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I've run events with NASA before, but always in DE. Waaaaay back in March at RRR I was signed off for a provisional TT license based off my SCCA licenses, and only needed to do one clean TT weekend for a full license.
Stuff happened, so I didn't get a chance to do that till 8 months later.
December 3/4 with NASA-SE at Road Atlanta.
I absolutely love Road Atlanta. It's my home track, it's challenging, its old school, it's fast, its appears deceptively simple, and it's undoubtedly deadly to machine if you don't treat it with respect in many spots. I have multiple hundreds of laps here and I still don't feel like I have it mastered.
The sun rose on very wet Saturday and I was more scared then I remember being in a long time. Light showers had passed though just an hour or so before hand and the track was soaked, a very fine mist still coming down, enough to make a race suit feel cold and clammy.
I hadn't brought rain tires.
I was about to jump into "qualification" in a car with double the horsepower, a foreign powerband, wildly different gearing, surrounded by much faster competition cars, all on stone cold slicks. A paddock buddy noted that he hadn't seen me that jumpy and nervous before, and it was true. I half expected to eat wall on my first lap.
I turned the boost down to wastegate, crossed my fingers, gridded up, and hoped muscle memory and reflex would keep the car straight.
My god, that session was so fun.
There were two DE sessions in front of us, so the track had the faintest hint of patchiness. Enough you could lean on the tires to build heat, but also damp enough that a FIRM hand had to be kept on the rear and patience with the front end. I kept it on the track the entire time and came back with a headsplitting smile.
The gearing was different, but they still went up and down. The car was faster, but it wasn't untamable. The track was damp, but it was still Road Atlanta and it still went right at T1. By the end of the session I had my confidence back and was comfortable doing 130mph into 10a- the most fun I've had doing 1:50 laps there(which is like stock miata in DE2 slow in normal conditions) and set the sessions fastest time.
Session two was our first real TT outing. The rain had paused and there was a dryish line. I turned the boost controller on and set it to 10psi, ready to have some fun and actually take a crack at my PB.
This was the first time I was really able to let the car eat for more than a few gear pulls, and holy cow it scoots even "turned down" to 10psi. I could pull on Mustangs and BMW's and actually complete passes between T7 and T10 with ease! It felt like cheating!
I also was able to get a somewhat good launch down the back straight out of T7. which is when I found out that a 6spd and 4.3 is waaaay to goddam short a gear to have in something putting down 300ish whp. I would hit limiter in 6th at 145mph and hold it for 4-5 seconds before I was remotely close to the braking zone. Actually made it a little awkward rocketing past a car out of T7, only for them to catch me in T10 as I'm hammering limiter...
I discovered that my brakes, while they had been fine for 230whp and hot July days, were NOT ok with the additional speed, even in much cooler temps. Two hot laps and then pedal would go straight to the floor midway though the third. Two cooldown laps at cruising pace would bring them back but... yikes. Not having my brake ducts(due to intercooler piping blocking the routing and a lack of time to build a solution) definitely wasn't helping matters.
We got about 1.5 dryish sessions, then the rain returned in force and we were back to soaked track to close out the day. Still, I had knocked 4 seconds off my previous PB, gained a ton of confidence, and kept it out of the kitty litter. Other then having a single exhaust manifold nut loosen and fall off, the car had zero mechanical issues. Oh, a headlight cover flew off at some point. Never saw it leave, but it was pointed out to me when I got back to paddock.
The day ended without a fully dry session, but the forecast for Sunday looked like it would be dry. I refilled the ~20gal worth of E85 the car had gulped down like a greedy hooker and studied the video I did have, planning to try and crack into the low 1:30's, track conditions permitting.
The sun didn't really rise Sunday... it kinda... gloomed?
This photo was taken about an hour after the first TT session was scheduled. They had to hold for over 1.5hrs due to extremely thick fog, scrubbing several DE sessions and a TT session.
When we did get to go out, the track was in much the same conditions as the day before, still damp, but a solid dry line formed. The car could be pushed, but curbs were deadly and the front end not quite as willing to grip as it should be.
I came in from that session with a mix of oil smoke and steam billowing from my hood vents. After a day of no issues mechanicals issues had all hit at once.
My catch can had overflowed and dumped oil all over the exhaust side of the bay. I'm used to emptying the can once a month at most, but apparently sustained usage of E85 and boost greatly increases the amount of fluid production. Not a big deal, just another item on the checklist.
A water feed line to the turbo had also cracked and sprung a leak. Probably should have seen this coming, but the rubber lines were more a temporary measure that hadn't been made un-temporary yet.
Thankfully I had the foresight to make the lines longer than needed, so I trimmed the line, re-installed, and added some heat tape. The rear radiator cap made bleeding coolant in paddock with no funnel a breeze and repairs were complete with plenty of time to spare.
Headed back out and somehow "Miatas" were leading the pack? Weird feeling. If you know this car then you know...
Around this point the car stopped wanting to rev much past 7800, which really killed top speed. Looking back I'm pretty sure the spark plugs were dieing, as they had been there for a few days of street driving, 2.5hrs of dyno time, and 1.5 days of track use. But I didn't think of that trackside, so just kinda... painfully powered through it.
