Intake Elbow - Found the restriction?

[Slider]

With all of the talk about modifying or change the upper intake elbow on the 2V, I become very curious as to what the big deal was about. I took the elbow off of my car today to give it a thorough inspection to see if I could see any problems.

Well, I noticed right away that there was a noticeable amount of extra casting. In the attached picture you can see some of it. There is more around the bend towards the throttle body, but I could not get a good picture of it. I assume a lot of people that are porting their elbows at home are basically getting rid of this. My elbow is pretty bad on the floor right before it makes the 90 degree bend. There is a decent size ridge of metal that runs from one side to the other. I can only imagine what kind of turbulence it is causing.

I kept thinking that there has to be something bigger wrong with the stock design for there to be several aftermarket intake elbows on the market. Well, I think I might have found the main problem. The problem lies in that the throttle body opening is round and the opening into the plenum is more rectangular. Basically, the elbow is molded not only for the 90 degree bend, but to change from the round shape to the rectangular shape. I think the problem is that the Ford engineers did not do a good job transferring from one shape to the other. As the round intake opening goes down the elbow it needs to become narrower on the sides and taller from top to bottom. I think this idea is fine, but the problem is how the elbow does this.

Instead of converting to the rectangular shape first and then making the bend. The stock piece tries to do both at the same time. Before the bend the circular inlet becomes narrower from side to side, but the inlet does not increase in height. The height is not increased until is starts to make the bend. This means that there is a region within the intake elbow where the inlet has the height of the round throttle body opening, but the narrower width of the plenum opening. This problem occurs right before the bend. If you look at the attached diagram you can see what I mean. The yellow areas represent the amount that the throttle body opening has been narrowed before the bend. The blue areas are the regions that should have been removed before the bend, but are not until during/after the bend. That means that the intake elbow has been pinched.

From my rough calculations, this area is optimistically only 88% the size of the throttle body opening. Just so you know, the plenum and throttle body opening are the exact same size in terms of area. They are just shaped different. The throttle body side of the elbow is approximately 72 mm in diameter, which yields a cross sectional area of 4060 mm^2. 88% of this will give you an approximate circular opening of 67 mm. That is a decrease of 5 mm, which is the size increase to the next throttle body size (70mm). I think fixing this problem along with the excess casting could really help flow, and thus make the same power as the $200 aftermarket elbows.

Well, that is my opinion any ways. I just thought I would share that with you guys. I hope it helps. My next step is to break out my porting tools and see if I can make some more power

 

[Rekokulous]

Hey, good write up.

 

[Slider]

Hey, good write up.

Thanks.

My only worry is that there is not enough material on the top and bottom to shape the the round inlet in to the rectangular one before it makes the turn. Maybe I will have to try widing it instead, but most likely it will have to be a little of both.

 

[Orions98GT]

great write up.

 

[AdRock]

I just got done porting my stock plenum tonight. I have 2 so I was able to do it over a few days without having to not have a car. In the pic above, all of the material next to the opening for the EGR can be taken out. And the casting seems can be smoother over. For doing these 2 spots in the shortest amout of time I used my Dremel and a cutting wheel. Just use the edge and move over that spot. It's definitely the quickest way to remove a lot of material. After I had those parts shaved down I went to town with the grinding bit on the rest of the plenum. Then I used an 80 grit sanding barrel to open up the body openings. Once I had all the material out that I wanted out I went in first with the 80 grit sander, then the 120 sander on high speed. Then finished it up with two different buffing wheels. The inside of the plenum is a smooth as a baby's bottom now. I tried to take some pics to post but my digicam sux and they came out blurry with the flash.

 

[Greenbird]

The way the stock elbow makes the bend is a problem as well, the turn radius is almost zero, for best flow it should be 3", minimum.

This is not possible with the stock plenum, or maybe even the stock hood.

 

[Slider]

In the pic above, all of the material next to the opening for the EGR can be taken out.

Me guess is that the bump is supposed to help mix the fresh air with the exhaust gases. That little bump looks just like the bump in the cylinder heads (tumble port).

The thing that I was most amazed about was simply how bad a job that they did designing the elbow. They put all the time and effort into the lower intake and engine in general, but the upper looks like a first year engineering student designed it. You can easily see down the t/b side of the elbow how much smaller the diameter is right before the trun when compared to the ouput into the plenum. Someone just did not do their homework with this design. It was probably all done in CAD software, and no one ever gave it a good real world testing.

 

[StangPro]

I've been working on one in my spare (aka non-existent) time.

Even when you start grinding on it, the casting is very porous and in general very poor.

The EGR bump can be taken out, and the ridge smoothed.

The corners of the short side radius (or lack of radius...) can be smoothed also.
Coming in from the bottom, you can attempt to improve the radius, but there's not a lot of material there to work with.

So far I've spent 4 hours on it. A lot of that time was on grinding down the ride on the top as I removed the lame horse sticker and smoothed the whole exterior out.
To be of a quality that I'd put on a car I think it has another two hours to go.
If I were to do another one, I think it'd take 2 hours to do start to finish.
Take the cost of that time and what I've spend on rolls and bits plus new gaskets and a new plenum is the way to go.

The only time I can say using the stock plenum makes sense is when a person has a lot of skill and free time and would rather port the stocker.

