Exhaust analretentitis

[bmxpunk]

So I maybe young or dumb or anal, but tonight after getting my exhaust manifolds off to get them ceramic coated, I went over the top. I spent the last 3.5 hours with a die-grinder, an dremel tool, millions of bits and my manifold. What I accomplished, was grinding out the metal to match the gasket. I made the ports nice and straight and super smooth. Then I ground off most all of the "seams" from the casting. Am I crazy or do I just love wrenching on my car? Has anybody else done this?

[THAWA]

From what I understand, the way it is setup increases low end torque without sacrificing anything else, so doing what you just did, you have lost some torque with no increase in anything. I'll try to find the link.

[tris91ricer]

You had the right idea, kiddo, just poor application. You were thinking something along the lines of a pnp job on heads, right, then applying that principle to your exhaust manifold?
My advice to you is just to get a set of headers. Look for a used set, if price is an issue. I just scored used 2.5RS headers for less than $200, so check around. Those (2.5RS) fit, and I think (think, not sure) that the WRX ones may as well, but a search could yield more specific information..
Sorry it didn't work out the way you wanted!
You don't have a turbo, right? I think what thawa is getting at, is that NAs require a certain amount of backpressure in order to achieve good flow/power ratios.. it's proper exhaust tuning, which is why exhaust can can be pretty spendy, especially for more complicated systems, as well as headers/DPs.

just my .02, correct me if I'm wrong somewhere...

[bmxpunk]

no, I do have a turbo. It is a 93 turbo legacy motor that is going into my impreza. And what I did was just smmoth out the the exhaust flow from the heads. I've read tht headers do nothing for these motors that you actually lose torque with no gains like you said. But being that I just smoothed out the flow coming from the heads and left the rest of the manifold and cross-over pipe alone, it shouldn't hurt anything, right? And i only did it for the first 3/4"-1" deep and it tapers nicely into the original inner diameter. Not to mention that once they are ceramic coated, the exhaust temperature will be higher and move faster going to the turbo, so it should spool quicker resulting in quicker spool and more torque, correct?

I am gettint the entire exhaust ceramic coated, including the turbo along (with port and polish by Deadbolt), including my new Stromung 3" turbo back ( I have everthing but can't decide if I want to go catless-we don't have emissions in Wyoming )

Hope that clears some of it up.

[tris91ricer]

Sweet. Glad you got it planned out, then.

[bmxpunk]

So do you think that will work alright? Though I read about this stuff alot, This is my first time really going through a car like this. Engine, tranny, and brake swap. I am trying to be as thurough as possible. Powdercoated intake manifold, parrallel fuel mod, bigger fuel pump, standalone engine management, etc. I want to make some power and be super reliable. So I am up for suggestions and critism.

[tris91ricer]

To begin with:

Cheap, Fast, Reliable, pick TWO.

I'll let someone else take the helm from here....

[-K-]

Good point, pick two.
Depends on how much power you want, I've never heard about problems with the Legacy RS or WRX and they make a good deal more power stock than we do.

I wouldn't worry about the port work you did. I don't think I would go that far and maybe not even bother with the coating but I don't think it will hurt.

[scottzg]

Those guys are thinking of the "step" the manifold makes relative to the head. Grinding that away to match the ports results in a slight loss of torque. Or so the spdusa website says.

[BAC5.2]

Ported stock manifolds can flow better than aftermarket manifolds.

For our cars, not so much an issue. When you can spin to 8500RPM, that's when it becomes a top end issue.

I doubt you did any harm, and probably made things a little bit more free flowing. No harm, I'd do the same if I wasn't so lazy.

[dzx]

To begin with:

Cheap, Fast, Reliable, pick TWO.

I'll let someone else take the helm from here....

Shouldn't it be something like pick one?

[bmxpunk]

But that step wouldn't matter if it were turbo charged correct? I understand that the NA cars need the back pressure to have torque, but I didn't think the turbo cars did. I was under the impression that the faster the turbo can spool, the better torque you have. Isn't that why with the stock Legacy turbo the RB5 or VF11 or whatever it is, has only 160 hp, but it has peak torque of 190ftlb @ 2800 RPM? So if the exhaust can leave the cylinder smoother and faster, than it can spool the turbo faster: producing torque.

I don't know.

I also honed out the intake manifold Does anyone see problem with this?

I under stand the "Pick two". I am trying not to do this cheaply. I have gone through the motor and done everything short of rebuilding it. Same with the differential, brakes and transmission. The ceramic coating of the exhaust for example, not only has it shown to increase in power for many cars, (wrc cars use it), I am out to protect the $1000 investment in the exhaust system alone.

[dzx]

A lot of places would charge you to polish the intake manifold so that won't be a problem. You just wont see any gains from it since you dont have the top end.

It's pretty hard to go fast for cheap but I can see going fast and being reliable costing money.

[THAWA]

No engine needs backpressure, ever.

The step helps any type of engine apparently. And yes it applies to the head and not the header. Though you may have done something else if the distance/size of the step has anything to do with the torque made with no losses, and I'm almost certain it does.

The reason the turbo engine makes so much torque so low is because of cams, valve size, and turbo size primarily.

[bmxpunk]

Thawa- I don't exactly follow your reply. So are you saying the step important on the exhaust maniflod or is it the one on the actual cylinder head?

The back pressure comment also confuses me because I was always told that without back pressure, N/A cars don't have lowend torque. And according to the members of the ULtimate subaru message Board it is neccesary on some subarus to help keep the Air/fuel charge in the cylinder during the small amount of valve overlap. This was especially true, I was told on older models.

[THAWA]

I'm fairly sure they're confusing velocity with backpressure, but a guru can correct me.

What scott said above is correct, the step from the cylinder head to the exhaust header is what creates the torque with no sacrifice to anything. By making the step larger you've changed this. For better or worse I couldn't tell you.

[bmxpunk]

Now I am really confused. Is it a stpe down? Here is where I am coming from. I am assuming that the port coming out of the cylinder is so big. Then the gasket has tow openings that are slightly bigger. What i did was openup the holes in the exhaust manifold to just about (but not quite as big as the holes in the gasket. It was mostly smoothing things out, since there was ALOT of carbon build up on this "STEP."

And now I am really confused because if no car needs back pressure and I did very little to reduce it, will Ireally lose torque?

Sorry I may sound like I am mocking you but I am not, just trying to learn.

[THAWA]

It's kinda like this



Forgive the poor quality

click to enlarge

The part labeled port is the part of the head, the big square thing is supposed to be the exhaust header. and the taper is what you removed.

[scottzg]

I know that n/a cars need the backpressure because it's the only thing keeping the intake air going into the cyl, rather than wandering out the exhaust. The turbo cars don't have any valve overlap though, so im not sure they need the backpressure. I *think* they benefit because the combustion cyl has something to push against, but im not sure.

Hardy's drawing has the head at the top and the manifold at the bottom.

The turbo cars have a bunch of torque because the small size piping/valves/etc get ideal velocity at a low rpm. Off boost is where the step is important.

I suspect we're just scaring you.

[bmxpunk]

Indeed scaring the hell out of me. Like how big of a loss could I reall have from a couple of millimeters? Its like 2-3mm. Will it be impossible to drive off of boost?

What you posted about backpressure was exactly what I ad heard before.

I am keeping the rest of the manifold the same so I shouldn't have any exhasut gas velocity issues that can come from aftermarket headers, right? I thought I read that these motors don't need headers unless you are making LOTS of power. Is this wrong?

[dzx]

You should be fine with what you've done and headers are mostly for sound. 3" TBE, headers and cams would make it sound pretty damn mean.