49 replies to this topic

[Grant]

Hello, we're building an NC for ChampCar. This means 7 to 24 hour races. My current plan is below; any comments or suggestions are greatly appreciated.

 

- RX8 front hubs, stock rear hubs. My car will be far lighter than the MX-5 Cup Cars which experienced rear hub failure. I'm hoping this plus the use of street tires and a vented rear rotor will mean no hub failures? We can't upgrade to RX8 rear spindles and hubs without being penalized.

 

- RX8 brakes all around, on Rayesbestos ST43s in the front, and whatever gets the brake bias right in the rear.

 

- Keep the stock radiator since upgrading costs points, but relocate or remove all the stock in front of the engine and heavily vent the hood. No fan. Hopefully this will provide sufficient cooling? What do the MX-5 cup cars run?

 

- Stock oil cooler, since upgrading costs points. From what I understand oil temps will probably stabilize around 260F?

 

- ecutek tuning for the no-lift-to-shift functionality.

 

- Header, full exhaust, and cams. The cams and header will have to be matched together. From what I've seen, the stock cam profile and VVT system results in little to no overlap at high RPM, so tuned-length longtubes are out-performed by shorties. I'm expecting this not to be the case with aftermarket cams.

 

- An intake which goes straight from the throttle body elbow to the front bumper (ram air), with an inline filter.

 

- Lastly, there's no minimum weight in ChampCar. We're going to remove the windshield and frame, and eventually experiment with different ways to reduce drag over the empty passenger compartment (probably with a flexible cover or balsa wood).

 

Does anyone know what was done to the sealed MX-5 Cup motors to get them to 200 bhp?

[Johnny D]

Endurance = needs to last, go figure : )

You don’t want it to break it, spending time in pits.
You don’t want to hit or get hit by anything.

I’ve lost at the 25 to some team that didnt have 4th gear because we broke down more.

Finish, learn from mistakes, return.
But fastest lap times doesn’t always mean winner.

Somebody else can speak on all your parts.

J~

[chris haldeman]

You seem to be on the right track. Not sure I would do cams as they move power up in the rpm range and will cause you to need to wind it up eating fuel and lowering reliability. The sealed mx5 motors were 100% stock and more like 157hp at the wheels. A full on stl mx5 isn’t much over 200hp at the wheels and has a very short life span. Aka you might need a new one at every event. 10-16k

[Steve Scheifler]

What Chris said. And if you want to play wirh cams and cam timing, build towards a broader torque curve rather than some arbitrary peak HP number. “Area under the curve” should always be an important consideration but all the more so for endurance racing.

[Grant]

The sealed mx5 motors were 100% stock and more like 157hp at the wheels.

 

Thanks, this speaks well of the potential of the platform. I assumed they made more like 170whp.

We have won 14 hour enduros before, so we know what it takes. Maximal weight reduction is key for lowering costs, increasing speed and reliability. I'm definitely not raising the (NC2) rev limiter, and will size the cams and header for a 5,000 to 7,400 powerband.

[Grant]

Do you guys have any motor oil, transmission and diff fluid recommendations?

[Danny Steyn]

Grant - I run a 2007 MX-5  STL  that puts out 210HP, 155 TQ at rear wheels on Dynojet. I bought 6 engines in 3 years, and not one of them would last one of your races. So be wary of building it to the max. I think if you build it to around 185HP you will have a great motor, capable of running the entire season

[Jeff Wasilko]

Hello, we're building an NC for ChampCar. This means 7 to 24 hour races. My current plan is below; any comments or suggestions are greatly appreciated.

 

 

- Keep the stock radiator since upgrading costs points, but relocate or remove all the stock in front of the engine and heavily vent the hood. No fan. Hopefully this will provide sufficient cooling? What do the MX-5 cup cars run?

 

What do you do when there's a FCY and you're creeping around the track, or worse if there's a red flag?

 

I'd certainly want a fan in a race car.

[Grant]

Grant - I run a 2007 MX-5  STL  that puts out 210HP, 155 TQ at rear wheels on Dynojet. I bought 6 engines in 3 years, and not one of them would last one of your races. So be wary of building it to the max. I think if you build it to around 185HP you will have a great motor, capable of running the entire season

 

Thanks for the input. How would you recommend we keep these motors alive? Any rev limit recommendations? I was assuming the stock 7,400 rpm limit and gentle cams would be safe. We're used to running completely stock engines with fresh rod and main bearings. We have a VG30DE which probably went 250 hours, until a timing belt failure killed it. A friend of mine has a 2JZ-GE which has lasted over 120 hours and still runs strong.

 

What do you do when there's a FCY and you're creeping around the track, or worse if there's a red flag?

 

I'd certainly want a fan in a race car.

 

During FCYs we catch up to the car in front of us, then lug in the highest possible gear to conserve fuel. No fan needed as we're always moving. If there's a red flag we pull over and shut the car off, so again no fan needed.

 

A fan is a nice thing to have. My friend's fanless SC300 had it's head warped because the rental driver forgot to shut the car off after he got stuck in a gravel trap. However it's weight hanging off the front end, something of a cooling restriction at speed, and I don't intend to let people unfamiliar with the car drive it.

[Grant]

Oh, does anyone know if fuel starvation is an issue on these cars? From the pictures I can't tell if the stock fuel pump assembly includes a venturi-powered internal surge tank, which is common on newer cars.

