Porting The 2G TB Elbow To Match a 1G 60mm TB - Why?

[DSMunknown]

So I've been thinking. I recently attained a 1G 60mm TB, and am obviously well aware of the write-ups that are floating around regarding this process. But I’m not sure if it makes sense to me. One thing that strikes me is that everyone labels the inside diameter of a TB by this measurement (that is to say, everyone knows this TB to be the "60mm throttle body"). But we all know (those of us who have looked at a TB) that this immediately decreases in size. I can't find my damn dial caliper right now, but the TB throat collapses to about 53mm. Obviously, the TB plate is slightly smaller (but only slightly). So why do we actually acknowledge this TB (in particular, since it’s the one I will be referring to) as a 60mm TB? It seems to me that the "size” of the TB should only be related to the size of the TB plate, and nothing else.

In addition, why does the beginning of the TB start at this diameter and then neck down in the first place? Is there a rule in aerodynamics or something else I am overlooking? I see there are two holes directly on the "lip" of the TB, both in regards to idling. But why did Mitsubishi reduce the ID? Why not just keep the ID at 60mm?

Now to my main question, the reason why I started this thread. Looking through this article and RRE about matching up a 2G TB elbow to a 1G 60mm TB makes me wonder. Here is the link I have been looking for all day. It shows some photos of the porting that people do to the 2G elbow. And this is a common practice in the DSM community. So I’m asking “Why?” The ID of the 2G TB is 2.125 inches, or 53.975mm. And the 1G TB I have begins with a 60mm ID, but (as I said before) immediately necks down to about 53mm. So why should I port my 2G elbow in the first place? So that for about half an inch the elbow will match right up to the beginning of the TB?! It doesn’t make sense to me. I can understand trying to get air into the two holes mentioned before for idling purposes, but I figure air will find its way, regardless if I chose to slightly port the elbow or not. Ideally IMHO, from the intercooler the ID of the piping should match the TB, instead of trying to do this Mickey Mouse job of porting the 2G elbow.

[allwheelTSI]

Ok, I don't know why people refer to it as a 60, probably because they measure the backside with a set of calipers and see 60. The proper way would be to use inside mic's and measure where the plate hits the inside of the bore.


The reason why you want to port it to match is because if you don't there's gonna be a lip. Air will find its way to it's destination no matter what, but the point is we want efficiency. By port matching you are removing areas that may cause turbulence(Refer "lip") which will be a flow restriction and hinder your car's performance.

The smaller portion in the middle of the throttle body is called a venturi, they have been using it on carburetors forever. It increases air velocity.

[fourreGsixty3]

Well you want it to match because if the entrance to the TB is larger then the elbow low pressure pockets exist (where the 2 holes for idle are), and you want the air to flow as evenly & smoothly as possible.

It most likely decrease in size is to increase velocity, then the air can quickly expand to the plenum), and slightly lower the air temps (opposite of compressing matter).

[dsm-onster]

DSMUnknown, it's only done to smooth the path. Studying head/intake porting, you quickly see that a smooth path is paramount to a slightly larger OR smaller diameter path.

Back to the 2g elbow. It is better because most intecooler piping comes out to the same diameter as the 2g elbow. Knowing the previous paragraph to be true, the 2g elbow yields a nasty lip when mated to a 1g throttlebody. So we port the elbow to match. That is all better than accepting a tiny diameter neck down when running a stock elbow and 2.5 inch intecooler piping . . .

Other than that, your soap box has washed .

[DSMunknown]

Originally Posted by allwheelTSI

The reason why you want to port it to match is because if you don't there's gonna be a lip. Air will find its way to it's destination no matter what, but the point is we want efficiency. By port matching you are removing areas that may cause turbulence(Refer "lip") which will be a flow restriction and hinder your car's performance.

Okay, but there’s going to be a lip anyways, between the TB and the plenum. I am looking to match this TB with my Lancer Evo III intake manifold, which has about an 60.5mm opening. I just measured the back of the TB, and it’s about 54mm. So there is another lip, from 54mm at the end of the TB to a big jump of 60mm.

