Judge the donor by what it saves, not what it promises

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Course: Race a Spec Miata by the rulebook

Module: Buy or build without inheriting problems

Estimated duration: 55 minutes

Principle: a Spec Miata donor is valuable only to the extent that it moves you closer to the legal, equalized final car.

When you shop a donor, the seller will usually sell a story. The car is fast. The motor is strong. The previous owner knew what he was doing. The car has expensive parts. None of that is the first question. In a spec or near-spec Miata environment, the first question is what the donor saves you after the rules, the class equalization, and the known Miata weak points have finished taking their bite.

That changes the way you look at the car. You are not buying potential in the abstract. You are buying a starting position. A good donor already contains parts you would have had to buy anyway, avoids rework you would have had to undo anyway, and reduces reliability risk in places the platform is known to punish. A bad donor can look cheap and still be expensive because it comes with the wrong drivetrain, a cooling package that will not survive race use, illegal or useless modifications, or shiny parts that do not move the final car closer to the class target.

This lesson sits between three sibling skills. It does not decide whether buying beats building from zero; that is a separate financial decision. It does not teach a complete cage audit; the cage is too important and too permanent to treat as one line item in a donor ledger. It also does not let an unofficial guide outrank the rulebook. The skill here is narrower: once you are looking at a specific Miata, you judge it by the legally useful work it has already done for you.

The mechanism: equalization turns some promises into noise.

The supplied SuperMiata guide makes the logic blunt. The guide describes a basic S2 target with a 140 whp power cap, a capped sum of power points from 5000 to 7000 rpm, a single-adjustable shock boundary, a 2300 lb minimum competition weight, and a spec tire. It also says the 1990-2005 Miata parts interchange broadly, and that all of them are equalized once built. Those two ideas are the buyer's filter. If the finished car is constrained by power, weight, tire, shock, and rules, then the donor year is not magic. The year matters only when it saves you something you would otherwise need to acquire.

That is why an NB five-speed donor can be worth more than an otherwise similar car. The guide says an NB five-speed can save an engine because the NB engines make the most power, and can potentially save the cost of a 4.3 Torsen. It also ranks used transmissions by shift quality, with NB2 five-speed best, NB1 next, and NA last. Those are not personality traits. They are line items. If the car already contains a better transmission, a stronger starting engine, and the diff ratio you probably need, it has real donor value because it reduces the distance to the final build.

But the same equalization logic cuts against seller hype. A claim about big power means less in a class with a 140 whp cap and an area-under-the-curve limit. The guide even points out that the useful target is not only peak power, but being close to the capped total across the specified rpm points. If the engine is already tuned near the limit, that can be useful. If it is only described as built, fast, or healthy without showing that it fits the target, it is just a promise.

Rule fit is the second half of the mechanism. The supplied regional rules state that Spec Miata and related regional versions run under the SCCA GCR and class specifications, with tire rules and class-specific overlays. The supplied NASA rules show how detailed the legal boundary can be even inside the driver compartment: insulation, carpets, spare tire equipment, passenger seat parts, pedal modifications, door gutting, vent windows, airbags, and floor-pan changes all have conditions. A donor that saves you money in one rule set can become rework in another. You do not value a modification because it exists. You value it because it is legal and useful in the class you intend to run.

The buyer's method: build the finished car on paper first.

Before you inspect the donor, write the target car in six buckets. The first bucket is rule legality. Which exact series, class, tire rule, weight rule, power rule, interior rule, and safety rule will you run? The second is the cage and safety structure, but for this lesson you only record pass, fail, or needs specialist review and then send the detail to the cage-audit skill. The third is drivetrain: engine, ECU, transmission, diff, clutch, flywheel, driveshaft-related requirements if your class has them, and any known drivetrain bracing. The fourth is cooling and survival: radiator, undertray, ducting, radiator opening, mesh, hood extractor, oil cooler risk, water pressure warning, and cooling-system bleeding. The fifth is control and setup hardware: brake prop valve, ABS if present, extended lower ball joints if legal for your target, aero pieces, and ballast plan. The sixth is driver fit and interior compliance: seat position, pedal access, door modifications, vent windows, airbag removal, and whether the modifications serve only the allowed purpose.

