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dlmater
dlmater Reader
4/18/24 8:42 a.m.

The next morning, Friday, revealed cool temperatures, bright sunshine, and a dry race surface with a 5-mph tail wind blowing directly down the runway.  I readied the car, triple checked everything, suited up and we made our way to the starting line.  For us, the first pass needed to be a licensing pass. 


mfennell
mfennell HalfDork
4/18/24 8:42 a.m.

Nice to see Mitch Piper's shop.  IIRC, he started out subletting space from Bret dePedro, the RX7 guy.

dlmater
dlmater Reader
4/18/24 8:43 a.m.

A couple more, just because...

pushrod36
pushrod36 HalfDork
4/18/24 8:56 a.m.

I'm so happy to see this!  I was at your place to see the E24 you were selling in late 2020, and this build was underway.

 

golfduke
golfduke Dork
4/18/24 9:23 a.m.

something about a clownshoe with a parachute pack... hnggggggg.  

dlmater
dlmater Reader
4/18/24 9:31 a.m.
pushrod36 said:

I'm so happy to see this!  I was at your place to see the E24 you were selling in late 2020, and this build was underway.

 

Hey! It was great meeting you then.  I did finally sell the E24 to a gentleman from PA.  

dlmater
dlmater Reader
4/18/24 9:34 a.m.

Again, the first pass for us was a licensing pass.  For the licensing pass, you were to accelerate to the ¾ mile marker, then hold that speed through the mile finish demonstrating car control abilities. My first pass revealed a speed of 165 MPH. That was the fastest speed I had ever driven, or traveled, in a car previously in my 59 years of life.   

During that pass, the OEM small plastic belly pan under the radiator detached and exited out from under the back of the car.  I never felt or heard anything amiss during the run and was surprised when I was told what happened afterwards.   That panel had successfully resisted 137 MPH years before, but obviously somewhere between 137 MPH and 165 MPH was the limit of its capability to stay in place.  A few minor repairs were needed as a result.  I also strategically added some “200 MPH” tape (foreshadowing pun) blocking off the brake duct cooling intakes in the front fascia. I also added some machine screws/nuts and tape to secure a couple newly created loose edges of plastic under the car. 

dlmater
dlmater Reader
4/18/24 9:43 a.m.

My son took the next two passes repeating the same procedure but increasing the speed on his second run.  Given all the work and modifications I had performed on the car, I had planned out multiple shakedown passes at slowly increased speeds for the weekend.  I had mentally stressed myself for weeks over the multitude of negative scenarios I could envision.  Thus, I was trying my best to proceed cautiously despite the competing desire to just “send it”.

After a return to the pits from his runs, my son reported he was having issues making some of the gear shifts, not getting the stick to go all the way into the chosen gear.  We later determined that he was not fully disengaging the clutch, inadvertently releasing it early, given his shorter legs and the seat position.  The current seat position was a compromise for our height differences, favoring my much longer legs.

At this point we both believed the car was capable of 200+ MPH. Other than the plastic radiator pan breaking loose on the first run, the car had performed flawlessly and felt very stable at speed.  But again, out of an abundance of caution I was trying to slowly ease our way in the direction of 200 mph.

prodarwin
prodarwin MegaDork
4/18/24 9:43 a.m.
jharry3 said:
dlmater said:
buzzboy said:

I love clown shoes! 137 in the mile is pretty awesome.

I was surprised with that result as well.  That was a key contributing factor for my decision to use the car for this purpose.  I subsequently spent quite a bit of time internet researching the frontal area and drag coefficient for these cars.  In a relative sense to some other cars, the frontal area value is low.  It is a small car.  However at the time, the drag coefficient values I found were contradictory. Thus, I just roughed out a needed horsepower number for 200mph based on wind resistance is the square of speed.  

I just looked this up to verify it:

  • As the vehicle’s speed increases, the power required to overcome drag increases cubically due to the velocity term in the drag force equation.

Yes, just to clarify,

Wind resistance increases with the square of velocity
Power increases with the cube of velocity

tuna55
tuna55 MegaDork
4/18/24 9:47 a.m.

Wow. 

dyintorace
dyintorace UltimaDork
4/18/24 10:05 a.m.

Love everything about this so far!

Xceler8x
Xceler8x UberDork
4/18/24 10:55 a.m.

RVA represent! 

 

Please continue! 

dlmater
dlmater Reader
4/18/24 11:04 a.m.

