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Thunder Roadster Modifier for 2015?


LJ32

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  • LJ32

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There is a lot of misunderstanding going on in this discussion about torque and horsepower. I will use your numbers posted above as an illustration to show that horsepower is what matters. I will assume a car traveling at 50 mph with a final drive ratio of 3.42 and a 25.5 inch tall tire.

 

Using your example of 300 HP at 3000 rpm = 525 Tq and using the assumptions above would require a transmission gear ratio of 1.33 to achieve 50 mph.

 

Using your example of 300 HP at 11,000 rpm = 143.2 Tq and using the same assumptions above would require a transmission gear ratio of 4.88 to achieve the same 50 mph.

 

Now lets calculate the torque at the output shaft of the transmission.

525 Tq * 1.33(trans gear ratio) = 698 Tq

143.2 Tq * 4.88(trans gear ratio) = 698 Tq

 

Amazingly they are the same torque at the output shaft of the trans, both of these examples would accelerate the exact same. The reason is because they have the same horsepower even though the torque is vastly different. Horsepower takes into account the torque multiplication you can get through gearing and that is why we use horsepower as the unit of measure in determining a pw/wt class.

 

If the rules were changed to penalize having more torque than horsepower, all we would do is build higher reving engines to get around the penalty. We would achieve the same horsepower but at a higher rpm and this would raise the cost to be competitive.

 

I have to admit that I was once a believer in big torque meaning more acceleration but someone smarter than me properly explained it the right way using science and not beliefs.

 

At the end of the day horsepower is king and is the unit of measure that matters when discussing how a car accelerates.

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Right, and also implementing that theoretical maga torquer is a different story (i.e., a fairy tale in a "Production" car).

My ST2 car is lighter than Kevin's (100% legal) ST3 car and has 100lb/ft more torque (~30% more), with optimized gearing and shift points and I have larger, stickier tires. Despite all that, Kevin and I have approximately identical acceleration from a ~50mph turn, before material aero effects kick in. How do we reconcile that vs theory? (honestly, because I can't figure it out)

 

Finally, looking at the engine in isolation, as you know and David pointed out, is useless without considering how that power is translated into acceleration. Has anyone put together acceleration ("thrust") curves for a TR, using typical and theoretically ideal gearing?

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From a non-busa TR driver, the acceleration from 30-100 is pretty good. Watching videos of starts and certain parts of the track, the busa powered ones seem to hang decently with the higher powered cars taking the green and through most parts of the track. Coming out of corner onto an incline seems to favor the bigger engines, but the longer straights where you start getting 110+, the cars completely leave the TR's in the dust.

What's the hp/wt in ST3?

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The #/hp ratio works out to be pretty even between the Corvettes and TRs until they get the speeds up where aerodynamic effects become an issue. There the Corvettes have a distinct advantage. Not that they necessarily have a "cleaner" shape, but their horsepower to aerodynamic drag ratio is more better.

 

Coming out of turn 7 at Road Atlanta demonstrates the concept. TRs keep the Corvettes close until the track flattens out approaching the black flag stand, beyond that point there isn't any contest.

 

I drive a Busa powered Thunder Roadster and have followed Kevin's Corvette enough at this point that I can speak from experience rather than theory. We are, all of us, doing this for the thrill not for money. I have run in an event that after the third lap I couldnt see the second place car in my mirrors and the rest of the race might as well have been a HPDE 4 session. I prefer close racing over winning. I do like to win though.

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9.0 lbs/hp. But there are other factors involved. Type of transmission, overall weight, tire size/type, TR modification factor, etc. My TR has a Gen 1 Busa motor making 158 hp at the wheels and 1620 lbs. After all the math was done I was at 9.6 lbs/hp. I brought a knife to a gun fight because most of the other TR owners I spoke with were right at the 9.0 lbs/ hp limit. But thats my fault for not pushing the car to the limit. I was able to finish 5th overall with minimal seat time at RA. It was a learning experience for me, leave nothing on the table!

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I still say give me a Thunder Roadster with a Busa engine built to 9:1 and I know exactly how I would run it at Road Atlanta and I guarantee it would give my car a run for my money at Road Atlanta. The magical combination for you guys, at a long track, is still there in the formula and available to you.

 

As most of you sit, the exact setup you have, is extremely competitive at the shorter tracks. You need to be willing to change some things for the longer tracks. Same as me for the shorter tracks. There are changes I need to make, within the available limits of the formulas, to make the car more competitive at the short tracks.

 

 

Experimentation and testing is the key... you have an entire year to do it. Get busy.

 

I know I will be hitting VIR hard and heavy next year and I already have a laundry list of things to try out. I haven't been there since I was in TTA trim, never even raced PTA there in my Vette.

 

 

 

 

-Kevin

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I also want to bring up an example of a car that beats the snot out of the V8 Corvettes with a much smaller engine: Greg V's Lotus. He has won everything I have seen him enter at Road Atlanta. He was leading when he had an incident on the front straight in the Championship race. And this is in ST2!!!

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Haha true story^ lol he spanks ST1 cars in the central region. he's running the bigger v6 in it tho... Installing it in a new chromed out chassis as we speak!

 

So let's say tq was added into the power to weight ratio. How would you do the math on both? Or would you just have 2 figures. One tq/weight and one hp/weight?

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Kevin

 

could you pls give few tips how to my TR faster like yours or ziglers on a back straights like RA. please don't tell me bungee cord

 

regards to all

 

firouz

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Kevin

 

could you pls give few tips how to my TR faster like yours or ziglers on a back straights like RA. please don't tell me bungee cord

 

regards to all

 

firouz

 

 

I'll tell you next year after VIR... Maybe. Either way, your TR would never fit back into the Spec TR class.

 

No different than when we were forced out of PTA into ST... Testing and learning and playing with new combinations.

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I will not go to gun fight with a sword again . TR with a v8 hayabusa should do the job..

 

firouz

You'll need another axle on your trailer to carry the ballast with that kind of power and change the springs on your TR from 250#s to 600#s. Uh oh!

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