How Would You Modify a '94 Miata Chumpcar

I have a '94 Miata Chumpcar. Chumpcar has a specific set of rules which apply only to their series. It creates an interesting conundrum in terms of how to modify each vehicle. Below is a list of the "cost" of each modification. I thought it would be interesting to get your opinion on what you would do with "$100" of modification value? Please convince me of your opinion, links/references are encouraged. :)

My sub-par driving abilities are an obvious area for improvement, but let's avoid that topic for now.

• Non-OE replacement shock absorber or strut: $25/corner
• Any adjustable shock (valve, shim, gas cylinder or knob-select): $75/corner
• Non-OE coil springs (including ¡¥coil-over¡¦ kit): $20/corner
• Cutting springs: $0
• Pair of custom/commercially-made adjustable camber/caster plates: $20 F/$20 R
• Pair of homemade adjustable camber/caster plates: $5 F /$5 R
• Shock/Strut-tower reinforcement bar (commercial or homemade): $20 each
• Non-OE suspension component: $10 per component
• Wheel spacers/hub adapters: $5 each
• Non-OE sway-bar: $50 F / $30 R
• Non-OE radiator (except aluminum): $5
• Non-OE aluminum radiator: $35
• Non-OE oil cooler (engine, transmission and/or differential): $20 each
• Accusump and/or Oil Accumulator: $10 (max limit 3 Qt.)
• Dry-sump assembly: $500
• Commercial racing oil pan: $75 (homemade or custom-made, see 4.5.5)
• Exhaust Header: $50 per engine
• Aftermarket Ignition Coil: $30 single coil; $50 multiple coils
• Performance distributor or aftermarket ignition system: $50
• Heim joint tie rods: $5/end
• Non-OE suspension bushings: $25/car
• Non-OE engine/transmission mounts: $10 per engine / $10 per transmission
• Non-OE CV or axles: $50 per pair of CV, axles
• Non-OE driveshaft: $50 per single driveshaft
• Non-OE differential cover: $10
• Non-OE ECU or chip replacement or chip re-programming: $75
• Non-OE carburetion, induction or metering components/assembly/system: $100
• Non-OE cylinder head(s): $150 per engine
• Non-OE camshaft or valve train: $100 per engine
• Non-OE master brake cylinder: $50
• Non-OE proportioning valve: $25
• Option components (not offered as standard on all models) shall also be assessed a value; e.g. Mazda Miata removable hardtop ¡V OEM ($250); Aftermarket ($75).

I assume we're starting with a vehicle that is mechanically healthy and not in dire need of something - for example, does the stock suspension work?

Are you allowed to use OE parts from other variants of the car? For example, can a 1994 base use shocks from a 1994 R package? Or is that an option component? Can you use OE parts from other years, such as the shocks from a 2004?

$100 doesn't give us much budget. I'd start with a 1994R for the Bilsteins, throw on some non-OE bumpstops ($40 or $10, not sure), a front sway bar ($50) and a proportioning valve ($25). I'd also have a $5 non-OE radiator simply so it doesn't blow up on me.

Those prices all look mighty optimistic. Aluminum radiator for $35? A dry sump system for $500? Coilovers for $80?

That stuff is nowhere near that cheap even if you do all your own fab work and have connections to lots of cheap parts.

GameboyRMH wrote: Those prices all look mighty optimistic. Aluminum radiator for $35? A dry sump system for $500? Coilovers for $80? That stuff is nowhere near that cheap even if you do all your own fab work and have connections to lots of cheap parts.

The dollars don't mean anything. Think of it as a total of 500 points. In this case, your car is worth 400 points. You have 100 points to spend.

Stock Bilsteins, cut springs lower it .5-1" it is a race car, Looks like you can do a CAI for free or is that an intake?, and header back exhaust is free.

It only lists no OE head, port that bad boy :)

For the money?????

Wider wheels do not see that listed, but cant be free Then Bushings $25 Sway bar front $50

ChumpCars can go over budget, but doing so earns penalty laps.

