What the words mean.

Every term Moddo uses on a build sheet or a chooser is one link away from the plain explanation below. Nothing here is legal or engineering advice; see the terms of use for that.

CARB EO

A CARB Executive Order (EO) is a number the California Air Resources Board issues for one specific aftermarket part, in a format like D-123-45. It says that part does not defeat a car’s emissions controls, so it can be sold and installed under California’s anti-tampering law.

Since 2020, federal policy treats an emissions-related part with no CARB EO (or EPA acceptance) as tampering everywhere in the United States, not only in California. What actually varies by state is whether anyone checks for a missing EO at registration: California, plus CO, CT, DE, ME, MD, MA, MN, NV, NJ, NM, NY, OR, PA, RI, VT, VA, WA and DC follow California’s emissions rules and check for one; everywhere else, nothing about the part changes, only whether Moddo’s note beside the chip says anyone looks.

Only parts for systems that touch emissions carry one: intake, headers and exhaust, forced induction, tune, engine internals, ignition, and injectors and fuel rails. Brakes, suspension, wheels, cooling, clutch, axles, exterior & aero, lighting and interior & safety are never regulated this way, so Moddo never asks about an EO for them.

To look one up, use CARB’s own aftermarket parts search, or check the part maker’s own page, where an EO is usually printed.

The four things Moddo can say about a part’s EO

Moddo tells apart four different truths, one chip per regulated part, everywhere, not only where the state checks:

• Certified (green): an EO is on file for this exact part, from the maker’s own page, a listing, or an owner’s own report. When that EO’s own text lists which vehicles it covers and your car is on the list, the chip says so (“covers your car”); when the EO names no vehicles to check, the chip is silent on that and just shows the number.
• EO on file, not for your car (amber): the same as certified, except the EO’s own vehicle list is known and your car is not on it. That EO is real, it is just filed for a different application.
• Not certified (amber): this part’s maker has EOs on file for other parts, just not this part number. That is a real gap, not a missing search.
• Unknown (grey): nothing is on file either way, for this part or this maker. Moddo has not found the paperwork; that is not the same as the part being illegal.

None of the four changes what a missing EO means: since 2020, federal policy treats an emissions-related part with no CARB EO as tampering everywhere, whether or not anyone checks for it. The note beside every chip, “checked at registration in CA” or “not checked at registration in TX”, says only whether your build’s own state looks for a missing EO at registration, never whether the part is allowed.

“(reported by an owner)” means the number came from an owner typing it in, not from the maker or a listing. Moddo shows it as certified right away; that label stays until a second, independent source (the maker’s own page, a listing, or CARB’s own database) agrees, so you can see the difference between one person’s word and a confirmed record.

Before you buy, check the maker’s own product page, where an EO is usually printed, and confirm with your state if you plan to register the car for the street.

Noise (dB)

The dB chip is an exhaust part’s own stated noise figure, read straight off the maker’s page or a listing’s own text, never measured by Moddo and never estimated.

Many states and tracks set a maximum dB level for a car on the street or at a tech inspection. Moddo does not yet know your state’s own limit, so the chip shows the figure alone; check your state’s exact rule and any track’s own tech sheet before you buy or run one.

Lift and lowering height

The lift chip is a suspension part’s own stated ride-height change, in inches, read off the maker’s page or a listing’s own text: a positive number lifts the car, a negative number lowers it.

Some states cap how far a car may be lifted or lowered and still pass inspection. Moddo does not yet know your state’s own limit, so the chip shows the figure alone; check your state’s exact rule before you buy.

Tint VLT

VLT, visible light transmission, is the percentage of light a window film lets through; the chip is a tint product’s own stated VLT, read off the maker’s page or a listing’s own text.

Every state sets its own minimum VLT for different windows on a car, and they vary widely. Moddo does not yet know your state’s own minimum, so the chip shows the figure alone; check your state’s exact rule before you buy or install.

whp against crank horsepower

Whp is wheel horsepower: power measured at the wheels on a dyno, after the drivetrain. Crank horsepower, the number most makers advertise, is measured at the engine before the drivetrain takes its cut.

