Laminar's RX-8 EcoBoost swap thread

[Berg87]

Mikael you're making great progress.  We have approached some of the same issues in very similar ways. we're using the same Drive Shafts, Same NC Miata Steering racks, Different Transmissions, I'm using the T5 from the 2010 era V6 Mustang with remote mounted shift linkage similar to the MT82 you're using,  but same way of relocating the shift arm.  Also after cutting and welding up the stock RX8 Front sub-frame I bought the NC Miata sub-frame, makes fitting the rack a touch easier. 
As for your Steering rack, if you're not using Hydraulic assist, cut all the external posts off and weld up the holes to gain oil pan clearance.  I've performed the "Full De-Powered" steps to mine, which is to have welded up the rotary valve. 

As for Steering rack location, just how low can it be and have the drop tie rod ends fit and the geometry work?  Same with how far forward? 

Where are you taking reference measurements for side to side center line and  horizontal datum line for measuring Fore and Aft Engine tilt? 
Thanks,
Rich

[Laminar]

What engine are you using??

Did you follow a specific guide for depowering the NC rack? I can find lots of info on NA/NB racks but nothing really for NC. I've already chopped off the port that was hitting my oil pan but finishing the depowering is still on my to-do list.

I would guess with the Mustang bump steer kit I bought, the rack can be dropped 1-1.5" and still work. Not sure what the forward limit is, though that doesn't seem to affect bump steer as much as it does other behaviors.

I don't remember where I measured side to side, but I made a mark on the oil pan for the centerline of the car for steering rack mockup purposes. I think it was maybe the inside face of the frame horns? I'll have to double and triple check that before I finish weld the rack brackets. I took the angle off of the pinch welds on each side as a "level" to estimate engine tilt.

Do you have a build thread anywhere? I love seeing how different people solve these RX-8 specific hurdles.

[Berg87]

No build thread anywhere, I can send some of the pictures I still have, some were lost in digital mishaps.  De-powering the NC steering rack is much like the NA/NB units, some differences such as a special size/shape socket to remove the large rack tube nut on the side with the pinion...I made one of these tools and you're welcome to borrow it as well as there are two inner tie rod end lock washers that are to be replaced when doing this; I have two extra and you're welcome to those as well. 

My engine is 302 SBF, I was motivated after seeing your E36 project a few years ago, and for better and seemingly mostly worse I'm a Ford guy.  So I too like the suffering. No doubt about the "easy" button is an LS, not saying it's easy but certainly there are fitment advantages namely total engine height. From crank center downward, and crank center upward GM created a really short package if using the appropriate oil pan and intake manifold. 

You mentioned the weight of a dressed LS, what's the dressed weight of the Wankel ? 

In checking level on the frame rail pinch weld, placement of the level by only a few inches changes your readings.  Pics 1&4 are with the level approc 5 inches reward and this shows slightly out of level where as pic 2&3 are with the Level all the way forward on the frame rail, showing level. Also used two digital angle finders and though there was a bit of repeatability issues, both digital levels matched the regular level. 

Happy to help in anyway with your build. 

[Laminar]

That’s awesome! What intake are you using? I’m lucky that the Explorer intake fit my M3 with just a little trimming, but there didn’t seem to be great options for low profile intakes on the 302.

I weighed the stock RX8 drivetrain at 450lbs:
https://www.rx8club.com/rx-8-racing-25/laminars-sii-sport-autocrosser-272733/page4/#post4951957

[Laminar]

Started work on mounting up the steering rack. I cut off the old brackets and got a little plate welded to the subframe to both cover the hole I cut and provide a solid mounting surface for the rack. Immediately ran out of MIG gas.



Dug around and found my radiator brackets and bolts, so I put them in place just to see what I had done to myself by moving the rack forward.





Looks like the driver's side rack mount bolt is going to interfere with the radiator. I'll do what I can to minimize that interference, but I may have to push the radiator forward a touch. I even bought a stock-replacement aluminum radiator in hopes that the whole setup would bolt up like stock. But here we are. 

[Laminar]

Sneaked out to the garage a couple of times this weekend. Decided to get the steering rack locked in place so I could move on with my life. Started with cardboard cutouts and transferred that to 1/8" plate to box in the mounts. I redid the steering shaft extension so I could set the rack angle properly. I did cheat the rack over to the driver's side about 1/2" to get more steering shaft/turbo clearance. I know that messes up my lock and tie rod length side to side, so I may have to account for that.





The old rack bracket is still tacked to the bottom of the subframe. I'll probably scoot that over to tie it into the new bracket, I want to mount a skid plate to that lower bracket as it's about level with the bottom of the oil pan:





These brackets stick out off of the subframe quite a bit, so I ended up putting a couple of braces on the sides to take some of the side load.



Threw the radiator in place just to see what kind of trouble I've made for myself. There's...some trouble.





