enlarged throttle body?

[johnmaccow]

Has anyone done this or bought one from eBay?
Are there any gains? Can't see it improving flow that much as it's just a small reduction at the flap.

[steve_k]

Send a pm to maggspower on here he does them on exchange & i'm sure he could explain to you in more detail.

[Cloggy Saint]

I heard (here) that they just mess up the idle.

[steve_k]

I heard (here) that they just mess up the idle.

Really?? Had one on mine for a few years with no problems at all,

[motormanmick]

See wiki page link below, has all the details and dyno graphs to compare

http://www.e30zone.net/e30zonewiki/inde ... tle_Bodies

[Brianmoooore]

Short answer is it depends whether the throttle body is impeding air flow at WOT.
BMW know how to build engines, and specified a M20B25 TB of sufficient flow rate when fitted to a standard M20B25 engine.
Looking at the power outputs for the engine in the graphs, it's clear that this is far from a standard engine, which will be flowing much more air than BMW intended, so it's not surprising that a larger bore TB gives noticeable gains.
The M52B28 is fitted with a restrictive inlet manifold as standard, to improve the spread of torque, and has a TB to match. Again, if the engine's air demands are increased, such as by fitting the much less restrictive M50B25 inlet manifold, then it's a reasonable assumption that a larger TB will give gains as well.

[jimbom30cab]

I've got an enlarged TB on my M52B28 and the idle is 100% factory perfect.

[mattxr2]

My one bent the butterfly and caused idle issues

[Brianmoooore]

My one bent the butterfly and caused idle issues

In that case it wasn't set up properly. The closed and WO stops should be set so that there is never any load on the butterfly shaft.

[reggid]

Can’t see it doing anything on a stock or basically stock engine except affecting throttle response atleast that was my experience. A tube 60mm diameter tube flows a lot of air and is not the biggest impediment to flow. Youd be getting rid of the AFM before thinking about a BBTB IMO and even that "upgrade" wont blow your mind on a stock car. I’d only look at it on a stroker or engine making a lot more power than factory

[motormanmick]

I have read that you can get around a 12% increase in airflow through the BBTB, but that doesn't mean you get 12% extra bhp or torque, you may get a couple of bhp and ftlb extra. We used to race in a class where we where very limited in what we could do within the rules, so for us offset grinding the crank for a 20 thou increase in stroke, port and polish and bbth could mean the 118 bhp instead of 110, not a lot for the effort, but it was the difference that counted. So it's the end result and why you want to do it.