Oversize Throttle Body on 3.2L Engine

[dkirk]

The latest engine mod performed on my 1988 911 was the installation of a large-bore throttle body. My engine was previously modified with 964 cams, SSI exhaust with a Dansk 2-in, 1-out “Sport” muffler. Heads were rebuilt by Anchor Atlantic with a 3-angle valve and seat cut and manifold to head match and mild port work done by myself. The finishing touch (and the least mechanically intense modification) was the installation of the larger throttle body fitted to the Bosch Motronic injection system, already equipped with a 911Chips (Steve Wong) custom chip.

911Chips offers this throttle body modification, consisting of boring the throttle body 3.0 mm oversize and installing a matching, stainless-steel throttle plate.

https://www.911chips.com/engine.htm

While this may seem minimal, the actual WOT area is increased by approximately 10%. Over the winter I purchased a throttle body from Bruns Motorsports (highly recommended) and sent to 911Chips for modification which took about 6 weeks. This past weekend I did the swap and drove it for the first time today.

Most noticeable is the much-improved throttle response – now feels more like a carbureted engine. Throttle blips for downshifts are much nicer. WOT acceleration, using the seat-of-the-pants dyno, is more difficult to judge but it certainly seems to climb up the rev range more rapidly. I’m quite pleased with the results and feel it was well worth the money spent.

Below is a picture of both throttle bodies on the bench with the modified one on the right. The quality of machining and fitment of the throttle plate was perfect.

[jmh61]

Had the throttle body modification done by Steve Wong on my '86 Carrera as well. (Steve does excellent work, can't recommend highly enough.)

My engine mods are similar to yours, headers, 20/21 cam, larger intake valves, Steve Wong chip, etc.

Biggest difference for me was throttle response. Much improved coming out of the corners!

Recommend the mod, but pair it with a chip.

[mepstein]

There are a couple places that do it for a lot less than 911 chips. Chances are he sends the TB to another vendor.

[Peter M]

I installed one on my modified 3.2 as well and found the same joy you guys experienced.

Then I thought I'd try and validate the change in performance by some sort of objective means, accurately measured 3rd gear acceleration runs using electronic data recording in my case

This confirmed yet again how woefully inadequate butt dynos are.

Full story here:
http://forums.pelicanparts.com/porsche-911-technical-forum/1115802-myth-busters-does-larger-throttle-body-add-power-3-2-a.html#post11983096

[darrin]

Peter M -- could our butt dynos AND your myth bust BOTH be right? Specifically, wouldn't increasing the size of the throttle body/plate change (increase) the amount of airflow at part throttle (larger body/plate let in more air at same part throttle position than smaller one) and cause a significant difference in "throttle response" while going to full throttle but still have no effect on the engine's maximum (sustained full throttle) output?

[PeteKz]

Hey, if it makes your butt dyno tingle, then do it. Some people like super-clean engine compartments too. It's a hobby, do what you like.

For the record, I'm with the other Peter on this.

[917_Langheck]

But if you read Steve's response in the other thread you find this test by Peter is not really an apples to apples comparison for those of us not running a motec system (Peter's test has two variables). The test would be better served with all other systems being equal and with the use of a standardizable calibration system, i.e., a dyno. Absent that we have only a well-documented but unsystematic test and result. Thus, as darrin questioned, yes, both conditions are represented.

[Peter M]

Originally Posted by darrin

Peter M -- could our butt dynos AND your myth bust BOTH be right?

darrin,
Yes, we are both right if you want to look at it that way.

I specifically set out to objectively measure the increase in WOT power as there has been countless post references in the past inferring a larger TB on a 3.2 would deliver greater power. I even linked a post above quoting an extrude honed intake and larger TB will deliver "7hp" on a Dynojet. Even this thread opens with a post inferring this outcome.

As for increased responsiveness, if you compare a standard TB with an enlarged TB at PART THROTTLE OPENINGS on a butterfly angle only basis this is irrefutable. So the argument that many like the "feel" of the larger TB is very valid. However our right foot doesn't work like that in practice and our brain learn irrespective of the TB installed to open the throttle at the required speed and to the required position to provide the level of torque we want at that particular moment. My car was already very responsive at part throttle so maybe this was the reason as well that I didn't notice much change.