No such thing as too much horsepower. At any rate the easiest thing to do would be to trade it in on some econobox. Your daughter will probably loathe you for it and you’ll end up in third rate nursing home.
Why can?t I drive a vehicle with a 70 mph top speed? I shouldn?t need to worry about accelerating a Hummer onto the freeway slowly.
(see next post)
You can probably get the ECU reprogramed to have the max speed limited to whatever you want. However then it becomes a saftey/liability issue. Why did you get your daughter a V8 Mustang if you were concerned about her having too much power in the first place? Also the H2 and V8 H3 Hummers have plenty of power, the H2 sports a near 400 HP V8 and the H3 Alpha has about 300 HP, no need to worry about slow acceleration there.
Is it a V6? Then it has about 210 hp. Either way, there’s no good way to modify it to reduce power without creating the risk that the ‘fix’ will mess up something, or prove to be a problem in an emergency situation. That leaves surveillance, as mentioned, education (driving schools that teach how to handle a powerful car), or trading in (but don’t downsize, injuries are higher in smaller cars - something like a 4-cyl Altima or a small SUV like a Forester would be good). I’m going through the same issues with my male teenager (even worse!).
Are there not some cars that operate at a lower power level by design? What I mean is a “valet” power mode where engine power is limited. Curious,how is this reduced power mode made possible(software mod?)Special “valet” ignition key?
The Subaru Legacy GT Spec B comes with “SI Drive”. This feature utilizes a rotary knob on the center console and (alternatively) steering wheel-mounted controls to select engine power output levels (and also transmission shift points on the automatic model). The engine power is reduced by selecting “Intelligent” mode, and this is accomplished by reducing turbo pressure and also by altering ignition timing, I believe.
I can tell you from having taken one on a test drive that the “Intelligent” setting effectively masks the fact that there is a 243 hp turbo-charged engine under the hood. When I selected “Sport”, the incredible power of that engine was very evident. As I was on fairly congested streets at the time, I decided not to select “Sport Sharp”, as that is apparently the full power boost setting, and the “Sport” setting delivered more than enough power for the circumstances. However, if I can manage to drive one on the highway, it would be really nice to try that “Sport Sharp” setting.
You might be able to get some custom program to put the car in a top-speed limiting mode. I know how to do it on most VWs fairly easily- the relevant field is usually changed to eliminate the top speed limiter, but it can also accept negative values- theoretically I can limit a VW to 45mph if I wanted to.
That said, you should not have gotten your kid a car capable of 300hp if you were concerned about how it would be driven. Hell, the first car I regularly used was an '83 Renault Alliance. 63hp, and I still managed to almost kill myself a few times. The problem with too much HP is how little margin for error it leaves- and yes, teenagers are error prone due to recklessness and inexperience.
Drop the ridiculous modification ideas- playing with injectors and whatnot. You’re going to wreck the car’s durability once you start monkeying with the fuel delivery system.
Are Americans going to send all the gas guzzlers to the crusher in favor of hybrids? Since the physics of energy dictates that more power requires more energy we can?t have a savings in MPG without a drop in HP. This seems like an opportunity for aftermarket bolt-ons to make otherwise nice cars usable with $4.00+ gas.
A circa 1983 Ford 5.8L V8 (2bbl) produced about 156 HP . A cira 2004 Honda 2.0L I4 produces about 240 HP. Quick call Stephen Hawking, Honda broke the laws of physics!!
Excuse me, I mean in the same car. For instance adding a blower to increase horsepower would burn more gas.
Not necessarily, look up the mileage ratings for some different cars. For example for the Dodge Dakota 4WD. The 4.7L V8 gets better mileage than the 3.7L V6. The Volvo S60 with the 2.4L turbo gets worse mileage than the 2.5L turbo model, and the Turbo’d Pontiac Solstice gets better mileage than the non-turbo model. Lots of people seem to be violating the laws of physics lately 
I think limiting the RPM would improve gas mileage more than limiting top speed. That is my question. How to get more MPG from EFI?
Physics says nothing about a larger engine (more potential power output) requiring more energy. In fact, the energy required to operate a vehicle in the steady-state environment is determined by the power required to overcome rolling and aero resistance. If a 4000# vehicle requires 30 whp to cruise at 60 mph, it will require 30 whp regardless of the size of the engine providing the power!
Now, a quirk of the internal-combustion engine is that they “typically” get better power-specific fuel consumption as they approach max continuous power output. Thus, a 80 hp engine will “usually” produce said 30 hp more efficiently than a 500hp engine would. (This is how hybrids get good mileage: they use and engine optimally sized for steady-state ops (but undersized for peak power output) and use an auxillary electric motor to make up the difference.)
That is exactly my question. What if I prefer a car with more mass than a Honda Fit? Most any new car now will go 90-100 mph. What if I don?t need or want that excess. Cars used to need the extra horsepower when transmissions had 3 or 4 gears. Most transmissions now provide plenty of pick up with 5 or 6 speeds.
Nobody is forcing you to use that extra power. Better to have more than you need and not need it than to have less than you need and need it. If you desire a large car with no power try to find a mid-80’s Benz with a diesel.
burnsm,
Been there, done that. Am still here, will do it, again. I have a “real” 21 year-old son and “real” 14 year-old daughter.
I wouldn’t detune that Stang. I would have a heart-to-heart talk with your “theoretical” daughter and imagine yourself ordering a monitor, like CAR CHIP, for one. I believe they are at www.carchip.com. See if they make one for your car. Lay down ground rules and consequenses and demonstrate the monitor. It’s because you care. You trust her, but not peer pressures and teen-age lapses of sound judgement. I explained to my son that he would absorb any increases in premiums caused by violations/accidents. You can explain the monitor is there to help, too. Good luck.
I think that’s what I’m going to do this time around.
P.S. I notice some insurance companies are giving discounts to people volunteering for monitors and some fleets use them.
P.P.S. This idea was also “really” posted by Hellokit on 8/5/08.
Thanks for all the tips guys. But my question was about increasing gas mileage. The statement about my daughters Mustang was just theoretical.
Yes. The Chrysler Hemi has cylinder disable to improve fuel economy…read their ads.
The GM trucks have cylinder disable on the V8s to improve fuel economy.
Getting more fuel economy from EFI would be less difficult than getting more fuel economy from the car overall. For example, if the car has a manual transmission, you can get more MPG by lowering your shift points. Try shifting at a lower RPM than you normally do. If the car is an automatic, being gentle with the throttle will let the transmission shift at lower points automatically.
There are sooooooo many things you can do for better fuel economy. Unfortunately, the most effective steps you can take are related to driver behavior, not re-engineering your engine.