Tales from the Batcave (RX-7, rallycross, misc. stuff content)

cghstang_chris said:

Charles looks happy :)

He was ecstatic when he found out I was driving The Car at the national challenge.  Somewhat amazed on Sunday when he realized that I drove it there, no trailer.

Well heck, I want to drive a car, and the SWVR site is only 225mi from my house, basically straight shot down I-77.  Same distance as Smoke & Mirrors and other WOR sites.

Speaking of which, I may flip my SCCA region to OVR.  There was an OVR only group photo and Orion shooed me in, saying I was "honorary OVR" and that got me to thinking.

On the car front.  Trans makes a weird high pitched growl under high load in 2nd and 3rd gear only.  What is weird is it sounds like it is coming from the rearend direction, not the trans.  It does not make the noise in 4th or 5th, which would make rearend sense due to the lower torque on the driveshaft... except it also does not make the noise in 1st, which puts max torque on the driveshaft.

Odd.

I wonder if the little snout bearing between the input and output shafts is failing, and the input shaft is flexing away, causing gear mesh to go wonky.  The transmission is not racking, so I know the main output bearing is good, and being limited to only those two gears leads me to to believe that the countershaft bearings and input shaft bearing are good.

Getting stuck in 3rd that time makes me wonder if a piece of one of the shift key springs broke off and got into something, or if something got into it.  Hmm.  Not going to pull it apart now for all sorts of reasons.  End of season is coming soon, want to enjoy the car as much as possible before then.  I think it may be time to line up another transmission to be ready.  I have like six smoothcase transmissions and they are all kinda junk, this is the one I'd rebuilt in 2020.

So the other morning, I had to stop by The Batcave before work to pick up some tools I would need that day at work, which is now a shop a half mile up the road.  Stopped at a light, pull up next to a blue Fox body Mustang.

Okay, here we go.  I am in the heavily bestickered '81 and he starts blipping the throttle at me.  Happens a lot.  Dude, srsly a first gen Prius is faster... but then he rolls down his window and asks if I'm going to rallycross at Nelson Ledges.

Uh?  Brain reboot time.  I mumbleshout some sort of vague affirmative as he drives off since his light just turned green.

Who was that?  I know/thought Frank Coletti lived in the vicinity but I thought much further southeast.  Confused.  Didn't recognize someone from 20 feet away in a moving car.

So, I go to NEOhio SCCA website to get contact info.  Find this.

Er, yeah I rallycross at Nelson 

Speaking of the black car.

Through some incidental searching, I found that Erie Vo-vo has some Volvo RN cylinder heads ready to go for less money than it would take to have my existing RN head rebuilt, if it can be rebuilt. (allegedly it has .017" of warp)  I have a S60R block and the 2.4l T5 block that I rebuilt, wrapped in plastic.

Then I found that I can get a whiteblock to RX-8 bellhousing adaptor frighteningly cheap.  I have a rotary to Mustang T5 adaptor and trans on the shelf courtesy of a GRM member.  That leaves the clutch and flywheel, which are hideously expensive for this engine because they incorporate the 60-2 trigger wheel.

Found that I can buy these parts cheaper in Europe and ship to the US than to buy them in the US.  This engine was used in the Mk2 Focus RS after all.

Hm.  Patrick's RB26 sounds great but Pete likes the 5 cylinder howl even more and a R or T5 engine is good to 600 at the crank according to the Internet.  Plans coming together.

Went to Summit to buy some Milwaukee stuff and push me over the edge to get another Summit gift card. There was some sort of C5 convention happening in the parking lot, and as I got out of my car a guy started his up and it sounded like complete popcorn popper.  Very nice.

Perusing the discount shelf, found a bunch of Chevy spline 9.5" clutch disks, which would be needed to mate a Chevy gearset to a Volvo clutch and flywheel.  That would be additional expense to change gearsets, maybe cheaper to get a Ford disk made.

Then I saw this.

Pat knows exactly what it is, why it is useful, and why I bought it.  It was his idea, after all.

Automotive ADD is a cursed thing.

Back to working on Colin, which has a minor yet major change in direction, which is a subject for another thread

...realized i need to head back to summit for something.  Saw something interesting on the racks, bought all eight of them.

I would say that I am at the point where I am buying engine parts for a project that has not started yet, but I have had the oil pan for about four years already, so... too late?

Made a couple mistakes that cost me some seconds, and I was sure I was going to run a 49.x on my fifth run but one of the yahoos at corner four was holding the red flag up over their head, unfurled in both hands, but all I know was I saw "RED FLAG" so I stopped.  They waved me through, I asked what happened on course for the red flag, because I saw nothing happen, and I was told I was the cause of the red flag because I stopped on course.

So, long story short, I got a rerun.

i also stuffed up my fourth afternoon run (we ran five and four) after hooking a rut or something. Need to watch the incar.  But, I cannot say that any one mistake cost me the win: I was simply outdriven.

To be honest, running this close to a more powerful, lighter, better handling car, on ancient rock hard tires, feels like a moral victory.

