Thanks for the great read . You have some skillz man !

April 2016 – Atlanta Motorsports Park (AMP), SCCA Track Night

The next track day (or, night) with the FD was at AMP. I’ve gone to quite a few of these SCCA Track Night in America events, and they’ve always been awesome. AMP is 3 hours from where I live, so it’s easy enough to just take off work at lunch and drive down for a mid-week track day. It’s always really laid-back too; just turn in a tech sheet, put on a wristband and have at it. The pace is a bit slow though, I was usually the quickest car in the advanced group in my RX-8, so the FD would surely have some traffic issues.

Anyway, after my last track day at VIR, I had a short list of things to improve on the car. Here’s what I did between then and this track night at AMP:

Brakes:
At VIR I used 100% of my XP10 front brake pads and damaged my front brake rotors enough to have a massive shudder each time I touched the brakes. Rear brakes (XP8) were fine though.

I replaced the front rotors with some new blanks and swapped to Hawk DTC 60 pads. I decided on the Hawks for a couple of reasons; 1 – they’re cheap and easy to get (Amazon prime), 2 – they have a seem to have a high temperature tolerance compared to the XP10s.

Bottoming:
I had been bottoming on the left-front fender liner through hog-pen at VIR. AMP has a similar “compression corner,” turn 11, which is a quick-ish right across a dip. If I was bottoming at VIR, I was going to bottom out at AMP too, so I needed to take some steps to improve that.

I decided to try to increase my roll stiffness with some aftermarket sway bars, with the hope that the reduced roll angle would be enough to keep the outside wheel out of the fender liner in a dip. I was patiently waiting to find a used tripoint front sway bar, so in the meantime I decided to try some cheap “Godspeed” sway bars. $120 for front and rear bars was worth it just for the experiment:

https://cimg0.ibsrv.net/gimg/www.rx7...26346a40a9.jpg

First impressions, these things are HEAVY. I didn’t realize it when I ordered them, but they’re completely solid, both front and rear. Weights are 15.25 lbs front and 7.13 lbs rear (stock bars are ~7.5 lbs front and ~3.5 lbs rear). My calculated stiffness values for these were 858 lbs/in for the front and 290 lbs/in for the rear (compared to 400 / 105 stock).

Something that I don’t like about this style of sway bar; the way the front end-link attaches to the end of the bar with a stud/stub-shaft and nut:

https://cimg0.ibsrv.net/gimg/www.rx7...56312e877e.jpg

The “stud” is already put under a lot of tensile stress from the nut clamp load; and then the end-link is applying a shear force of up to 1000 lbs… I’m sure the stress in this thing is through the roof, especially at the internal corner. It’s a crap design for the stock sway bar and an even crappier design for an aftermarket sway bar where the loads are higher. Anyway, angry engineer rant over…

I also bought some Improved racing endlinks front and rear. These are really nice, they’re just M10 teflon-lined rod ends with the supporting hardware:

Front:
https://cimg4.ibsrv.net/gimg/www.rx7...aae042e6c8.jpg

Rear:
https://cimg6.ibsrv.net/gimg/www.rx7...c44e5df104.jpg

And for the front sway bar mounts, I bought AWR steel mounts (the LS1 versions since I have a v-mount and don’t need the radiator mount). They seem well-built and should hold up to some abuse.

https://cimg7.ibsrv.net/gimg/www.rx7...7c2ba3c85a.jpg

With the new hardware, here are my calculated changes in car setup:
- Front TLLTD went from 54.4% to 55.2% (some shift toward understeer in theory, but realistically a tiny change)
- Roll stiffness went from 1.77 deg/g to 1.39 deg/g.

The last thing I needed to fix after VIR was the catch can, but I was too lazy to make a bigger one so I kept my “parallel catch-can” setup with my small aluminum can and Dasani water bottle.

