Answers for diesel and performance shop owners.
Long builds, deposit math, dyno time, customer-supplied parts, and the tuning liability nobody warns you about.
26 questions, 26 of them with a word-for-word script, the actual math, or a template you can copy.
Finance
All finance →How do I calculate my shop's effective labor rate?
Total labor dollars collected divided by total hours actually worked by techs. If it's below your posted door rate by more than 20 percent, you're bleeding time somewhere.
The math ChecklistIs it okay if my best tech makes more money than I do?
Yes, and if you're the owner still turning wrenches, it should happen more often than it scares you. Your job is to make money on the shop, not out-earn your best employee at the bench.
The mathShould I take on fleet accounts that pay net 60?
Only if the volume and margin are worth financing them for two months, and only with a credit application and a hard cap on how much unpaid balance you'll carry at once.
The math ChecklistHow should I structure progress billing on a build that takes months?
Bill on defined milestones tied to work actually completed, not on a calendar schedule, and never let more than a few weeks of unbilled labor pile up. A build that runs four months with one invoice at the end is a build where you're financing the customer's project with your own payroll.
The math TemplateShould I charge myself shop rate for time spent on my own project or demo car?
Yes, track it at your real shop rate even if no money changes hands, because untracked owner time on a demo build is the easiest way to quietly lose money without noticing. If it's not on the books, it's not real to your numbers.
The mathShould I buy or lease my next big piece of equipment?
Buy what holds its value and you'll run for years past the loan term. Lease what changes fast, gets used seasonally, or you'd want to upgrade in three years anyway.
The math
Hiring
All hiring →Should I pay my techs flat rate or hourly?
Flat rate rewards speed and can pay your best techs very well, but it needs steady work volume and honest time standards or it backfires fast. Hourly is simpler and safer for a smaller or newer shop.
The mathHow do I hire and pay a builder differently from a general tech?
Pay a builder for judgment and problem-solving, not flat-rate hours, because build work has no book time to measure against. Hourly or salary with a bonus tied to build quality and customer outcomes fits this role better than flat rate ever will.
The math ChecklistShould I pay for an employee's training, and how do I make sure they don't take it straight to a competitor?
Pay for training that makes your team better, and use a simple repayment agreement tied to a time period, not a non-compete. It protects your investment without pretending you can stop someone from leaving.
Template Checklist
Pricing
All pricing →How much deposit should I take on a diesel or performance build?
Fifty percent up front, nonrefundable once parts are ordered, with progress payments tied to milestones on anything over a few thousand dollars. Anything less and you're financing someone else's project car with your own cash flow.
The math TemplateHow do I quote a custom build that always scope-creeps past the original number?
Quote the build in phases with a written spec sheet, and price every change beyond that spec as a separate change order before you touch it. The scope creep isn't the customer's fault if you never wrote down what was actually included.
Script ChecklistCan I charge for R&D and diagnostic time on a one-off build with no established procedure?
Yes, and you should bill it as its own line item, separate from install labor. Figuring out how to fab a mount that doesn't exist yet or chasing a custom tune issue with no baseline is real shop time, not something you eat because there's no flat-rate number for it.
Script The mathHow should I price dyno time and tuning sessions?
Charge by the hour or by the pull, not a flat 'tune' fee, and separate dyno rental from tuner labor if they're different costs to you. A stock combination might tune in one hour, a custom one can eat an entire afternoon.
The math ChecklistShould I charge a teardown fee if a customer backs out mid-build?
Yes, bill actual labor hours already performed plus a documented restocking or return cost on any parts already ordered. You don't work for free because someone changed their mind after you already had the engine apart.
The math TemplateHow much should I mark up special-order performance and diesel parts?
Enough to cover the freight, the returns risk, and the capital tied up while you wait on backordered parts, typically 25 to 50 percent over your cost depending on how obscure the part is. Treating special-order performance parts like a stock brake pad markup leaves real money on the table.
The mathShould I mark up sublet machine work, and how much?
Yes, 15 to 25 percent over what the machine shop charges you, because you're managing the vendor, the timeline, and the quality risk on the customer's behalf. Passing sublet costs through at zero markup means you're doing project management for free.
The math Checklist
Operations
All operations →What's my legal exposure for tuning a customer's diesel or gas engine, especially around emissions?
Real, and it's bigger than most shops treat it. Delete tunes and defeat devices carry federal penalties that land on the shop, not just the customer, so know your state and federal rules before you sell a tune.
Template ChecklistShould I install customer-supplied parts on a performance or diesel build?
Only with full labor rate, a signed waiver, and the customer paying for the parts you'd need to correct a bad or wrong part after you're already into the job. On a build, a customer's cheap online turbo can cost you a full week of labor if it fails on the stand.
TemplateCan I charge storage fees on a build the customer abandoned or stopped paying for?
Yes, and you should have it in writing before the vehicle ever comes in the door. A daily storage fee that starts after a defined grace period is standard in this trade and gives you real leverage when a customer goes quiet.
The math TemplateDo I warranty labor on a modified or built engine, and how much?
Warranty your workmanship, not the parts and not the customer's driving habits. A short, specific labor warranty with clear exclusions protects you far better than a vague 'we stand behind our work' line that means nothing when a rod lets go.
Template ChecklistHow do I manage a waiting list and lead times for build work without losing customers?
Quote lead time honestly, in writing, with a range not a date, and require a deposit to hold a slot on the calendar. A waiting list you manage loosely turns into a dozen angry customers all convinced they were promised a spot that doesn't exist.
Script ChecklistWhen do I fire a build customer instead of finishing the job?
When they've changed the scope three or more times without paying for it, when they treat every invoice as a negotiation, or when they've made it clear they'll blame you the moment anything goes wrong. Finishing a bad build relationship rarely gets easier the further into it you go.
Script ChecklistWhat do I do when a customer wants more power than their platform can reliably handle?
Tell them the real ceiling in writing, offer the supporting mods that would actually get them there safely, and let them choose with full information instead of quietly building past what the parts can take. Building it anyway without saying anything puts the eventual failure on your invoice, not just their decision.
Script TemplateHow do I handle a customer blaming the shop for a blown motor after a tune or build?
Pull the logs, pull the paperwork, and separate what you can actually prove from what you're just being accused of. If your documentation is solid, stay calm and factual; if it's thin, that's the lesson for next time, not a reason to cave on a claim you don't actually owe.
Script ChecklistHow do I know when to stop taking one-off custom build jobs?
When your R&D and rework hours are consistently eating your margin on novel builds, or when a couple of repeatable builds would fill your bays with far less risk and headache. One-off work is often more prestige than profit once you actually run the numbers on the hours it eats.
The math Checklist
Marketing
All marketing →Every owner hits these
Not specific to your trade, but they show up in every shop that has employees, customers, and a bank account.