is strings circling, moving irratically, which is an indicator of detached flow.

Hard to see, but this photo is from a higher quality HD video. The video shows the movement of the tufts pretty well.

Previously seen photo of the VGs
Surprising results.  Flow stays attached all the way to the bottom of the hardtop; at about the bottom 2-3 inches it separates a little bit, then reattaches on the trunklid.  It shows attached flow all the way to the end of the spoiler.  Sucess!  Looks like the Airtab® Vortex Generators are doing a great job.

Another interesting thing to note is that air seems to leak out to the side edges, under the spoiler.  It affects the flow on the quarter panels.  Interesting.  No doubt I'm losing out on some lift there.

Some other interesting, lo-cost flow visualization methods.  Pictures tell a thousand words:

This was done by Jeff at Slick Auto using a high velocity air gun.  The model is Guardair 80LJ.  There is a piece of 5' cotton string taped on.  Thanks for the tips Jeff!

Technical Advisors:
Andrew Brilliant, well-known aerodynamicist in the motorsports industry.
Unnamed engineer who worked on developing the Airtab® VGs.
Jeff @ Slickauto

1.8L Brake Upgrade

There are many articles out there on how to change out the 1.6l brakes to the 1.8l brakes.  So I won't go over it step-by-step.  I did, however, take a bunch of pictures to put things into perspective.

Link to a very good step-by-step: Miataturbo how-to

Things you need: All you need are rotors and caliper brackets from each corner of the wheel.  I got a pretty killer deal for it in Tampa.

I only did the front swap because I didn't have enough money to do the rear brakes.  Data shows that my braking improved a little bit, but not much.  Given the same pedal pressure, I think the rear brake upgrade will help a lot.

I didn't think the pictures on the Miataturbo website shows the difference for most people, even though it is a more accurate picture.  So here are mine:

Friday, March 25, 2011

Game day

Its 3AM, and I just got done bedding in my brakes and fixing my splitter.  I didn't get around to finishing my wing mounts, but I will still have my spoiler and splitter on the track tomorrow.  Tomorrow is the day.

I finally have competitive wheels and tires.  Its time to make a serious run at my first target: breaking the 1 minute mark at Gainesville International.  I don't know if I will get there, but I am going to make a very serious run for it.

I have to go to a conference in the afternoon, so I will only have 2-3 hours of track time.  I am splitting my day with Luis' brother.  Alls well, since the fastest part of the day is in the morning.

Aside from the wheels and tires, I also added some extra travel in my suspension with NB tophats.  I am very looking forward to the day.  Wish me good luck!