Throttle Body Improvements: 986 e-gas - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Kirk · 07-09-2008, 07:53 AM

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

Adam · 07-09-2008, 10:40 AM

Thanks for the info Kirk. I was curious about this myself. It's not the best, but here is a pic of an E-gas TB.

blinkwatt · 07-09-2008, 12:17 PM

Kirk could you fit 996 parts in there as an upgrade?

Topless · 07-09-2008, 01:01 PM

Quote:

Originally Posted by blinkwatt

Kirk could you fit 996 parts in there as an upgrade?

Sure can Blink! Big HP gains especially if you connect it to a 996 motor

.

Remember guys, tuning an intake is a lot like tuning a saxophone or a ported subwoofer cabinet. Bigger isn't always better. Consider engine displacement, air mass, air volume, air velocity at target rpm, resonant frequency at target rpm, air turbulence at target rpm when designing your upgrade. A larger diameter TB will allow more air volume but reduce velocity and turbulence and change the resonant frequency. The result is often reduced HP due to less O2 actually packing the cylinders. Porsche designed their high performance intake and TB by the numbers so without a change in engine displacement the motor cannot make good use of larger TB air volume. Drop in a 3.6L motor and then mount a tuned intake and TB... Wham!

Lil bastard · 07-09-2008, 08:22 PM

Topless- agreed...but to add, unless you also swap injectors and tweek the software to take advantage of the increased flow, you'll get next to nothing in terms of more power.

Also, FYI, a smooth bore on the intake (whatever the diameter) is NOT the way to go!

In F1 testing, they've found that a 'rough' (or cross-hatched) intake ID creates much smoother flow than the traditional 'polished' intake - a boundary layer of turbulent flow at the surface provides much smoother flow to the bulk of the intake charge.

Kirk · 07-09-2008, 08:45 PM

As promised here are a couple photos I snapped tonight of the 3.2L e-gas throttle body. Again, I don't see a lot of potential for improvement, but please correct me if you feel I'm wrong. The first one is the back and the second is the front.

Topless · 07-10-2008, 06:38 AM

Quote:

Originally Posted by Lil bastard

Topless- agreed...but to add, unless you also swap injectors and tweek the software to take advantage of the increased flow, you'll get next to nothing in terms of more power.

Also, FYI, a smooth bore on the intake (whatever the diameter) is NOT the way to go!

In F1 testing, they've found that a 'rough' (or cross-hatched) intake ID creates much smoother flow than the traditional 'polished' intake - a boundary layer of turbulent flow at the surface provides much smoother flow to the bulk of the intake charge.

Yep,
That boundary layer creates laminar flow in the intake. This slightly roughened surface improves automotive engine intakes, jet engine intakes, and racing yacht hulls and foils.

2000SoCalBoxsterS · 07-11-2008, 06:49 PM

I agree with Lil Bastard that more volume is not necessarily better if it reduces air velocity and pressure. Take a drinking straw and point it at the palm of your hand and blow through it. Feel the force and air speed, pressure. Now take a paper towel tube and do the same thing using the same amout of force of your breath. Big difference. I think Porsche optimized the TB for the best balance and performance.

Gary in BR · 07-14-2008, 08:01 AM

I don't know enough about this to be considered an expert but I will give my thoughts.

We desorkel and see a HP increase.
The "cold air intakes" increase air flow and we see a hp increase.
The new plenums that are being sold for the Cayman and 996, 997 models change the airflow and sees a hp increase.

So logic seems to dictate a larger TB will bring more HP.

I think this is something worth looking into, I would like to see pre and post dynoes along with track times.

Topless · 07-14-2008, 09:39 AM

There is a pretty good book on this subject written by Jeff Harmon. He has done more engine hot rodding over the years than anyone I know. It is not the final word on this but it is well written, reasonably current, and does a good job of showing you how to make more power with any engine platform while dispelling the engine mod myths floating around on the internet these days. This is a useful reference for anyone interested in hot rodding or power mods. It gives you the knowledge to separate true performance improvements from marketing hype. Worth a look.

Here is the link: http://books.google.com/books?id=ze_w0i3xZmAC&printsec=frontcover#PPA53,M1