Throttle Body butterfly 'added plates'

[creeves328]

Question for the E39 540i folks..

I recently purchased a 540i TB (OBD II, cable not drive-by-wire) for a project on my e36. I noticed the TB butterfly has added plates, which I suspect are for gas mileage, and added as part of the OBD II changes. Reason I say suspect is because the e36 line had something similar, but to the bore instead of butterfly.

Question is... Has anyone removed these added plates in a quest for more HP/TQ? Its an obvious obstruction to flow.

I did a quick search and found tons of posts, nothing in particular about this. Apologies if this is a frequently discussed topic.

[CBi]

Originally Posted by creeves328

Question is... Has anyone removed these added plates in a quest for more HP/TQ? Its an obvious obstruction to flow.

The "extra" throttle plate in front of your throttle body is for the ASC system. The throttle body is naturally in the fully open position and is used to limit engine power output in the event of ASC activation.

[creeves328]

Originally Posted by CBi

The "extra" throttle plate in front of your throttle body is for the ASC system. The throttle body is naturally in the fully open position and is used to limit engine power output in the event of ASC activation.

Think we're talking 2 different things. Its not in-front of the TB, its physically attached to the TB's butterfly, not part of the ASC.

1st pic is the backside of the TB, fully open. 2nd pic is front, part throttle (showing the screw holes), 3rd is front, fully open. Pretty certain this was an OBD II change.

Anyone remove these for a power increase? It will hurt gas mileage, and part throttle should be more reactive (25% throttle is more like 35% w/plates). A similar approach was taken on the e36 OBD-II cars, where they added a ridge to the bore.

[CBi]

Originally Posted by creeves328

Think we're talking 2 different things.

Indeed.

I've seen those things on some of the 6 cylinder motors, and I've honestly never paid much attention to them. It's possible they were added for a vacuum port (again, I'm only guessing, since I don't have the throttle body in my hand) or for part throttle operation.

They are certainly impeding airflow at full throttle. How much impedence is unknown, but it's probably minimal, and would not be something that would register on a butt dyno.

However, if you're bored, and like to tinker, take them out and see what happens. Make sure to Loc-tite and/or stake the throttle body screws if you put the parts back on, or they may come loose and be inhaled by your engine.

[creeves328]

^^^ For me, I don't think they'll make any difference, performance-wise, for my project (its an e36 m52 2.8L).

However, for those with a 540i and wanting performance, here are the measurements..

Total butterfly diameter = 3 1/16"
Total area of butterfly = 7.36"
WOT area, taking into acct area consumed by TB butterfly w/ plates = little less than 6.59"
WOT, taking into acct area consumed by TB butterfly, W/O these plates = 6.97"

So, you would gain roughly 5.5% total throttle body area, at the TB venturi (butterfly), without the plates. These measurements are estimates, I didn't mic these, but should be close.

[creeves328]

Addl Pic --- Closeup showing the joining of the butterfly and the plate. The combination is about 1/4" thick, and the butterfly itself is thinner than this addl plate.

Anyway, hope someone finds this useful. As I mentioned, it won't help me for my project, but if you want a Big Bore TB for the 540i, I'd check it out on your car. The Dinan TB has a new butterfly, and as expected, they never created new versions of these plates.

[billzcat1]

That plate is actually somewhat important and I would recommend leaving it in. The plate increases apparent throttle resolution at low throttle angles. Basically, it gives you finer control of the throttle at low throttle levels. Removing it makes part-throttle application a lot less smooth. I have BTDT with a couple different VWs and did not like the results. There was no apparent increase in power and it just made part throttle "jerkier".

[zparker]

I doubt the intention was for smooth throttle operation as a performance mod. But you have to have a dme that is smart enough to adapt for the new air or get a reflash to allow more fuel for the additional air.

[creeves328]

Originally Posted by billzcat1

That plate is actually somewhat important and I would recommend leaving it in. The plate increases apparent throttle resolution at low throttle angles.

This is true, but its really meaning is for gas mileage. I'm pretty certain about it being added for OBD II, but I don't have 540i documentation on it.

Originally Posted by billzcat1

Basically, it gives you finer control of the throttle at low throttle levels. Removing it makes part-throttle application a lot less smooth. I have BTDT with a couple different VWs and did not like the results. There was no apparent increase in power and it just made part throttle "jerkier".

I think removing it is more justifiable on the 540i owners with mods already, supporting the need for a larger TB. Anyway, just informational for those that are thinking of upgrading their 540i's to a BBTB. Removing these, putting the screws back in (so you don't have open holes) would increase area much like a BBTB would. And the BBTB's don't retain any of these added plates.

Happy modding!

[NNY528I]

The only time this could be of any advantage would be when you exceed the flow capacity of the TB. IF the vacuum droips to 0 during WOT then there is no point or value to opening up the TB.

[zparker]

partially correct. If you used a MAP sensor to watch the actual manifold pressure you would see you are not getting maxium flow after 4500. You will probably see pressure numbers of 95-88 depending on what type of intake restrictions you have. I thought my car had 0 manifold vacuum under wot but was incorrect which i found the other night on the dyno.

[billzcat1]

The only time the vacuum in my intake manifold reads zero is when the car is not running. Should this occur during normal driving, then your gauge is incorrect. Fluids flow from areas of high pressure to low pressure. A naturally aspirated car will always have some deviation from ambient pressure in the intake manifold.

[zparker]

around peak torque i have ambiant pressure under WOT, after peak torque as closing to redline the issues in flow related to the filter, pipes and size of the plenum will cause vacuum to develop. Do some reseach on port tuning like formula one uses and you will see they use resonance to acheive 1.25bar which would be 3.625 PSI above atmospheric.

A good watch would be

YouTube

YouTube

[NNY528I]

Originally Posted by zparker

around peak torque i have ambiant pressure under WOT, after peak torque as closing to redline the issues in flow related to the filter, pipes and size of the plenum will cause vacuum to develop. Do some reseach on port tuning like formula one uses and you will see they use resonance to acheive 1.25bar which would be 3.625 PSI above atmospheric.

A good watch would be http://www.youtube.com/watch?v=-NHEAxKGw8Y

yeah what he said

[bigmansM]

Just go buy a big bore throttle body from Riot Racing, WestCoastRiots.com and have a simple bolt on with no issues

[Fiziks]

Originally Posted by bigmansM

Just go buy a big bore throttle body from Riot Racing, WestCoastRiots.com and have a simple bolt on with no issues

Interesting. Says compatible the i6 e39's and 1996-1999 540's.

[NewEnglandJason]

Originally Posted by Fiziks

Interesting. Says compatible the i6 e39's and 1996-1999 540's.

Only 6cyl. though????

[Fiziks]

Originally Posted by NewEnglandJason

Only 6cyl. though????

You're correct, I misread. Only available for i6.

FITS: 1996-1999 6 cylinder 3 series engines
1996-1999 6 cylinder 5 series engines
Z3 2.8L and 3.2L engines (will also fit M applications)