Whp is always lower than the crank figure, by whatever the drivetrain loses to friction. Moddo puts every figure on the same whp ladder so parts from different sources can be compared fairly.

Moddo’s whp figures are estimates, and the sheet says so; treat them as a way to compare choices, not a promise of what a dyno will read.

Estimated output

Est. output is Moddo’s estimate of what the car makes at the wheels with the parts you’ve picked, given what is known and what is missing.

On a chooser card, a line like “228 to 380 whp” is before-to-after for that one candidate: what the build makes now, and what it would make with that part added, before any other change.

Use it to compare candidates against each other. It is an estimate built from the same evidence as the rest of the sheet, not a dyno guarantee.

Where a supercharger or turbo kit’s maker rates the complete kit’s output for a named car (“825 hp at the flywheel on 93 octane”), that rating is the kit’s figure. A rating at the flywheel is turned into wheel horsepower with your car’s own drivetrain loss, and the card shows both. The rating is for the maker’s own car on its stated fuel, so yours will differ.

The ladder, ceilings and the binding system

Each system on the car, fuel, clutch, engine internals and the rest, has a ceiling: the most whp it can support before something gives. The ladder lists those ceilings from lowest to highest.

The lowest ceiling is the one that binds: it is what actually limits the car right now, no matter how strong the other parts are. Moddo names the binding system so you know which one to look at first.

Resolving the binding system, usually by upgrading whatever caps it, moves the limit up to the next system on the ladder, which becomes the new binding system.

A clutch and a gearbox are rated in torque (lb-ft), not horsepower. Moddo places them on the ladder with the car’s own ratio of stock wheel horsepower to rated torque, so a gearbox rated 10% above the engine’s torque sits 10% above stock output. Makers often rate the factory gearbox at exactly the engine’s torque. The gearbox then binds at stock output: any gain runs it past what its maker rates it for. That uses up its margin; it does not mean it breaks on the next drive.

“No data” and the grey mark

“No data” means Moddo has no figure, from the maker or anywhere else, for that system. The check has nothing to compare against, so it cannot say anything about that limit.

The grey outlined mark is how that shows up on a build sheet: the check ran blind for that part.

No data is never a pass. Treat a system marked this way as unknown, not as cleared.

Fitment

“Fits” on Moddo means the part’s listed application matches your car’s year, chassis and engine, according to whoever wrote the listing.

On a marketplace listing, EXACT fitment is set per model year by the seller; Moddo shows it but does not independently verify it. A part maker’s own fitment page is the stronger claim, since they built the part for a specific list of cars. A “universal” part fits a wide range and carries no specific-fitment claim at all.

Confirm fitment with the seller, or with the maker’s own page, before you buy.

Sister-platform parts

A platform is the shared chassis, engine and running gear underneath what may be sold as several different makes and models, or badges. A 2022+ Toyota GR86 and Subaru BRZ, for example, are the same car built on the same line, badged and sold two ways; a part for one already fits the other.

Moddo’s fitment data is per platform, so a part listed for a sister badge, like a BRZ part on a GR86 build, already shows up in your chooser without you searching for it separately. When a listing’s own title names that sister badge instead of your car’s, Moddo adds a chip saying so, just to tell you why an unfamiliar name is showing up as a match.

“Already installed” and “on the car”

Marking a part “already installed” or “on the car” tells Moddo it is something you already have, not something to shop for.

Moddo still runs the part through every check and counts its numbers on the ladder, but it leaves the part out of what you’d need to buy, so the parts total only reflects what is left on your list.

Use it any time you are recording what is already on the car rather than planning a purchase, from a chooser card or from the custom part form.

Example catalog

“Example” on a part means it is placeholder catalog data, not a real listing you can buy today.

Every example part carries a visible tag, so it is never mistaken for a real offer.