Last session I turned the car up as much as I felt I really safely could (14psi, around 330whp) to try and drop into the 1:33's as I was only a few tenth shy. I cracked out a 1:34.14, maddeningly close.
This was also the point that I realized I had fucked up massively all weekend.
Going into 10a, I missed the shift down to third and found 5th instead. Already down 4/10th, I said **** it and left it in 5th. And watched with astonishment as I rocketed out of 10b with more speed then before, going from 4/10 slower to 3/10 faster. Out of sheer surprise and having more speed then I was prepared for I had to lift slightly in 12, losing a tenth, but still running my fastest lap by 2/10th. I started my cool down lap wondering what madness had occured there.
It wasn't till later in the paddock I put the pieces together and realized my gearing had screwed me over in more ways than just limiting top speed.
I was having so much fun all weekend with my super tight gears(6spd, 4.3), shifting every 3 seconds like a fast and furious protagonist, that it never even crossed my mind just how much time I was spending shifting. The 6spd+4.3 combo is optimized for a low torque, all top end, N/A motor setup that you have to strangle and beat to get speed out of. Which is what I was used to driving. The turbo gives it a completely different powerband, producing 300+ft/lbs as low as 3500rpm and dropping off at the top. Every lap around the course I was dropping down to the lowest gear possible, using ~2000RPM worth, then shifting, rinse, repeat, making full use of 3/4/5/6, which is what I was used to.
What I should have done is driven the entire course in 5/6th, sticking the motor down to ~4K where it makes heaps and heaps of torque to haul me out of corners and stay in boost for more than three seconds. Which is exactly what I accidently did that last lap in 10A, and saw a full half second gain in time in just two corners worth.
To prove my theory I overlaid my fastest lap with a friends K24A2 car. The acceleration rates between my 330whp(blue) and his 240whp(red) are nearly identical under 100mph- I'm accelerating faster while in gear, but loosing all that time shifting. You can even see in the final corner where my speed trace suddenly shoots higher then his at a much lower speed- which is where my accidental 5th is. Right before I scared myself in 12 and lifted.
There's lots of other data and interesting points from this single overlay, but that's the main takeaway.
I'd estimate that if I came back with a new mindset on how to drive the car, and a longer diff, I could find an easy 2-3 seconds, placing me much closer to the 1:30 that had been my goal coming into the weekend.
Not that the 1:30 would have taken the Miata track record anyway, as the 9 Lives Racing shop car(pictured above), equipped with a pro driver and stickers, reset that record to a blistering 1:25.
I came into the weekend 9 seconds off the record, went 6 seconds faster, and am still 9 seconds off the record. lol
No more records are going to be set on these tires though. A few lockups in the damp and one panic lock while dry killed these stupidly expensive tires. I need to find a way to prevent that, as I came to the realization long ago that braking is my weak point.
The car made it back home under its own power without further issue. It was nice to be close to home, unpacked, and showered before 8:00pm.
I ran the entire weekend clean in TT, so one goal accomplished. I didn't get to reset any records like hoped, but it is what it is. I shook the car down, found the weak areas of the turbo, and have plenty of stuff to do over the winter now. Upgrades and improvements are already on the way.
Closing thought, Miata's are far, far more stable at 145mph then I had anticipated. I expected the car to feel like it was going to fall apart, but it felt... calm is not the right word by any means, but it wasn't the hair raising experience I had expected. I'm still painfully aware that it badly needs additional caging.
Good stuff! The car looks like a rocket ship now. It's still amazing the gains this engine gets with just a turbo. Your gearing is certainly way too short for the new power, obviously lol.
One thing that helped me stay more consistent is better ergonomics for the steering wheel. Getting it closer to the chest to use more and bigger muscles helps with finesse and overall confidence. A common sign of this is when one of your arms is fully extended at 90* and even more so if it's getting fully extended before 90*. I highly recommend something like this: https://www.sparcousa.com/product/steering-wheel-spacer
One thing that helped me stay more consistent is better ergonomics for the steering wheel. Getting it closer to the chest to use more and bigger muscles helps with finesse and overall confidence. A common sign of this is when one of your arms is fully extended at 90* and even more so if it's getting fully extended before 90*. I highly recommend something like this: https://www.sparcousa.com/product/steering-wheel-spacer
I've played around with different steering wheel distances, any closer always just feels awkward and I end up elbowing my ribs. With the EPS the steering wheel is not heavy by any means, so it's not a strain to haul it around even with big slicks.
Originally Posted by turbofan
Always fun to read your updates. Congrats on a successful, clean day.
Being the nerd that I am, I've been working on a tractive force calculator to help visually understand gear maps plotted over the powertrain torque curve. All this, to simply better understand what ideal shift points would be to optimize for force output to the wheels at all times. Going to use your data as a helpful learning point for myself (and maybe you). The short and sweet is that it paints the same picture that you are seeing in just a different manner. You have the same gearset as me right now (6spd/4.3) so plotting your numbers was really easy for me as I just updated my powertrain torque curve to match your low boost dyno sheet as shown roughly below.