Then inspect the donor against that paper car. Every item receives one of four labels.

Already saves you money means the part is legal, appropriate, already installed correctly enough to keep, and something you would have bought. A 4.3 diff in a SuperMiata-style build is a strong example because the guide calls the 4.3 fastest at most tracks and says it is a must in that environment. A good NB transmission can be another. A legal hardtop can be useful, but the guide reminds you that the expensive OEM top is not always the race value; a lighter fiberglass race top can be the better economic answer if the class permits it.

Already saves you risk means the part is not just a performance item, but a known platform problem already handled. A sealed radiator duct, undertray, adequate radiator opening, properly bled cooling system, and radiator that is not an old brown-plastic stock unit can save you from the classic Miata heat spiral. A diff brace can matter because the guide points to a factory housing notch that can break under bump drafting or curb use, with a Mazda Motorsports brace as the repair path. A water pressure warning light can matter because the guide notes that wheel-to-wheel drivers do not constantly watch gauges, and a major coolant leak can unfold before the next gauge check.

Creates rework means the part is either illegal for your target, likely to fail, or forces you to undo someone else's idea before you can build the car correctly. Drilled rotors are the cleanest example from the bond. The guide treats them as wrong for track duty. A too-small radiator opening with restrictive mesh is another. It may look intentional, but the guide warns that small openings depend on perfect ducting, and that many cars missing the rest of the cooling package will not survive 110F bump-drafting use. An oil cooler can also land in this bucket if the installation puts a cooler in front of the radiator, adds vulnerable lines, or creates puncture and rubbing risk.

No donor value means the item may be nice, but it does not reduce the cost or risk of the final car. A big fan is an example. The guide says radiator fans rarely matter once the car is moving. A seller may point to it as a cooling upgrade, but your ledger should value moving-air cooling: radiator condition, undertray, ducting, opening size, airflow path, and pressure warning. Likewise, a generic claim that the car is light is not enough. The SuperMiata guide aims for 2310 lb at zero fuel, and says an even better path is a lighter car carrying strategic ballast for weight distribution. A donor that is light in a random way may still require work if you cannot place ballast where you want or if the weight came from illegal gutting.

Sub-skill: separate included cost from included quality.

A part installed on a donor is not automatically an asset. You need to ask three questions. Would I buy this exact type of part for my target class? Is the installation legal and reliable enough to keep? Does keeping it reduce future work more than it creates future risk?

The oil cooler passage is the model for this kind of thinking. The guide is not anti-cooling; it says the author has oil coolers in most race cars. But it also lists failures caused by punctured coolers, rubbing oil lines, undrained old oil, and radiator efficiency loss when the cooler is mounted in front of the radiator. That is how you judge a donor part. The presence of an oil cooler is not a plus by itself. A clean, protected, well-routed installation that helps cooling without hurting the radiator may be a plus. A vulnerable or heat-stacking installation is a liability.

Use the same pattern for the hardtop. An OEM hardtop has resale value and street-car value, but the guide says SuperMiata does not require the expensive heavy OEM top and points to cheaper lighter fiberglass race tops. If the donor includes an OEM hardtop, you might count it as resale value rather than race value. If it includes a race-fit fiberglass top that is legal and matches your use, count it differently. The part is the same category, but the buyer value changes with the final target.

Use the same pattern for drivetrain pieces. A seller may call any short shifter an upgrade. The guide specifically values the Miata Roadster shifter because it improves Miata shifting quality, while saying most short-shift kits do not. That means you do not price the donor as if every installed shifter is equal. You ask what the exact part is, whether it solves the actual Miata problem, and whether you would otherwise spend money on it.

Sub-skill: turn equalization into a donor ledger.

Your equalization ledger is a two-column worksheet: final target on the left, donor evidence on the right. You are trying to convert a visual inspection into build-distance. Do not start with asking whether the car is nice. Start with asking which final-form requirements are already satisfied.