Snrub - are you and your team more concerned with where you finish on the leaderboard, or learning racecraft? Personally, I have more fun racing a car I'm comfortable with so I'd probably throw on an adjustable suspension and take my penalty.

Ah OK. I missed the quotes around "$100." Not sure what they represent, but whatever.

Here's how I'd spend it:

• Cutting springs: $0
• Pair of homemade adjustable camber/caster plates: $5 F + $5 R
• Non-OE radiator (except aluminum): $5
• Second Keith's Non-OE bumpstops all around: $40. You'll be riding on them a lot.
• Second Keith's $25 proportioning valve
• Non-OE engine oil cooler $20
• Front strut bar $20 (although I think an FM butterfly brace would help more, dunno what the value is)

aftermarket strut inserts paints to match OEM into OEM housing. aftermarket spring powder coated to match OE. Exhaust cam swap, it's technically OE and came on the car. Then as Keith mentioned, bumpstops, I'd go aluminum radiator, I'd be hard pressed on deciding whether to replace the suspension bushings, do front caster plates or heim joints in the front next.

Forget the proportioning valve. They don't work. In other words, without a 2 cylinder master, the proportioning valve only limits rear pressure on a linear rate of time. So, if you were to be in a braking event for a few seconds (end of teh straight at VIR), just about when you let off the brake, the rears will be at the stock pressure and can upset the car.

A proportioning valve limits flow, not pressure. Unless you spend TONS of dollars. A less aggressive rear pad is the easier cheaper better way to go.

Next, if you can slot the front shock towers for more camber using a drill to slot the top holes, that is free (it is done with readily available hand tools).

A brand new stock radiator should be fine. Make sure you duct air into it appropriately.

Get KYB GR2 struts all around (Listed as the best non value add strut). They work fine with some slightly cut stock springs.

Take all the weight out you can!

Find out (by emailing your regional tech director) about the bumpstops. Definetly a good idea.

Run some 15 x 8" wheels and 225 45 15 rivals - make sure you set the pressures correct and have 3 deg of camber. They will last just fine if you do. 30-34 psi Hot for this type of racing. A Tire temp probe will verify what your car likes.

Sooo, all of these items are free except the bump stops.

Take off your rear sway before you add a front one.

Upgrade all of the bushing for the car. This is where you can take advantage of the $25.00 per car rule. Can you get specialty bushings for certain parts of the car that help? Like more caster with just a bushing, get it. Super stiff swaybar bushings, get them.

So, I would spend $25.00 + bumpstops + if needed to fit wheels, + $10 for front spacers.

What I wrote is essentially what we did to our 1987 Mazda RX7 (that has won both Chump and Lemons events).

With my extra money (if you go the route I listed and it is less than $50.00) I would also add a header (we did that on our RX7).

Handling and braking in these races is everything! Horsepower just consumes resources after a certain point. Do you have a power to weight ratio around 15 or better? If so, go race without worrying about HP. If not, lose weight! Everywhere!

Our fast lap was 9 seconds faster this year at VIR with the same exact drivetrain as last year. We have since lost about 100 pounds off the car AND improved the suspension GEOMETRY (same struts and springs) using a die grinder and bushings.

Good Luck!

Rob R.

captdownshift wrote: aftermarket strut inserts paints to match OEM into OEM housing. aftermarket spring powder coated to match OE. Exhaust cam swap, it's technically OE and came on the car. Then as Keith mentioned, bumpstops, I'd go aluminum radiator, I'd be hard pressed on deciding whether to replace the suspension bushings, do front caster plates or heim joints in the front next.

You WILL get caught doing this. Heim joints are $5.00 per joint.

Oh yeah, port that bitch!

wvumtnbkr wrote:

captdownshift wrote: aftermarket strut inserts paints to match OEM into OEM housing. aftermarket spring powder coated to match OE. Exhaust cam swap, it's technically OE and came on the car. Then as Keith mentioned, bumpstops, I'd go aluminum radiator, I'd be hard pressed on deciding whether to replace the suspension bushings, do front caster plates or heim joints in the front next.