Treat prices and fitment on an example part as illustrative only, not something to check out with.

“Seen N ago” on a price

“Seen N ago” is how long ago Moddo last read that price from the store or listing that offers it.

Prices change without notice, so this tells you how fresh a number is instead of implying it is live right now.

For anything more than a day or two old, check the store’s own page before you buy.

Rated part against supporting part

A rated part carries its own figure that a check reads, like a clutch’s torque capacity or an intake’s airflow. Every other part on a system row falls into one of four roles instead: supporting (a hanger or an install kit, which only helps install a rated part), accessory (a skid plate, guard or cosmetic body panel: weight only, no rating), consumable (a fluid, filter or a pad or plug sold for replacement, with a refill interval rather than a rating), or instrumentation (a gauge, sensor or logger that observes a system without claiming anything about it).

Only a rated part can move a ceiling on the ladder. Adding a part in any of the other four roles will not change what a system can support. Its price still adds to the row and the parts total, and the chooser shows it separately, under “Supporting parts,” with its role as a small label.

Wheels & tires and brakes are the two rows that can hold more than one rated part at once, whether a wheel and a tire, or a mix of front/rear pads, rotors, calipers and lines, each in its own slot, priced and removed on its own line under the row.

Registration state and use

Registration state is where you plan to register the car; use is how you plan to drive it: street, track or drag.

State decides whether CARB’s emissions rules apply to the build. Use affects how much an off-road-only part matters: a car that only ever runs track or drag has less reason to care about a missing CARB EO than one registered for the street.

Change either from the build sheet at any time; Moddo re-checks the whole sheet against the new choice.

Stock rows and “included”

A “Stock” row is whatever part the car came with from the factory for that system. “Included” means it is already accounted for in the build without you choosing anything.

Not every system needs a decision from you: stock is a real, valid choice, and Moddo’s checks treat it as one rather than as a gap.

Open the system and choose a part any time you want to upgrade past stock.

Injector duty

Duty cycle is how much of the time your injectors spend open, as a percentage, to deliver the fuel an engine needs at a given power level. The Simulations card’s injector duty table reads your build’s total injector flow and the stock-versus-forced-induction fuel assumption the fuel check already uses (the same figure behind the fuel system’s ceiling), then shows duty at each 50 whp step from stock to where that flow runs out.

85% is the usual tuner caution line, marked amber on the table: past it there is little headroom left before the injectors are open essentially all the time, which is the point most tuners start planning a bigger set rather than a hard failure by itself.

This is a model, not a dyno reading: it carries a stated error band (the fuel assumption’s own spread) beside the table. If you have a real duty reading from a tune log, use “I measured this” under the result to tell Moddo what you actually saw.

Quarter mile estimate

These are estimates from your build’s power-to-weight, using the standard published drag-strip formulas (elapsed time and trap speed from power and weight), not a measurement and not a promise. Weight is your car’s weight plus the weight your parts add; power is this build’s estimated output converted the same way the formulas were originally calibrated.

Moddo used to show a 0 to 60 time here and no longer does. It was derived by assuming the car accelerates evenly all the way down the strip, and that assumption disagrees with the elapsed time and trap speed sitting beside it, because it puts the car about a thousand feet down a quarter-mile track. The times it produced were roughly two seconds slow. Rather than replace one guess with another, the figure is gone until there is measured data to check a new one against.

The stated band beside the numbers is the model’s own claimed precision, not a guarantee for your specific car, driver or track surface. Ran the strip? Use “I measured this” under the result to record what you actually got.

Gearing

The gearing table shows how fast each gear runs out at redline, and what engine speed a highway cruise (70 mph, in the tallest gear) asks for, from your platform’s own published gear ratios, final drive and stock tire size, using the standard gear-ratio speed formula rather than a guess.

Change the tire size and the numbers change with it: a taller tire raises every gear’s top speed and lowers cruising rpm for the same ratios, which is the whole reason this table exists rather than a single number.