For the next series of passes, I was targeting 175 – 180 MPH with the only goal to test release the Stroud Safety parachute.  I had originally called Bob Stroud in 2018 and he had specified a Bonneville style chute for the car with recommended mounting location and other considerations.  Bob went above and beyond my expectations, walking me through and educating me on potential issues to address.  For the first parachute trial pass, the chute deployed flawlessly.  What a thrill it was to feel the chute deploy and press my body up against the harness belts.  That was the first time I had ever deployed a car parachute, and quickly concluded I wanted to experience that feeling again.

However, it was apparent that the overwhelming mental nature of making these first runs made it difficult to repeatedly glance down at the dash checking speeds.  I thought I had probably finished this last pass, as a chute deployment test, around the 185-mph mark based on the only quick glance to the dash I was comfortable to attempt. 

My son met me at the timing trailer on my return drive back to the pits.  As he was walking over with a obviously forced stoic face, I could tell he was trying to hide his excitement.  Without saying a word, he handed me the time slip and I saw the number ….. 205.339 MPH!  I couldn’t contain my excitement, laughing hysterically.  We both were thrilled. 

 

You can see/hear in the video I am still short shifting somewhat through all the gears and easing into the accelerator.  More speed was there to be realized.

Keith Tanner
Keith Tanner MegaDork
4/18/24 11:05 a.m.
prodarwin said:
jharry3 said:
dlmater said:
buzzboy said:

I love clown shoes! 137 in the mile is pretty awesome.

I was surprised with that result as well.  That was a key contributing factor for my decision to use the car for this purpose.  I subsequently spent quite a bit of time internet researching the frontal area and drag coefficient for these cars.  In a relative sense to some other cars, the frontal area value is low.  It is a small car.  However at the time, the drag coefficient values I found were contradictory. Thus, I just roughed out a needed horsepower number for 200mph based on wind resistance is the square of speed.  

I just looked this up to verify it:

  • As the vehicle’s speed increases, the power required to overcome drag increases cubically due to the velocity term in the drag force equation.

Yes, just to clarify,

Wind resistance increases with the square of velocity
Power increases with the cube of velocity

My post yesterday doesn't seem to be showing up - but if you do the math: the previous result was 137 mph with 240 hp. So we're looking for 50% more speed, which means 338% of the current power level. 240*3.38 = 810, which is right where dlmater was aiming.

I'm not surprised body parts are coming loose, the load on those mounting points is going up exponentially as well. The choice of a clownshoe is an interesting one as they're likely not very slippery at all, I don't imagine aero efficiency was a big factor. It's small, but it's probably not very clean.

There was a 200 mph Miata project back in 1999. I was only peripherally involved at the time, but I seem to recall a calculated power requirement of "only" 450 or so. Of course, the engineer doing that was not the best one so it's quite possible he missed an exponent. The project died when it turned out the car donated by Mazda was preproduction and needed to be crushed. I've often wondered if my LS3 car could get there, it's got the gearing and it's small. It's also more slippery than stock if I take the wing off.

dlmater
dlmater Reader
4/18/24 11:06 a.m.

Five very long years I had worked on this car.  At the last dyno tuning session in August 2023 before the event, I had commented to my tuner I was completely burned out from working on the car.  Seeing the 200+ MPH time slip and realizing my goal that soon on the first day of the event provided me great satisfaction and validation for all my efforts. 

At this point, I needed some time to reset the car again, re-pack the chute, make inspections, and re-check all the fluids.  After which, racing was suspended for the day and we loaded up the trailer and headed to a celebratory steak dinner.  

My son and I had only planned to stay two days, Friday and Saturday, as I had to leave town very early Monday morning on a business trip and he had some family obligations at home.  Given the long 14-hour drive back home for me, including stops, racing and leaving later on Sunday was just not reasonable.  At dinner Friday night, I told my son I certainly had already exceeded my expectations for the weekend.  I really wanted him to get a pass at 200 MPH, if he was comfortable doing so, before we had to leave Saturday evening.  Thus, the plan for Saturday was set.  He would take successive passes until he reached 200 mph.

golfduke
golfduke Dork
4/18/24 12:25 p.m.

That youtube video has all the suspense of a dad going to drop his kids off at school.  Just a seemingly effortless 200mph.  Very very impressive. 

 

dlmater
dlmater Reader
4/18/24 12:38 p.m.
Keith Tanner said:
prodarwin said:
jharry3 said:
dlmater said:
buzzboy said:

I love clown shoes! 137 in the mile is pretty awesome.

I was surprised with that result as well.  That was a key contributing factor for my decision to use the car for this purpose.  I subsequently spent quite a bit of time internet researching the frontal area and drag coefficient for these cars.  In a relative sense to some other cars, the frontal area value is low.  It is a small car.  However at the time, the drag coefficient values I found were contradictory. Thus, I just roughed out a needed horsepower number for 200mph based on wind resistance is the square of speed.  