Also, I preach ease of flow, “generalized” efficiency, volumetric efficiency, and the importance of avoiding turbulence all the time. I am well aware of wanting the air to have smooth transitions from point A to point B and then to point C and so on. I just don’t see how this could possibly make a humongous difference. On the other hand, I would naturally tell myself to do it anyways and quit bitching about it. But honestly, would I even notice this hindrance other than a slight change in the idle? (I would be adjusting the BISS anyways, regardless.) I doubt it.

Originally Posted by fourreGsixty3

Well you want it to match because if the entrance to the TB is larger then the elbow low pressure pockets exist (where the 2 holes for idle are), and you want the air to flow as evenly & smoothly as possible.

It most likely decrease in size is to increase velocity, then the air can quickly expand to the plenum), and slightly lower the air temps (opposite of compressing matter).

But honestly Dustin, will I really notice a difference whether I decide to do it or not? I would bet the answer would be something like "Well, not really. But it’s good to do anyways."

Originally Posted by dsm-onster

DSMUnknown, it's only done to smooth the path. Studying head/intake porting, you quickly see that a smooth path is paramount to a slightly larger OR smaller diameter path.

Back to the 2g elbow. It is better because most intecooler piping comes out to the same diameter as the 2g elbow. Knowing the previous paragraph to be true, the 2g elbow yields a nasty lip when mated to a 1g throttlebody. So we port the elbow to match. That is all better than accepting a tiny diameter neck down when running a stock elbow and 2.5 inch intecooler piping . . .

Other than that, your soap box has washed .

But again, there is nothing "smooth" about the rear of the TB to the beginning of the plenum; it’s just one big step. Oh, and I like to keep my soap box a little dirty... to give it some character.

Something related - I bought the TB-to-IM gasket (part number MD146399). I borrowed this photo below from MachV and modified it a little bit. The one on the right is what I will be referring to now.



I was just mocking up the gaskets to the 1G TB just for kicks (and to make sure I bought the correct gaskets). I noticed that the gasket blocks a few things, including both vents for idling. I indicated four blocked holes in all with the red blotches. Should I just cut out the excess gasket that I don’t need? I was thinking about doing the same thing to the part of the gasket in blue (don’t see it doing much harm if I did). And as for the top of the gasket, the red line is where the gasket comes into contact with the three hose barbs on top of the TB. I’m going to cut that little bit off as well. (This is only a problem because it doesn't allow the bolt holes to line up properly.) But why doesn’t the OEM gasket initially accommodate for these (minor) issues?

[fourreGsixty3]

Originally Posted by DSMunknown

But honestly Dustin, will I really notice a difference whether I decide to do it or not? I would bet the answer would be something like "Well, not really. But it’s good to do anyways."

Yes Anthony that would be my awnser, BUT to you I will say this...

You have spent lots of time searching for everything E3 to compliment each other, and your questioning me on making your 2G elbow flow well with your 1G TB?

[MrBoxx]

Anthony, recently I had my throttle body off to clean it and replace the FIAV lines. I had new TB gaskets from SBR and they looked identical to the ones in the pic above. I also found I had to cut the red section off to avoid hitting the nipples. I tried bending the nipples up, but decided I didn't want to break anything, so the gasket got trimmed. Had I gotten curious, I might have compared the size of the 2g TB inlet to my dejontool UICP to see if there was any lip or difference in diameter, as well as to the 1g IM that my car now has.

As for the TB to E3 mani difference, if the Intake manifold opening is larger than the TB exit, I'd say you don't need to do much of anything, since there won't be anything hindering flow.

[wishihadatalon]

I am working on an e3 intake manifold project for my girlfriend. I just paid for a bbk 2g 62mm tb. I will let you know if there is the internal taper like on a stock throttle body. Another option is to get a evo 3 throttle body, if they are any different than a 1g one.

Also what cams are you going to run? I might try to find a set of 93 cams if at all possible. Maybe if I find a good set I will do a 264/272 combo.

[talon187]

well looks like ive got to order some gaskets and pull my elbow off and do some porting. thanks for the info guys

[DSMunknown]

Originally Posted by MrBoxx

As for the TB to E3 mani difference, if the Intake manifold opening is larger than the TB exit, I'd say you don't need to do much of anything, since there won't be anything hindering flow.

No, there's just a big drop off from the rear of the 1G TB to the E3 IM throat. Probably shouldn't worry myself over that aspect of my parts collection.

