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I think this is the first time I've looked at your build since I'm not into rx7s. FWIW, very nice job all around.

Well I have been putting this step off, mainly due to not having the guts to destroy otherwise good parts and not really knowing what I wanted to end up with. The Plan is to use as much of the intake system as possible so I do not have to fabricate that what is already done. The S5 RX7 intake is made up of a Lower Intake Manifold (LIM); an Upper Intake Manifold (UIM); a Plenum, a throttle body and a Mass Air Flow metering system. This is not counting the miscellaneous air tubes and filter housings etc. I plan on a Megasquirt system to control everything.

The LIM consists of 5th and 6th port actuators that I wanted to leave operable to help with lower end power. This meant that the LIM had to remain. The UIM contains the Bypass Air Control (BAC), 2 of the 4 fuel injectors (the other 2 mount directly to the center housing) and a black magic sort of thing referred to a Variable Dynamic Effect Intake valve (VDI). The Plenum mounts above the UIM. The Throttle body is a 3-barrel system with some progressive linkage opening 2 of the three barrels later.

I knew that I did not want to accommodate the height of the factory intake system as this would affect the hood (bonnet) of the Locost. I needed to figure out some other means. My fabrication tools are fairly extensive but I do not have access to Mills and lathes.

So today I got brave and decided to eliminate everything that didn’t look like it would fit but keep everything else. So I carefully eyeballed the point on the UIM where the air passages were perpendicular to the centerline of the engine and started using the cutoff wheel and Sawzall. The photos show the result. I have kept all the stock locations for the injectors and fuel rails. I kept the BAC valve I got to keep the 5th and 6th intake port actuators. I threw out the MAF sensor as I will be sensing the manifold vacuum for the Megasquirt.

It is very easy for me to visualize the remainder of the design from here. Add a new plenum to the existing ½ UIM and a new throttle body. Keep it low and point it out the front of the engine where the alternator used to be. I quickly worked up a sample of what the plenum might look like. The only aluminum welding needed will be to construct the plenum and attach it to the remaining ½ UIM. Everything will fit under the bonnet with room to clear.

I hope to receive the radiator and fan later this week.

You've got 'Cajones' my friend...

I love the rotary mill. A few RX-7's in my past made me really want rotary power in my locost, but I just couldn't find a donor I liked, and quite frankly I wasn't wild about the conversion of MacPherson struts to A-arms up front so I went Miata. If I'd seen your posts before I pulled the trigger on the miata I might have still gone RX-7. You're fab is excellent. Nice work.
I'll be interested to hear how the torque curve comes out as a result of monkeying with the intake manfold volume/ runner length. I have a well worn miata mill I will probably drive till it blows up, then swap in a decent 13B.

Keep posting!

Nice looking build. I'm doing a similar project - Here is my website http://sites.google.com/site/millerlocost/

I have additional pictures I'll be adding tomorrow. I finished welding up the fuel tank and mounted it with the fuel pump and float unit installed over the holiday break.

I don't have much info on the rotory but I received the donor car for free, so I figured I'd use it. Apparently one rotor is leaking but it runs - I'm going to get it in the locost and hopefully running - maybe after that I'll do a rebuild with new rotor seals and such, but I'd like to get it in the car and running first.

I am having trouble locating the rear brake calipers as the emergency brake thing hits the chassis - I see that you swapped some hardware from one caliper to another to make it work. Can you let me know how you swapped things and if you have a close up picture of your cable mounting bracket?

Phil, nice looking build you have going. This is my first rotary engine too. Mine has 0 compression on one rotor and will have to be rebuilt.

I see you ran into the same emergency brake issue that I did. The part that I swapped between the left and the right side was the eccentric that gets rotated by the cable. I swapped the eccentric shaft and the brackets bolted to them as a set and the return spring. I had to fab the bracket that now holds the return spring/stop-limit and the brake cable. By doing this swap, I lost some range of motion that the eccentric pushes on the egg-shaped rod internally. I think I have enough to perform the brake function but I have not gotten any further on that part of the build. You would have to check for yourself if it workable. I currently have about 1/4" clearance to the frame which I think will work throughout the suspension range.