I just looked this up to verify it:

  • As the vehicle’s speed increases, the power required to overcome drag increases cubically due to the velocity term in the drag force equation.

Yes, just to clarify,

Wind resistance increases with the square of velocity
Power increases with the cube of velocity

My post yesterday doesn't seem to be showing up - but if you do the math: the previous result was 137 mph with 240 hp. So we're looking for 50% more speed, which means 338% of the current power level. 240*3.38 = 810, which is right where dlmater was aiming.

I'm not surprised body parts are coming loose, the load on those mounting points is going up exponentially as well. The choice of a clownshoe is an interesting one as they're likely not very slippery at all, I don't imagine aero efficiency was a big factor. It's small, but it's probably not very clean.

There was a 200 mph Miata project back in 1999. I was only peripherally involved at the time, but I seem to recall a calculated power requirement of "only" 450 or so. Of course, the engineer doing that was not the best one so it's quite possible he missed an exponent. The project died when it turned out the car donated by Mazda was preproduction and needed to be crushed. I've often wondered if my LS3 car could get there, it's got the gearing and it's small. It's also more slippery than stock if I take the wing off.

Jumping ahead a little in the conversation, your body parts comment was of concern to me before the event, and remains so today.  The sides of that pan screwed directly into the front wings of the inner fender liners, all plastic.  Inspecting the area after it blew out, it appears the air coming in the brake duct openings was pressurizing this whole area.  The brake ducts themselves had been removed as the intercooler piping on both sides intersected with them.  Thus the front inner fender liners were being forced inward somewhat, contributing to the failure of the pan mounting points, in my assessment.  Blocking off the brake duct openings with tape seemed to solve this issue based on my subsequent inspections after each pass.  

I have since gone back now replacing the inner fender liners, fabricating a steel reinforcement perimeter for the front liner wings that ties back into the front bumper and front frame rails.  I did the same for the bottom of the front bumper fascia.  I also fabricated steel block-off plates for the brake duct openings, bolting them to the front bumper.  I am leaving the pan off.  I should have done all of this before the event.

dlmater
dlmater Reader
4/18/24 1:06 p.m.

Saturday was another perfect weather day.  We arrived at the track early and prepped the car.  My son was one of the first racers in line for a pass. 

He took his first pass for the day.  Again though, he was having issues shifting and still trying to take it somewhat easy based on my continued verbalized concerns for safety. 

The pass resulted in a speed of 199.260 MPH.  Somewhat frustrated, he was ever so close.  This speed was obtained despite some short shifts in the run and a missed shift from 4th to 5th.  Once again, he was unable to fully engage the shifter into 5th on his first try, backing off the accelerator and shifting back into 5th gear.   For the next outing, I plan to fabricate a foam seat insert to better position him in the car.

 

dlmater
dlmater Reader
4/18/24 1:08 p.m.

After the car reset, making all necessary checks, repacking the chute, etc., my son lined up for his second pass of the day.  I helped buckle him in, double checking all the safety items and left him in the staging lane early.  I wanted to get back down to the finish line to get a video of the car crossing the mile finish with the chute deployment. 

I made it back down to the mile marker finish line.  But soon before my son’s pass, ECTA experienced an issue with the timing equipment.  Thus, we had to wait quite a while for the problem to be resolved.  After racing resumed, another car or two took passes before my son.  I heard the announcement of my son pulling into position for his run.   I could hear him screaming down the runway before I could see him.  After he crossed the finish line, I heard the announcer broadcast his speed.  This pass netted the best speed for the car to date, 209.888 MPH!! 

You can hear the PA announcer stating the final speed at the end of the video

 

dlmater
dlmater Reader
4/18/24 1:11 p.m.

Meeting back at the timing trailer we both, once again, were laughing with excitement.  Many, many texts were sent to family and friends.

 

We took the car back to the pits.  It was now lunchtime and during my inspection of the car, I noticed the supercharger belt was beginning to fray on one edge.  By this time, the belt had 12 or so dyno pulls and 5 to 6 high RPM/ high load runs down the runway.  I had spare belts with me and my son was excited for me to go back out, making a final pass or two for the weekend, increasing the speed.

But by this time, I could no longer ignore my anxious feelings and the nagging voice in my head.  I thought we needed to take a safety pause.  I told my son I thought we had pushed our luck far enough for the first time out with the car.  We had inadvertently jumped ahead in the shakedown pass speed progression plan.  We also had exceeded the speed I had given Stroud as the expected maximum for the chute. I felt it prudent to get the car home, up into the air and give the entire undercarriage, every nut and bolt, all the systems, etc. a thorough re-inspection.   There were a few other safety considerations I’ll outline later for the group’s input.  I was fine not making a final pass at this point. 

