Merry Christmas!

Merry Christmas readers!

My blog readership is growing every month. I truly appreciate all you readers. I enjoy writing on this blog more and more.

I hope your holidays go well! I am currently with the in-laws for Christmas dinner.

Coming soon:

1. Aerodynamics projects and finished items.

2. How to start your own track hobby.

3. Simple fabrication tips - tools of the trade.

Drive safe and see you again soon.

*Above picture is not mine. From www.medgadget.com via google

S4 RX-7 Air Flow Meter and Adaptor Part 1.

First of all, please remember. Do the projects in my blog at your own risk. If something happens to you, it is your fault. Don't try this unless you agree with the disclaimer at the top of my blog! 

Oct 30th is my next track day. The weather is improving and it is a good chance to shoot for my 60 second goal. Unfortunately, my tires are wearing down also. I still need to do everyhing I can to bring down my laptimes. This time, I'm going to take some more drastic measures. I only have a couple of days. Need more power!

 
Check out my new intake setup. My RX-7 AFM is finally installed. Stock 1.6L airflow meter flows at about 165 CFM. At 7000 rpm, the stock 1.6L motor requires about 178 CFM.* The stock AFM is only good to about 6000 rpms. This is probably the biggest restriction in the intake system. The most cheapest and simplest way to remedy this situation is to go with an RX-7 AFM. If you got the money though, buy a good ECU and go with a MAP setup so you can do away with an AFM altogether. One thing to note: this will work for a stock 1.6L AFM also.

Which Air-Flow Meter?
The AFM out of the Series 4 ("s4") FC RX-7 (1986-1988) is the one you want. This AFM comes off of 13b rotory engines. This unit is compatible with the miata AFM. It is basically the same AFM with different dimensions. All you have to do is calibrate it a bit.

As you can see from the picture, the intake to the AFM is rectangular. It is also bigger than the hole in the stock AFM. Therefore, you cannot use the stock airbox, nor can you simply mount an aftermarket air filter on it. There are many adaptors out there that will work.

Choosing an adaptor
Many web-based vendors well cheap, simple mounting-plate type adaptors as pictured here. You can find these for less than 10 dollars on E-bay, and sometimes on Amazon. The problem with these is that the abrupt round-to-square transition is not very good for airflow. You want air to enter the AFM as laminar and fast as possible. You want the flow to stay attached to the surfaces of the intake tract as long as possible.

These are cast or machined units. Most of them are made from aluminum, but I think a few of them are made of steel or some sort of plastic. HKS, Bonez, Weapon-R are some brand-names that make this and I believe a few users on a Rx-7 forum make and sell this adaptor. Some of these companies used to sell theirs for under 30 dollars in the early 2000's. They are around 50-60 dollars now. Wow, 50 bucks for a mass produced adaptor of this sort? That disqualifies these units from our consideration. Lets make a Hi-Kick version of it. The adaptor I made has the tapered surface and should be plenty strong enough. Furthermore, the adaptor I chose is longer, and because of this the tapering is more gradual. It might even flow better!
 

Instructions

Okay, we're splitting peas here. The gains you get from having a tapered surface probably is not super-significant. And we're not going racing, where every gram of advantage counts. So why care? Because taper features apparently cost 40-50 more dollars, so we're going to come up with a solution and kick the problem in the head.
 
There are many ways to do this, but here are the specific parts I used.

1. Spectre Air Sensor Adaptor, Part 8141 or 81413   ($10-13)
2. Sheet of rubber, RTV sealant, or a usable OEM gasket on the AFM. ($5-8)
3. AFM off of a 86-88 RX-7 ($20-50)
4. JB-Stik or other putty-type expoxy that bonds to metal as well as plastic ($5-7)
5.Air Filter - From an S2000 or Honda Prelude. Prelude Part numbers: ($9-20, more in the $10 rage for the Prelude part)

  Fram CA6543
  Purolator AF4486
  Honda 17220-PK2-661

  STP CA6543
6. 3" Rubber or silicone coupler (PN: Spectre 8771) ($3-5)

Tools and other stuff you need

1. Dremel with a grinding wheel 
2. Sandpaper
3. Drill and 1/4" bit

The Spectre kit can be found on autozone or advance auto parts in the rice section. Everything else is available at your local parts store. The Prelude air filter is half the price of the S2000 filter.


Step 1. Line up the AFM, plastic plate, and the aluminum adaptor. Get the edges of the adaptor to line up with the opening in the inlet side of the AFM. Clamp it down. The holes on the adaptor plate of this particular kit line up perfectly with the AFM's holes. Mark the holes using a permanent marker, and then drill the holes using a 1/4" bit. This way, you have some room to move the items around since the holes are bigger than the holes in the AFM.