I can clean the rack bracket up a bit but that still doesn't get me into the hole:



The big showstopper is the lower hose outlet. I think I'll have to raise the radiator up about an inch to clear it comfortably:



Also had a few spare minutes last night so I whipped up some Ackerman correction brackets just to see what they would look like:









Still not 100% sure I'm going to make these, but I can't imagine the geometry is great without them. I did get a 16mmx1.0 tap, but I still have to source some M16x1.0 bolts, which aren't available on Bell Metric, McMaster, or Fastenal.

[Bermuda]

if this is one of the ebay aluminum radiators, one of the lower 09-11 fan shroud mounts wont work with it

[Laminar]

It's a CXRacing radiator. I'm actually swapping to a PWM fan off a Lincoln Zephyr. I run the same one on my E36. I originally planned to use the original RX-8 fans but after going through the complexity of activating multiple relays for multiple reasons it seemed simpler (and saved me some valuable outputs) to just use a single PWM value.

[Laminar]

Work has cooled down so I popped back out to the garage and whipped up a couple of Ackerman correction bits. I need to actually measure Ackerman and see if they're needed.





If I decide to keep them I'll clean up the edges and round everything out nicely.

[shainiac]

I made something similar to those offset adapter. My issue was that I couldn't get the outer tie rod any higher without hitting the spindle, so the inner tie rod needed lowered to correct bump steering. The attached photo is the only one I could find, but I welded a high-misalignment spacer between where the bolt head touches the adapter and the adapter touches the end of the rack. The mis-alignment spacer does a couple things, it gives you an OD to put the rack boot over to keep junk out of the rack, and it keeps the adapter from being the rack stop. I put a big washer between the rack end and the mis-alignment adapter so that it became the rack stop. I was worried about the offset tab being the rack stop because it would be under bending every time it hit travel limit. I was worried about it eventually loosening.

I only used this for a year or so before ditching the Mustang knuckles that were giving me the bumpsteer grief. They did drastically improve my bumpsteer issue and hadn't come loose. Are you using the locating tabs? My FC rack didn't have them, so I just used red Loctite and Nordlock washers.

[Laminar]

Those are great notes - I figured I'd have to get some kind of expanded boot that would fit around the whole assembly somehow. If I actually plan to daily this thing I'll need all weather protection so no skimping there. If it turns out I need these guys I do want to find a way to integrate the locating tabs and and the anti-backout washers for the stock inner tie rods.

[Laminar]

Finally got off my butt and took some measurements. Made my own hacky angle plates:





The adapter on the wheel captures the ruler, which extends straight to the ground. I used a jack to put the spindle at ride height. It's not a perfect system but I figured it would at least give me a ballpark answer.

My goal was to see the effects of shifting the rack forward on my Ackermann angle and to decide if I need the little brackets that push the arms back. I found an equation on the Formula SAE forums to define the steering angle as a percentage of perfect Ackermann.

I set the wheel straight ahead and put the angle readout at 0 degrees. Then I turned the wheel in 1/4 turn increments and recorded the angles. The driver's side had no adapter and the passenger side did have an adapter, so I was able to get measurements with and without my change.

The ruler extended straight down from the centerline of the wheel mounting surface, but due to the scrub radius of the suspension geometry, the ruler didn't just rotate perfectly still, it moved in an arc. I did my best to keep the measurements consistent, but I know there's some error. Here's what I ended up with:



Stock is the rack without my compensation bracket, results are maybe mid-80s, average of 90%. Mod is the rack with my bracket, results are more in the mid-90s, average of 99%.

Is geometry better with the bracket? Signs point to yes. Downsides of the bracket are having homemade components in the steering linkage (danger), stock tie rod boots won't fit (corrosion on a street car), brackets shorten effective tie rod length (bump steer geometry). At this point I'm going to move forward without the brackets, assuming 80-90% of perfect Ackermann will be acceptable and is a good tradeoff for the safety and longevity keeping the stock tie rod retention system in place.

[Exidous]

Pretty cool test. You could always refine the setup to make it less homebrew if necessary.

[Laminar]

Here's a real version for a different car. Even if someone made a real one for the RX-8, it would certainly be for "off-road use only" and nothing I'd want to take on the highway with my kids in the backseat. Fine for autocross or drifting but this car will have to do more than that.

https://shop.battlegarage-rs.com/products/offset-steering-rack-spacers-for-the-ae86-aw11-te72-ke70-etc

[Laminar]

Decided I needed to keep moving, so I started working on the wastegate actuator mounts. I had previously made some brackets that would pick up the compressor side bolts, so I took one of those and clearanced it for the steering shaft now that I have that geometry set.





Then I made another bracket that picks up the actuator bolt pattern. I held everything in place where I needed it and connected the two brackets.



Started working on the passenger side. I found that the absolute best place for that actuator was exactly where I ran one of my turbo coolant lines. 

I was running out of time but I pulled that line and got everything lined up about where it should be, then had to call it for the day.



Both of the turbo exits are really tight and potentially will rub the silicon couplers on the body. I'm thinking about maybe welding aluminum elbows straight to the compressor housing so that I have solid chassis clearance and I'm not crushing couplers.