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PostPosted: Wed Jul 18, 2018 5:22 pm 
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Will our clutches survive multiple standing start launches at max power?

It's not a rule change or anything :mrgreen: Although what a great april 1 post...

A local car club is having a charity event at the dragstrip and I was planning on taking one of my SCCA cars that has a twin disk 7.25 clutch/slicks/a tall trans gear/ and power is north of an EP car by 50-100 hp...

Will it live? 2 times? 6 times? 50 times?

Sam


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PostPosted: Thu Jul 19, 2018 4:52 am 
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S. Henry wrote:
...has a twin disk 7.25 clutch/slicks/a tall trans gear/ and power is north of an EP car by 50-100 hp...

Uhhh...well, I like your optimism! :lol:

With any luck, you'll just stall it out before anything breaks..

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PostPosted: Thu Jul 19, 2018 5:06 am 
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This proves that Randy Pobst is wrong (The answer is not always miata).


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PostPosted: Thu Jul 19, 2018 5:21 am 
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blamkin86 wrote:
This proves that Randy Pobst is wrong (The answer is not always miata).


Come on down lam.... I got a grand that my 100% legal scca FP miata gets down the 1/4 faster than your EP BMW... its for charity... south east Kansas. Practically 1/2 way. :mrgreen:


Now what about the clutch? Speculation allowed.


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PostPosted: Thu Jul 19, 2018 5:50 am 
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S. Henry wrote:

Come on down lam.... I got a grand that my 100% legal scca FP miata gets down the 1/4 faster than your EP BMW... its for charity... south east Kansas. Practically 1/2 way. :mrgreen:


Now what about the clutch? Speculation allowed.


Now that would be fun. I'm running the stock gearbox with super short final drive. I'm also running a *stock* clutch out of an M5 which has double my torque - that said since it's stock it couldn't be easier to drive (which is good for me).

For your setup, you won't get to slip the clutch much without smoking (overheating) it. So you'll have to avoid slipping, and with a tall first gear is goin to be super hard to do.

I'll expect youtube videos.


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PostPosted: Thu Jul 19, 2018 6:17 am 
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With sticky tires, tiny clutch, and tall first gear, your clutch will not last long doing drag starts. given how much torque you have and how little traction is really necessary once you get rolling, you *might* do Ok mounting some street tires and spinning the tires off the line so you save the clutch.

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PostPosted: Thu Jul 19, 2018 6:45 am 
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S. Henry wrote:
Will our clutches survive multiple standing start launches at max power?

It's not a rule change or anything :mrgreen: Although what a great april 1 post...

A local car club is having a charity event at the dragstrip and I was planning on taking one of my SCCA cars that has a twin disk 7.25 clutch/slicks/a tall trans gear/ and power is north of an EP car by 50-100 hp...

Will it live? 2 times? 6 times? 50 times?

Sam


The autocross guys do ProSolo drag race starts with small multi disc clutches and sticky tires all the time... The failures are usually downstream of the clutch.

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Last edited by Jason@SportsCar on Thu Jul 19, 2018 1:13 pm, edited 1 time in total.

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PostPosted: Thu Jul 19, 2018 11:58 am 
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Jason@SportsCar wrote:
The autocross guys do ProSolo drag race starts with small multi disc clutches and sticky tires all the time... They failures are usually downstream of the clutch.

those autocross guys also usually don't have a 1st gear capable of >50mph. With such a tall first gear in a road race box, it puts a lot more stress on the clutch and input shaft.

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Matt Blehm
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PostPosted: Thu Jul 19, 2018 1:17 pm 
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Standing starts in old GP 1147 Spitfires broke many a inner stub axle


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PostPosted: Thu Jul 19, 2018 2:18 pm 
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first gear is worthless in this car as it is too low, so I plan to launch in 2nd which is a 51 mph gear at redline so it's like a 1.5 street car first... The car just spins (and hops) in first regardless of how you apply throttle... I've had better luck in 2nd when trying to make fast starts on non-drag strip surfaces and just letting it spin some in second with a aggressive launch vs. bog...


I thought about street tires too, but I'm afraid it will not hook up in third because the rivals sitting in my shop are OLD OLD... and I know it will not hook up in second on street tires... I was going to split the difference and take a set of 8 cycle slicks...

Just to clarify, this is my FP autocross miata which is pretty strong... But it's very prod like in drivetrain and suspension. twin disk... tubular arms... penske's... springs approiate for a truck... 2450lb w/ driver, 50.5% rear


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