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chaparral
chaparral Dork
1/17/21 10:42 a.m.

In reply to AaronT :

That's cheating, That weight is without the driver! Usually the minimum weight including driver is between 375# and 425#  A 45-hp KZ would be OK for local races; at nationals they have 49. That's still nearly 300 bhp/ton. The Rush has a higher power-to-weight ratio with the driver onboard.

flatlander937
flatlander937 HalfDork
1/17/21 10:48 a.m.

These things have my attention. The size/weight/low consumable cost/speed is really hard to beat. Maybe in a few years...

Also I'm fairly confident I could add headlights and turn signals and street tires to make it legal in VA due to pretty loose kit car laws... devil

chaparral
chaparral Dork
1/17/21 11:11 a.m.

In reply to flatlander937 :

You'll have to fly a large American  flag from a mast attached to the roll hoop! Pictures of the car without a driver don't show how small it is.

AaronT
AaronT Reader
1/17/21 11:30 a.m.

In reply to chaparral :

Good point re: driver weight. 
 

There is a pic on the website where the rush is being followed by a corvette and the vette looks huge. The Rush is probably smaller than the Japanese Kei cars and those make Miatas look big.

chaparral
chaparral Dork
1/17/21 11:38 a.m.

In reply to AaronT :

and that's a C6, which is the smallest Corvette in fifty years!

sevenracer
sevenracer Reader
1/17/21 11:58 a.m.

I'm liking this, is there an SCCA road racing class for it? Seems pretty similar in concept to a Spec racer ford, also not too far off in price.  But motorcycle based drivetrain vs auto for SRF.

chaparral
chaparral Dork
1/17/21 12:11 p.m.

In reply to sevenracer :

P2, but until SCCA approves it with a stock specification like it does with the Radicals it will have to run with restrictors and ballast.

wearymicrobe
wearymicrobe PowerDork
1/17/21 1:47 p.m.

I dig it but them thinking they can sell boatloads of them, IE triple digits a year is farcical for a track only car even then the pricing is really low. Say they are 15K in each unit in parts cost, not sure what the labor costs and sqf costs where they are building. Not a lot of meat on that bone and building bigger numbers means a lot more space and people then you would think. 

Radical with a almost single piece body and seriously depreciated jigs and a lot of experience selling is at 60K usd right now. 

chaparral
chaparral Dork
1/17/21 5:47 p.m.

In reply to wearymicrobe :

They built the factory in an existing building in West Houston during the worst oil bust and worst commercial real-estate bust anyone can remember.

MrFancypants
MrFancypants Reader
1/20/21 2:22 p.m.

Random thought...  this, and the price of it, makes me excited for the future of amateur motorsports.  If things continue to move in this direction, especially with electrification, I might actually be able to afford to go racing some day.

chaparral
chaparral Dork
1/20/21 4:21 p.m.

In reply to MrFancypants :

You'll soon be able to drive one of these at a racing school.  Driving the SR might convince you to start saving! 

Loweguy5 (Forum Supporter)
Loweguy5 (Forum Supporter) Reader
1/20/21 8:00 p.m.

Wow what a great idea combined with solid execution!  And it makes cool race car noises.

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
1/20/21 8:51 p.m.
MrFancypants said:
Tom1200 said:

From the video it seemed pretty forgiving over the kerbs. The car being on treaded tires should help with the running costs, albeit at the cost of lap times.

On the VIR video the driver seems to be struggling with the down shifts in some places??

Looks very fun to drive.

I believe it has a sequential dog-leg style motorcycle gearbox.  Using those on a motorcycle you generally don't need to use the clutch on upshifts, or at least not fully disengage the clutch; a very light touch would typically give a quick and smooth shift. 

Downshifts do require you to completely disengage the clutch to get the desired gear to engage, and given that this box is hooked up to paddle shifters I'd guess that they've set up a motor on the shift lever....  so I imagine the timing between your foot on the clutch and the paddle shifter takes some getting used to, add braking and rev matching with the other foot and I'm sure it all feels a little odd if you only ever drive standard syncro gearboxes.

Shouldn't a slipper clutch fix that right up? Then if the tires are over-spinning the engine the shift just goes in and the wheels are allowed to overspeed until they slow down enough.

This can also save engines on over downshifting.

Kubotai
Kubotai New Reader
1/20/21 9:31 p.m.
Robbie (Forum Supporter) said:

Shouldn't a slipper clutch fix that right up? Then if the tires are over-spinning the engine the shift just goes in and the wheels are allowed to overspeed until they slow down enough.

This can also save engines on over downshifting.

No, the slipper clutch won't fix the issue of downshifting without using the clutch.  On the overrun, the wheels load the dogs in the gearbox.  The slipper will limit the load on the dogs but it is still enough to prevent the shift.  To shift, you need to unload the dogs.  There are a couple of ways to do this.  You can release the clutch using the clutch pedal or you can blip the throttle very briefly.  The throttle blip is what the various shift software devices (like the Flatshifter Pro) do.  Typically these are air shifters so when activated, the air cylinder loads the shift fork and the dogs.  The system then blips the throttle.  As the engine speeds up, it unloads the dogs and the air cylinder completes the shift.  A typical system has a throttle blip time of around .065 seconds so it doesn't take much.  This is really the same as the 'upshift without lifting' but in the other direction.  For the upshift without lifting off the throttle, you also have to unload the dogs and the shift software does this by briefly killing the ignition (or injectors) so that the power stops very briefly and the dogs unload.  The engine kill times for the upshift are similar - in the 0.060 second range.