You WILL get caught doing this. Heim joints are $5.00 per joint. Oh yeah, port that bitch!

I haven't been yet

The head and throttle body porting I did during when the head was off was mild though

Head and throttle body porting are okay. The blatantly cheating is not.

What team and car do you have again?

wvumtnbkr wrote: Forget the proportioning valve. They don't work. In other words, without a 2 cylinder master, the proportioning valve only limits rear pressure on a linear rate of time. So, if you were to be in a braking event for a few seconds (end of teh straight at VIR), just about when you let off the brake, the rears will be at the stock pressure and can upset the car.

That's true for the type that goes on the line going to the rear of the car, if you get the type that replaces the stock proportioning valve then you have full control of front/rear bias.

Bad info about the proportioning valve. They're not time-based. At least, none of the ones I've met have been.

Stock proportioning valve info for the Miata.
http://www.flyinmiata.com/tech/stock_bpv.php

The Wilwood one has an adjustable knee, with the lower slope at 44% of front pressure IIRC.

Miatas have shocks, not struts. You guys suggesting slotting shock mounts or building camber/caster plates, it's not going to work. There also aren't strut housings.

To answer questions:

I do want to avoid exceeding the "$100" value.

The car is mechanically healthy and just finished a 12 hour race without an issue. OEM equivalent parts are acceptable for no value. For instance, I currently have KYB Excel-G shocks (aka. GR-2), which are $0. "Special" models receive a different valuation, so I believe the R models shocks would be $25/corner, especially since they're essentially Bilstein HDs.

Regarding wheels. They have a "2x" OEM value allowed rule and the same for brakes. I'm running TRM C3M 15x9" rims with BFG Rival 225/45/15.

Intake in front of the AFM is free, as is exhaust after the header. I have more or less addressed this. Porting has value.

I can't get to 3" camber, I'm running -1.6 front, -1.9 rear.

We definitely have more weight we could lose, but I don't think we're super terrible right now.

What about installing a factory ABS unit to act as a sort of brake bias device? I believe it would be $0 because some cars have it.

Do these answers change any of your responses?

I'd cut the springs to drop the car, which would also give you more negative camber and more spring rate. I have heard rumors of Spec Miatas having "accidents" that bend the upper control arms, leading to more negative camber. I have witnessed one of these "accidents" in the pits at the 25 Hours of Thunderhill.

Would a Bilstein HD not be considered equivalent to a KYB GR2? It's non-adjustable, OE dimensions, marketed as an OE replacement. It would pair well with those stiffer springs. And of course, the bumpstops.

The 2001+ cars have ABS that can act as brake proportioning. I think you'll do better trying to get the bias right from the start. It may be possible to alter the Miata valve, I've never tried. It's certainly very difficult to tell the different versions apart - reference the link I posted above - which gives you a certain number of bolt-on options all the way to no valve at all. I've always wondered if this was being done in Spec.

What are you allowed to do to the body? Can you do a "Crusher" nose? More downforce, less drag. Go with smaller mirrors, or tuck them inside the car as on Crusher. It's easier to lose drag than it is to gain power on your budget. You get improved cooling and better ducting to the brakes (allowed?) to boot. Even better if you add a splitter.

do whatever you want to it.. don't get too caught up in the valuations unless you actually think you will win the race and get all the money, fame, and females that comes with winning a Chumpcar race..

Take full advantage of the things that are free. Remove everything that isn't necessary. Our 97' caged, wet, and ready to race weighed 1944lbs and I believe sub 1900 would be possible. Cutting out the trunk floor between the rails and riveting in a think piece of aluminum took 9lbs out of the car. Borrow a plasma cutter and get carried away with it. Weight reduction and reducing drag are bot free and will make a miata better at what it does best- maintain momentum.