I hope that these pictures and the above description help you resolve your issue. The parts are on the car right now and difficult to get good comparison photos.

If I were to do it over, I would look into swapping the entire left and right side hubs and brakes. This would put the brake caliperss behind the axle and that would get the cable away from the frame. But this would require redesign of the entire rear suspension components and I am not willing at this time to go backwards in my build. I'm not even sure if, functionally, it is a good idea.

I'm in process of a similar build but am going a little different route on the intake clearance.... I bought a pair of ITBs from Tweakit.net (not locost...) . These are going to protrude through the hood, but should look pretty good - somehow... I bought a MS system designed for a rotary, along with a CAS and a stim board. I got a great deal on a Haltech and picked that up as well. If you are interested in the MS system, PM me. I'll let it go for a fair price . Good luck on everything - try to keep the runners the same length as they were - there are some complicated reverberation pulses generated at certain rpm/loads. You will lose HP if you shorten them!

Geauxkart, I really understand, at about a 5% level, the acoustic charge bit with the rotary engine. I have some limitations as to what I can do and what I can't. I have to balance that with my goals for the car. What I can't do is replicate the factory intake system in a flatter package. I just don't have the skills. What I can do is a bit of design and fabrication but not any TIG welding. I too, have been told
What I don't understand is the fact that the weber DCOE & ITM bodies routinely get more HP and they run on significantly shorter runner lengths. How do those two statements coexist? There must be other things that come into play. However, I am not trying to squeeze out every last HP from my engine. My first goal is to be able to sit in the seat, turn on the ignition, andfire up the engine. Having the MS will give me more fun in tuning it from there.

My design will have about the same intake volume as the factory setup. My thinking is that the acoustic charge MAY still occur at the same RPM as sound MAY reflect off the back wall of my plenum. The distance to do this is about the same as stock. I have yet to decide whether to use the stock throttle body or make a swap to a Mustang type 75mm body. The latter is smaller and easier to implement. If I can find a used one at a reasonable cost, then that is the direction I will go.

As for the Megasquirt, Santa was good to me so I am already into the building stage of my kit. I have been in the electronics field for many years and the building of the kit doesn't scare me. In reality, I wish that they made the SMT version (V3.4?) available as a kit. I can't wait to complete it and flash some lights! I still need a stim board but have decided on the JimStim over the std stim board.

There are several of us here building with the rotary engine. Each of us are going in slightly different directions as to intake and exhaust designs. It would be very interesting to see the results of these builds side by side.

Thanks for posting the pics RX7locost, I think that will help. I'm currently trying to install new rear wheel bearings and its a real bitch. I removed the old ones easy enough by knocking them out (hammer and chisel) and removing the outside races by welding a bar inside the race and whacking it with a hammer. I don't have a press to install the new bearing "pack" so I'm trying to come up with a homemade tool. Once I get these in I can work on the calipers and install the ebrake cables. I'll let ya'll know how they come out.

I thought I needed to change my rear bearings. I noticed they were very loose as I was doing some fab & fitting work. I found out that the inner bearings were 2-piece assemblies and needed to be held tight to each other. When I installed the axle and snugged down the axle bolt, all the slop went away.

I looked long and hard before I went down the road of changing out the bearing. I even have one new bearing sitting on the shelf that I bought just in case. It is from that new bearing that I learned about the 2-piece construction.

I hope you succeed in your efforts. If not, then a quick trip to the local shop to have it pressed in may be in order.

There are a couple of potential issues with modifying the length of your intake runners, but I doubt any of them will be major deal breakers. First because a rotary doesn't have valves when the apex of a rotor crosses the intake port alot of pressure is forced backwards up the intake runner. I believe the volume of the original runners is based on the mass of air needed to resist or minimize the effects of that back-pressure. Second rotaries do not develop alot of torque and they do generally create more torque (just like most piston engines) when a longer intake track is used.

I believe the reason ITB and dual carb configurations make more power is because they generally are fitted with less restrictive intake runners and a much less restrictive intake system overall. Many of those setups do trade off some low end torque for more top end HP, though.

