DEAR CAR TALK: I recently purchased a GMC 3500 with a Duramax diesel engine. Friends with diesel engine trucks are telling me of increased power and gas mileage obtained by adding aftermarket chips or tuners.

My first thought was, that if they are that great, why don’t the manufacturers install them as standard equipment?

My second thought was, you don’t get anything for free, right? So, are you harming the engine in any way by using these chips?

I eagerly await your erudite response. – Bill

RAY: If you want an erudite response, Bill, you’re going to have to wait a lot longer. In the meantime, I’ll give you one of my usual thoughtless responses.

As VW taught us all recently, the only way you can increase power and mileage electronically is by sacrificing emissions. And that’s what many of these “reprogramming devices” do.

So sure, you can get more power out of your engine. But you’ll be giving the rest of us cancer, lung disease and polluted water with your NOx emissions. Not to mention it’s against the law, so you’ll be a criminal, too.

You’re absolutely right, Bill. If the manufacturers could increase power and mileage, without breaking the emissions laws, they would have done it – and advertised it – before they sold you the truck.

You’re right on your second point, too. You absolutely could be harming the engine. These devices can change pretty much every parameter of the engine management’s system, including things like the turbo boost. If you punch up the turbo boost, don’t you think there’s a chance the turbo might not last as long?

And what do you think the increased force of those bigger explosions in the cylinders will do to the life of your engine?

That’s why manufacturers are within their rights to void your warranty if they conclude that you’ve used an unauthorized aftermarket reprogramming device. They don’t even have to catch you in the act. There’s a lot of information stored in your car’s computer these days that they can download and use to sic Robert Mueller on you.

And I think you’d be miffed if you went to your dealer after 10,000 miles with a multi-thousand-dollar engine problem and your claim got denied.

So I’d try to be satisfied with a brand new truck, Bill. That alone gives you more power and better mileage than most of us.

Got a question about cars? Email Car Talk’s Ray Magliozzi by visiting the Car Talk website, www.cartalk.com.