Prior to AMP, I took the car up to DGRR 2016 for a quick shake-down and to show it off. Lucky for me, the DGRR car show is only 45 minutes from my house, so it’s an easy day trip.

https://cimg4.ibsrv.net/gimg/www.rx7...0e7b181870.jpg

If anyone knows who took the above picture, let me know and I’ll give them credit. I lifted it from a photo album somewhere but I can’t remember where.


Anyway, on to AMP. If you’re close to this track and you’ve never been... just go, it’s awesome. It’s a lot more technical than most tracks in the South East, but it’s really forgiving and easy to drive at 10/10 all of the time.

https://cimg1.ibsrv.net/gimg/www.rx7...464303dd1e.jpg

I spent most of the time caught up in traffic at this track night as I expected, but I did manage to get a few good laps in:

(hot lap starts at 1:30)

https://youtu.be/SublJLKMzjc

Stats from AMP
Lap time: 1:32.1
Boost map: 12 psi
Weather: High 82F
Max coolant temp: 228F
Max oil temp: 256F
Max IAT: 140F
Top speed: 122 mph

https://cimg6.ibsrv.net/gimg/www.rx7...6f5cdf6e21.png

Overall, it was a fun track night. I didn’t have any brake issues with the new DTC 60s and new rotors, but AMP is very easy on brakes compared to VIR. The car was a bit oversteery, as you may notice from the video. Also, I didn’t fix the bottoming issue at all, it would rub really hard on the left-front fender liner if I took the inside line through turn 11.

Temperatures were also a bit higher than I would have liked (see stats above). I expected a bit of an increase since it was a hotter day and AMP is a slow-speed-but-still-high-revving track. I need to invest in some bigger oil coolers in the future…

That’s all for now! I’ll keep trying to get this thread up to date, I still have a few more 2016 track updates to work on.

i love seeing track updates!

I ran AMP in my SC300 and it was my least favorite track (compared to Barber, Road Atlanta, Corvette Museum and Putnam) though i did the others in my RX7s. to me it felt like a track where the Miata guys can finally be super fast because there are zero straightaways. maybe i just really like getting up to 150-160mph and flooring the brake pedal, i dont know, but i didn't enjoy AMP as much as i thought i would.

you are getting me pumped for my next track day! hopefully at road atlanta in April.

Great build and fabrication; thanks for sharing the track footage :icon_tup:

Interesting, I think I like AMP for the same reasons you don't like it. Getting a good lap there is really rewarding since there's no time to rest or reset during the lap; a mistake in one corner will ruin the following corners, it's a pretty intense track despite the lower top speeds. It also helps that I learned that track in my RX8, and at that point it made me feel like a pro driver rather than pointing people by on the back straight at Road Atlanta.

The next couple of updates for this thread in my backlog are from Road Atlanta. I'll probably skip the NASA event there in March so I can circle back to some other tracks early this year. I'm thinking VIR in March and NCM in April. Let me know when you decide which events to attend and I'll see if I can make it to the same ones.

Anyway, one interesting piece of data from AMP that I forgot to include:

https://cimg9.ibsrv.net/gimg/www.rx7...89e499ab3c.png

I overlaid my Harry's lap timer data on a speed vs. distance on the track plot for my RX8 and FD. The RX8 had a similar setup to the FD at the time; coilovers, 200tw tires (RX8 had Dunlop ZII's vs Hankook RS3's on the FD), similar alignment, etc. The power difference is really clear on the straights (185 hp RX8 vs ~320 hp FD). Corner speeds seem pretty similar between the two cars. The RX8 lap was definitely much cleaner; I made a mistake in turn 6 with the FD and had to avoid the dip in turn 11. I think the GPS speed data gets a bit choppy after turn 15 - my speed trace from my Megasquirt log looks a lot cleaner. Lap times were 1:32 in the FD and 1:38 in the RX8, so the extra power seems to be worth 6 seconds at this track (probably 7 with a better lap).

how do you like the megasquirt gauges display? do you have any closeups of the tablet to show what it looks like?
how is the refresh rate?