For power, the target is not a heroic dyno number. In the SuperMiata guide, the target is the cap and the area-under-curve limit. A semi-healthy NA 1.8 with intake, header, exhaust, ECU, MAF delete, and E85 can reach about 140 whp in that source. A healthy BP4W with the right supporting parts can exceed the cap and must be managed back into the legal window. That means a donor with a decent 1.8 and tune path may save money, while a donor advertised as overbuilt power may not save anything if you have to detune, verify, or replace pieces to fit the rules.

For gearing, the target is whether the car already has the ratio that works in your target series and tracks. The guide treats 4.3 as fastest at most tracks and says the driver will feel even small power differences while drag racing similar cars. Gearing and power are linked in the final race package. A donor without the right diff may still be fine, but you put the diff cost back into the price.

For weight, the target is not simply lightest possible. The guide's preferred path is close to minimum at zero fuel, or lighter with strategic ballast. The buyer lesson is that weight removed randomly is not the same as weight positioned intelligently and legally. A stripped car with questionable interior changes may not be a gift. A car that is light, legal, and leaves room to ballast strategically is more valuable.

For cooling, the target is race-condition survival, not parking-lot idle stability. The guide values crossflow radiators in hot, long-WOT, bump-drafting conditions; undertrays because engine-bay pressure hurts radiator efficiency; quick foam sealing around the radiator; adequate openings; and caution with mesh because even open mesh blocks radiator surface. A donor that ran winter HPDE sessions without overheating has not proven the same thing as a donor with the airflow path needed for race heat, drafting, and long wide-open-throttle sections.

For control hardware, the target is whether the driver can actually use the tire and brake package. The guide values an in-cabin brake prop valve because conditions change and because locking brakes costs tires and braking power. It treats ABS as usually not an advantage, but useful in certain situations such as wet, dust, and brake-duel conditions, and says NB ABS works better than NA ABS. It values extended lower ball joints because they add front camber, allow more suspension travel, and address bump steer. Each item belongs in the ledger only if legal for your class and relevant to your track use.

Sub-skill: inspect reliability as a race-use system, not a collection of parts.

Cooling is the biggest example in the supplied bond because it appears across several chunks. A crossflow radiator is not enough if the car is missing the undertray. An undertray is not enough if air bypasses the radiator. Duct sealing is cheap and high value, but it still depends on an opening and exit path that make sense. Mesh can protect the radiator at rocky tracks, but too much mesh can cut effective cooling area. Hood extractors can help engine-bay cooling if placed in low-pressure areas. A pressure warning light can save an engine when a leak happens between gauge checks. This is not a pile of independent upgrades. It is an airflow and warning system.

That matters during donor evaluation because many sellers assemble parts without assembling a system. A big aluminum radiator with no undertray is not the same as a sealed, ducted, undertray-equipped, bled cooling package. A tiny radiator opening copied from a faster car is not the same if the faster car also had crossflow radiator, fan, E85, custom undertray, oil cooler, extractor hood, ducting, and sealed opening. The guide explicitly warns that copying the visible opening without the rest of the package is questionable in 110F race conditions.

Brakes get the same treatment. The bond does not give you a full Spec Miata brake build recipe, and this lesson should not invent one. It does give one clean negative rule of thumb: drilled rotors are wrong for track duty, while plain rotors are the safe baseline and slotted rotors may be acceptable if you have extra money. It also values brake bias adjustment. So in a donor inspection, you do not give credit for flashy rotors. You give credit for legal, durable, maintainable brake hardware and for adjustment that lets you keep the tire working without lockup.

Sub-skill: read interior work through legality and driver fit.

The NASA Spec Miata chunk is useful because it shows how fine the interior line can be. Some things may be removed: insulation, carpets, passenger seat, spare tire, tools, airbag systems. Some changes are conditional: door gutting has side-protection requirements, vent-window removal affects where ducting may go, floor-pan modification for a larger or taller driver must stay inside dimensional and material limits and serve only seating position. Pedals may be modified for comfort and accessibility, with strengthening allowed if it serves no other purpose.