Your setup will probably be acceptable with the much lower weight of your car. And if you go forced induction everything above essentially gets tossed out the window anyway. Um, kind of anyway .. when the car is running in vacuum (most driving) it will still follow the above tendencies; when the car is in boost the the positive pressure in the intake track will essentially make runner length immaterial.

Not much happening in the Garage lately. It is hard to get motivated when it doesn't get above zero degrees (F) all day long like today!


Santa was good to me and I received my Megasquirt 3.0 board running the MSII processor. I've been doing a lot of reading about it. I have built it up. Boy are there a lot of build decisions to be made along the way depending on what it is intended to operate. I have not configured it yet but have decided to run the RX7 dual VR ignition input and drive the std RX7 ignition system. I will have to build a 2nd VR circuit as the std 3.0 board has only one VR input.

I just finished my Digikey order to mod the MSII for BAC (Mazda term for idle air control) and the parts for the 2nd VR circuit. I also ordered the Jimstim 1.4 to test everything out.

Keep warm!

The Jimstim is completed along with the mods on the Megasquirt for the 2nd VR input from the CAS. I have been playing with it for a day or so on tbe bench. It seems to be working out fine. For you techno-geeks, it is a Megasquirt with MS2 processor on a 3.0 PCB running beta 2.1.0 firmware. So far, the lights are blinking and the gauges on the computer seem to be doing what they are supposed to do. Time to pack it up and put it on the shelf for a bit until it is needed.

Again not much to report. I scored a throttle body on e-bay. Not a Mustang TB like I originally planned but a Taurus TB. It was more Locost than the Mustang TB at $15.00 delivered. It is only 50mm diameter. I've done some research and with the limited power (<200HP) capability of the N/A engine, this should still meet my needs up to my redline of 9,000 RPM. At least to start with. It will present less than 1 psi pressure drop and keep the air speed only slightly above 300fps. When I get it all together. if I need more HP, the larger Mustang TB should drop right in. I found a nice website for comparing flow, air speed and pressure drop based on tube diamater. Not an exact modelling of a TB, but a good relative comparison of variables.

http://www.not2fast.com/gasflow/velocity.shtml

In keeping with Colin's "make it lighter", the Taurus throttle body weighs in at 1lb-7oz, and is 5lbs-11 oz lighter than the RX7 TB. WOW!

In addition to the "lightness", it should be easier to fit in the engine bay.

More computer progress made on the car. I have finalized the intake manifold design for the rotary mill. As shown in the attached file, the throttle body will mount to the opposite side of the intake runners. All of the raw materials are on order. I have yet to decide if I will tig weld the intake plenum directly to the intake runners or if I will provide stubs to mount using silicon rubber couplers.

Any ideas welded vs flex?

I have also finished the design and build of the emergency brake cable mount. This allows for the trimming of the brake cables to fit and align with the emergency brake lever. I found with the reduced track and the shortened distance to the emergency brake on the locost, shortening has to be made. As you can see, the inner brake cable slides through a steel tube that is bent at 90 deg. There is identical but reversed geometry on the bottom of the plate. Hidden behind the mounting tabs is where the outer sleeve fits into a barrel welded to the plate. This barrel could be crimped down on the sleeve if required. At this time, I don't think it will be neccessary.The plate is designed to bolt on the cross piece of the chassis at the top-rear of the tunnel. The cable sleeves will need to be trimmed. This will leave more of the inner cable extending forward for the 2 into 1 adapter. The barrels are just steel rod, cross drilled for the cable and end drilled and tapped for 10/32 set screws to clamp them together. I will have to get some right-length set screws.

I also just ordered the exhaust header parts from Racing beat. Header flange, 2" 180 turns plus 2 and 2-1/2 inch steel tube (all .120 thick for the hot rotary exhaust). This should be fun.......

Chuck,

Keep us rotary types posted on the exhaust progress. This is on the horizon for me also. Any ideas on how to make it reasonably quiet? I was thinking of an exhaust that actually runs all the way to the back. I fear sound control issues in the future for the solo community.

By the way, the nose cone fits nicely. Thanks!

Mark