From there, with some tire size and gearset math, you can get a fancy output that looks like this when you plot MPH against forward pushing force on the tire.
I have it setup that I can compare two independent gearsets and dyno curves to one another, but for the sake this simplified chart (and legend), just understand that T1 means "transmission/gearset #1" and G1 means "gear indication". Each different color line represents a gear and each gear line has 7 points plotted that align to the dyno chart input (eg: first dot is 2500rpm, second is 3500rpm, third is 4500rpm, etc). A few key takeaways:
Shift points
Due to torque falling off up top and having a really meaty low end, you have a benefit to short shift every single gear. There's zero reason to be revving it out above 7500rpm with this torque input I've used unless you are simply revving it out to get to the braking zone and avoiding additional shifting
It appears that you could shift at 7500 in every gear without a detriment and actually it looks like shifting into 6th at 6500 would probably be a good thing.
Tractive Force Delta Between Gears
Based on your lap time plot, your minimum speed was ~50mph. You could see a short benefit to being in 3rd on that corner, but odds are that staying in 4th would be faster as it would save you a shift and by time the car gets to 6500rpm in 3rd, the force to the wheels in 4th is pretty damn close to the same already anyways.
Once you get into the 4th, 5th, and 6th gears the force difference between gears gets really close. Specifically, looking at the difference between 4th & 5th you can see that 5500rpm in 4th is damn close to what 4500rpm in 5th is at 70mph. You are getting to that 70mph min corner speed range about 3 different times on various corners across the track, so like you said, staying in 5th would likely be faster as you are giving up minimal tractive force at the tire, but saving yourself a shift.
Feel free to make whatever other assessments you'd like from the chart. Hope it helps you see things in another helpful way. I can make adjustments to the graph if you'd like to see other things, so feel free to reach out. Car looks like a riot to drive and congrats on it surviving its first true test!
Being the nerd that I am, I've been working on a tractive force calculator to help visually understand gear maps plotted over the powertrain torque curve.
Yo, can you share this calculator so I play with it too?
Yo, can you share this calculator so I play with it too?
Without cluttering this thread too much, I plan to get final details nailed down on it shortly and I can make a new thread explaining how it works and attaching it for all to download and play with as they please.
As of right now, all the calcs appear to be working well, but its not super user friendly how I've laid out all my input/output tables and charts. A little cleanup work on organizing will go a long ways. Essentially, the way I have it set up now is that you can compare different rear end gearsets, different transmissions (up to 8spds), different dyno charts (and therefore different rev limits), and different tire sizes all independently with a handy chart output so that you can really understand how changes affect power to your rear tire.
If I get more advanced with this, a guy could plot average acceleration by gear (which would require some logged data to reference) and have a user specified average shift time input in order to have the spreadsheet essentially tell you at what RPM and gear it makes sense to short shift or what RPM it makes sense to down shift, but a wise user should be able to look at the tractive force plots and make some of those conclusions himself like I did above...
Being the nerd that I am, I've been working on a tractive force calculator to help visually understand gear maps plotted over the powertrain torque curve.
Dude! Thats ******* awesome. I've been using the graf garage calculator( Gearing Calculator - Graf Garage ), to look at potential gearing combinations and shift points, but that doesn't allow me to plot in powerband's like yours does. Agreed that if you get it working in a manner anyone can input data, that will be a huge help for finding optimal gearing. Your calculator helps to have definitive data for what took me an entire weekend to realize- I need a longer diff baddd, and yeah, there's not a ton of point reving the motor out to 8K in higher gears if I don't need to(which saddens me a smidge, as I like motors that rev).
Originally Posted by Lokiel
Your engine always reminds of an Esky (Australian term for any brand of "cooler box")
I giggled. Took out a dumpster of a powerplant, installed an icebox.
Dude! Thats ******* awesome. I've been using the graf garage calculator( Gearing Calculator - Graf Garage ), to look at potential gearing combinations and shift points, but that doesn't allow me to plot in powerband's like yours does. Agreed that if you get it working in a manner anyone can input data, that will be a huge help for finding optimal gearing. Your calculator helps to have definitive data for what took me an entire weekend to realize- I need a longer diff baddd, and yeah, there's not a ton of point reving the motor out to 8K in higher gears if I don't need to(which saddens me a smidge, as I like motors that rev).
Ryan and I tried to work out a way to do a thrust/tractive force plot using the information, but it requires a lot of manual input of data from the dyno plot. Sadly the thrust/tractive force plot calculator I have for my own personal use doesn't like being turned into a Google Sheet and then back to Excel
I just re-did the spreadsheet of mine last night. I think it's all good to go. It doesn't work well in Google Sheets due to Google's garbage charting capability, so I'll share it via Excel file in a new MT post/thread sometime in the next couple of days once I get a walkthrough written up on how to use it
I really love revvy engines too but a BP just eats itself up too quickly and yields jack in return when revved above 7500ish in my unprofessional opinion. Lifespan of the engine goes through the floor.
The motor stayed in the car this year. I'll take that as a good sign for 2023.
Also hitting 5 years with this chassis. Here's to another five *chugs apple juice*
12-06-2022, 01:18 AM
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