yeah i know this is a newbie post but whatever...

i have a stock honda accord 2002SE obviously you can tell by my name...

anyways i was wondering how can i get a slight boost in my HP. my friend says to let him install a custom cold air intake. then my other friend says get a new exhaust. so im really confused up to this point on who to go with. any help would be nice :D

 

Actually, both of them are right...If you go to howstuffworks.com and read up about how car engines work, it will tell you that you want as little resistance as possible in both the intake and exhaust. The engine has to breathe out just as easily as it breathes in, otherwise the intake or exhaust mods won't be as effective. Contrary to what people say, a car will run its best with zero backpressure in the exhaust...The less resistance air has as it flows through that whole system, the better your car will run. Howstuffworks.com says that backpressure in the exhaust system makes it harder for the engine to breathe out, and that resistance robs the engine of power. Also, you might want to invest in heat shields for the intake, so that the intake temperature is cooler. Cooler air expands more when it combusts, so the cooler you can get the intake air temperature, the more power you will get. I doubt California will allow you to take off the catalytic converter, so to gain more horsepower while staying street legal, invest in a MagnaFlo High-Performance Catalytic Converter. Every car engine is a 4-stroke engine...The first stroke is the "intake stroke", where air is sucked into the cylinders (down), the second stroke is the compression stroke (up), the third stroke is the "combustion" stroke (down), and the fourth stroke is the exhaust stroke (up), so no, intake vacuum is not affected by backpressure in the exhaust. DO NOT let anyone try to convince you of that, because the physics of a four-stroke show that its not true. The amount of air an engine sucks in is proportionate to the size of the cylinder during the "intake stroke". The exhaust stroke forces the burned air/fuel mix out the exhaust, and note I said FORCES. This means that any backpressure will slow down the airflow out the exhaust and make the engine work harder to get the air out. This robs the engine of power and fuel.

With a combination of the intake and exhaust mods and the intake heat shields, I am going to estimate that you will get at most a 10 to 15 horsepower gain and a gain of about 4 miles per gallon with the mods, if you find mods that will provide unrestricted airflow through the engine.

As a general rule of thumb, it is safe to assume the airflow through the engine is around 100 cubic feet of air per minute for each cylinder. You want an intake and exhaust that can flow more air than the engine itself can pump. This will provide unrestricted airflow through the engine, which will free up all that hidden power. Keep in mind that an automobile engine is a giant air pump, and the small spurt of gasoline or diesel is there to keep the engine running. The fuel that the system injects into the engine is fixed...To a point. It is usually around 9.5 parts air to 1 part fuel all the time, so the more air you can get traveling through the engine, the better your fuel mileage will be. However, the engine will try to compensate for massive amounts of air coming into the engine, and the point at which it does so is the upper limit for your fuel economy. The speed range in most cars where you would get the best gas mileage is around 40 to 50 miles per hour. In some newer cars, its between 50 and 60 miles per hour, but as a rule of thumb, the engine is at peak fuel efficiency between 2,000 and 2,500 rotations per minute.

One way to save gas is to stick the car in Neutral when you are coasting to a stop, and remain in neutral as long as you are stopped, only shifting back into gear when you want to get moving again. Doing this reduces the load on the engine, and since the engine does not have to work as hard, it burns less fuel.

Do NOT go with one of those "fart-can" mufflers. Go with a REAL exhaust, like a DynoMax exhaust, and make sure you get the whole exhaust kit, not just a high-flow muffler. Make sure the exhaust can flow more air than the engine can pump, and do the same with the intake.


Modified by otacon122 at 4:01 AM 10/18/2007

 

boosting it will get you an increase of horsepower

 

wow thanks otocon, that really helped :D

 

Nice write up.

I thought most engine management systems tend to run an engine at a ratio of 14.7 parts air to 1 part fuel? Wouldn't 9.5 parts Air to 1 part Fuel be a rich AFR?

 

Ghost, I have heard conflicting reports on that...Some people say 9.5:1 is stoichiometric, while some say 14.7:1 is stoichiometric. The ones who say 9.5:1 is stoichiometric say that 14.7:1 mix is so lean the car won't run, and those who say 14.7:1 is stoichiometric say 9.5:1 is so rich the fuel won't combust...It'll burn, but not explode. So its hard to know what's the truth and what isn't...All I can say is that the AFR is fixed, so that when the car is at idle, the mixture is rich, and as you accelerate, the mixture becomes leaner, and when the acceleration gets to the point where more air is coming into the engine than what is required for stoichiometric mix, the ECU compensates by telling the injectors to inject more fuel into the cylinders...Usually, this occurs around 2,500rpms, which equates to roughly 45 to 55 miles per hour. If you want maximum fuel economy, do not let the RPMs climb much higher than that, as doing so would cause the engine to compensate for a too-lean AFR by using more gas. This is why "racing" the car is not good for gas mileage. A lean mix is good for gas mileage, while a rich mix is good for more power. This is why most cars get better gas mileage at highway speeds than in the city, and its also how racecar drivers get more power out of their cars...If you don't care about sending more than $100 a month to the terrorists in Iraq for more oil, then you can enrich the AFR on your car a little to get more power at the expense of gas mileage, but if you want to save gas and don't mind the car being slow to accelerate, lean the mix a little. The ECU determines the AFR by the throttle position, which means that if you run WOT, the engine anticipates the massive amount of incoming air and compensates by shooting more fuel into the engine, and that is bad...bad, bad, bad.


Modified by otacon122 at 3:50 PM 10/18/2007

 

why not get a custom exhaust, in CA you may want to go that route but if your wanting to get the same results outta short ram or CAI mod, then go to your muffler shop and throw on a custom exhuast. Why spend $200- $300 more on exhaust with magnaflow writen on it for on a cai or ram intake setup?