The intake tracts on our subarus are often overlooked. The intake manifold and TGV's are the last destination for the intake flow before it enters into our almighty boxer engines. To keep it simple, we want to keep the air in this section as cool as possible and as smooth as possible(no steps in flow, etc). Now the stock location of the Subaru intake manifolds is not that great...it sits on top of the engine so all of the heat from the super heated engine naturally flows up into the intake manifold(which we want to keep cool!!). obviously this isnt great. Your options as to moving the intake manifold are next to zero so we need to work the stock location intake manifold in order to gain back some of this lost power due to heat. On to flow. In terms of intake flow you want the smoothest transition from pipe to pipe as you can possible get. When Subaru made our cars this was not a concern to them so there is some room to work there. Also, Subaru gave us these nice Tumble Generator Valves(TGVs) that are used on start up for emission purposes. TGVs are not needed. Some people have said they have rough cold start up idle for a few seconds but i sure havent had any issues here with the Minnesota winter. How to fix this mess you ask? Resolving the heat issue. The aluminum intake manifold sits directly on top of the aluminum super heated engine, obviously this isnt ideal. We will start out by putting a GrimmSpeed Thermal Spacer between the Intake Manifold/TGVs and the piping hot engine. These work amazing for blocking the transer of heat...they block like 300 Spartans!! Next we will deal with the issue of the radient engine heat rising up into the intake manifold. Here comes our second blocker, Therma Barrier Coating. Putting Thermal Barrier on your Intake Manifold will block the radient heat that rises off the engine into the bottom of the intake manifold thus reducing the temperatures of the air flowing through the manifold thus creating a horsepower gain. The saying is for every 10 degree drop in temperature there is a 1% increase in power. The Throttle Body is another little area where the stock setup isnt the most logical for power output...Subaru decided to run an engine coolant line through the throttle body. Warning: you will want to keep this if you are in -50 degree outdoor temperatures regularly. For those of you who are not, we want to get that very hot engine coolant from running through our throttle body(which we want to keep cool). There is a very simple mod for this, take of the inlet coolant hose and outlet coolant hose and join them together with a metal connector. What this does is simple bypasses the throttle body thuse keeping that 200+ degree coolant out of it keeping it cooler. There are also a few companies that sell throttle body spacers that will make the intake manfild plenum bigger which have shown to make gains, i believe Group A makes a nice one. On my project car in addition to the heat coating on the intake manifold i am also going to strap a thermal blanket on the bottom of the intake manifold to block even more of the radient engine heat from entering the manifold. my guess is that this will work very effectively. Resolving the flow issue. Tumble Generator Valves(TGVs) are a great starting point to quicken the intake velocity. By completely gutting out the TGV which takes out the bar, divider plate, and butterfly plate, this completely takes out all the restrictions to flow which existed in the stock form. Like stated earlier these are only used for a very short time on startup and are not needed. Many dynos have shown a 10hp gain with this mod alone. Next we will want to smooth out any steps there may be in flow from connection pipes/couplers/etc. We will start with the Throttle body. Here we can knife edge the inlet lip to create a much smoother transition from the TB hose to the actual TB thus creating less turbulence. Transition #2 we will want to get rid of the step between the intake manifold and the TGVs. This can be done by porting out the outlets of the intake manifld runners and the inlets of the TGV's to be matching diameters. At this point we have have both connections(TB Hose> TB and IM>TGV) matched up perfectly for the smoothest flow possible. Not to bad for working with the stock pieces eh? Justin Grimm www.grimmspeed.com AIM: GrimmSpd
Those tips do sound simple to DIY, but how about those of us who aren't soo handly, who can help make these modifications for us and will we need to get our car's tuned?
grimmspeed can do most of these things for you. outlined here: as for tuning, you will definitely need a way to shut off the TGV CELs because you will no longer have the TGV sensor/motor hooked up. Its a very easy CEL to turn off, know of a few local guys that can do it.
And will the TB coolant bypass effect my idle when cold starting, cuz I know it did back in my Honda days. I'll have to give it a shot.
Mine is removed, and I idle just fine. And I was under the impression that the coolant through the TB was an emissions device. I could be completely wrong on this one, but it pre-heats incoming air to keep emissions down.
Justin, We'll need to talk this afternoon. More and more I'm looking at doing some of these 'simple' mods on the Legacy (even with the crappy stock intake manifold) to see what kind of fun I can have. Of course, I many just be being silly and trying to polish the turd.
That wouldn't work too well when the engine's off. Does that butterfly get opened at all when you're starting the car?
yeah good point. maybe it is just an emissions thing only then. i'd have to go do more research to find out the exact answer.
On a related note, over on Naisoc on the e-85 thread: http://forums.nasioc.com/forums/showthread.php?t=803341&pp=25&page=53 There is some discussion on heating some of these parts to aid startup (apparently a problem with e-85 in cold weather). Just thought I'd bring it up, in case someone might be planning on running E-85, and using a couple of these mods.