Step 2. Take the plastic plate that comes with the Spectre kit, and dremel or file down the opening so it will more closely match the opening on the AFM. Have the plate bolted in, along with the adaptor tube when you do this so it won't shift when you dremel the plastic plate. Resulting shape should be a rectangle with rounded edges.

Step 3. Sand down the plastic surface of the plate and the inner surfaces of the aluminum adaptor, on the areas that you will apply putty to. Wash it off with water and mild soap, rinse, and make sure it is completely dry before going to the next step. 
Optional step: Cut off the rubber plug that the Sepctre kit somes with.

Step 4. You can skip the sealant part of this step, but I took RTV and made a ring around the adaptor tubing, taking care to not to use excessive sealant lest it seeped into the surfaces where we are about to put epoxy on.

Optional step: before you start epoxying the entire thing, plug the hole made by the removal of the rubber plug.
Take the adaptor tube and mount it on the plastic plate, and bolt it in as how it would be when the kit is installed. Care to line it up properly. Don't mix up up and down, since the dremelwork will not be perfect. Mix up your epoxy and start filling the area left on the edges of the circle. Do one edge at a time, since you only have 5 minutes or so before the epoxy gets too hard. Be sure to press it in well so it will fill all the crevices and rough surfaces from the sanding.

Follow this diagram that I've attached, but it should be more elongated and gradual. You want a both convex and concave shape for it (I think there is a word for such shapes). Basically, you want the air to follow it up, over, and into the AFM without seperation. Try to get the surface as smooth as possible and the curvature as symmetrical as possible. Try to get the surface of the epoxy as smooth as possible with minimum bumps. Here is how to make sure the surface leading up to the AFM is flat: gob in excessive epoxy, then use a straight edge and press down, using the AFM inlet itself as a brace. Try to get the putty as smooth as possible with the least amount of bumps. It is kind of hard to do with your fingers. Matthew Wilson gave me this tip. Wet your fingertips with water, and it will allow your finger to move over the surface without gripping at it too much. It is also useful when making the edges of the epoxy more filleted. Remember: the smoother it is, the less sanding you will have to do.

Example of bad putty-work ;-)

Step 5. Let it cure for a few hours. Sand the surface of the epoxy with fine grit sandpaper until you are satisfied with the finish.

Step 6. If the gasket in your AFM is toast, use Silicone RTV to seal it properly by tracing the edges on the AFM where it is supposed to seal.

Step 7. Assemble. Self-explanatory. In order to use the Honda OEM filters, you have to use a flexible coupler since both the filter and adaptor opening is solid and inflexible.

Tada! Your adaptor is complete. J-B stik putty is pretty tough and resists vibration, so it should be good for this application. This should flow pretty well, though it might be a bit heavy side (maybe an ounce or two). Now that the adaptor is complete, you can mount any type of filter on it that has a 3" opening. Looks kinda cool doesn't it?

Enjoy!

Dog doesn't care about this new AFM set-up

Next up is an article on how to tweak the RX-7 AFM to run more optimally on your 1.6L engine, and how to mount it on the car.

* Flow data from www.solomiata.com, maintained by www.flyinmiata.com.  

Related links: Tuning the RX-7 AFM

Installed Seat & Harness Install (Seat / Harness install part 3)

It took a lot of trying-and-discovering-shit-it-doesn't-work to make the seat mounts. The harness install is much more straightforward and acceptable. Before installing, read the SFI and manufacturer warning on your harness. If you bought your harness used, which I don't recommend doing, go on the SFI foundation website and your manufacturer's website and read online versions of the guidelines. This is important and your life depends on it!

I used all stock mounting holes so there was no need to drill anything. This is possible on my year Miata because the right seat belt receiver bolts onto the transmission tunnel. This hole exists on all NA Miatas but on later models it might not be threaded.

I bolted in my sub and hip belts onto the stock mounting holes along with the stock seat belts so I can use the stock seat belt on the street. On the left side of the driver's side, loop the belt through the left harness slot so you can do this, or remove the stock seat belt altogether if you don't drive your car on the street.

No install is perfect, and here are my concerns of this install.

1. On my hard dog roll bar, the harness bar is a bit low. With the mount I made for the seat, the harness bar is about 1.5" lower than the shoulder harness slots on the Sparco sprint seat. This is barely acceptable. The harness mounting point should be on the same level or up to 10 degrees higher, and at most, -5 degrees lower. The solution would be to bypass the harness bar and bolt on to the rear deck using backing plates.

2. The sub strap is connected to the left seat belt mounting point. I hope the sub-strap hole on this seat is strong to keep the sub strap in line in the case of an impact. The sub strap, ideally would be mounted behind the sub strap hole on the floor under the seat or behind the seat. Instead, the strap on my setup goes to the side.

3. The hip belt angle works nice at my seating position. It looks like its at 45 - 50 degrees. Check out the picture with reference to the seat rails for reference.

