Make your throttle MOAR better!!!1

[tjts1]

I had some time on my hands last night (rare) so I decided to finally move up from 19# to 22# injectors and fix a few things that have been bothering me about the throttle body. First of all the throttle plates are 1/8" thick and completely blunt on both ends. The solution is to knife edge one side of each plate on opposite ends. I was going to thin out the throttle shafts but I couldn't figure out how the disassemble the damn thing. Oh well.


The second problem is in the TB linkage. When you reach WOT, the throttle plates are not parallel and they both move past 90 degrees and actually block airflow.


The solution is 2 fold. First the linkage between the 2 plates must be modified in order to make the throttle plates parallel at WOT, and the throttle stop needs to be moved.


The throttle cable pulls on the small TB plate (top) and opens it part way before it starts moving the larger (lower) throttle plate. The solution is to notch the linkage where the small throttle pushes the large throttle. I also added an aluminum plate to the throttle stop in order to the throttle plates earlier (blue circle).


When its all finished both throttle plates are parallel to air flow at WOT

Adjust the throttle cable and you're good to go.

[BrandC]

So let me clarify and make sure I understand:

The corner circled in red needs to be ground down/notched. This is so the small TB linkage can open parallel?

Also, how did you attached the aluminum throttle stop?

Good work as always Justin!

[dude8383]

What about a review on whether or not you FELT something??

[ClodKing]

I would like to know whether or not you noticed a difference aswell.

Also, howcome you didn't knife edge all the way around?? The other blunt edge will still cause turbulance, will it not?

I'm trying my best to make those statements NOT sound prickish. It is so very hard to do on the intraweb:D

[tjts1]

So let me clarify and make sure I understand:

The corner circled in red needs to be ground down/notched. This is so the small TB linkage can open parallel?

Also, how did you attached the aluminum throttle stop?

Good work as always Justin!

It probably makes more sense when you have it in hand. The notch allows the small throttle plate to rotate further before it starts pushing open the large throttle plate. In stock form, when one throttle plate reached WOT the other would be slightly closed and vice versa. If you play around with it a few minutes it starts to make sense.

The throttle stop (more of a spacer) was a 1/16" thick 1cm square piece of aluminum plate superglued on top of the existing throttle stop. It stops the throttle plates from traveling further than WOT. Again, it makes more sense when you see it in hand.

What about a review on whether or not you FELT something??

Well I sure as hell felt the 22# injectors. I couldn't give you an honest answer on whether or not the throttle modification did anything. But since I was taking it apart anyway, I figured I might as well optimiza it as much as possible. It does respond to small throttle inputs very quickly.

When knife edging the throttle plate, do the side that is beveled toward the throttle body wall. You want to reduce the thickness of the edge to about half of what it already is. You still need some of the blunt edge in order to allow the throttle to seal properly. Google "knife edge throttle plate" for more information.

Also, howcome you didn't knife edge all the way around?? The other blunt edge will still cause turbulance, will it not?

Imagine the throttle is open a little bit, say 5 degrees. You only want to knife edge the side that is closest to the throttle body wall. Thats where the the air has the squeeze through at high velocity. You still need to leave about 1/2 the thickness of the throttle plate untouched in order to allow it to seal properly.

In this picture the top surface on the left side has been knife edged. After the picture was taken I also knife edged the bottom surface on the right side. The edges of the throttle plate are extremely sharp. It bit me once.

The throttle plates are aluminum and therefore extremely easy to work with a file. The throttle linkage is steel.

[colin86325]

I wonder why BMW would've allowed the throttle plates to extend past 90 degrees at WOT?

[nomad]

they may have wanted the throttle cable to be adjusted to the perfect opening when the pedal is fully bottomed out. This way, if its adjusted so that you are meeting the throttle stops before the pedal is bottomed out you are not putting your whole leg weight on the small hinges of the throttle body. Those little brackets should not be what stops the pedal travel, the floor should.

Best way is to have someone floor the pedal and then adjust cable to WOT.

On the other hand, if the plates are not perfectly in sync like they should be then you'll always have a partial opening of one or the other at WOT.

[tjts1]

I wonder why BMW would've allowed the throttle plates to extend past 90 degrees at WOT?

Good question. Why does the car need 2 throttle plates in the first place? One large plate with with a variable diameter throttle wheel would have done the job. I suspect they over size the throttle plate slightly to allow for this kind of wide tolerance. The throttle body is not restrictive for this engine. All the restriction happens at the airbox intake tube.

they may have wanted the throttle cable to be adjusted to the perfect opening when the pedal is fully bottomed out. This way, if its adjusted so that you are meeting the throttle stops before the pedal is bottomed out you are not putting your whole leg weight on the small hinges of the throttle body. Those little brackets should not be what stops the pedal travel, the floor should.

Best way is to have someone floor the pedal and then adjust cable to WOT.

On the other hand, if the plates are not perfectly in sync like they should be then you'll always have a partial opening of one or the other at WOT.

On my car the gas pedal took the throttle plates past 90 degrees all the way to the point where it was touching the throttle stop at the TB. The throttle cable itself will absorb most of the extra tension from the pedal by stretch or deforming long before it puts any significant tension on the TB itself at WOT. I don't think thats the ideal setup (the cable will wear out eventually) but thats how it was setup from the factory.

[BrandC]

Justin,
   Do you have a picture of your cold-air intake setup?

[tjts1]

Justin,
   Do you have a picture of your cold-air intake setup?

http://www.m42club.com/forums/showpost.php?p=48698&postcount=9

[Boyracer]

[tjts1]

I wonder why BMW would've allowed the throttle plates to extend past 90 degrees at WOT?

Your question got me thinking again so I took the TB linkage apart yet again (got to love being self employed )

This is is the stock throttle linkage.


On the other side of the bracket theres a shorter side to the throttle arm to hook up the cable. The throttle was designed with 2 throttle response rates.

When you take out the cable they look identical except for height.


MMMM cable.


And install it on the other side.


Then adjust the gas pedal stop (18mm) to allow the throttle to rotate all the way to its stop.


Linkage all the way open.


I put a big weight on the gas pedal.



I drove it like this to get lunch and the throttle is very very touchy. This would be a nice setup for autoX or if gas cost $1/gallon, but I think I'm going to move the throttle cable back to the other side and adjust the gas pedal stop to allow me to open the throttle all the way. The gas pedal feels too much like an on off switch. In normal driving I don't have enough control to make small adjustment and keep my fuel economy in check. But its nice to know its there.

[dude8383]

Was there an change to your chip after upgrading to the 22# injectors? I have 24# injectors I'd throw onto mine just for the hell of it to see if there is any difference.

[tjts1]

No electronic changes.

[nomad]

ha, sounds like the short side throttle cable is a good mod when you try to sell the car.
Oh the power!