My son agreed with my thoughts and we loaded the car into the trailer.  We spent a little time walking the pits again, looking at the other cars before departing for home.  We had an amazing time talking to other racers and watching their runs the entire weekend.  

kb58
kb58 UltraDork
4/18/24 4:39 p.m.
jharry3 said:
dlmater said:
buzzboy said:

I love clown shoes! 137 in the mile is pretty awesome.

I was surprised with that result as well.  That was a key contributing factor for my decision to use the car for this purpose.  I subsequently spent quite a bit of time internet researching the frontal area and drag coefficient for these cars.  In a relative sense to some other cars, the frontal area value is low.  It is a small car.  However at the time, the drag coefficient values I found were contradictory. Thus, I just roughed out a needed horsepower number for 200mph based on wind resistance is the square of speed.  

I just looked this up to verify it:

  • As the vehicle’s speed increases, the power required to overcome drag increases cubically due to the velocity term in the drag force equation.

Yes, based on the numbers he ran with the stock engine, the math says that he needs 750+ at the crank, so he was all set.

NOHOME
NOHOME MegaDork
4/18/24 5:18 p.m.

Awesome read.

So what did you find when you got home and went over the car?

dlmater
dlmater Reader
4/18/24 8:14 p.m.
NOHOME said:

Awesome read.

So what did you find when you got home and went over the car?

Actually, I am still working on that task.  The past few months I have been extremely busy with work and other commitments.  As mentioned a few posts ago, I did go through the entire front body work, correcting the weaknesses seen on that first pass.  However, I did not find anything new.  I did check all the front engine accessory and supercharger drive pulleys, front suspension, and some other engine compartment items. I'm trying to work my way from the front back to the rear of the car.  I have found nothing of note at this point.

I did have a couple conversations with Stroud Safety on the parachute.  They reviewed all the information requested and advised the current chute I have is adequate for up to 230MPH for the car.  I was expecting them to recommend smaller dual chutes, but in the end their technical department advised to stay with the current chute. I did send the chute back to them for a full inspection and cleaning.  They did not charge me for that service!

dlmater
dlmater Reader
4/18/24 8:44 p.m.

An extension of NOHOME's question, I do have some unresolved concerns. 

My approach going forward will be to optimize the set-up I have and push the car harder to determine where the speed limitations may be realized; most likely horsepower vs. aerodynamics.  From there I will reevaluate next steps for another goal and perhaps additional modifications.  I do not have clarity yet on how far I personally want to push this pursuit above 200MPH. ECTA does have a 2-kilometer run option, which I will probably opt for next time there.  At 210 MPH we are right at the engine rpm limiter (7,200 RPM) setpoint in 5th gear.  A few additional MPH, we will need to shift into 6th gear.

For now, my top two safety concerns before the next event (pending other discovered issues) are proper tire choice and aerodynamics.

Aerodynamics:

I'll start a separate thread in the aero forum for this discussion.  But in overview my main concern here is not extracting every last MPH potential from the car.  My main concern is understanding any currently unknown negative handling artifacts that may arise due to increasing speeds.  Does the car produce problematic lift tendencies, negative consequences in rear yaw attitudes, etc. at different speeds?  Which part(s) of the stock body may need modifications to prevent wind force damage.  I have had an initial conversation with a wind tunnel in NC, which indicated they could me with these questions.  In my mind, I need to do much work here to better understand the dynamics of the car at speed.

Tires:

The current tires on the car, as ran in Oct. are staggered size Sumitomo HTR Z5 with a rating of 98Y (no parentheses).  My understanding is the tires were originally tested for speeds up to 186 MPH.  I need to better understand if I am pushing a tire of this rating too much with occasional speeds above that number. 

I have found Michelin Pilot Sport PS2 in the sizes I need with a rating of (98Y).  The presence of the parentheses denote the tires were tested above speeds of 186 MPH.  Michelin’s website states for speeds over 186 MPH, consult with your local tire dealer or car manufacturer for fitness for use determinations.  In my case, I do not think my local tire dealer nor BMW would provide a meaningful response to this question. 

Thus, I am not certain of the risks here and need to do more research to determine proper tire choice.  knowledgeable comments greatly appreciated.

GameboyRMH
GameboyRMH MegaDork
4/18/24 8:58 p.m.

Impressive! I wouldn't be surprised if you got up to 220mph with a full-power run.

Different seat inserts are a common way to handle drivers of different sizes with fixed seats, one time I drove a Radical SR3 at a supercar track day and they had to take out all the foam so I sat on the bare carbon tub...and I still looked like a giraffe next to the instructor cheeky

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