That means a donor's interior should not be judged by how stripped it looks. Judge it by whether the work solves allowed problems. Does the seat and pedal position help the driver fit legally? Were door modifications made only where the cage side protection supports them? Does cooling ducting respect body and window constraints? Was the floor modified for the allowed seating purpose, or did someone create a compliance problem? A rough interior can be a good donor if it is legal, purposeful, and safe. A clean interior can be a bad donor if it hides illegal cutting or leaves a tall driver unable to sit correctly.

Technique: the inspection sequence.

First, name the rule set. Do not inspect the car as a generic track Miata. Inspect it as the car you intend to own. SuperMiata-style assumptions, SCCA Spec Miata assumptions, NASA Spec Miata assumptions, and regional overlays do not have identical value maps. The supplied 2023 regional extract, for example, ties Spec Miata to the SCCA GCR and tire rules while also describing related regional classes and exceptions. The supplied NASA extract gives detailed permitted interior work. The rule set decides whether an included part is a credit, a neutral item, or rework.

Second, do the cage triage but do not bury yourself there. If the cage fails the sibling cage-audit standard, the donor is not saved by a good engine, a 4.3 diff, or a clever cooling package. Record the cage as pass, fail, or expert review needed, then move on only if it remains a viable candidate. This is not because the cage is less important. It is because the cage has its own lesson and because you cannot practically swap it like a transmission or radiator.

Third, price the drivetrain by avoided purchases. Is the engine the one you would want for the target? Is it already in the likely legal power window, or will you spend money tuning and verifying it? Is the transmission an NB2, NB1, or NA five-speed? Is the diff the ratio you want? Is there diff bracing if your use includes curbing or bump drafting? Is the flywheel and clutch package useful? Each answer is a price adjustment, not a feeling.

Fourth, inspect cooling in flow order. Start at the opening. Is the opening too small for the rest of the package, or is the car depending on perfect ducting it does not have? Is mesh protecting against rocks without blocking too much area? Is air sealed to the radiator with foam or ducting? Is an undertray present? Is the radiator condition acceptable, and is the old brown-plastic stock radiator avoided? Has the system been bled correctly? Is there a pressure warning light or other way to catch a sudden coolant loss? If the donor has an oil cooler, does it help without creating line, puncture, or radiator-efficiency problems?

Fifth, inspect the control package by use case. A brake prop valve is valuable when it lets you stop locking a tire and tune the car to conditions. ABS may not matter most of the time, but if two cars are otherwise equal, the guide would rather start with ABS, especially NB ABS. Extended lower ball joints, if legal for your target, can be valuable because they open up camber and ride-height options. Aero pieces and spoiler angle should be judged by whether they are installed per the target rule and whether the track actually needs downforce.

Sixth, inspect the interior and driver fit as a legality problem. Sit in the car if you can. Check pedal reach. Check whether floor-pan work, door gutting, vent-window ducting, and airbag removal are inside the kind of allowances the rule set provides. A driver who cannot sit legally and comfortably has not found a cheap donor; he has found a car that still needs fabrication.

Finally, convert the car into a remaining-build list. The best donor is not the one with the longest parts list. It is the one whose remaining list is short, legal, and predictable. You should be able to say: this car saves me the engine and diff, but I must fix cooling; or this car saves me cooling and transmission, but the diff and power verification remain; or this car is cheap because it saves almost nothing.

Calibration cues: what good judgment feels like.

As you improve at this skill, your inspection notes get less emotional. You stop writing fast, clean, built, and lots of parts. You write legal 4.3 present, NB2 five-speed present, cooling duct incomplete, undertray missing, stock radiator suspect, prop valve present, ABS present, interior modifications need rule check, hardtop resale value not race value. Your notes become closer to a work order.