I see what you mean! maybe I need to go back in my FD.
let me know when you go to NCM. that one is only an hour from us so it's easy.

You guys think you'll pass the sound restrictions at NCM? I have marked it off of my list of probables because I figured with a full 3" that I'd never pass.

The gauge display is awesome. It's an app called MSDroid on my Nexus 7 - it just connects to the Megasquirt via USB. I log to the tablet when on track too. Here's a screenshot of the display:

https://cimg4.ibsrv.net/gimg/www.rx7...3e75b9bc92.png

Data is logged to the tablet at 10hz, so I assume the display refresh rate is the same. Whatever it is, it's buttery smooth.

I think (hope) I'll be fine. My exhaust is 3" all the way, but I have a big Magnaflow muffler in the midpipe (RX7store) and a Racing Beat catback, so it's usually one of the quieter cars at track days.

AMP was my first ever track day with my car. I previously tracked sportbikes (Much cheaper)
I loved the track. Very rewarding track IMO. coming onto the straight was the one place I would see some of the novices really stuff it. One guy put his 2week old evo into the wall coming on the straight.... it was a bad sight

Almost been a year, anything else going on?

Updates! Sway bars
 

Alright, time to get this build thread up to date.

Up to this point I had used some cheap ebay sway bars. They were completely solid steel, very heavy, and limited in adjustment.

For the front - the obvious choice is the Tri-point sway bar. They're hard to find these days, but I managed to snag the "arms" by placing a WTB ad on here:
https://cimg5.ibsrv.net/gimg/www.rx7...979d0721b8.jpg

For the "tube," I bought a 1-1/4" 48 spline 3/16" wall 35" long bar from HRP. Fitment is perfect with this bar to the Tri-point arms:
https://cimg2.ibsrv.net/gimg/www.rx7...f6c4b194af.jpg

For the rear, I couldn't find a good off-the-shelf solution. The stock rear bar is too soft, and all of the aftermarket bars are too stiff for what I need. Based on my suspension spreadsheet that I shared earlier in this thread, I spec-ed out my own rear sway bar stiffness and fired up the mill and TIG welder.
My custom rear sway bar arms. Just some rectangular steel that I drilled on the mill:
https://cimg4.ibsrv.net/gimg/www.rx7...52c2e76152.jpg

The tube is a 3/4" 0.095" wall DOM tube. I did some stress calculations to make sure there would be no yielding with this setup, and it looks really safe.
In the jig for welding (notice I had to put a very slight bend in the tube, this is to clear the fuel tank):
https://cimg0.ibsrv.net/gimg/www.rx7...a3cd302588.jpg

Welded:
https://cimg2.ibsrv.net/gimg/www.rx7...0fc590c422.jpg

Painted:
https://cimg7.ibsrv.net/gimg/www.rx7...609a53d56c.jpg

Installed:
https://cimg0.ibsrv.net/gimg/www.rx7...f3423b7473.jpg

Lots of nice and useful information here man.

Nice build and write up.

Subscribed and keep us posted. :D

Any ideas about how you will proceed with the brakes upgrade?

Regards,
Kostas.

Just found this thread and it's damn brilliant. Nothing better than an engineer who gets his hands on an FD!

Keep up the good work!

Dale

Glad you asked. That's the next thing to dive into.

At this point in the build, I had done 4 days on track and had killed 2 pairs of front brake rotors. The failure mechanism showed itself as a massive brake vibration - steering wheel shaking, brake pedal pulsing, interior bits falling off, and the pads getting knocked back on straights. I can only assume that the brakes were overheating and depositing a ton of pad material onto the rotors. Once the material started to get deposited unevenly, I guess it quickly snow-balled out of control to create the massive vibrations. Below is a table showing the tracks, rotor replacements, and pad choices:

https://cimg1.ibsrv.net/gimg/www.rx7...71f6ac97b8.png

The Hawk DTC-60 was on the upper end of the temperature capability spectrum for the stock calipers - so I feel like I had basically maxed out the capability of the stock front brakes. At this point, I started doing some research into big brake kits. As I tend to do, I made a big spreadsheet to work through some brake calculations, the results of which I posted in the following thread: https://www.rx7club.com/race-car-tec...-info-1094941/