Brakes don't affect the budget for the most part. Sport brakes with cobalt pads in a light car are phenomenal

Spend lost of your time making the car absolutely reliable, race it then figure out where your money would be best spent.

Many of the Miatas we run against in ChumpCar with our really, totally legal Miata have forced induction or engine swaps. I am surprised that they have this detailed a rule set laid out now.

I still feel, reliability, driver training and crew training and organization, along with a bit of luck are what it take to succeed in endurance racing. Give me four drivers of Randy Pobst's caliber and a real pit crew and a well prepped, stock Miata, and I believe good things would happen.

Thanks for all of the replies.

Regarding the shocks - I believe the Bilstein HDs are considered better than OEM equivalent, while the B4s are OEM equivalent, but even it would be up to the discretion of the tech inspector. Bilstein's website says the following for the B4 model: "The BILSTEIN B4 Series provides the same OEM quality and ride stability for the aftermarket." Using "OEM equivalent" shocks (assuming you don't recommend the shocks alone), do you still think it makes sense to significantly cut the springs and go with bumpstops? At the moment I'm running a set of lowering springs.

I could fabricate some sort of front air dam out of simple materials: "4.5.5.1.1. Not every possible material used in “home-” and/or “hand-made” fabricated components can be addressed within the BCR; however, many components fabricated from standard materials (listed below) will be assigned a value using the following material rates: 4.5.5.1.1.1. Plywood (up to 0.5”) - $1 / sq. ft. 4.5.5.1.1.2. Sheet Aluminum / Steel (up to 0.25”) - $2 / sq. ft. 4.5.5.1.1.3. Sheet Plastic / Polycarbonate (up to 0.38”) - $3 / sq. ft. 4.5.5.1.1.4. Carbon-fiber - $5 / sq. ft."

Regarding turbo - With the current rule set, Chumpcar has made a concerted effort to equalize performance. I suppose if you started with a 1.6L Miata which has a MPV of "$325" (maximum penalty free is "$500", '94 is "$400", you might be able to do a turbo. You would add $100 for non-OEM induction, $75 ECU, and some sort of value for the other components. I suspect you'd be charged for a non-OEM header - $50 and a value for some of the plumbing in front of the turbo. The math on engine swaps get a bit crazy, but I don't think it can be easily done on a '94 Miata without penalty in the current rule set, but possibly with a 1.6L model. There are definitely people out there with swaps in various cars.

1944lbs wet sounds crazy. Any chance you have pictures, etc?

For brakes we ran stock with Hawk DTC-30 pads and we had no issues. I thought the pads were a little grabby, but the other guys on the team liked them. I couldn't swap to 2001+ ABS, but I believe '94 ABS would be allowed.

I completely agree with driver improvements being the area for the largest improvement, but I'm done for the season. :) I can't even work on the car for ~4-6 months.

I'd run bump stops for sure and work on the aero and brakes. Chasing power is expensive by comparison.

Of course drivers and preparation are important. Consider them a control - if all teams are made of Randy clones and are run by Audi, it's the fastest car that will prevail. So it's worth working on the car.

Give me your email and I can send you a bunch. The car is up in the northeast now being ran by another team. You may see it

Sorry for the confusion. I did not mean to imply that the prop valve worked by using a timer or anything. I meant that most of the prop valves that go inline simply reduce flow, not pressure. Over time (during a braking event) the pressure will rise as the flow trickles through the Valve.

Also, sorry about the ignorance of Miata suspension. I had no idea that they aren't strut front ends.

Lose weight, add aero.

I would modify it by recruiting Randy Pobst as one of your drivers. He was way faster than the other guys on his team driving a beat-up Miata at VIR Chump earlier this year

When one of the other drivers was in there, he spent 2 hours going back and forth with me in our ETA 325 (which is not terribly fast). When Pobst was in there, he lapped me twice in 2 hours. True story.

One further question, how much do you think I should cut the OEM springs? Do I need to be concerned with the fact that the shocks will be working in a more retracted range of travel?