nKoan Posted February 7, 2005 Share Posted February 7, 2005 I finally popped the plastic engine cover off my LGT last night, and I noticed that the Intake Manifold is plastic. I did a search, and found a little information, but not really what I was looking for. Also noticed that the throttle body is down on the right rather then sitting right on top of the intake manifold. What are the positives of this design (less engine noise?)? Any negatives? Has anyone done extensive tests? The plastic feels almost sturdy as alumnium (from my extensive rapping on the plastic test ), so I don't think strength is an issue. I'm also curious what the flow is like compared to the FXT or STi manifold. Obviously you'd have to replace the intercooler and intake manifold at the same time, but I was just wondering if anyone knew what gains/trade-offs are to be expected. Link to comment Share on other sites More sharing options...
bemani Posted February 8, 2005 Share Posted February 8, 2005 Its for weight saving. Money for Subaru too maybe. Link to comment Share on other sites More sharing options...
Eric L Posted February 8, 2005 Share Posted February 8, 2005 GM uses plastic intake manifolds on the LSx series of engines... theres nothing wrong with it.. Link to comment Share on other sites More sharing options...
nendo Posted February 8, 2005 Share Posted February 8, 2005 i think i read somewhere that the plastic and design of the manifold is geared more for low and mid range power instead of topend, not sure if that is true or not Link to comment Share on other sites More sharing options...
offthacliff Posted February 8, 2005 Share Posted February 8, 2005 I would love to gain some clarity on this subject myself... I have heared the LGT's TMIC and IntakeManifold, are more effecient than the STI's... Visually I could see some truth to that, but I find it hard to believe Subaru wouldn't change the STI set up if it were so. I am interested in Twin Scroll set ups on the LGT. I would love to know for sure If I should go with a perrin TMIC/stock Intakemanni and adapt the turbo outlet to fit, OR go with the STI intakemani, and get an ESX (STI) TMIC that would bolt up. Hmmmmmm Link to comment Share on other sites More sharing options...
Xenonk Posted February 8, 2005 Share Posted February 8, 2005 plastic = less heat soak, easier to make, less top-weight, no need for welding and the shape is more flexible to manage vs. metal. throttle location = it's ETC, they can put it anywhere since it's drive-by-wire. It doesn't have to be in a place where it use to be a mechanical challenge to make sure the throttle cable wouldn't have a problem with it's routing. Keefe Keefe Link to comment Share on other sites More sharing options...
ChruiSSer Posted February 8, 2005 Share Posted February 8, 2005 Yea Keefe's right. The composite plastic doesn't absorb heat as much as metal. Link to comment Share on other sites More sharing options...
firedawgs Posted February 8, 2005 Share Posted February 8, 2005 Yes, plastic is less heat absorbing and less weight. The downer is that it cracks easier. I had a 95' ford thunderbird. Ford used plastic intakes and were notorious for crack intake manifolds. I have not heard of any problems yet on the legacy yet, but again it is new. Updated my vBGarage: Link to comment Share on other sites More sharing options...
Jaxx Posted February 8, 2005 Share Posted February 8, 2005 i would also point out the high torque numbers that the stage 2 LGTS are making as evidence that the manafold makes better torque too Link to comment Share on other sites More sharing options...
offthacliff Posted February 8, 2005 Share Posted February 8, 2005 Is that credited to the Manifold? Hmmmmm Wait... Ive drivin STI'sand they are way more torqy! Smoother tq band maby... Link to comment Share on other sites More sharing options...
John M Posted February 8, 2005 Share Posted February 8, 2005 The Ford 4.6 intake manifolds cracked because they also ran a coolant line through the plastic section. When they realized this breaks things, they re-designed the intake to use an aluminum section for the water passage and the rest is still plastic. We won't have that issue on these cars. Anyway, I would say it's the design of a manifold that decides tq and hp characteristics, not the material. Being plastic also means the runners are perfectly smooth - no boring or extrude honing required. Link to comment Share on other sites More sharing options...
RobY Posted February 8, 2005 Share Posted February 8, 2005 I beleive M3s also use plastic manifolds... Link to comment Share on other sites More sharing options...
Jedi Pimp Posted February 8, 2005 Share Posted February 8, 2005 Being plastic also means the runners are perfectly smooth - no boring or extrude honing required. WERD!! Link to comment Share on other sites More sharing options...
offthacliff Posted February 8, 2005 Share Posted February 8, 2005 Plastic aside, it seems to be shapped more efficiently... I heared somone say the WRC car has a manifold like ours. Link to comment Share on other sites More sharing options...
Guest *Jedimaster* Posted February 8, 2005 Share Posted February 8, 2005 Plastic intakes have been around long enough that we shouldn't have any problems :crossesfingers: The Ford ones, were, well, from Ford Link to comment Share on other sites More sharing options...
driggity Posted February 8, 2005 Share Posted February 8, 2005 i would also point out the high torque numbers that the stage 2 LGTS are making as evidence that the manafold makes better torque too I don't know that you can draw much from that. Both the Cobb and PDXtuning stage 2 setups make less torque on a Legacy than an STi. Unfortunately the Cobb setups aren't exactly the same as their Legacy stage 2 dyno plots seem to leave the up-pipe cat in place but I doubt that the up-pipe is lowering peak torque by 30 ft/lb at the wheels. The Legacy appears to be making a lot of torque because the peak torque is a good deal higher than the peak HP but I think that this just shows that something (possibly the turbo's hotside) is really restricting flow at high rpms. Link to comment Share on other sites More sharing options...
offthacliff Posted February 8, 2005 Share Posted February 8, 2005 that, to me, would be more likely... I cant wait to see more options like turbo kits for the LGT! Link to comment Share on other sites More sharing options...
Guest JessterCPA Posted February 8, 2005 Share Posted February 8, 2005 BMW has been using them for a few years now, but they call it "composite". Link to comment Share on other sites More sharing options...
Guest *Jedimaster* Posted February 8, 2005 Share Posted February 8, 2005 I don't know that you can draw much from that. Both the Cobb and PDXtuning stage 2 setups make less torque on a Legacy than an STi. Unfortunately the Cobb setups aren't exactly the same as their Legacy stage 2 dyno plots seem to leave the up-pipe cat in place but I doubt that the up-pipe is lowering peak torque by 30 ft/lb at the wheels. The Legacy appears to be making a lot of torque because the peak torque is a good deal higher than the peak HP but I think that this just shows that something (possibly the turbo's hotside) is really restricting flow at high rpms. That's more to do with the size of the turbo. You can get a plastic manifold to flow good because you can make them to very particular standards. Easier to make than traditional metal ones. Link to comment Share on other sites More sharing options...
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