Can anyone tell me why the intake manifold has runners that go all the way to the top of the motor? I don't get it. I figure the shorter the distance travelled, the more power there is. So i'm seriously stumped here.

 

my understanding is that (generally) longer runners cost you some high end HP, but make for better low end torque

 

ahh, ic, thanks.

I still think it looks weird since no other honda's had one like it up til now.

 

it's all about harmonics...
longer runners will move the tq peak lower in the rpm range...with the sacrifice of your power falling off quicker. too long and the cars sluggish

shorter runners raise this tq peak to later in the rpm range...and make for more top end. too short, and you the cars sluggish.

manifolds like the edlebrock b-series manifold have VERY short runners...and are really only good on boosted applications...but SOME n/a engines can use it and make power (example...my old 2.1L RLZ built ITR)

the stock mani does have long runners...and don't be suprised to see manifold eventually come out with somewhat shorter runners.....

 

The ENGINE in a Fit has long runners that go over the HOT ENGINE because it's built for mileage not performance. That's also why it runs at 210 degrees Hot engine = less emissions and more fuel economy.

 

but going over the motor heats it up too. I don't think the runners are long so as to escape heat...having the runners go over the motor is reexposing it to the warm element. Having shorter runners (think K20's intake manifold) would be better at escaping heat since it doesn't unneccesarily curve the route the air takes over the heat of the engine.

 

"but going over the motor heats it up too"


?? That's the point I make they purposefully go over the engine to heat them up. The Honda engineers WANT the intake charge as Hot as it is.

 

so you're saying that they're using warm air to limit the engine's output so as to increase economy? Isn't that the same as not using the full capacity of the engine's displacement? Since you're not using cooler air, which is more dense and allows for better combustion efficiency, and instead using warmer air, isn't it the same as using a smaller engine with cooler air?

i'm sorry, but i'm still confused

 

Cold air doesn't burn as efficiently and doesn't atomize the fuel as well as warm air. Intake charges as hot as they can be just before pre-ignition temperatures are the most efficient for fuel mileage and emission control.

Cooler intake charges make more power at the expense of fuel economy and emissions and Honda went with the hot air to achieve higher fuel mileage (after all that's one of the major selling points for the Fit) and to meet strict USA emissions requirements.

 

ohhh that makes more sense. Thanks!