Throttle Body Improvements: 986 e-gas

[Kirk]

I’ve got a 2000 Boxster S (3.2 L e-gas) and I’ve been curious as to what kind of improvements could possibly be made to the throttle body to get better flow. I’ve done a significant amount of boring and modifications to the throttle body on my Honduh daily driver. So last night I was bored (me, not the TB) and tore out the intake T after the TB, the TB, and the intake piping.

After some careful examination my conclusion is that there is basically nothing you can do with the stock TB if you’re going to reuse the intake piping/manifold. On the back side of the TB the TB mates up perfectly with the plastic T piece that distributes the air post-TB to the two heads. Boring out the TB here would require also boring out the plastic T intake manifold piece. That’s not real feasible IMHO without screwing it up. I know they make an aftermarket version of this piece for the Cayman and 987. If something like that with a larger bore could be used, then there might be some benefit of modifying the stock ’00-’04 e-gas TB, but with the stock piece I just don’t see anything reasonable that you can do on the back side.

On the front of the TB (intake side) again the TB matches up pretty well with the intake tube. There’s not really any benefit to putting a knife edge on the TB circumference as the flat edge mates up to a groove in the plastic intake tube. You could also put a knife edge on the TB plate itself, but again I didn’t see much benefit of this with the large shaft there that the TB plate is mounted to. The TB plate screws on the shaft are fairly flush.

The ID of the TB where the plate rotates is also pretty large, smooth, and free of any obstructions. So I didn’t see much benefit in polishing the surface, it’s already pretty smooth and only a small portion on the front and back edges are not polished.

So…. for my e-gas TB any way I didn’t see much of an opportunity for improvement. It’s no surprise to me that Porsche designed these parts well, with maximum performance in mind. Still I’m going to play with it some more and see if I can adapt one of the local auto parts store’s Honduh intake tubes to replace the stock plastic intake and see if there’s any room to improve there.

As a side note, there has been some discussion of TB sizes before. My TB measured out to be about 70-71 mm in diameter. I know that FVD sells a non-egas TB that’s 76.4 mm. But when looking at bigger bore TBs like this, one must keep in mind that it’s useless without also making the intake manifold pieces match the size increase. I think that’s the biggest limitation for 986 owners going to a larger TB or modifying their stock TB.

I know this thread needs pictures. I’ll try to get some to post later this week.

Kirk