Hi, I'm Kenku or Dani; you might remember me from the tube chassis car thread where I did a bunch of ambitious engineering **** and then got burned out.

Having learned nothing, I'm narrowing my focus a bit for an SCCA EProd 1st gen RX-7. Long story short, the tube car enthusiasm faltered when I realized that some of the individual bits would be Too Expensive, and the class was dying anyway. Also some medical stuff and other real life ****. Anyway EProd on the other hand, while requiring a unibody car, is still alive and well. And a lot of the bits I started getting together still work.

So let's see, in no particular order

Cutaway of an Ohlins TTX46 strut I started reverse engineering from drawings - enough to figure out how stuff was working and what manufacturing constraints they were working under. I have some ideas I want to borrow and some things they didn't do that I think would be neat. Probably I'll start with some revalved and modified Taiwanese coilover bodies to get things rolling but we'll see.


3d scanned FB strut with a CAD model of one of the old RE Speed (IYKYK) bearing adapters to put FC hubs on. The simplest and least expensive way to get OK hubs on the car.


... yeah nah. So bearing adapter to go to ... honestly a lot of stuff I had engineered for the GT-3 car. So nice big stiff bearings, Wilwood Superlite calipers, 11.75x1.25" rotors, etc. Not fully optimized; inner bearing should move further inboards, stuff like that, but setting thoughts out.


Just for grins, let's plunk the Ohlins strut in that assembly. Doesn't that look right there?


Renesis rotor sectioned for 3d scanning. In the end going to make a whole CAD model and maybe try to work up to doing iron castings eventually, but in the short term, want to know where metal is put on the casting and so on.


Great tool to have available tbh.


3d scanned 12A front cover on one of the mostly-accurate 13B CAD models that's floating around. Have some stuff to do here too.

So yea, blah blah blah. EProd is a unibody based wheel to wheel class in SCCA; it's the same goofy slicks GT-3 uses that run about 10" wide tread, so mild widebody, no wings or underbody aero. Spec I'm building will be non-original synchronized trans (I'm targeting AZ6 with 1st gear blocked off), behind an injected 13B - I think competitive 13Bs for the class are in the neighborhood of 260-270hp at the flywheel, I actually have fully ported handmedown irons and rotor housings for 3 engines from someone who moved from GSL-SE to S5 irons and housings years ago. Minimum weight for the spec is around 2100lbs with driver.

Right now I have more time than money so it's my intent do to as much of the design work and fabrication as far to the limit of the rules as practical, and also try to do some interesting things to build my design and fabrication skills.

 

Kinda catching up with where I was documenting elsewhere.



Forgot about this one; scanned 12A SDJ header (another IYKYK sorta part) that I was reverse engineering curves and stuff... intent is to rework basic design for 13B spacing and shorten runners a bit.



12A rotor scanned to get an idea of combustion chamber differences/etc between those and the later rotors. Will do an S5 NA one eventually too.

 

So OK, 3d scanned SDJ header... 3d sketches drawn at weld beads, circle extrapolated on those, voila. Where I left off from a different view.



Where I got to so far today... I'll extend those to the collector and the rest because this is a known "this fits in the car" and so on. But the point of the exercise is now there's a centerline arc down both primaries.

According to CAD, they're 541.6mm vs 539.5mm, which is interesting! I wouldn't swear that the measurements are that precise given my method (I'm trying to get a feel for things rather than a perfectly precise reverse engineering job) so that it ended up that close without any fiddling is neat.

Unfortunately, while this is a really great header for a stock port engine, that's _not_ what I'm doing.

All right, let's start figuring out the header. I'm targeting 17 inch primaries as kind of a rule of thumb guesstimate for a first cut.



After a bunch of painstaking work to jig up 3d sketches and figure out how to twiddle them within constraints, there we go! 17 inch primaries to there, 2" 20ga runners, equal length to less than a MM.



Collector put on... oohhhh yeah that's looking good. Let's just drop it on the 13B CAD model I use for mockup...



...

...

... dang it. That's not going to work.

 

There, fixed. Also dropped the primaries down to 14.8" long - which is actually great because I can just add straight sections to the end to adjust primaries from 14.8 to 18 inches to check on the dyno, as I _think_ optimum length is somewhere in there but I'm not 100% sure where.

This is possibly more boring but saw a video that had me thinking


Like, I'd been thinking of something like that for a while and PVC was an interesting touch... but really what I'd want is something with more room to telescope the tubes into the jig to fiddle lengths.



My take on the idea... fasteners and stuff omitted, but the idea is the tubes will have bolt to pinch a tube that's slid in there - loosen bolt, slide stuff back and forth a smidge for fine position.

Oh hey, what's this, a hundred bucks for 4 of those worth of laser cut plates from sendcutsend?



A little more chipping away... modified the bearing adapter and hub a little to take advantage of available space, roughed out caliper bracket (Wilwood Superlite because why not?) and moved a couple things around. Todo is to get the steering horn in, brake duct designed, and then make sure I didn't miss anything. Well, and finally try to get the engine bay scanned.

 

Thinking a little... realized that of all possible "big tools" I could finish... the balancer would be nice but I have at least one balanced rotating assembly, the engine dyno is going to be nice but there's a chassis dyno all of 15 minutes drive away I can use for tuning... but I really don't have a replacement for a shock dyno without paying someone a lot of money to do it for me.

