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Discussion Starter · #1 ·
I have been noticing some people say that the Y pipe that comes with the ssautochrome tmic needs to be ported some to equal stock. Would it be beneficial to port and polish the intake manifold as well (have to take it off for injector and aps inlet install.)

thanx

James
 

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id have to say no to the p&p. but defenately to a portmatch. im new to the sti thing, but for most of the other cars ive dealt with if you polish the inside of the intake manifold, that creates alot less turbulance which is actually a bad thing. it will not allow the mixture to mix properly and youll actually lose performance. anyone step in and correct me if im wrong with the sti here. just tryin to help.
 

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Discussion Starter · #3 ·
i would think that less turbulance would be a good thing.
 

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siusti said:
i would think that less turbulance would be a good thing.
thats what everyone would naturally think. there needs to be turbulance for the air and the fuel to mix properly. its like putting something into a blender and taking the cup and just shaking it in a smooth circular motion (no turbulance). it wouldnt mix as good as if you turned the blender on. inside the cup when the blender is on, there is mass confusion lol. everything is going in every wich way, but its mixing alot better. (turbulance) thats the only way i can think of to describe it, if it doesent make sense, then im sorry.
 

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basicly you're saying if there is no turbulance the air and fuel would sort of just sit side by side instead of mixed?
 

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Discussion Starter · #6 ·
I understand that you are saying, but it doesn't make any sense. Atomization of an air to fuel mixture will change some when you introduce more air into the system. However, thats why we tune the cars. More air equals more fuel, which hopefully equals more power.

Well, lets think of this for a second.. The moment you add an intake, inlet tube, bigger turbo.. etc.. You are going to change something dealing with how the air rushes through the intake manifold. What your suggesting is that any change in how air flows through a manifold is bad.
 

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siusti said:
What your suggesting is that any change in how air flows through a manifold is bad.
yes...the manifold. im not talking about the intake, intercooler, turbo inlet, etc. the intake manifold. you do not want to polish that.

edit: i googled it, and the first thing i clicked on had someone who realizes why its bad to polish the manifold. ironically its on an evo so click my link and go down to post #13. http://forums.evolutionm.net/showthread.php?t=169688
 

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johnlude85 said:
thats what everyone would naturally think. there needs to be turbulance for the air and the fuel to mix properly. its like putting something into a blender and taking the cup and just shaking it in a smooth circular motion (no turbulance). it wouldnt mix as good as if you turned the blender on. inside the cup when the blender is on, there is mass confusion lol. everything is going in every wich way, but its mixing alot better. (turbulance) thats the only way i can think of to describe it, if it doesent make sense, then im sorry.
Do you know where the fuel injectors are on an STi? Have you had the intake manifold off and seen where the fuel is injected into?

There is this little port thing, that works like a venturi I think, and speeds the air over the injecter to better atomize the fuel.
 

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I can see where a little turbulance in the manifold might actually help a little in a carburated or TBI application where the fuel comes in pre-manifold but the STi injectors are mounted low on the risers right above the intake ports. Any turbulance would have to occur around the area of the risers and intake ports, plus that turbulance would only help at lower loads. From my understanding, this is the function of the TGVs at idle to improve low end fuel atomization for lower emissions on cold starts - kind of like a choke but for EFI.
 

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Discussion Starter · #10 ·
johnlude85 said:
yes...the manifold. im not talking about the intake, intercooler, turbo inlet, etc. the intake manifold. you do not want to polish that.

edit: i googled it, and the first thing i clicked on had someone who realizes why its bad to polish the manifold. ironically its on an evo so click my link and go down to post #13. http://forums.evolutionm.net/showthread.php?t=169688

Well, obviously an EVO is a completely different car.

Does anyone have any more comments about this procedure?
 

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porting

porting is nearly a black art. n/a motors see no diff to a glass smooth or sl rough as boundry layer air insulates the metal from all but air flow nearing supersonic. yes air intake at full chat is that fast. we dont have evap concerns but we still want no "eddys" in our port flow. turbos do change that some what. for real world, port match then smooth 2-3 inches. if you gotta have top flow extrude hone or pay some one whos been there and does it for a living. ive personally had a intake ported by a *pro* and lost overall power. you dont want hogged out ports it kills port velocity leading to unwanted turbulance. you can have high flow and high velocity its just harder to do.
 