As you said, the slipper will help save the engine from overrevving if you go a gear to low, however.

 

Edit: Maybe downshifting without a clutch is not the problem you were trying to fix with a slipper.  In that case, umm...nevermind.

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
1/21/21 8:25 a.m.

In reply to Kubotai :

no, it was. I thought the slipper was enough to relieve the pressure from the dogs. (and I do have a motorcycle engined car that does clutchless upshifts - I just rarely if ever downshift it in anger)

At least it would allow the driver to be ham fisted with releasing the clutch pedal on the downshift without causing a break in traction at the rear wheels. But it sounds like it would probably be easiest to do it clutch-less, just have the driver squeeze the downshift paddle to preload the shifter, then have the driver blip. Just like a heel toe or even easier if the driver is left foot braking. 

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
1/21/21 8:31 a.m.

I should add that I went with a hand clutch on mine for simplicity of building, and honestly it is hard for me to think about driving it with a real clutch pedal. 

cyow5
cyow5 Reader
1/21/21 11:42 a.m.
MrFancypants said:
Tom1200 said:

From the video it seemed pretty forgiving over the kerbs. The car being on treaded tires should help with the running costs, albeit at the cost of lap times.

On the VIR video the driver seems to be struggling with the down shifts in some places??

Looks very fun to drive.

I believe it has a sequential dog-leg style motorcycle gearbox.  Using those on a motorcycle you generally don't need to use the clutch on upshifts, or at least not fully disengage the clutch; a very light touch would typically give a quick and smooth shift. 

Downshifts do require you to completely disengage the clutch to get the desired gear to engage, and given that this box is hooked up to paddle shifters I'd guess that they've set up a motor on the shift lever....  so I imagine the timing between your foot on the clutch and the paddle shifter takes some getting used to, add braking and rev matching with the other foot and I'm sure it all feels a little odd if you only ever drive standard syncro gearboxes.

The whole reason you need a clutch for shifting is to get a zero torque state. Since the engine is going from positive torque (accelerating) to negative torque (when you lift and it drags), the torque curve crosses through zero. At that instance plus or minus some tolerance of the gearbox, is when you can shift up clutchless-ly. The same can actually be done with downshifts. Starting in overrun, the engine is producing negative torque. Instead of clutching in, a tiny amount of throttle will shift it to a zero torque state, and a shift can be done. I can do this manually on my motorcycle, and it was a great way to get home with a sprained left wrist one time, but it is far better (read: reliable) to do it with the ECU. Most proper race ECUs and gearbox controllers can talk to each to coordinate engine torque to get a smooth shift - up or down - without clutch intervention. Getting this timing right can take some development though. 

chaparral
chaparral Dork
1/21/21 1:06 p.m.

I think the autoblip and upshift interrupt timing was still under development when that video was made. 

On the other hand, engine braking as the car turns in can change the balance of the car - even while you're in the same gear.

 

chaparral
chaparral Dork
1/22/21 8:08 a.m.

If any GRM staff member or contributor would like to drive the car and review it, we have unused Delta and Spirit flight vouchers that could be used for your trip to Houston.  With any luck the COVID case counts will drop to where you're comfortable with the idea of taking the trip before May, which is when Houston starts having 97/97 days. 

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
1/22/21 9:02 a.m.

In reply to chaparral :

Hi Chaparral,

If you send me the tickets you can call me JG or David or Tom, whatever you like. 

Thanks!

chaparral
chaparral Dork
1/22/21 9:12 a.m.

In reply to Robbie (Forum Supporter) :

Pitch (GRM) David on the story successfully and we'll find a day that works for (RAW) David, the car, the track, and you. 

 

 

Patientzero
Patientzero HalfDork
1/22/21 4:46 p.m.

That looks AWESOME!

mazdeuce - Seth
mazdeuce - Seth Mod Squad
1/22/21 4:51 p.m.

I can write a fair and cleverly worded article. Bonus, I can be at the kart track in 11 minutes. Alternately, if anyone comes to town to drive them and the driving is at Speedsportz, you can stay in the Grosh! 

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
1/22/21 5:31 p.m.
chaparral said:

In reply to Robbie (Forum Supporter) :

Pitch (GRM) David on the story successfully and we'll find a day that works for (RAW) David, the car, the track, and you. 

 

 

I just sent you a PM, let me know if you didnt get it. I have some ideas. 

Tom1200
Tom1200 SuperDork
1/22/21 6:00 p.m.

Just an FYI and to reiterate; I'm not the only one but you really don't need any fancy software to downshift without depressing the clutch, you can do this by simply preloading the throttle. It honestly isn't that hard in my opinion. Shifter kart drivers do this all day long.

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