At the time of that thread, the Sakebomb Wilwood kit wasn't available yet. When I originally did those calculations, I wasn't satisfied with any of the available BBK's due to either brake bias or cost. But just at the right time, Sakebomb came out with their Wilwood FSLI kit: https://www.rx7club.com/sakebomb-gar...y-kit-1101811/

These are my brake bias vs. piston size results I posted in the Sakebomb thread:
Stock (36mm piston and smaller rotors) - 68.2% front
Wilwood 32mm pistons - 65.1% front
Wilwood 35mm pistons - 69.5% front
Wilwood 41mm pistons - 75.8% front

I was really a big fan of the stock brake bias - the car had been really easy to trail brake into corners with a small (but not excessive) amount of rotation. To keep a relatively stock brake bias, I chose the 35mm kit.

The next issue: I had ordered the brakes and was waiting for them to arrive, but I fully assumed that my 17x9 +45 Enkei RPF1s would have to go. Every indication I had seen in other threads said that these wheels will not clear a big brake kit. Since I was the first person to try it with the new Sakebomb Wilwood kit, I was in a wait-and-see situation, but I fully expected to have to buy new wheels to get these brakes to fit. Fast-forward to the day I got the Wilwoods in the mail, I threw them on the car, picked up one of my wheels to put it on the car, expected it to smash into the side of the brake rotor... but the wheel clicked right into place with almost perfect fitment relative to the caliper. It was a VERY good feeling to not have to buy new wheels:

https://cimg6.ibsrv.net/gimg/www.rx7...67b9ae4e4f.jpg
https://cimg6.ibsrv.net/gimg/www.rx7...07158eabfd.jpg
https://cimg9.ibsrv.net/gimg/www.rx7...585fce1768.jpg
https://cimg0.ibsrv.net/gimg/www.rx7...3ffc8b19ff.jpg

I can get into details about the results in some future track updates, but I'll provide my overall "review" here. Performance-wise, these brakes have been pretty much perfect. The brake pedal feel is better than stock - no excessive flexing like some of the other Wilwood calipers are known for. I've never had any brake fade or brake vibrations. Brake bias is very good - it feels the same as stock. The only minor drawback of these brakes is that they do make a little bit of a hum noise when the brakes are applied. This comes from the milled J-grooves in the surface of the rotor - sounds a bit like playing cards in bicycle spokes. It's not very loud or annoying though.

For pads, I started out with DTC-60s. The were ok, but made a lot of dust, had rapid wear, and had a long warm-up time. I've since switched to PFC 11s - and they've been extremely good. Low wear, no noise, good consistency at all temperatures. I doubt I'll ever look for a different pad than this.

For reference, the rotors show some significant surface cracking after hard track use. I'm assuming it's nothing to be concerned about because I see the same thing on most track cars with large brakes. Regardless, it's something I keep a close eye on, and I bought a backup set of rotors just in case.

https://cimg7.ibsrv.net/gimg/www.rx7...042dbc5159.jpg

We call it "good cracking" :-)

But that seems a little extensive for just an event... I usually see some hairlines for a few events, and then they start to look like that later, before they go. Pay careful attention that none are getting more than about 1/8" to the edge.

Looks like you need some dedicated brake ducting. Also, I've had great experience with PFC 08s in front. They are cheaper than 11s, and they last better than anything else I've used.

I'm still around a year in the past on this build thread - that picture was taken recently, after 8-10 track days. So I think the cracks are right on schedule, lol. Brake ducts are something I've been considering for a while; I'm sure I'll get to it eventually.