Your questions to the seller also change. Instead of asking whether the car makes power, you ask what rule cap it was tuned for and when it was last tuned. Instead of asking whether it runs cool, you ask about radiator, undertray, ducting, opening, mesh, bleeding, and hot-weather race use. Instead of asking whether the brakes are upgraded, you ask whether the rotors are track-suitable and whether bias can be adjusted. Instead of asking whether the interior is gutted, you ask what was removed, why, and under which rule allowance.

The budget signature changes too. A good donor moves money out of surprise categories. You still expect consumables, setup, fluids, and verification. But you should not discover after purchase that you need a different engine, different transmission, different diff, different cooling package, legal interior repair, and basic airflow pieces. If the post-purchase list looks like a full build, you did not buy savings. You bought a story.

The lap-time signature is indirect. This lesson is not about finding a magic fast car. It is about getting to the same legal window sooner and with fewer unknowns. In an equalized field, the payoff is that you spend your first events dialing the driver, setup, tune, weight, cooling, and reliability rather than undoing inherited decisions. The guide's own logic points that way: small power differences matter when cars are similar, weight matters on a two-minute course, brake lockup wastes tire and braking, and cooling failures end weekends. Donor judgment protects the work that follows.

Failure modes.

The first failure mode is buying horsepower in a capped class. A seller's power story can feel convincing, especially when the dyno number is high. But if the target class caps peak and area under the curve, excess power may be irrelevant or may create detuning and verification work. What good looks like: you value a motor by how cheaply and reliably it can live at the legal target, not by how much it once claimed.

The second failure mode is treating year as destiny. The guide says year does not matter once the cars are built and equalized, but also points out that NB donors can save an engine and possibly a 4.3 Torsen. Those statements belong together. Year alone is not value; included final-form parts are value. What good looks like: an NB donor gets credit only for the useful components actually present and healthy.

The third failure mode is paying for bling. Drilled rotors, flashy shifters, complicated cooling add-ons, and expensive street-oriented hardtops can inflate seller confidence without reducing your race build distance. What good looks like: the item must be legal, durable, relevant, and something you would have bought anyway.

The fourth failure mode is underpricing cooling work. A Miata that survives slow HPDE traffic in mild weather has not proven it will survive hot race conditions, bump drafting, or long WOT sections. What good looks like: you judge the whole airflow path, not just the radiator brand.

The fifth failure mode is ignoring driver fit because the car is otherwise attractive. The NASA interior chunk makes clear that floor, pedal, door, and ducting changes can be legal only under specific purposes and constraints. What good looks like: the donor puts the driver in a legal, comfortable, safe position without requiring major corrective fabrication.

The sixth failure mode is confusing unofficial setup lore with permission. The supplied SuperMiata guide is useful, but it is explicitly unofficial and from 2018. The regional and NASA rule chunks show that official rules and overlays define the legal boundary. What good looks like: the guide helps you ask better questions, then the applicable rulebook answers the legality question.

Cross-references.

Use Decide when buying beats building before this lesson if you have not yet chosen the financial path. Use Audit the cage before everything else as a hard gate before you let drivetrain savings tempt you. Use Keep unofficial guides below the rules whenever a donor's value depends on a modification being legal. This lesson gives you the buyer ledger after those boundaries are understood.

Worked example: the NB donor that saves real build money

You are comparing an NB five-speed donor with a legal cage candidate, an NB engine, a 4.3 Torsen, a clean-shifting transmission, and a basic but incomplete cooling package. The seller describes it as a strong car. Your ledger ignores the adjective and starts assigning credits.

The engine receives provisional credit because the supplied guide says NB engines make the most power, and that NB1 BP4W and NB2 VVT engines are strong junkyard starting points. The diff receives a strong credit if the target is SuperMiata-style racing because the guide treats the 4.3 as fastest at most tracks and a must-have. The transmission receives credit if it is an NB2 five-speed, less if NB1, less again if NA, because the guide ranks them by shift quality. These are real savings because they are parts you might otherwise have to find, buy, swap, and verify.