The stated band accounts for a tire’s actual rolling diameter running a little larger than its nominal size at speed. Without a curated final drive or gear set for your platform yet, this block shows “no data” naming what is missing rather than guessing a ratio.

Track-day tech sheet

Every build has a printable tech sheet (find it beside “Copy this build” on the build sheet): the car line, then a checklist grouped by brakes, wheels and tires, suspension, engine bay, interior, exterior and driver, each line a checkbox plus a blank to fill in by hand for whatever Moddo can’t know from the build alone. Where the build carries a relevant part, its name shows beside the line: a harness under “Harness date if fitted,” a cage under its own line, an exhaust’s own stated dB figure beside the venue’s sound-limit blank.

This checklist is generic, and says so at the top: it is not any one sanctioning body’s own tech form, and that form always wins over Moddo’s. Treat it as a packing list before you go, not a pass slip.

State rules

Some states publish an exact, citable rule for a few of the things a build’s legality flags already track: an exhaust noise limit in dB, or a minimum tint on the front side windows. Where Moddo has read that rule straight off the state’s own statute site (or its legislature’s own hosting of it) and can quote the line, the tech sheet cites it beside the matching blank.

The build sheet and chooser’s own noise, lift and tint chips do the same thing beside your registration state: when your state’s rule is on file, the chip says so in one sentence, amber when the part is on the wrong side of it (“95 dB, over TX’s 92 dB limit”, “35% VLT, under CA’s 70% front minimum”) and grey when it clears (“95 dB, within CA’s 95 dB”), linked to the statute either way. When your state has no rule on file for that one figure, the chip stays grey and says so plainly (“95 dB, no rule on file for TX”) rather than guessing.

This table is small on purpose: a state is left out rather than guessed at, so a state you don’t see here simply has no citation on file yet, not a rule that says anything is allowed. Always check your own state’s exact current rule before you buy, install or register.

Buy order

Buy order is the sequence to actually buy and fit what is on your sheet, so nothing sits in a box waiting for something else and nothing is done twice.

It is worked out from the checks already on the sheet, not from a rule of thumb. A part that another part needs comes first. After that comes whatever is binding, the thing capping the car today, where money spent anywhere else changes nothing measurable until it is done. Everything left is ordered lowest limit first, and the sheet says plainly when nothing waits on a part, so you can fit it whenever suits.

Parts marked already on the car never appear: a part you own has no place in a buying sequence.

If two parts each require the other, the sheet says so instead of inventing an order, because there is no sequence that works until one of them is resolved.

Plan to a target

“Plan to a target” finds the cheapest set of parts on file for your car that gets it to a whp figure you give, checked the same way as anything you add yourself. It raises whatever is binding, and where what caps the car is what its parts are rated for, it looks at the kits whose makers rate their output. Leave the target blank and it aims 50 whp past where the car binds today.

It never picks a part that breaks a structural limit, and never a kit whose name says it is for another version of your car (a Bullitt kit on a Mustang GT). Where a limit that matters for power has no figure for your car yet, the result names it as not checked, since no figure means nothing was there to stop the plan. Each kit it proposes is shown with its maker’s own figure and conditions, since the result rests on that figure. When nothing on file gets there, it says how far the best route reaches and why. “Add all to the sheet” adds every part it found, the same way choosing one from a list does, and the buy order then says what to fit first.

The card appears only on cars where some kit on file is rated past what the build already makes.

Budget

The budget is what you told Moddo you have to spend, asked once when you picked the car. Every price after that is shown against it: what is left on the sheet, and what each part in a list would leave if you added it.

It is a figure to plan against, never a rule. Nothing is hidden, disabled or reordered for being expensive, and going over budget is your call to make, not Moddo’s to block. The sheet just stops pretending it does not know.

The balance counts what you still have to buy. Parts already on the car were paid for before this build existed, so they are shown separately and never counted against the budget.

Leaving the budget blank is a real answer and not the same as a budget of zero: with no budget set, no balance is shown anywhere.