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random hero

What's the car to build for ST4?

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random hero

I'm currently figuring out my 2017 plans, ran ptd/ttd past 2 years and the class has shrunk down to nothing in both regions I race (Texas and Rocky Mountain). Considering an e36 or e46 M3 next year, but open to thoughts on ST4 ideal builds. I haven't been through the 14 page thread yet, and it seems as though things are still being ironed out... Just curious what you guys/gals are thinking would make a great ST4 car.

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kbrew8991

C5 Corvette

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TWI
C5 Corvette

 

Too many letters to spell Miata Is Always The Answer.

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kbrew8991

For ST/6/7 yeah Miata. Not 4. Ha.

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flier129

Depends on the track!

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Arca_ex

NB Miata with a K series swap and probably 275mm 15" Hoosiers.

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kbrew8991

wouldn't you have to take a pretty decent assessment for the alternate "k-member" to fit the K-series? Or can it be done on the stock stuff with more work?

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shuko

 

A K-swapped Miata is definitely viable. With a well developed stock K24 (tune, etc) and a REALLY light Miata, you can fit into ST3 pretty well. Downtune that to ST4 and you have a potential class dominator.

 

I would not say it's the "car to build" for ST4. S2000 would be my first choice.

 

A K swap Miata does require the non-production adjustment due to the tubular subframe. And yes, you probably need 225 R7's or maybe wider to make it viable.

 

Also, putting together a race-reliable K-miata has been a huge challenge for me. Great for DE or TT sessions, but race abuse is a whole new level of heat, vibration, and stress! Not to mention you have a few one-off parts that can't be easily replaced when you break them at the track. (A cracked header got me this last weekend at TWS...)

 

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Mrsideways

Having a K24 Swap S2000 that I think will be a good TT4 car. I would say something with Very good factory aero and the engine mounted in the rear.... err rear ish. AKA Cayman S or some sort of slower 911. A cayman S will out run my S2000 in a straight line despite the S2000 having a similar or better avg hp to weight numbers. P cars = Slippery, good tq and often great gearing. Only problem with any P car that meets this HP to weight ratio is they all have that stupid Intermediate shaft bearing issue. So your gonna put motors in them left and right.

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kbrew8991
Only problem with any P car that meets this HP to weight ratio is they all have that stupid Intermediate shaft bearing issue. So your gonna put motors in them left and right.

I thought that was a relatively easy fix with a retrofit part, do it once correctly and you're fine..?

 

Good point on OEM aero though, and mid engine may put down power a bit better too.

 

I still vote base C5 though....

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Mrsideways

From what my limited internet research has shown is the only permanent fix is a LS1

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mcmmotorsports

Definitely not a Legends car.

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takjak2

Detuned corvette is usually the easy and correct answer. With the lower PWR limits and recently increased mod factors, it might be possible to build an over powered FWD sedan if you can get it to handle well enough.

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shuko
NB Miata with a K series swap and probably 275mm 15" Hoosiers.

 

As of now, ST4 rules don't allow tubular subframe (i.e. - non-production vehicle.)

 

So no K-swapped Miatas running in ST4. Just SR20 and Ecotec swapped Miatas.

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Ckdevil

This might be wishfull thinking condidering my plans but could see a 350z/370z being competitive in tt4. Would be SpecZ less 300lb with aero. Zs had varying success in ttb and tt3 but where either underpowered or underpreped in those classes.

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esr

How do you come up with spec z minus 300lbs.

Spec z is already 12:1 power to weight.

 

 

 

 

uote="Ckdevil"]This might be wishfull thinking condidering my plans but could see a 350z/370z being competitive in tt4. Would be SpecZ less 300lb with aero. Zs had varying success in ttb and tt3 but where either underpowered or underpreped in those classes.

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esr

And that is for the least powerful 03-04 models.

 

How do you come up with spec z minus 300lbs.

Spec z is already 12:1 power to weight.

 

 

 

 

uote="Ckdevil"]This might be wishfull thinking condidering my plans but could see a 350z/370z being competitive in tt4. Would be SpecZ less 300lb with aero. Zs had varying success in ttb and tt3 but where either underpowered or underpreped in those classes.

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esr

After doing some research an talking to a director seems like you are kind if right.

Taking 300lbs from a spec z which is 3100lbs with driver would be pretty Dificult and or expensive.

Turns out that the 12:1 is average horsepower so that means that my spec z which is at 12:1 pick power at 260whp would be at about 240 or less average horse power.

Then you take off 0.3 for 275 tires

Take off 0.4 from factory aero or no aero as specz

That gives you 11.3:1 for a spec z

That means that you would have to be at 295 or so peak whp to be at the ideal power to weight in spec z trim.

That is hard to do on a de engine with just bolt on stuff.

 

So the HR would be the way to go for simplicity sake.

 

 

 

uote="Ckdevil"]This might be wishfull thinking condidering my plans but could see a 350z/370z being competitive in tt4. Would be SpecZ less 300lb with aero. Zs had varying success in ttb and tt3 but where either underpowered or underpreped in those classes.

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scotts300

So the HR would be the way to go for simplicity sake.

 

 

The HR is not very reliable, in my experience, in modified trim. When stock, it will run 25 minutes without an issue on a cool day, but once modified and running hotter, they need substantial investment. Clutch Slave Cylinder modification ($$), oil cooler, big radiator with cooling ducts, etc. They are also heavier, but can make 310whp without much modification. Basically a SpecZ with a higher horsepower allowance (HR is 275whp for SpecZ at 3400 (or 3450?) race weight). I still preferred the rev-up DE version and 260whp allowance at the lower weight.

 

Maybe I'll revive my NISMO for competition, depending on if either of my Miatas can become ST4 competitive.

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