Performance Tune Your Car! But Kiss Its Resale Value Goodbye

Jim Motavalli

Jim Motavalli | Sep 19, 2016

OK, here goes, and you’re free to disagree with me: Don’t “performance tune” your car if you want to ever resell it.

I'm sure the owner loves his "Low Poke" Miata, and it probably corners on rails. But finding a buyer? (Jake Plumley/Flickr)

The exact same principles apply to people who build customized “dream houses” with expensive, weirdo features that only they’d want—a 50-seat theater, a guitar-shaped swimming pool—and then get stuck with an expensive white elephant at resale time.

I’m a Mazda Miata owner, and there’s a huge aftermarket dedicated to making them go faster. You can turbo them, supercharge them, lower them, add rollbars, wider tires, trick suspensions and shocks, and chip tune them for extra power. If you’re going racing (via the excellent Spec Miata series, perhaps), or plan to keep the car to the bitter end, go for it. But here’s the paradox—those “improvements” become obsolete, and they lower the value of the car.

I have evidence, and not just with Miatas. Collector cars of all makes, listed on eBay, Craigslist or often have lower asking prices that seem directly proportional to how much they’ve been modified. In the pits at the classic races at Amelia Island, for instance, I noticed many race-ready cars for sale—at much lower prices than a stock restored version would bring.

Dare I suggest that a stock '57 Chevy Belair--with continental kit and tissue dispenser--is worth more? (John Fowler/Flickr)

I for one don’t want to climb over a roll bar in a car I’m commuting in, or using for Sunday drives. And the cars I’ve driven or ridden in with speed equipment are often finicky and rattly—some of the stuff doesn’t play well together. I remember a modded Sunbeam Tiger that felt like it was going to shake apart. And performance stuff (unless it’s super rare and from the 50s) dates.

It might have been wiser--fiscally at least--to leave this classic Camaro alone. (John Shaffer/Flickr)

Here is an example: a Craigslist ’95 M Edition Miata with, among other things, Jackson Racing supercharger, Jackson Racing pipe intercooler, MSD ignition box, fuel controller/regulator, remote oil filter relocation, Bilstein shocks, front triangulated tower brace, upgraded rear sway bar, Borla catback exhaust, cross-drilled rotors and EBC green brake pads.

Mazda actually sells ready-to-race Miatas that are a lot of fun--but probably not good investments. (Jim Motavalli photo)

I’m sure that Miata is fast, but it’s probably also deafening and not fun around town. My friend has this same year/model and the aftermarket “performance” exhaust is so loud I’d be down at Midas 10 minutes after buying it.

Here’s a comment after the Craigslist Miata ad was re-posted on Bringatrailer: "Back in 2001, this is what I wanted to do to my ‘95 M Edition… And I’m glad I didn’t! The Jackson Racing bits were state of the art in 2000, but now are beyond obsolete. I wish I could advise the seller to sell this car without any ‘performance’ bits!” Amen. And there isn’t even a roll bar.

One local Miata is so low the exhaust pipe is almost touching the ground, and it also sports ugly extensions so that big low-profile tires and wheels will fit. It must be fun on speed bumps.

Ben Hunting campaigns his Miata. He says performance mods return 30 cents on the dollar. (courtesy Benjamin Hunting)

My friend Ben Hunting, who writes for eBay’s car blog and a bunch of other sites, has a long history of modding cars, including a Miata that perished in a flood and his latest Datsun Z car. But, perhaps surprisingly, he agrees with me about all this:

I don't think I can provide a rebuttal, as I completely agree with your point—modifying any car from stock will lower its value in the future, assuming it's a collectible, because stock examples are typically prized above all others. There are some exceptions for period-correct modifications, or cars with actual racing heritage, but generally, you will get 30 cents on the dollar for every mod you make, and that's if you are very lucky. I made money on my car after the flood because I was able to part it out and sell the parts individually—but if I had sold the car as a whole, I would have lost considerable money.

My Datsun, right now, is seriously modified, and it would require me putting it back to stock to sell it as an original car. As a modified car, it's of interest only to someone who wants to do the same thing I do with it.

Thinking of “chip tuning”? Be careful. According to, “The problem from the factory’s point of view is that changes to the ECU [engine control unit] tuning all have a potentially negative impact on reliability. Leaner fuel maps mean more power, but are far more vulnerable to a bad tank of gas or higher air temperatures. If tuned improperly, it can cause immediate and serious engine damage.”

I wrote in the New York Times in 2004, “Garage operators across the country say they are seeing more cars with burned-out engines, partly because reprogrammed chips sometimes supply too much fuel and allow turbo pressure to exceed recommended limits. And even if the engine seems to be running better, it could be running dirtier and might not pass some states' emissions tests.”

One Porsche owner who installed a chip kit himself and gained 40 horsepower “had a big smile on his face” for a week, then turned it upside down after the engine blew up.

All I’m saying is this—a few judicious and discreet mods aren’t a bad thing, but don’t go nuts. If you do, you’ll regret it later.

In this video, our young Miata owner has just mounted some 17-inch wheels—but complications ensue. It’s an illustration of the adage that one upgrade leads to another—and a reminder that the factory knew what it was doing:

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One