I'll have a full write-up with pics of the whole process up eventaully, I just keep getting into other projects that are higher priority.

 

[GT_y2k]

I The inside of the plenum is a smooth as a baby's bottom now.

Maybe i am way off base here but wouldn't a smooth inner surface hinder flow compared to having a slightly rough "hone" type surface?

Maybe the designer of the plenuem was thinking of the Ram air effect..converging area increases velocity...

Thanks for the write up.

 

[CaliLifeStyle]

Maybe i am way off base here but wouldn't a smooth inner surface hinder flow compared to having a slightly rough "hone" type surface?

Maybe the designer of the plenuem was thinking of the Ram air effect..converging area increases velocity...

Thanks for the write up.

Do you mean the Venturi effect? Like a Carburetor?

 

[Dark Knight GT]

I think having a smoother surface on the intake plenum would be better than a rough surface. Here is why. Our cars are not carburated. A carb vehicle injects the gasoline in with the air inside the carburator. Naturally, a rougher surface on the carb will allow for better air/fuel mixture. That is not the case for our GT's, since they are port injected. The fuel doesn't mix with the air till it reaches the cylinder heads(approximately). The plenum is quite a ways before this. By making the plenum surface smoother on the inside, you increase the rate at which air itself can flow.

We did this to my brothers BBK plenum and got great results with it. Adrock, what kind of sanding tools are you using ? I don't think I quite have access to the type of tools you're using. I know I use a 320 grit sanding block to produe a mirror smooth finish, but its a lot of work to do by hand. If I had access to some sort of different grit grinding tools, I could probably speed things up.

 

[GT_y2k]

Do you mean the Venturi effect? Like a Carburetor?

if that is what the proper term on how a converging diameter increases the speed of air movement. its not how the intake elbow works but i thought it was funny to compare. as far as the smoothness of the inside surfaces i question the theory of smoother means better. With my old turbo'ed car(GSX) polishing the interior flowed less than a spiral honed pattern. From my understang of this a smooth surface gives no guide to conistensy(sp) of the flow path where as a spiral hone does. i really hope i can find flow data for smooth compared to a spiral pattern.

 

[Pertums]

i've been working on a spare stocker i picked up on ebay with a dremel and have been able to remove a decent amount of material out of it so far. i really don't think the roughness was a design since there's also a large seam from the casting on the inside. the interior roughness is pretty much the same as the exteriors roughness.

i've got probably an hour or two of solid grinding in on it using my dremel and different grinding stones, and now i'm up to sanding buffs. next up i'll polish it out.

the exterior i painted to give it a different look. the raised pony is white and the rest is black to match the upper intake.

 

[YellowJacketGT]

The only way to tell for sure the cost in rwh is a dyno comparison. It probably would not make as much difference at lower cfm requirements.

I wanted a CAI the had some shine to it compared to the plastic unit KB provided. The unit I used was polished and provided some looks.

Turns out the shape of the CAI caused restrictions that cost me 60rwh. 4" of vacuum was caused by the shap.

Plastic also does not retain heat...

BTW the inside of the polished CAI was much smoother than the plastic unit.

So it really depends on mods and a dyno to really demonstrate hp cost.

 

[GoofNOff]

X2C Motorsports out in SoCal has done some portwork on the elbow and came up with some good results. MM&FF did a tech feature on it and a ported upper with a 70mm TB came up with 10hp at the wheels. I'll have to dig up the issue to see at what rpm range the difference was at but it looked like a good deal. I believe you can call X2C and order one (if you don't feel like doing the portwork yourself) for about 150-200 bucks but will give you a $50 core charge back if you send them your old one.

 

[Dark Knight GT]

X2C Motorsports out in SoCal has done some portwork on the elbow and came up with some good results. MM&FF did a tech feature on it and a ported upper with a 70mm TB came up with 10hp at the wheels. I'll have to dig up the issue to see at what rpm range the difference was at but it looked like a good deal. I believe you can call X2C and order one (if you don't feel like doing the portwork yourself) for about 150-200 bucks but will give you a $50 core charge back if you send them your old one.

Yeah, I remember reading the issue in MM&FF concerning porting the stock upper plenum. The 10rwhp is gained at around 6,000rpms, which is not where our power band is really at with the stock heads and cams. A ported and polished stock plenum on average will yield only a 2-3rwhp on a basic bolt-on GT itself. Combine it with a thorttle body and intake spacer, you may see a few more. I personally don't think its worth 150-200 dolars to buy a stock plenum that is ported. You would be better off investing in a nice aftermarket plenum, like one from Accufab, BBK, or C&L. Especially since most aftermarket plenums can be purchased for between 150-200 dollars. Some are even cheaper.

 

[mity2]

good write up. But wouldn't it easier just buy C&L for like $139?

 

[Pertums]

good write up. But wouldn't it easier just buy C&L for like $139?

for me personally, the c&l is ugly as sin. i prefer a subtle look not the bling bling appeal of an accufab. so port & polish then paint, and you get this as a result. and total cost was around 40$ all said and done and i still have a stocker i can resell on ebay for 20$ or whatever it goes for nowadays. sure i might not get as many hp as an accufab / dragon / c&l / etc. but i get the enjoyment of customizing it myself, and most likely a higher gain per $$ spent ratio.

 

[Dark Knight GT]

Dude, that looks pretty sweet. Nice custom job.