Now the cooling package gets inspected without being blinded by the drivetrain score. If the car has a decent aluminum radiator but no undertray, poor foam sealing, a small opening copied from another car, and restrictive mesh, you do not call the cooling done. The guide values undertray, radiator sealing, appropriate opening size, and caution with mesh. It warns that a small opening can be questionable when the car lacks the rest of the cooling system. So the donor might still be worth buying, but the offer should include cooling rework.

The conclusion is not buy or walk away automatically. The correct conclusion is priced distance. This donor may save a major drivetrain spend while still needing airflow work. That is a good candidate if the price reflects the remaining work and if the cage and rules checks pass. It is a bad candidate if the seller prices it as complete because it has the expensive drivetrain pieces but ignores the hot-weather survival work.

Worked example: the cheap NA6 that only makes sense under the right target

A clean NA6 donor shows up at a low price. It has a basic cage candidate, an NA transmission, no 4.3 diff, a stock cooling arrangement, and a seller who says it is a great low-cost Spec Miata start. This is where equalization keeps you honest.

For a SuperMiata-style S2 target, the donor does not get much drivetrain credit. The supplied guide describes the NA6 engine as weak in its own blunt style, says NB engines save you an engine because they make the most power, and treats the 4.3 diff as a must. It also ranks NA transmissions last among the used five-speeds. That does not make the car worthless, but it means the low price has to absorb a likely engine path, diff path, transmission disadvantage, tuning path, and cooling path.

But the same shell could make more sense if your target is a regional class specifically intended to keep 1.6 cars running at low cost. The supplied regional rule extract says SMSE was created to give 1.6 Mazda Miata owners a low-cost class and ties the class to current Spec Miata rules. That changes the ledger. The car is no longer being judged as a shortcut to a SuperMiata S2-style target. It is judged against the 1.6-friendly target.

This is the core lesson in miniature. The donor did not change. The rule target changed. Under one target, the cheap NA6 saves little and may become expensive. Under another target, it may preserve the whole point of the class. Good buyer judgment is not brand loyalty or chassis folklore. It is target-aware accounting.

Worked example: the winter-HPDE car with a summer-race cooling debt

A seller says the car has never overheated. It has run several winter HPDE days, has an aluminum radiator, and looks clean. You inspect it for a hot race environment and find the stock undertray missing, no foam around the radiator, a narrow opening, fine mesh, no pressure warning light, and an oil cooler mounted in front of the radiator.

The seller's experience may be true and still not be enough. The supplied guide separates HPDE or slower use from hot bump-drafting and long WOT use. It recommends crossflow radiators for hard hot conditions, says not to run without some type of undertray, calls radiator ducting highly effective, warns that mesh blocks radiator surface, and warns that copying a small radiator opening assumes near-perfect ducting. It also notes that oil coolers can create failures and can reduce radiator efficiency depending on placement.

The right inspection result is not that the seller lied. The right result is that the car has not proven the use you plan. You price it as a car with cooling debt. If the drivetrain and cage are strong, you may still buy it. But you do not let the statement that it ran winter HPDE fine erase the parts of the cooling system that the bond says matter under harder conditions.

Common mistakes and what good looks like

Mistake one: counting every installed part as savings. Good looks like asking whether you would install that exact part, in that exact way, for your target rule set. An oil cooler with vulnerable lines may be negative value. A generic short shifter may be neutral. A legal, useful 4.3 diff can be real value.

Mistake two: treating shiny brakes as race brakes. Good looks like rejecting drilled rotors for track duty and valuing durable, legal, maintainable brake parts plus bias control where allowed and useful.

Mistake three: ignoring the cooling path because the radiator is new. Good looks like checking opening, mesh, sealing, undertray, ducting, exit path, bleed state, warning strategy, and whether any oil cooler hurts the radiator.

Mistake four: buying a dyno story instead of a legal power package. Good looks like asking whether the engine and ECU can live at the cap and area target, and whether the tune has been kept current as the engine ages.

Mistake five: treating lightness as automatically good. Good looks like checking whether the car can meet minimum weight legally and whether ballast can be placed strategically rather than discovering that random gutting created compliance or balance problems.

