Can a PROM chip help boost horsepower in my slightly gutless Explorer?

Dear Car Talk

Dear Car Talk | Oct 01, 1998

Dear Tom and Ray:

I am the proud owner of a 1997 Ford Expedition. Although I know you guys think
it's too big and a gas guzzler, I like it. The only problem is that I wish I had
gotten the 5.4 liter engine instead of the 4.6. The horses don't seem to be
enough sometimes, especially when passing on two-lane roads. I have heard of
some sort of chip you can buy that can increase horsepower in certain engines.
Do you recommend these? --Ray

TOM: No, we don't. You're talking about a PROM chip that tells the on-board
computer the specifications of the engine. And there are some advertisements in
the backs of car-geek magazines that offer replacement chips that effectively
"fool" the computer into thinking the specifications are different.

RAY: And there are two problems with these replacement PROMs. First, they'll
take your gas mileage down to single digits. If you thought 12 miles per gallon
was bad, wait 'til you try four!

TOM: The other problem is that you'll be beating the heck out of your engine. If
an engine is designed by the manufacturer to produce 215 horsepower, and by
altering the advance curve and the fuel/air ratio, you get it to produce 25 more
horsepower, you're beating on it! And you'd better believe the engine will break
down sooner and won't last as long. Plus you'll void your warranty. And
rightfully so.

RAY: So rather than screw around with the computer, Ray, why don't you just go
right to the heart of the problem: The power to weight ratio. This truck weighs
about 5,000 pounds, giving it about one horsepower for every 23 pounds or so of
heft. So rather than increase the horsepower, why not consider reducing the
truck's weight? Maybe you can just drill a bunch of holes in it.

TOM: Or better yet, take a "Sawzall" and cut off the last two feet of the truck
-- everything behind the rear wheels. Then you'll not only have much better
acceleration, but the thing will be easier to park, too!

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