Originally Posted by wishihadatalon

I am working on an e3 intake manifold project for my girlfriend. I just paid for a bbk 2g 62mm tb. I will let you know if there is the internal taper like on a stock throttle body. Another option is to get a evo 3 throttle body, if they are any different than a 1g one.

Also what cams are you going to run? I might try to find a set of 93 cams if at all possible. Maybe if I find a good set I will do a 264/272 combo.

Just curious, what kind of project is this (that is, what exactly will you be doing)? The Evo 3 TB does not do any "tapering" of any kind. It's somewhat similar to the 1G NT TBs, with a snout or throat that protrudes from the throttle plate. This makes it utterly impossible to attach a 2G TB elbow to this TB (not something I'm particularly worried about). I'll be sticking with my 1G TB, just to make my life that much easier.

In the very distant future, I'm probably looking at the DKS 264/272 combo from FFWD. But that's way in the future.

Dustin, you're probably right, but I'm still sticking with the last sentence of post #1. Hopefully when I finally get all this shit together, I'll go with a custom UICP that will mirror the 60mm measurement before the taper.

In regards to the four spots on the gasket I colored red, I took some small drill bits and went to work. Seemed to do the job. The box cutter knife was no help, though.

[wishihadatalon]

Originally Posted by DSMunknown

No, there's just a big drop off from the rear of the 1G TB to the E3 IM throat. Probably shouldn't worry myself over that aspect of my parts collection.











Just curious, what kind of project is this (that is, what exactly will you be doing)? The Evo 3 TB does not do any "tapering" of any kind. It's somewhat similar to the 1G NT TBs, with a snout or throat that protrudes from the throttle plate. This makes it utterly impossible to attach a 2G TB elbow to this TB (not something I'm particularly worried about). I'll be sticking with my 1G TB, just to make my life that much easier.

In the very distant future, I'm probably looking at the DKS 264/272 combo from FFWD. But that's way in the future.

Dustin, you're probably right, but I'm still sticking with the last sentence of post #1. Hopefully when I finally get all this shit together, I'll go with a custom UICP that will mirror the 60mm measurement before the taper.

In regards to the four spots on the gasket I colored red, I took some small drill bits and went to work. Seemed to do the job. The box cutter knife was no help, though.

1g rods with 2g pistons, fp race manifold, 16g (most likely ported compressor cover and turbine housing), lots of fuel (e85 car probably), e3 intake manifold, hopefully a custom side mount, that throttle body, and mega squirt ems. I would like a mid 12 second daily driver out of it, as that was what mine was with a 16g, but this will have better parts.

[talon187]

just wondering ive got a 1g n/t throttle body siting downstairs i was told it was bigger then my stock 1g what would i need to do to use it?

[yokotabrat]

I'm curious what 1g throttle body you have. I just measured an extra in my garage (turbo throttle body) and it measures 60mm on both sides of the throttle body.

[talon187]

im not home at the moment when i go home tomrrow after noon ill pull it out and mesure it and see what i come up with i was told the n/t 2.0s are bigger then the 2.0 turbo ones i dont really know and i dont know if it will just bolt up or not

[wishihadatalon]

Originally Posted by talon187

im not home at the moment when i go home tomrrow after noon ill pull it out and mesure it and see what i come up with i was told the n/t 2.0s are bigger then the 2.0 turbo ones i dont really know and i dont know if it will just bolt up or not

The inlet is larger, but I have been told that they taper down to the same size as a 1g turbo tb.

[yokotabrat]

Originally Posted by wishihadatalon

The inlet is larger, but I have been told that they taper down to the same size as a 1g turbo tb.

This is what I've heard and what my extra NT throttle body measures as well. It's about 63-64mm at the inlet (inner diameter) and 60mm at the outlet.

[romeen]

Originally Posted by DSMunknown

In regards to the four spots on the gasket I colored red, I took some small drill bits and went to work. Seemed to do the job. The box cutter knife was no help, though.

Anthony, are you sure that those spots need to be opened up? I purchased the exact same oem gaskets from the dealership when I swapped over to a 1G TB. I also wondered why the gasket would seal those holes up basically creating a dead end of the passages. But I decided there must be some reason that I am missing. So I used them as is and have not had any problems. Besides, even with the holes you made in the gasket won't those passages just run into the solid metal of the IM-TB flange now?

Still unsure why it is the way it is.