JL8Jeff

Headers will help pretty much any engine breathe better and make more power, be more efficient and get better gas mileage too. The Toyota V6 trucks with that awful crossover pipe is one of the worst stock exhaust setps ever made so header will definitely help. But you will also need a better cat, muffler and cat-back to really take advantage of the headers. The cold air intake is also needed to complete the package. The cost of the headers and the install is where the real debate is. I can't see paying more than $400 for any headers no matter what vehicle. But I've put headers on almost every vehicle I've had and they all made more power and got better gas mileage. As for the computer adjusting and losing the power gain, that's not true because the computer will adjust to keep the exhaust at the optimum mixture which means it might lean out the fuel at part throttle since the engine is making more power to go a certain speed. WOT is the only point at which you could gain more power by adding more fuel than what the stock computer wants to add. I can't wait to put headers on my 88 4Runner, but I won't have any money or time until my 69 Z28 restoration is finished.

midiwall

Ummm... ????

How is the engine making more power on less fuel ("lean out the fuel at part throttle")?

Tomsriv

Technically it won't make more power on less fuel, but because it can breathe easier it will make more power at a lower rpm so you won't have to give it as much gas.

cootees

It is half-way making sense to me. I think the teminology used could have been avoided. I believe he is trying to say that if you doing 60 mph then you will be on less throttle(which is really not that much less) because with the fipk the ecu is compensating for more fuel to be delivered at a lower RPM than usual.

midiwall

We need Jeff to come back and explain what he meant.


But until then, I can buy that with better breathing (more air, better exhale) then there will be more power at a lower RPM. But...

We need to be clear that the ECU isn't leaning things out because of the airflow. It's richening the mixture because of the airflow, this can be seen with an OBD II reader by watching the ECU adjust the fuel trims.

In closed loop, the ECU will _always_ push the fuel trims for Stoichiometric conditions, which is that magic 14.7:1 Air/Fuel ratio. When you bring in more air, you HAVE to bring in more fuel to hit Stoich. It's just the way the math works.

Now, what will happen is that with more power available at a lower RPM, then you will need less RPM to do the same amount of work. BUT - there's still more fuel than before at that lower RPM. BUT - it may end up being a total of LESS fuel than was previously required at a higher RPM to do the same amount of work... that's how people get better mileage after doing things like adding cold-air intakes or superchargers. This of course will vary WILDLY based on how you use your right foot.


Cootees, I think I know what you meant, but just to be clear... remember that the drivetrain gearing is staying the same, so the engine will still have to be turning at a given RPM to produce a speed of 60mph. It may require less energy (fuel) to get to 60mph because the engine can do more work on a given amount of fuel, but at some point, you're still spinning at 2000rpm to get 60mph (or whatever your gearing calls for).

I just want to be sure that we're not trying to directly equate "less throttle" to lower RPM.

cootees

That's exactly what I was saying. It's a well known fact that with more air being put in the more fuel is being added. This is why I laugh when people think an intake system will get them better gas mileage. It will on the highway, but not in the city.