The Intake plenum is PLASTIC!??

So, I popped the engine cover off my Legacy last night and noticed the intake plenum was plastic?! WTF??? How long has Subaru been using a plastic intake on their motors? Is there a metal version on the STi car that you can swap it out with? I really don't think that plastic is a good idea, but are all the 2.5 motors this way? Is the STi intake just a red plastic version or is it actually metal, like cast aluminum or something?

 

Also, has anyone actually swapped to the STi version of the intake plenum on their Legacy GT/spec-B? If so, is the STi have a bigger bore and worth the upgrade?

There is nothing wrong with a plastic intake manifold.

 

People have done the STi swap, although mostly to allow a larger selection of turbos, not because it is metal.

omgwtfbbq!!!!!!!1111one

 

our intike manifold is more efficiant than the aluminum ones, insulates from the heat better, and is smoother on the inside, and is cheaper to make. Plastics seems like a good idea to me.

 

the STI one is aluminum.

Ok, wow. This IS my first subie, and it was just something odd to me. I was just not expecting it to be plastic. Thanks for the info, appreciate it.

The Corvette is going to blow up too

It's been tested up to 30psi..........

The detergent in automatic car washes will melt the plastic, make sure to plug the scoop when you drive through.

Well, I ONLY hand wash my car, so I don't have much to worry about there, but thanks for the info. That is a nice nugget to have.

 

30psi!!! Wow, that is way better than my friend and I thought. Nice.

Well, I ONLY hand wash my car, so I don't have much to worry about there, but thanks for the info. That is a nice nugget to have.

 

30psi!!! Wow, that is way better than my friend and I thought. Nice.

C'mon PhilT go easy on the newbie! He's obviously impressionable. :lol:

The detergent in automatic car washes will melt the plastic, make sure to plug the scoop when you drive through.

 

WTH?! I only know that it will melt the intercooler because of the soap water!

The 2nd Gen OB's had a cast intake manifold on the H6 - it was butyful!

http://www.familycar.com/RoadTests/SubaruOutback/Images/Engine-med.jpg

 

Starting in 2005 they went to a nylon intake manifold, like most of the industry. It weighs something like 6 lbs less, likely resonates less, gives the designer more design flexibility, and likely costs 1/6th to 1/3rd as much. DuPont is the primary manufacturer of the material and has many case studies.

 

If they're good enough for Porsche, Jaguar, Audi, Toyota, Chevrolet [Corvette V8], Rover, Nissan, etc, it's a safe bet for Subaru. It's also being used for rocker covers.

Cadillac has been using plastic intakes on the Northstar V8 for almost 10 years now. This isn't anything new.

But it is plastic, not metal. Plus it isn't red. It has to suck...

:lol:

The Corvette is going to blow up too

 

mine is still going strong. bosco

mine is still going strong. bosco

 

Of course, It will last forever if you drive it like a grandma

Of course, It will last forever if you drive it like a grandma

 

"grandpa" and yes your probably right. bosco

Cadillac has been using plastic intakes on the Northstar V8 for almost 10 years now. This isn't anything new.

 

So, that must be part of the reason Caddies don't hold their value... too many plastic parts....

 

J/K around. I really don't care if it is plastic or cast whatever, it was just something I noticed and I was just surprised by it. I'm over it, now lets move on...

Oct 1, 2006

General Motors had this great idea to make their intake manifolds out of plastic to save weight and thus save fuel. But was it such a good idea?

 

I guess I should start off by saying I was never a fan of General Motors or the vehicles they build. After 40 years of fixing them, talking to factory reps and engineers I am more than familiar with their quality, or lack thereof. It's a well-known fact that General Motors is the worlds leader in motor vehicle recalls. 2005 was a record year for GM recalls with a recall on almost every make and model it builds for at least one problem and as many as 9 different problems on some vehicles. In the last four months there were 21 mandatory and voluntarily recalls on GM vehicles.

 

When GM was asked to comment on this they were rather proud in saying that they had greatly improved their vehicle inspection procedures. All this means is they aren’t making better cars, just getting better at finding defects that previously went undetected.

 

Now the problem is the intake manifolds and gaskets. They started making their intake manifolds out of a plastic material in order to save engine weight and thus save precious fuel. The problem is that the plastic cannot withstand the heat in that part of the engine and as a consequence the material fails, often with catastrophic results. For example, the owner of a 1998 Pontiac Bonneville where "the manifold shattered and caused an engine fire. Our mechanic showed us the melted gas line and told us he was seconds from the gas tank blowing up."

 

I personally have seen 14 broken plastic intake manifolds in the last year. That's aside from the number of intake manifold gaskets replaced. These are not high mileage vehicles either. I have seen intake manifolds and gaskets go bad with as little as 31,000 miles on the vehicle.

 

GM recognizes this is a problem but they are doing noting to help the people who own these vehicles. On May 26, 2004 GM released a Technical Bulletin (TSB) 04-06-01-017 regarding “New Upper Intake Manifold and Gasket Kits”. In it, it says, “In addition some of the gaskets have been updated to a more robust design”. Only “some of the gaskets”, why not “all”?

 

Then on January 18, 2006 GM issued another TSB concerning this problem. In it, it says,

 

Condition:

Some owners may comment on excessive engine coolant consumption, or an engine coolant leak near or under the throttle body area of the upper intake manifold.

 

Cause:

Upper intake manifold composite material may degrade around the EGR stove pipe and could result in an internal or external coolant leak.

 

Then it goes on to detail the repair procedure.

 

Now a TSB is not a recall in any way, nor is it a free repair for the owners. A TBS is for known problems and the procedures to repair that problem.

 

The cost of intake manifold and gasket related repairs can range from $800.00 of a simple intake manifold gasket replacement all the way to, over. $3,500.00 for a complete engine replacement.

 

General Motors is not inclined to recall these vehicles or even help their customers with the cost of repairs simply because of the vast scope of the problem. It involves millions of V-6 engines from 1995 to the present. The cost to GM to fix this problem would run into the billions. Something financially strapped General Motors simply cannot afford. A class action lawsuit has been filed against General Motors on behalf of GM vehicle owners to recover the cost of repairs to their vehicles.

 

This lawsuit is ongoing but since I have been hired as an expert I will not be able to report an any details.

A class action lawsuit has been filed against General Motors to make some attorney(s) rich, and toss enough money to vehicle owners to buy a cup of coffee.

 

Fixed.

To date, I don't think any Legacy GT owners have had their plastic manifold fail... that being said, I wonder why the STi has a cast one?

 

Snob value

To date, I don't think any Legacy GT owners have had their plastic manifold fail... that being said, I wonder why the STi has a cast one?

It couldn't be because they simply took the one on the WRX which was basically the same design and slightly modified it, and then painted it...

 

The current LGT manifold is quite different from the old WRX and STi one. Why would they modify the STi engine to allow usage of the LGT manifold?

You ever see the picture of the guy with a newer civic ex with n2o, he had a little "burp" and his intake manifold was in a million peices. Wish I could find a link, great pic.