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johnlude85 said:
id have to say no to the p&p. but defenately to a portmatch. im new to the sti thing, but for most of the other cars ive dealt with if you polish the inside of the intake manifold, that creates alot less turbulance which is actually a bad thing. it will not allow the mixture to mix properly and youll actually lose performance. anyone step in and correct me if im wrong with the sti here. just tryin to help.
On the inside of the manifold just behind the throttle body,there are raised up ridges built into it. The ridges don't go down the runners at all its only on the flat spot behind the throttle body. Port matching and polishing the manifold probably wouldn't hurt(probably won't help either unless the heads were ported also).
 

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port match it and you do not have to polish it wont do nothing to help your hp gains just port match and smooth it up and that is all you need but you never polish before the ext. it makes for a place for the fuel to set and yes there is not fuel in the manifold but you dont want to polish it if it dont help but dont matter what Do not polish after the injectors then you are asking for the gas to find a place to sit on the runners.. but if anything port match it and try to do all of the runners the same and if you have a way to flow test them see if you can get them all within .5 to 1 from each other.. there is where you see the power the more you have equal a/f ratio in all runners will be better. and for polishing do it to the ext port match and polish the header to head and so on all the way out. and polish the ext runners in the heads too if you are going to port them and do a TAV job..
 

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Wow. This is like a cat telling a dog how to be a dog. Alot of this misinformation is a carry over from what are termed wet manifolds. A wet manifold is what you will find on a carberated or throttle body injected engine. A wet manifold needs some non laminar flow to help keep the atomized fuel in suspension and prevent puddling. Another difference in a wet manifold is the radius on the intake runners. Since fuel has more weight than air it will tend to fall out of suspension when going around sharp bends due to centrifugal force. If you look at the inside of a manifold for a small block chevy or similar that is meant for a carb or TBI setup it has a rough texture and some actually have a grid shape pattern on the floor of the manifold all to keep the turbulence at proper levels for atomization. These manifolds usually respond poorly to being smoothed out. On the other hand any manifold will respond well to a varying degree to port matching since this prevents localized reversion of the flow. In drag racing circles these manifolds are usually hogged out and smoothed since they are optimized for high RPMs and therefore have sufficient flow to keep the fuel suspended. This is also why they idle high and have poor low end throttle response among other reasons such as cam profiles etc.

What we have is a dry manifold meant to flow only dry air. Since non laminar flow will cause a reduction on overall flow through the manifold these types of manifolds usually respond well to both port matching and smoothing such as an Extrudhone. The exception would be if there is too much material removed and the velocity is reduced. This has the effect of reducing the inertia of the air column and therefore reduces cylinder scavenging and that little extra packing of the cylinder from the charge velocity. Nearly all of the atomization comes from the injector itself and the mixing is accompolished by the turbulence created as the air and fuel travel around the intake valves and into the cylinder.

With all that said my opinion is that port matching the stock manifold is a very good idea but having it smoothed out will not yield much for a street driven car. The heads are more of a bottle neck than the manifold is. A good port match and smoothing out the casting edges is where I'll call it quits as far as the manifold goes. YMMV:D
 

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^ Very nicely put. I also was skeptical about our cars mixing fuel in the intake manifold. I was like "where's the fuel comming from" haha.
 

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If you look down the bore of the TGV's you will notice a sharp angle right above the fuel injector bosses. This is purposely put their to induce turbulence right where the fuel sprays. Turbulence further up the manifold wont do much more than cost you power.
Additionally, I wouldn't do any radical altering of my intake manifold unless I could determine that all of the runners are flowing roughly equal to each other; lest you risk running one cylinder too lean.
 

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I'm curious now because I just ordered the PnP'd intake manifold and throttlebody from Grimmspeed. From what I read on their site all they do is get rid of the step going into the tgv's by matching the manifold to the tgv's. Shouldn't be harmful, right?
 

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It's still the dry portion just prior to the inlet to the TGV housing and up stream of the injectors. No problem in my opinion.
 
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