But... uh... well. Why do anything the simple way when there's a more fun way?



Oh god what have I done...

OK, more seriously. Moog servohydraulic valve, capable of flowing 15gpm of hydraulic fluid and controllably doing so at any amount between zero and full flow, and shifting from full flow one direction to the other at up to 100hz. I've been using hydraulic shakers based around these at work for 5 years now, and thinking of stuff based around them for 10-15 years... and I just happened to find someone on ebay who didn't know exactly what they had nor how to test it. I got it for... ah... around 2% of the price that used ones normally go for.

It also happens that I have a big electric motor sitting around and can bodge together most of the rest of the fixings. Need a hydraulic cylinder (might special order that, honestly) and some data acquisition and control hardware but all told will end up with a servohydraulic shock dyno that would let me do really wild things. Rough road simulation? Very high speed away from zero? Sure, why not.

At some point I want to make a one post chassis shaker for some experiments - basically a mockup of one corner of a car on linear bearings, including suspension and tire, sitting on a platform that can move up and down... but shock dyno is something I need, and simpler, and all the expensive parts will be the same.

I want to be clear that I've had in the back of my mind simpler versions of a shock dyno for a while and I could do those instead... but this is way more fun and that, to me, is a great reason to go this route.

And that's caught up... some stuff is going slow because there's a bunch of other stuff in my life too, but I want to build things this way so I'm going to.

 

so you need to keep it a strut front, but do you need to keep the stock spindle?
it would make life really easy if you could use some other spindle

you idea for the header is good, build it so you can add length and just see what works.
i think the gsl-se irons would have smaller runners than the s5, you might make more midrange with less top end?
it would be enough to have something run and then work on other things

 

Rules say stock spindle and stock steering arm (not shown yet) are required; ah SCCA. That's why in the CAD image of the hub/etc there's a bearing adapter to convert to a Wide 5 bearing package and so on; sort of the same idea as the MSF big bearing hubs, but my own twist. It _absolutely_ would be simpler and less expensive to use some other spindle.

The GSL-SE irons are ported for EProd... I'll take a picture of one after work, I'm not concerned about runner volume let's say. I'm not sure there's any way the fundamentals of things will fall short of an S5 based engine but one way or another I have the bits and one fully balanced-but-not-lightened S5 rotating assembly. Good enough to start. SCCA legalized EFI so long as it has chokes the same sizes as the legal carb, so doing that because oh my goodness do I not want to mess with carbs. Intent is a custom cast intake manifold (because I want to and most of the off the shelf ones have runner lengths that are "too long").

 

There is a questionnaire out to Production Racers regarding wheel width. The BMW that keeps winning in this class is allowed an 8" wide wheel and question is whether or not this width should be allowed for all cars in the class. Get on board with this. Whether you run bias ply cantilevers or the Hoosier radial, an extra inch of wheel width will make a positive difference.

EP is a cool class. It used to be the place to play with an RX7.

 

Found a pic I had kicking around of one of the front irons... yeah, like I said, port volume should be "enough".

I'm aware of the survey... in principle I'm annoyed by it a little since it's been 7" wide for ages but you know, I'm not going to turn down an edge... especially when I haven't bought wheels yet or even totally finished suspension design. Part of me also wonders the last time someone built a new RX-7 to the limit of the rules but, hey, the intent of SCCA's process is for people to do so and then they adjust, right?

From talking to Michael Lewis I'm planning on GY Bias for first cut... he tried all the options in GT-3 and the cars aren't that dissimilar. Actually, I should check the GCR and see what it'd take to double-dip into GT-3 or STU (but I repeat myself )

 

I think GT3 is in the best spot for the merger with STU. For my car, it would be better to convert to GT3 (I'm already legal just way to heavy) and take advantage of the better rotary engine options and shed weight. Also a GT3 car can run a 9" wide wheel with a weight penalty.

Yeah have no idea why the BMWs got eights. Took way too long to get a survey out for this. We have experience with cantilevers on 8" wide rims on the back of Corvairs. The tires work better on a wider wheel. We even stuck them on 10's and the car got faster.

 

Spec line says 17x8, rules say any wheel smaller than that is OK so... welp. But it's really only the Prather built car that's noticeably fast, the other BMWs are... fine, but unspectacular. And Hainsworth was really close, especially given some stuff from talking to him. It may be the nicest built FC in the class but it's still a 20 year old build.

 

there is an FD here locally on spec E46 tires, which are 17x8, and the FD just runs circles around the BMW's

 

EProd is in some ways a weird class. Each car/engine combination has a spec line and in theory they all should turn similar lap times if built to the limits of the rules but some combinations are less work than others to get there and drive. The BMW Z3 with the I6... one specific car has won the championship the last 5 years with 3 different drivers and kind of the problem is that that combination is also one of the most driveable options that can make lap time.

But you know, also also, that Z3 is also just plain a more recent build than a lot in the class, and there's various stuff that's allowed now that wasn't when some of the other frontrunning cars were built.

edit: Looks like I could maybe double-dip a prod FB into STU/GT3 with no restrictors, 200ish pounds of ballast and 245 DOTs on 15x8s if I pretend it's an STU car, or no restrictors, 130 pounds of ballast and 245 DOTs on 15x9s if I pretend it's a GT3 car? Might be fun way to get more track time.