And the courses ROCKED.  Very flowy with some mildly technical sections.  I was keeping the throttle pinned through three linked corners and not really slinging the car around, just finessing it through the corners.  I am starting to click with the car.

First rallycross of the year is in two days!

(The one a couple weekends ago did not count, as it was a Very Important Weekend for personal reasons so I couldn't be there)

RX-7 has a larger '83-85 radiator and an FC front mounted oil cooler to hopefully keep temperatures in check.  Also has a side mounted Dellorto 48DHLA carburetor to hopefully increase power beyond 100hp because there has to be something wrong with the Nikki.

Yep, got all those parts sitting on the shelf waiting to go on.  Haven't even touched the RX-7 since driving it on a road trip in the spring on my birthday weekend, and THAT was the first time driving it since November.  All of my focus has been on Colin.

Rallycross prep so far has consisted of verifying that it can start and that the gravel tires still have air.  The engine still has oil in the pan (changed in March) and a coolant like substance in the radiator (mostly water since blowing a hose apart in Michigan a couple years ago).  Should be good enough, we're just here to have fun.

I do have spare belts.  Probably should pack the tools to change them.

Driving around today, thinking.  Which is where problems usually start.

Y'know, what this thing needs is a turbo.

I have a lot of Volvo turbos, what are the specs vs. what are the specs of, say, a Hitachi turbo from a Turbo II?

Short answer: compressor is almost identical, turbine is slightly lower.

I don't like that answer.

Aaaand the gopro is officially dead

This car really needs better tires.  And more power.  And maybe a better suspension but I can't pin down exactly what it isn't doing as well as it could.

But at least I am out here out standing in a field, eating gas station food

There's something magical about a nice oily, vinegary pasta salad on a hot day.

Event over and halfway home.  The afternoon course was the same as the first course, but with some apexes pulled in and a right into hairpin left turned into a left, that I found that I could get through without lifting at all thanks to banking and a lack of outside cones.  I picked up a lot of time elsewhere with some judicious corner entry strategy at a certain corner with a deceptively late entry - turn in when you think you should and you screw up the next two corners.

If I were running in Mod, I would have placed 4th.

Draco destroyed MR with a PR car.  He was second overall.  Jeez.

I have a tire durometer now!  If you think I'm going to take it to the next rallycross and poke peoples' tread... you're right.

For funsies, two year old Bilzzaks are about a 45.

My 13" Black Rockets are about a 75.

Maybe that's why they grip like a hockey puck.

*googles "magic tire softener 30 points durometer"*

Driving around on the street again with the '81.

Feels nice.  Nostalgic.

Slightly annoying, though, that the black car made more power at 3000rpm than this does at peak.

And the exhaust smell is getting irritating.

Wonder if Ford still makes Ecoboost controls packs.

Let's finish Colin first before we go down that rabbit hole...

In reply to Pete. (l33t FS) :

For my TVR project I got one of the last Ecoboost 2.0 control packs that Ford made - that was back in 2018.  From what I've heard, there's a guy in Europe (Portugal?) selling cleaned-up ECUs for the 2.0.  Could be an option.

Ford still sells the control pack for the 2.3.  Lots more of those engines are out there now too.  Probably not too bad finding a good used one.  I've got a Mustang 6-spd trans sitting around if you go that way.

In reply to TVR Scott :

Oh, the idea would be to use a NC five speed because that is a bolt in proposition that allows the use of a cable speedometer (it's the same transmission as '81-91 nonturbo RX-7, and Mazda never stopped machining for a speedo drive gear, just swap a series 2/3 RX-7 tailhousing onto it) and a Ranger/Explorer engine because the HPFP is on the top of the engine and not in the firewall.

Well, this happened

The RX-7 is going back to where it came from for a weekend!

The recent article about haste leading to failure really struck a chord (in an "I feel attacked" sense  ) because Nationals is, well, Nationals.  And of course I always want to show up as good as I can be.  So I keep thinking about the Dell'Orto on the shelf waiting for me to figure out how to integrate the evap system, which is also the PCV system, and how to integrate a TPS so that the vacuum advance can work.  (Mazda ran the vacuum advance off of full time vacuum and a TPS controlled solenoid, which is actually ideal since DHLAs do not have a ported vacuum source)

Reality: First the car must stay reliable enough to drive 650 miles, compete, then drive 650 miles home.

More, somewhat brutal reality: I rarely if ever actually use full throttle on course, so more power isn't exactly warranted.  What we have is still enough.

So, what needs done?

Primarily... hmm.  I should make a list.

Drove the car for a week.  Made some notes and compared to how it drives on course.

For one, the rear suspension is awful.  The Bilsteins don't seem to be doing much damping when push comes to shove.  And when it got bouncy it would crash hard into the stops.

The car doesn't have the feel I like where you can power out of a slide.  Part of this is because it doesn't have a 3 link, but part is I think because the rear ride height is too high and it actually has a touch of prosquat as a result.