Mistake six: skipping the driver-fit legality check. Good looks like using the rule allowances to inspect pedals, seat position, door work, vent-window ducting, and any floor-pan changes before you decide the car is ready for you.

Mistake seven: letting a good drivetrain distract from a bad cage. Good looks like sending cage questions to the cage-audit gate first. If the cage fails, drivetrain savings do not rescue the purchase.

Mistake eight: letting an unofficial guide become your rulebook. Good looks like using the guide for platform traps and cost logic, then checking the current rule set for legality before assigning donor credit.

Drill: the three-listing equalization ledger

Before your next call or trackside inspection, choose three live Miata listings or paddock cars that could plausibly be donors. Spend 30 minutes per car. Do not contact the seller until the ledger is complete.

For each car, build six rows: rule legality, cage triage, drivetrain, cooling and survival, control and setup hardware, and interior and driver fit. Under each row, write only three kinds of phrases: saves money, creates rework, or unknown until verified. Force yourself to attach a reason. For example, 4.3 diff present saves money for the target. Missing undertray creates cooling rework. Oil cooler unknown until routing and radiator placement are inspected. Interior gutting unknown until door, vent, pedal, and floor rules are checked.

The success criterion is concrete. By the end of the drill, you must be able to rank the three cars without using the words fast, clean, built, or deal. You should be able to say which car saves the most final-form work, which car carries the most hidden rework, and which unknowns would change the price. If all three rankings still depend on seller adjectives, repeat the drill with the bonded categories in front of you.

At an actual event, compress the same drill into a 20-minute walkaround after the cage pass. Five minutes for drivetrain evidence, five for cooling airflow, five for control and setup hardware, and five for interior fit and legality. The drill is not a substitute for a professional inspection. It trains your eye to stop admiring parts and start pricing distance to the legal equalized car.

When this principle breaks down

The principle breaks down when the rule target is wrong. A 1.6 donor that is a poor shortcut for one class may be exactly the point of a 1.6 regional class. A modification that is useful in SuperMiata may be irrelevant or illegal elsewhere. Always choose the class first.

It also breaks down if the cage fails. This lesson can help you value drivetrain, cooling, controls, and interior work, but a bad cage is not a normal line item. The supplied guide itself treats the cage as the most important part because almost everything else can be swapped. If the cage is questionable, stop the donor valuation and use the cage-audit process.

It breaks down when you cannot inspect the system behind the part. A radiator brand without undertray and ducting evidence is not enough. A power claim without rule-target tune evidence is not enough. A stripped interior without legal-purpose evidence is not enough. Unknown does not mean worthless, but it cannot be priced like verified savings.

Finally, it breaks down when your use case is not the use case in the claim. A car that is adequate for HPDE, mild weather, and no bump drafting may not be adequate for hot wheel-to-wheel conditions. A car that is optimized for one track's downforce need may not be right at another. A donor only saves you what your use will actually require.

Author Review

No quiz questions are attached to this lesson.

Sources

#	Document	Chunk	Pages	Score	Collection
1	Unofficial SuperMiata Guide (2018)	bace066b8556de38b6b72ff90f1e2995	1	1	uio_books_raw_v1
2	Unofficial SuperMiata Guide (2018)	d362e728ca970912395cd0ab3a622603	5	1	uio_books_raw_v1
3	Unofficial SuperMiata Guide (2018)	4a22a8294996eb7111996b4bee77cc13	6	1	uio_books_raw_v1
4	Unofficial SuperMiata Guide (2018)	b0f4d9f57c34f92c14f2cd770c2f7c7e	12	1	uio_books_raw_v1
5	Unofficial SuperMiata Guide (2018)	ba8c8a395bf5ef1def6f201a06ace255	3	1	uio_books_raw_v1
6	2024 NASA Spec Miata Rules	e164a32416f99ff0fbd3ae603ec22e15	23	1	uio_books_raw_v1
7	2023 Regional Class Rules	63384ad5199ffa8ecc8abca763c50e09	4	1	uio_books_raw_v1