EJ inlet manifolds - 'plastic' or alloy ???

steptoe · Post by **steptoe** » Wed Jul 30, 2008 11:20 pm

I was looking under the bonnet of a 98 Forester EJ20 and noted plastic inlet manifold

what is the go on these, on some models and not others?

bobbyjimmy · Post by **bobbyjimmy** » Thu Jul 31, 2008 8:17 am

98? Should be alloy, unless someone put the plastic one on.
Plastic on the Liberty's & Outback's since MY04, and everything else followed after that.
Might of been on the MY00 - MY03 H6's too, can't remember now.

Saves weight, cheaper etc etc.

AndrewT · Post by **AndrewT** » Thu Jul 31, 2008 8:42 am

Yes, they are plastic on some models and alloy on others

Another crazy thing from Subaru I'd say, perhaps weight saving, perhaps cheaper to manufacture, lets just hope they don't start making everything out of plastic or we will all be driving Hyundai's!

(does that meet the approval of whatever Nazi deleted my previous post?)

daveosubi · Post by **daveosubi** » Thu Jul 31, 2008 10:51 am

Plastic intake manifolds are also quieter and cooler than metal ones, I remember reading about them when bmw or merc started using them in the 90's.

FROG · Post by **FROG** » Thu Jul 31, 2008 10:54 am

yep keeps air cooler which is what we want hey

AndrewT · Post by **AndrewT** » Thu Jul 31, 2008 11:36 am

That's interesting, I guess they wouldn't hold as much heat as an alloy one. I've never thought about how the inlet manifold itself could be changed to drop air temperatures. Maybe in the future we will see manifolds with large, dense heatsink fins incorporated into the design to increase surface area and dissipate heat. I'm guessing the plastic manifolds probably haven't come out in turbo models as they may not cope with boost.
I've been looking into the newer 6cyl EZ30R motors at little (dreaming more like) and they have a plastic manifold.

Jeff · Post by **Jeff** » Thu Jul 31, 2008 12:27 pm

newer liberty GT has plastic intake manifold

twilightprotege · Post by **twilightprotege** » Thu Jul 31, 2008 12:45 pm

i think the main reason for the change is cost. heaps cheaper to do it in plastic compared to alloy

YouTube · Post by **El_Freddo** » Thu Jul 31, 2008 2:59 pm

Being plastic one would expect a smoother surface than the alloy cast would have = better air flow with less turbulance.

I also wonder how these age - similar to the plastic end tanks on the radiator or better with newer plastic types used???

Bennie

Point · Post by **Point** » Thu Jul 31, 2008 5:23 pm

I remember years ago one of the car magazines did an article on putting a spacer in between the manifold and the cylinder head to insulate it from heat transfer. You can usually find them in between the carb and manifold too.

El_Freddo wrote:Being plastic one would expect a smoother surface than the alloy cast would have = better air flow with less turbulance.

actually it is recommended that you don't polish the ports as a slightly rough surface traps a film of air against it, which allows the air flowing into the engine to slide past it. A bit like the surface of a fighter jet...it's like sandpaper.

AlpineRaven · Post by **AlpineRaven** » Thu Jul 31, 2008 8:47 pm

Better flow....
Problem is due chemicals, exposure & heat and will become brittle and crack... so thats downside about plastic.
Cheers
AP

dfoyl · Post by **dfoyl** » Thu Jul 31, 2008 9:53 pm

Plastic intakes have been around for years...early 90s Dodge RAM's used them on the Chrysler small block V8 (LA, not G3 Hemi). I know of plenty with hundreds of thousands of km's on them with no issues of becoming brittle. There is also the advantage that the engine warms up much quicker than aluminium, so cold-weather idle time is reduced (better fuel economy / lower emissions).

Most carb spacers are made of phenonic, which is a hard light material that is also very easy to machine (we use it at work for making drill bit samples rather than use high-speed steel blanks). They are more often used to improve the flow of air between the carb and intake by increasing the length and thereby reducing the angle.

Dean.

steptoe · Post by **steptoe** » Thu Jul 31, 2008 10:43 pm

oops ! I shoulda said i know they exist in the auto world- just did not know subaru also had them and was wondering if there was a pattern to their appearance much like the four bolt to eight bolt change in EJ engine to gearbox happened at a particular model change

bobbyjimmy · Post by **bobbyjimmy** » Mon Aug 04, 2008 9:33 am

dfoyl wrote: Most carb spacers are made of phenonic, which is a hard light material that is also very easy to machine

http://www.grimmspeed.com/catalog/index ... ceck8qka51

I've got a set on my EJ25 with alloy manifold.

After driving for 30mins +, the manifold, as you can imagine, is pretty hot, can't touch it with a bare hand.
With the spacers, its actually cool to touch even after driving 3 hrs +.

NOTE - if anyone gets these, you'll need gaskets (I got 4, top and bottom of spacer) and then you'll also need longer bolts (the one's that are supplies are about 8 - 10mm to short as he doesn't take the gaskets into account.