It didn't really do anything- did it?

[fleming442]

So, Saturday night at about 1am, the drunken hotrodder in me came out. I have an 02 OB 2.5 and had heard tell of making cold air intakes out of PVC. Basically, all I did was remove the baffles in the tract between the snorkel on top of the rad. support and the airbox, and replace them with a straighter pipe. Now, I know the baffles are there to trap/drain water and quiet the intake. I'm a gearhead, so a little intake noise actually makes me happy. Also, I doubt that much water will actually get into the airbox, as the snorkel is above the grille opening.

 

The odd thing is; it seems to have more mid-range power (2-3000 rpm) and it improved mileage by a mile or two per gallon. Go figure. Am I suffering from "an oil change/ car wash makes my car run better" syndrome?

[nipper]

The odd thing is; it seems to have more mid-range power (2-3000 rpm) and it improved mileage by a mile or two per gallon. Go figure. Am I suffering from "an oil change/ car wash makes my car run better" syndrome?

 

 

Partially.

 

Replumbing the intake doesnt make more power, but it shifts the HP curve to the right. Since you have more power sooner to get the car up to speed faster, you MIGHT save a few mpg, but the feeling of extra power is real. But keep in mind that you did not add power, you just made it come on sooner, which means that the peak and valley will occure sooner too.

 

The giant sinus cavity under the right front fender is for water seperation. The other dangly bits are for noise levels.

 

Its one of the simplest things that you can fiddle with on the car and its reversable.

 

nipper

[idosubaru]

it can. and i believe it does change the curve, not just shifts it. Kevin did some awesome testing years ago. he's great, does things with a keen eye towards numbers and proof. he dyno's everything.

 

he did it with the XT6, trying 3 or so different intake setups and it did make a difference. you can search for the posts/charts.

 

then he got an SVX and he said the entire SVX crowd was telling him waste of time, so he went and dyno'ed it and it showed some gains.

 

they're not huge on an NA car but it does change things.

 

it makes sense too, here's a hypothetical test: if you blocked off the intake with a piece of plywood, i think that would hurt performance - gas mileage and hp. it might not even run.

 

that proves that intake modifications do make a difference.

 

if you gradually made a pin hole in said plywood....and made it bigger and bigger it would gradually...get to a point where it starts to run, runs better, and improves.

 

math dorks know the curve won't be discontinuous...meaning there will be a relationship between "hole size" and performance. it won't "not run" and then magically jump straight to the stock levels at some random point. rather it will be a curve with continuity. which means intake changes engine performance.

 

my guess is the stock set up is optimized for various things, allowing slight room for improvement depending what you want...throttle response, noise levels, torque, hp, safety, mileage, reliability, acceleration...etc.

Edited January 14, 2009 by grossgary

[mdjdc]

Would eliminating the airbox and going to a cone filter have any gains?

 

you could also get rid of all those air thingys between the air box and the throttlebody if you used a 2.2 intake pipe. Would that help with HP due to smoother flow?

[fleming442]

it makes sense too, here's a hypothetical test: if you blocked off the intake with a piece of plywood, i think that would hurt performance - gas mileage and hp. it might not even run.

 

that proves that intake modifications do make a difference.

 

if you gradually made a pin hole in said plywood....and made it bigger and bigger it would gradually...get to a point where it starts to run, runs better, and improves.

 

math dorks know the curve won't be discontinuous...meaning there will be a relationship between "hole size" and performance. it won't "not run" and then magically jump straight to the stock levels at some random point. rather it will be a curve with continuity. which means intake changes engine performance.

 

my guess is the stock set up is optimized for various things, allowing slight room for improvement depending what you want...throttle response, noise levels, torque, hp, safety, mileage, reliability, acceleration...etc.

 

I get that; it's just that I figured Fuji would have optimized the volume for max efficiency. I think my pipe may actually be smaller in diameter than factory, just straighter and smoother. Venturi effect anyone?