Rover with a turbo, or: How to build a reliable turbo track car. SPM S1, NASA ST3/4 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-31-2017, 12:07 AM   #1
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Default Rover with a turbo, or: How to build a reliable turbo track car. SPM S1, NASA ST3/4



The first ever Supermiata S1 race is in the books. I got my car finished first so I got the participation trophy, but there are six other cars in various states of build. This thread is about the first one, though. Rover has been the Trackspeed track ***** for a very long time. It served as a "rental-style" build from 2010 to 2012 with a stock VVT longblock and 6sp/4.30, then spent 2012 and 2013 as a national-caliber dyno-class PTE car with a 2-liter BP and 3,000rpm worth of flat power area. For the last few years it's been my sort-of-Supermiata S2 car, with roughly the right power and weight but no aero package.

The idea for a forced-induction race series was how Supermiata got started in the first place. We all wanted to race fast Miatas, but the parts just didn't exist at the time (back in 2011). After nearly a year of success with my turbo kit in Acamas, we decided to pull the trigger and structure the ruleset for Supermiata S1 around the Trackspeed EFR hotside parts. The spec for the series is a 220whp, 2300lb Miata with a DIY-ish aero package (2D aerofoil in back, airdam+splitter in front). Add a 245/40 Maxxis RC-1 and you have a relatively inexpensive recipe for a turbocharged Miata race car.



And as it turns out, they're also really fast. The first test at Sonoma (1:46.0) revealed that the cars will likely be capable of running 10-12 seconds under SM record at every track in CA with just 220whp on tap, and without the need for Hoosiers.

The current powertrain setup was selected to be a "worst-case" example for setting the S1 rules, so gone is my normal fare of VVT heads and forged pistons. The motor is a BP05 longblock, stock intake manifold, stock ports/cams/pistons. Supertech single valve springs, Manley rods, ACL bearings, ARP head/main studs, and a Mazda VVT oil pump are the only internal upgrades. Externally, it has an SPM damper and a Skunk2 throttle body. Rev limit is 7400.

Management is MSLabs MS3 Basic reading NB cam/crank sensors. Fuel system is currently all stock save for the Walbro 190lph (old school, yo) and FlowForce 640cc EV14s, but I will add a Fuelab 545 regulator, 818 filter, and a DW200. as well as replumb all the rubber hose with Earl's (same stuff I used on Acamas) for E85 compatability. It will be tuned to run up to 220whp on CA91, with a high-boost map in the ~280whp range on E85. Drivetrain is a stock 6-speed with a Supermiata ceramic twin and stock 3.9 Torsen.


Photo credit: Larry Koh

I will be wrenching on Rover for maintenance and upgrades all year so this is the thread where all that info goes.

Current to-do list:
  • Brakes. 1.8L calipers out, Superlite BBK and Singular ducts in.
  • Reinforce splitter mounts and tweak front ducting
  • Weight reduction. Currently 2420lbs race weight, goal is 2300lbs (S1 class spec). Lots of low hanging fruit (HVAC, headlights, etc), so this shouldn't be hard.
  • Full dyno tune. Roughly 200whp, now, need to get tunes for 220whp on gas (S1) and 280whp on E85 (goofing off), as well as a tune for NASA ST4 if I decide to run a race or three with them
  • Carbonmiata short flares and 15x10 6ULs
  • More front roll stiffness. Probably going back to 1000lb front springs and adding a bigger FSB. With the 245s and front splitter it will make use of all of it.
Should be a fun year
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Old 01-31-2017, 01:23 AM   #2
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To finish first, you must first finish. Before even that, you've got to show up. Winner winner!

Watching that vid and imagining a half dozen similar cars dicing it up at that pace... yeah baby. Excellent recipe. Spool and torque with that turbo are clearly on another level. The gap from sunset to sunrise gets gobbled up a lot faster than a typical "200hp" Miata can do.

So down 20hp, overweight, and on 9's rather than 10's... still looked quick. You know we still want to know lap times.
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Old 01-31-2017, 01:37 AM   #3
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So down 20hp, overweight, and on 9's rather than 10's... still looked quick. You know we still want to know lap times.
~200whp, ~2420lbs, and on 225/45 RC1s on 9s. 1:56.7 on Saturday, 1:55.4 on Sunday after a small wing tweak and more seat time. There's about a second left in the brakes alone, they were really bad on Sunday and failed completely 2 laps after I cut the 55.4. In full S1 trim in similar weather, the cars should consistently lap deep into the 53s.
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Old 01-31-2017, 03:04 AM   #4
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Why is it so heavy now?
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Old 01-31-2017, 04:40 AM   #5
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So did they redo the ruling for twin disk and small diameter clutches or are you switching to something else? I thought they were illegal but now I can't find anything about clutches in S2 or S1 rules.
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Old 01-31-2017, 01:17 PM   #6
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Looks like fun. The front air dam and rear wing balance out nicely.
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Old 01-31-2017, 01:54 PM   #7
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Heavy because I never really tried to make it light. When it was an HPDE car early on it had a full interior and power windows along with a full cage. As a PTE car, it needed to weigh ~2410lbs to be competitive. It still has functional popup headlights, all the HVAC gear under the stock dash, most of two full doors, etc. I can also go to a lighter hardtop if need be. 100lbs shouldn't be hard to find.