[Danny Steyn]

Trust me - run a SERIOUS fan - built MX-5's have serious cooling issues

[Michael Novak]

Put a fan on the car, and ask the drivers to loose the 2 pounds you might save. The penalty for not having it is way to high---  One red flag or even slow yellow will be enough to turn it on.

[Jim Drago]

Trust me - run a SERIOUS fan - built MX-5's have serious cooling issues

We built a really nice double pass radiator for the Freedom grand am cars that solved that problem for us. We had no luck with commercially available radiators either. we still have the drawings if ever needed. 

[Jim Drago]

Hello, we're building an NC for ChampCar. This means 7 to 24 hour races. My current plan is below; any comments or suggestions are greatly appreciated.
 
- RX8 front hubs, stock rear hubs. My car will be far lighter than the MX-5 Cup Cars which experienced rear hub failure. I'm hoping this plus the use of street tires and a vented rear rotor will mean no hub failures? We can't upgrade to RX8 rear spindles and hubs without being penalized.
 
- RX8 brakes all around, on Rayesbestos ST43s in the front, and whatever gets the brake bias right in the rear.

You will want the diff mount from the rx8 as well
 

- Keep the stock radiator since upgrading costs points, but relocate or remove all the stock in front of the engine and heavily vent the hood. No fan. Hopefully this will provide sufficient cooling? What do the MX-5 cup cars run?

IMO that is NOt a good call at all.


 

Does anyone know what was done to the sealed MX-5 Cup motors to get them to 200 bhp?

Stock sealed motors are under 160... I built a T4 engine to the rules and struggled to get over 164. The cupo cars were 165-170 with header, computer flash and air intake.. IMO, you will be VERY hard pressed to get to 200 or close with cams.. I think you will be looking like 180-185 and I think that is a good number that should be very reliable.

[Grant]

Well we'll definitely test with and without a fan. My local track (the FIRM) is really slow, and we've found if a car doesn't need a fan (upgrade) there it doesn't need it anywhere. The car will be tuned to safely richen up as it gets hotter, so the most important thing will be to keep coolant temps low enough that AFRs stay leaner (mostly for better fuel mileage, but also a wee bit more power).

 

Most ChampCars are older, and came with power-sapping mechanical fans that just get removed. With hood venting completely open, most champcars don't have cooling issues. I'm not sure if we can upgrade the stocker without incurring points. My thought was to take a hole-saw to the shroud so it flowed better at speed.

 

What do you guys think about running the crossmember the battery, airbox and power steering reservoir attach to? It looks structural, but I noticed most swaps as well as Goodwin's NC Light track car remove it. It's right in the way of airflow from the radiator going out the hood vent, so it'd be nice to be able to remove it.

[Camaro67racer]

Since this is an enduro car and you need it to last, you might want to rethink the Ecutek "no-lift-shift." I had strongly considered it for my T4 car, and I know some guys use it, but I had also heard that it is really hard on the clutch and components. Might be fine for sprint racing, but I wouldn't do it for the enduro.

[Grant]

Stock sealed motors are under 160... I built a T4 engine to the rules and struggled to get over 164. The cupo cars were 165-170 with header, computer flash and air intake.. IMO, you will be VERY hard pressed to get to 200 or close with cams.. I think you will be looking like 180-185 and I think that is a good number that should be very reliable.

 

180 at the wheels would be plenty of power, thanks. I'd probably turn down the rev limiter if the car made that much!

[Grant]

Since this is an enduro car and you need it to last, you might want to rethink the Ecutek "no-lift-shift." I had strongly considered it for my T4 car, and I know some guys use it, but I had also heard that it is really hard on the clutch and components. Might be fine for sprint racing, but I wouldn't do it for the enduro.

 

I believe the feature can be set up to hold or drop rpm while the clutch is disengaged. The former would obviously be terrible, while the latter would keep drivers from being able to destroy my transmission.

I found a relevant post on miata.net:

 

FWIW, I use FFS in my SCCA T4 MX-5. We've already had the transmission out for various reasons and were about to put a new clutch in because we could, but it looked like new so we didn't bother. I use FFS exclusively on everything but the out lap and have about 2500 track miles on the car now.

 

(There's a YouTube link to this car being flat-shifted at Laguna Seca, but it's not showing up when I paste it here).

[Johnny D]

Maybe Todd or  Winding Road can chim in on what they're doing in Spec MX-5 or maybe send them an email.

 

https://specmx-5.com/

 

J~

[Chris Lefferdink]

Well we'll definitely test with and without a fan. My local track (the FIRM) is really slow, and we've found if a car doesn't need a fan (upgrade) there it doesn't need it anywhere. The car will be tuned to safely richen up as it gets hotter, so the most important thing will be to keep coolant temps low enough that AFRs stay leaner (mostly for better fuel mileage, but also a wee bit more power).

 

Most ChampCars are older, and came with power-sapping mechanical fans that just get removed. With hood venting completely open, most champcars don't have cooling issues. I'm not sure if we can upgrade the stocker without incurring points. My thought was to take a hole-saw to the shroud so it flowed better at speed.

 

What do you guys think about running the crossmember the battery, airbox and power steering reservoir attach to? It looks structural, but I noticed most swaps as well as Goodwin's NC Light track car remove it. It's right in the way of airflow from the radiator going out the hood vent, so it'd be nice to be able to remove it.

 

If you run Daytona Champ Car, you will spend a lot of time drafting the big bore cars on the banking.  Even if you don't need a fan at FIRM, you will likely want one while drafting at Daytona.