Don't you have the AP calipers that Sakebomb sells? That AP caliper should use the exact same pads that my caliper uses. I'm using the same 7751 PFC that they recommend for the AP calipers, just in the 11 compound (7751.11.20.44).
http://www.sakebombgarage.com/conten...Pad%20Info.pdf

New Intake
 

One of the "unfinished" items on my car at this point was the temporary hot-air intake. Below is the "before" picture:

https://cimg7.ibsrv.net/gimg/www.rx7...aaee5d3928.jpg

I ended up running the intake down into the "V" between the intercooler and radiator. I used a couple of 3.5" aluminum elbows and a lot of trial-and-error to get it right.

After:
https://cimg8.ibsrv.net/gimg/www.rx7...2a591831a6.jpg

Without the duct in place:
https://cimg2.ibsrv.net/gimg/www.rx7...21b7d6cf96.jpg

The intake pipe:
https://cimg4.ibsrv.net/gimg/www.rx7...7082b4da62.jpg

The hottest temperatures I saw with the original intake were 158 degrees F (taken at the IAT sensor after the intercooler). This was at Road Atlanta in the middle of the summer, ambient temps in the low/mid 90s.

The hottest temperature I've seen with the new intake is 132 degrees F. The was also at Road Atlanta, but on a slightly cooler day (mid 80s).

So, not a perfect A to B comparison yet, but it looks like the new intake is helping things considerably.

Track update - VIR
 

Alright, time to catch up on some track videos.

This was in February of last year, I ran the Tarheel sports car club "frozen frenzy" at VIR. They run the full course on Saturday, and the 4.2 mile Grand West course on Sunday. Around this time, I was looking to buy a trailer - so this was the last event I would drive the car to. I was pretty nervous that this would be the one event where I would have some issue with the car and have to get towed home (felt pretty lucky that it hadn't happened so far). Ultimately, the car was flawless for this entire event. The temperatures were cooler (50s), so I could really lean on the car without having to worry about it. The brakes worked perfectly all weekend - I finally had an event where I didn't have to think about the brakes at all, they just worked consistently every time I smashed the pedal. I was still on the Hankook RS3s that I had been running for just over a year. They were starting to fall off a bit - they were like driving on ice during the out lap, and they weren't too forgiving even when hot. Overall grip wasn't bad when hot though. I ran the event on a ~10 psi boost map which crept to 11 psi at high RPM.

On the full course, I only improved a little bit from the previous year and ran a 2:11.6 (year before was a 2:12.x - didn't have a 10hz lap timer running). I attribute this mostly to the aging Hankooks, because I felt like I was getting more out of the car and track.

And on the Grand West course - holy crap this track is fun! This was my first time running it, and it certainly won't be my last. The corner sequences are never ending. From the time you enter the snake until you exit hog pen, it feels like you never stop throwing the car back and forth. I find myself trying to catch my breath each lap on the front straight, because it's such an intense track leading up to that. I had some issues getting caught up in traffic and ruining good laps (the track is so long that it's hard to avoid). I eventually lined up early to get at the front of the grid line and got a few un-disturbed laps in. Best lap was a 2:56.3.

Anyway, here's a video of 2 laps from the Grand West track:

One nice feature of VIR Grand West - Car & Driver runs their annual "Lightning Lap" event there, so there are a lot of production car lap times to compare against. My 2:56.3 would put me 47th out of 221 cars that have been tested there, and in some pretty good company.

https://cimg4.ibsrv.net/gimg/www.rx7...32714cd05f.jpg

Great thread, thanks for updating it. It seems there are a few more EFR-equipped RX-7's running around now, do you think the 7670 vs the 8374 is still the right choice for power goals around 300-350whp? Can you share anything about the Variable Turbine Volute (VTV) turbine housing now, or is it still a secret development project?

Intake looks great!
Very nice looking set-up all around.

One little nit-pick- when your 90deg silicone couplers in the IC piping do eventually split; I would weld in some aluminum 90degs in their place and use a single straight coupler per side (between turbo and IC and intake elbow ad IC) where some of the straight aluminum pipe is. You will be able to get a slightly larger radius bend in there and some added reliability as well.