Not sure about clutches in S2, but we decided to allow them in S1. They help the synchros in the transmission last a lot longer.

It is a riot to drive. Enough poke to make it fun without being too ridiculous. The aero grip north of 90mph is pretty wild.
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Old 02-01-2017, 03:24 AM   #8
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This is now the most interesting topic on the forum! Poscat awarded.
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Old 02-01-2017, 07:47 AM   #9
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The S1 version of Rover is what I initially envisioned when I moved over to the Miata platform for open track days. I can't imagine a better bang for the buck.

This is gonna be such a great series!
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Old 02-01-2017, 11:13 AM   #10
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We knew the S1 would be a bunch faster than the 140whp S2 class but frankly, we were surprised at just how much faster. I'm hoping that racers seeing a field of cost effective, reliable and stupid fast turbo Miatas will spur them into action. Either switching from some other platform that is either unreliable, has no competition, is too expensive or all of the above. I don't think we will get too many first timers, at least I hope we don't. S1 is way too fast to get drivers that have never done w2w.

Andrew has been a co-conspirator for a long time. Sharing tech info and ideas over the last decade, he has also been an integral part of the Supermiata Race Series planning. Kudos on getting the first S1 on track. Jelly.. but mine will be prettier
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Old 02-01-2017, 11:53 AM   #11
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I would LOVE to migrate from S2 to S1 in a few years on the east coast. That setup looks like an absolute blast and it's not even up to the specs.

I could pass people on the back straight at Road Atlanta omgeee want haz!
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Old 02-01-2017, 10:11 PM   #12
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Quote:
Originally Posted by Savington View Post
  • Brakes. 1.8L calipers out, Superlite BBK and Singular ducts in.
I cut my fastest lap of the weekend on the lap prior to this one. Brakes did not feel great and I was leaving lots of time on the table. Perhaps I should have left some more.



yeah...



...maybe a lot more.



Stock brakes on your S1 car: Not even once.
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Old 02-01-2017, 11:08 PM   #13
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LOLIRL
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Old 02-01-2017, 11:15 PM   #14
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Emilio
The horsepower is restricted to 220hp, but if the 6258 makes 325hp with TS the manifold, then the torque will be at around 275ftlbs or more at 4000ish rpm?
If 275tq is the right number the boost controller will have to go to work about 4500rpm or so and keep reducing from there to maintain 220bhp.
Which is why I assume the engine sounds so angry...because it is making well over 2X the torque of an S2!
It must accelerate out of slow and mid speed corners like it is being shot out of a canon?

Edit: My bad! Just read all of the rules 220Tq

Last edited by nbfather; 02-01-2017 at 11:26 PM. Reason: Stupid
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Old 02-01-2017, 11:25 PM   #15
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Not quite that much torque but close. But yes, that massive torque down low is chiefly why they are so much faster than the S2. They make a bunch of torque all the time everywhere. There is no gap in the powerband or gearing. It's like having a Tesla.

We know that the AZ6 will not survive long if they see 300 lbs for very long, thus the limits.
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Old 02-01-2017, 11:42 PM   #16
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Torque and additive power cap will depend on what kind of powerband my setup ends up making. I intentionally built the worst-case powerplant, which is a stock BP05 head/cam, stock 9:1 pistons, and CA91 pump gas. An E85-drinking 11:1 bottom end would make a lot more torque down low, but we want to make sure you don't have to build a crazy motor to easily make the power and be competitive.
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Old 02-02-2017, 12:38 AM   #17
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Thats awesome!
cant wait to come join you guys.

When did the rules get changed to allow for the twin disc?

D
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Old 02-02-2017, 01:27 AM   #18
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Quote:
Originally Posted by Savington View Post
Torque and additive power cap will depend on what kind of powerband my setup ends up making. I intentionally built the worst-case powerplant, which is a stock BP05 head/cam, stock 9:1 pistons, and CA91 pump gas. An E85-drinking 11:1 bottom end would make a lot more torque down low, but we want to make sure you don't have to build a crazy motor to easily make the power and be competitive.
Ah! I wondered why you were doing that!
Makes perfect sense!

Just showed the picture of your brakes to my son....Eyes bugged out of his head
As did mine!


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Not quite that much torque but close. But yes, that massive torque down low is chiefly why they are so much faster than the S2. They make a bunch of torque all the time everywhere. There is no gap in the powerband or gearing. It's like having a Tesla.

We know that the AZ6 will not survive long if they see 300 lbs for very long, thus the limits.
Sounds like so much fun!
I have heard the gearbox doesn't last very long at those torque levels under the heat generated by the track.

Andrew's T5 is on our phase 2 wishlist......If that project ever comes together.
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Old 02-02-2017, 02:07 AM   #19
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S2 rules are the same way. The 140 whp cap is easily achieved on corn with even a tired engine. We did not want to put the cap somewhere that required a lot of money or expertise to reach. So the S1 cap is a level that will be easy to keep cool, tune and run a stock head with just rods at the minimum.

What makes S1 even more fun is that if you do put a forged bottom end and a decent head on it you can turn the boost up for time attack or some other road racing classes.
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Old 02-02-2017, 02:12 AM   #20
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Quote:
Originally Posted by Savington View Post
The aero grip north of 90mph is pretty wild.
I've been running similar aero (little more front splitter) for over a year now and it still blows me away every time.
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