In for the updates!
In for the updates!
At the 200+ you are running how stable was the car?
Awesome read and sweet car. Thanks for sharing!
Yes, great read. Awesome story. Thanks!
DrMikeCSI said:At the 200+ you are running how stable was the car?
All things considered, it felt very stable. The car tracked well with very little steering inputs needed. There was one area in the runway with a slight depression, somewhere between the 1/2 mile and 3/4 mile. Every pass, I could feel the suspension loading/unloading at that same point. The rear never bounced around, but a noticeable event nonetheless.
But frankly speaking, the experience during the runs was all new to me and somewhat mentally overwhelming. I was trying to pay close attention to all the sensory inputs for any concerning issues, while simultaneously focusing on just driving the car, making the shifts, and preventing wheel spin. As I have aged, my sense of self-preservation has heightened significantly. I consider that somewhat of a good thing in this pursuit. But as a result, I felt quite a bit of anxiety keeping the accelerator flat on the floor at the big end of the runway.
To borrow a quote from a source I no longer remember: "It was like having my first sexual experience and being in my first car accident at the same moment"
That is an amazing choice for a top-speed car. I know the clown shoes have appreciated significantly, but it's great seeing one that isn't a garage queen
Do you have a desire to go faster each time you bring the car out to the track, or is going 209 fast/exciting enough that just doing it again will be sufficient?
Lof8 - Andy said:Do you have a desire to go faster each time you bring the car out to the track, or is going 209 fast/exciting enough that just doing it again will be sufficient?
Definitely, I have a desire to go faster each time, with the caveat of available budget. For now, I would like to do this again a few times, even at the same speeds. But also, I think there is plenty of room for optimizations in the current form to keep me interested.
About how long does each pass take?
Great job! I might have missed it but did you make any changes to the driveshaft, halfshafts, or rear end?
P3PPY said:About how long does each pass take?
Based off the video time stamps, right at 30 seconds from dead stop to crossing the finish line.
I think your next goal should be 220-221. Whatever it takes.
It would be interesting to play with drag reduction for the next step. For example, those rear view mirrors aren't helping. Are you required to have them? What's the flow separation look like on the top of the hatch? Etc.
We did an event in 2004 that involved a quarter mile start, a run through a road course and then a sprint to 140 and back to a full stop. We realized pretty early that the run up to 140 was the place we could pick up the most time for the least effort, so we showed up with a car that was built to be slippery. This was in the F&F era, so all the other cars were covered in wings and various aerodramatic addenda. By the end of the day, there was a big pile of discarded aero stuff by the pits even though the maximum speed had been dropped to 130.
dlmater said: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.
The NC tunnel you refer to is run by a great bunch of folks. They have my number and I am local if you decide to follow this path of aero development. I do this stuff weekly, so nothing new here. Send me a message if you want to talk further.
Keith Tanner said:It would be interesting to play with drag reduction for the next step. For example, those rear view mirrors aren't helping. Are you required to have them? What's the flow separation look like on the top of the hatch? Etc.
We did an event in 2004 that involved a quarter mile start, a run through a road course and then a sprint to 140 and back to a full stop. We realized pretty early that the run up to 140 was the place we could pick up the most time for the least effort, so we showed up with a car that was built to be slippery. This was in the F&F era, so all the other cars were covered in wings and various aerodramatic addenda. By the end of the day, there was a big pile of discarded aero stuff by the pits even though the maximum speed had been dropped to 130.
Agreed. I'm following along in spirit with a calculator, but I love this stuff.
Wind resistance = 1/2*(density)*(Cd)*(A)*(V^2)
Wind power= WR * V
So a reduction in drag coefficient will make a proportional reduction in wind load power. So a drop of say... 10% in Cd at 50mph would free up an additional 1hp for acceleration. A drop of 10%Cd at 220mph would free up an additional ~50hp
From a quick google, Cd for a Z3M Coupe is 0.37 - so its got a lot of room for improvement anyway :)
Drag area, per the SAE estimation method is: 1.74 x 1.28 x 0.8 = 1.782m^2
Since I am here doing math, 220mph in a Z3M coupe would appear to take around 530hp (assuming an infinite runway, not a standing mile like OP is doing)
VolvoHeretic said:Great job! I might have missed it but did you make any changes to the driveshaft, halfshafts, or rear end?
I had the driveshaft custom made by a local shop. I have a bolt on adapter to convert the stock BMW rear pinion yoke to accept a standard u-joint. The rear differential and half shafts are stock BMW, for now. I am not trying to hook up or execute hard launches at the start.
JG Pasterjak said:I think your next goal should be 220-221. Whatever it takes.
A classic! I use that line all the time, but fewer people get the reference these days.
Keith Tanner said:It would be interesting to play with drag reduction for the next step. For example, those rear view mirrors aren't helping. Are you required to have them? What's the flow separation look like on the top of the hatch? Etc.
I believe there is some low hanging fruit here. The mirrors were actually on my list for attention. I had left them on up to this point, because I was still driving it on the street occasionally trying to troubleshoot different issues. They are easily removed and I plan to do so. Now that the mechanical part of the car seems fairly sorted, I would like to transition my efforts to the aero as you suggest.
stafford1500 said:dlmater said: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.
The NC tunnel you refer to is run by a great bunch of folks. They have my number and I am local if you decide to follow this path of aero development. I do this stuff weekly, so nothing new here. Send me a message if you want to talk further.
Thanks, thanks, and thanks! I will definitely reach out when ready. I grew up in Charlotte and my sister lives there in Mooresville. I was visiting her and the family before Christmas and on a whim stopped by A2 Wind Tunnel. It didn't appear anyone was there. The lights were off inside, but I knocked on the door anyway. No answer. But as I walked away back to the car, the front door opened and the gentleman asked if he could help me. I explained very briefly what I needed help with and he invited me into his office. It was Gary Eaker, the owner. He spent 45 minutes with me talking about my car, sharing stories of his Bonneville efforts and other racing industry interactions. I could have hung out all afternoon with him, but didn't want to wear out my welcome on the first conversation. Thank you again for the offer! I have much to learn here.
In reply to dlmater :
Gary is a literal fountain of information in aero and land speed racing. Reach out anytime.
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