why did subaru.....

$$$

Better flow, better heat charachteristics...

I'm sure it was a combination of the 2

More the first reason than the second I am sure...

Not easy to sell a 32K legacy these days!!!! Each and every penny counts!!!

Flavio Zanetti

Boston, MA

not to mention that it is probably easier to produce, saving time, as well as money.

Lighter weight can't hurt much on an engine forward of the front wheels, either.

SOLID metal vs. plastic? which do you think is much lighter?

ya i know, but its not that much heavier that it would make a difference in cars acceleration, top speed, or handling. And wouldn't it be cooler when the engine is running?

ya i know, but its not that much heavier that it would make a difference in cars acceleration, top speed, or handling. And wouldn't it be cooler when the engine is running?

Depending on ambient air temperature and the speed at which the vehicle is traveling (and the airflow produced as a result of the speed) it can possibly be cooler, but the average daily driver is driven in stop-and-go traffic which negates this point.

The handling is affected by ANY weight in front of the axle. it may not be blatantly noticeable, but it makes a difference.

SOLID metal vs. plastic? which do you think is much lighter?

But they're not solid, they're quite hollow.

Me thinks it was done for weight reduction, MPG improvements, power improvements, and cost reduction.

Plastic intake manifolds aren't a bad thing. If a piece is made correctly, it can hold significant amounts of pressure.

The biggest reason is cost. Cost to manufacture a plastic part is significantly less than making an aluminum part.

One other advantage to molding a plastic part vs. using a cast aluminum part is you get a smooth interior surface without post processing. Rough surfaces from the casting increases the boundary layer which results in less airflow.

One other advantage to molding a plastic part vs. using a cast aluminum part is you get a smooth interior surface without post processing. Rough surfaces from the casting increases the boundary layer which results in less airflow.

How long until someone starts selling intake manifolds that are dimpled on the inside, like golfballs are on the outside?

(I don't even know if the airspeeds are comparable...)

http://www.infomine.com/investment/historicalcharts/showcharts.asp?c=Aluminum

http://www.corporate.basf.com/en/sustainability/oekoeffizienz/service/presse/000419.htm?id=V00-.fC.oARrjbcp4Cy

a couple of reasons. basically aluminum has tripled in price and plastics have become very good for engines efficiency.

so there is no point of swapping an sti manifold into a legacy?

if running stock boost, no

if manipulating boost or installing a larger turbo such as on the sti, then ultimately, aluminum is stronger than plastic and is better equipped to handle the increased pressure of higher boost levels

the advantage of swapping to the STI manifold is throttle body location.

Throttle body location dictates which intercooler and turbo can be used.

In order to use the STI intercooler and Turbo, you have to change to the STI manifold, to make the connection to the throttle body.

However, some STIs with FMICs are switching to Legacy-style plastic manifolds, because they can be rotated 180 degrees, and the throttle body doesn't take the same space as the alternator, but rather comes out on the passenger's side, near the stock airbox location, where the IC piping can easily meet it.

I highly doubt that a well made thermoplastic intake manifold is the weak link when upping boost pressure. You'd blow headgaskets and pistons under the resulting compression, first. Aluminum might be ultimately stronger, but at the pressures (less than 40psi) that turbos generate, plastic isn't going to fail, if designed and manufactured correctly. Plastic is used for liquid pipework at higher pressures than that.

Plastic manifolds designed to suit are very likely thinner and lighter than cast aluminum to suit the same usage specifications, including pressure.