On sedans race cars, some people mount all of the belts at the rearmost part of the race car to minimize any harsh angles and let the bolt-in tabs work at a more perfect angle. I don't recommend this because using really long belts or fully extended belts will result in too much stretching in the moment of an impact.















Final notes
I went on a test drive. This is my first experience in a race seat in a production car. Amazing! I felt very much connected to the car. The feedback received was very detailed. I won't talk about streetability here since that is not the focus of my blog, but it blocks rear view and hard to climb in and out of the car. Also, if you are road racing, you really should get a removable steering wheel.

I could not use any washers on the seat-tube mounting bolts. Also, the bolts were cut so that the thread length was only about 2.5 times the bolt head. I don't know if that is enough, but its slightly shorter than the stock bolts that screw into the stock seat. Also, the rectangular shape of the tube and the fact that the mount is four pieces makes me question how well it will take a side impact. For these reasons, it is my opinion that this is not safe enough for a road-racing application. Whether it is okay for track days, you decide.

Copyright 2009, 2010 (c) by Jerry Lee.

Fitment and Seat mount fabrication (Seat / Harness install part 2)

Disclaimer: I make no warranties on the safety of these mounts. Any claims I make here are unprofessional opinions. You must make your own independent judgment on whether to follow these instructions or not. I will not be liable for any injuries any persons or damage to your property resulting from anything you read from this blog.














Sub-disclaimer: personally, I would not use this mount for road racing. I'll state the reason why later.

The stock seat's mounting hole centers are 330mm apart. The sprint's mounting hole centers are 345mm apart. I started modifying the holes on the stock sliders/rail to make it work, but after a bit of drilling I realized it was not working. The 15mm difference in width does not allow for the bolt head to fit inside the slider properly. When the holes on the rail are widened enough to accept the Sparco seat, the bolt head will hit the slider. Others have narrowed the bolt heads to make it work, but the smaller bolt head, inability to use washers, and the widened holes on the already thin gauge steel on the sliders drove me away from using it. Therefore, I decided to make a simple adapter. Before I get started, measure twice and cut once! Saves a lot of time. Also, drilling by hand inevitably brings some error so be prepared to enlarge holes. Don't mess up too much. Things needed: -Two steel square or rectangular tubes. Make sure the steel is decent grade, ideally a cold-rolled steel like 4130/4140. The wall thickness should be pretty good, like 11 gauge (.125"). The tube must be at least 1 inch high. -four M8 bolts with a small head, shorter than 16mm. (I used a hex bolt) Use 10.9 gradr or higher. Thread pitch is 1.25mm -four M8 nuts with same thread pitch (10.9 or higher) -assortment of drill bits (small, medium bits leading up to 3/8") -dremel with grinder and cutting wheel -tape measure and straightedge

Preparation
Cut the tubes. Cut the tubes the same length as the sliders are. Should be around 14". Mark these tubes on all sides with a sharpie so you don't get confused. Arrows and writings will do: front, outside, inside, left and right. If you can't find a sharpie, masking tape and pen(cil) works too.

Tube - Slider mounting holes
Refer to this diagram if you are confused at any point.

Take a tape measure and measure the distance between each hole centers on the slider. Measure the distance to the ends of each hole and plot it out on the tube. To do this, measure the distance between A and D, then C and D. Add the two numbers and divide by two to find B and D. Using the distances, mark two dots for each distance on the tube. Draw a line using a straight edge and make lines like A, B and C. Stick one end of the slider and tube when finding an anchoring point for the tape measure, unless you can cut tubes perfectly. The picture is obviously not to scale, and keep in mind that for one hole C and D will be very close together. Mark the center point on the centerline of the tube along the longitudinal axis. Then, move the center points 2mm towards the center of the seat. This line is E2. The intersection of this line and the lines marking A, B, and C is where you will be drilling and where the sliders will bolt in. The hole sizes should be 8-9mm, or 3/8".


Tube - seat holes
Flip the tube over. Find and mark the longitudinal center axis. Draw another line parallel to the center 5.5mm apart, towards the outside of the center of the seat. At least 15mm behind the front hole you drilled on the other side, mark center points for two points that are 271mm apart. Find those points on the 5.5mm offset line and drill with the same size as the previous step.
Access Holes
You will need to find a way to put your hex key for the bolts that go into the seat. Using the holes you drilled on the seat side of the tube, drill straight down. Use the 3/8" bit so you can drill a small spot to find the center point. Then work your way up from a small bit to 1/4", or however big your hex key is.

Test fit and installation
After all these holes are drilled, test fit all the components and see if everything lines up. In my case, it fit at first try. Since rail-floor mounting holes are over-sized, if you followed proper directions this should work. Torque everything very well and install. If something doesn't line up and the error is minimal, dremel the holes a bit bigger. Use grade 8 washers whenever you can fit them.

Copyright 2009, 2010 (c) by Jerry Lee.