The brakes always felt weird.  The pedal is higher than any RX-7 that I had ever experienced, but when braking you get this weird sensation that the car is pitching about an axis about a foot behind the front wheels.  Very odd.

Lastly, I noted some detonation(!!) at high RPM on long pulls.  Naturally aspirated rotaries shouldn't detonate at all and if they do it shouldn't be at high RPM.

Let's see what I took photos of while working today.

First, the detonation issue.  I know my spark plugs were a bit crusty, and I am fairly sure that they are old plugs that came with the 13B engine I bought from GPB (I think) about ten years ago, that I ran in this car before I was able to put together a running 12A, then swapped those plugs in to the 12A.... shame on me.

Yeah... those are all heat range 8 plugs and they are done done done.  It was probably preignition from all the carbon.  Four new NGK 5777s installed and the engine is happy.

Next up is the brakes.  It used to be a thing I would do to remove the proportioning valve and replace it with two M10 unions.  I was going to do that when I put the car together but I could only ever find bubble flare unions, not double flare.  I finally found some locally and went to install them.

...then I realized that with only minor rebending, I could just connect the prop valves outlets directly to the master cylinder, no unions needed.

The result: Braking feels much, much more "solid" chassis wise.  And the pedal is lower like I expect from an RX-7.  I have a feeling that the prop valve was actually bound up and not sending pressure to the rear brakes at all.  Chalk this one up to "I should have done this five years ago before I started driving the car".  D'oh!

Next, the biggie, and what I actually had started on today.  The rear suspension.  The car had some form of height adjustable coils in the rear that I had thought were weight jackers over Eibach generic springs.  Turns out that they were apparently application specific adjusters and springs for a first gen RX-7.  The adjusters were, I thought, seized, but it turns out that they were merely under enough spring tension with the shocks installed that the adjusters wouldn't rotate.  I adjusted the rear ride height down about 15mm which coincidentally is also zero preload at full droop.  I also adjusted the front spring adjusters one turn higher to raise the front roll center a little and maybe get a little more turn in and a little less front body roll. No pictures.

I also replaced the Bilsteins with a set of KYB AGXs, because they are cheap adjustables and a known quantity because that's what I used on the black car and I know they work okay.  "But Pete," you protest, "KYB doesn't make AGXs for the SA/FB."

Ah, but I am 99% convinced that all AGXs have the same damping no matter the application, and the RX-7 has the same shock length and mounting type as a Fox body Mustang.  Two AGXs for the rear of an '83-85 Mustang were ordered, the lower eyes trimmed a little with Nik Blackhurst's Favourite Tool to narrow the eyelets 8mm or so, and they bolt right in.

I also addressed the bump stop issue, or lack thereof.  Enter some Energy Suspension bump stops courtesy Summit Racing.

Now a biggie, and more of a "why certain tuner shops suck", and the reason why I did all this at work at not at the Batcave where I would have to work on one side of the car at a time.

The first generation RX-7's rear suspension binds in roll.  It has nice long parallel lower links, but the upper links are short and heavily angled to clear the springs.  An angled 4 link will have its own defined roll center, and near as I have ever could figure, this roll center is up around the roof of the car.  The rearend also has a Watts link, with its center pivot offset to the right and 40mm above axle centerline.

I took some photos and played with jacks.

Here's ride height.

One upper link bolt is removed, axle is supported in the middle by a trans jack.

Now let's see what happens with a half inch of bump.

See how the holes don't line up?  This is because there are two described roll centers and they are fighting each other.

Let's go up another half inch.

Oof, that's getting a lot worse.  For the axle to articulate, all of the bushings must distort to allow for this.

Let's take the suspension up to where the bump stop would be, now.

Oooooof!!

This is why these cars have a reputation for snap spinning.  Trying to articulate creates an additional roll stiffness that ramps up significantly as roll increases.  Due to the geometry it also gets worse when the cars are lowered.

And certain tuner shops who have no idea how RX-7s work will sell you solid metal joints as an "upgrade" 

This is why RX-7s, especially the '84-85 models with worse geometry, like to rip the upper mounts off of the chassis.  Or as the axle housing twists back and forth, the pinion angle climbs upwards as the housing takes a permanent twist on both sides.

Back in the day, the road racers would replace the upper link bushings with roll bar padding ("any bushing material") and then install a 3rd link ("traction bar") to control axle rotation.

We can't do that in Prepared.  Bushings are free but we can't add other suspension devices.  We can't even modify the mounting points for things, which is why I narrowed the shocks instead of just bending the little tabs on the axle a little wider.  (They bend extremely easily)

But, bushings are free, and so I spent some quality time with a die grinder cutting out two half moons in the rubber about 14mm deep on each end of the upper links, on the "outsides" (outer face in back, inner face in front).  This will, hopefully, achieve two things.  First, it will make the bushings more compliant fore-aft, to allow for this geometrical discrepancy.  Second, because of WHERE I did it, the effective center points of the bushings has changed with the effect of making the upper links more parallel, to reduce the geometric bind in the first place.

Here's a really bad drawing, only one side shown.

129,856 to 131,470.

More later