Why install a larger throttle body when the airlflow sensor inlet is so small?
 

I am building a 3.2 into a 3.4 and will be ordering a Steve Wong ship for it.

Steve can enlarge your throttle body for a reasonable amount of money, but I am wondering what the benefit will be? Is it just throttle response? Since the the area of the flow sensor inlet is far smaller than the stock throttle body area, isn't the inlet at the air filter box the bottle neck in the induction system?

Or am I missing something here....?

Dave -- enjoy your 3.4, LOVE mine. As I understand it, the primary (only?) benefit of the larger throttle body IS enhanced throttle response, as you're opening a bigger "gate" and allowing in more air from the same throttle position with an enlarged throttle body. Since I had my throttle body enlarged in conjunction with my 3.4l rebuild, I can't speak to what/how the enlarged throttle body fits into the overall equation, but my 3.4 is noticeably stronger than the (stock and essentially healthy) 3.2 I started with.

Yes, your logic is spot on! It's waste of money, as numerous testings have determined.
Do more searching.

Oh OK, so you're guessing, right? But who really cares, it's only money?

Dave (mysocal911) -- I feel like we're both arguing the same side of the coin here (though I guess I could have been a bit clearer that I wasn't recommending that he drop the $$$ an enlarged throttle body) -- As I indicated above, I agree that the throttle body isn't a bottleneck and that enlarging it won't allow a Carrera engine to produce more power/torque. However, I stand by my comment that an enlarged throttle body could well have a positive affect on perceived part-throttle response, as an enlarged throttle body would allow more air to flow through the throttle body at the same part throttle setting (i.e., opening a 1 square meter window 1/4 of the way will let in more air than would come through a 1/2 square meter window opened 1/4 of the way). Presume we're on the same page, however, that a boring a 3.2 engine to 3.4l (and slightly increasing compression in the process) should result in a noticeably stronger engine than a stock 3.2.

this is a good post with empirical data :) https://forums.pelicanparts.com/porsche-911-technical-forum/1115802-myth-busters-does-larger-throttle-body-add-power-3-2-a-2.html

There are online vendors that have done this service for years. I doubt Steve does it in house.

Incredible that the Porsche Club Sport limited addition, with the special valves & DME ECM, never included a "wider" throttle body for more power?

It's so simple a mod, it makes you wonder about the engineers at Porsche.:confused:

Dave, you seem to have a wealth of knowledge to share. Have you considered posting helpful responses instead of passive aggressive and snide comments? I’ve witnessed multiple threads derailed by you, typically causing frustration and confusion for owners looking for answers from those with more experience. With the same amount of effort you could make contributions that help owners, and grow the community, instead simply trying to prove your own superiority.

Just imagine meeting Loren in person:)
Ivan

My sense is the original mechanical flapper box is the largest hindrance to throttle response. When I bought the car that originally contained my 3.2, it had an authority hot wire maf and chip, with Andial modded intake runners. I didn’t realize how much better it was from a responsiveness standpoint until I drove another 3.2. I’ve since built the engine to 3.4 with substantial mods to heads and Sal Carcellar’s setup, with Steve’s bored out throttle body, headers, and more. Steve used to make his own MAF. I would be curious to see his dyno data on that vs stock flapper. And then adding the bored out TB…


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Thanks for all the great responses, guys. I had not considered the possibility that at lower RPMs, where the flapper box isn’t yet hindering airflow to any great degree, that throttle bore size can affect airflow up until the flapper box becomes the limiting factor. Makes perfect sense. So if I understand this correctly, you can potentially make more power earlier in the power band, just not at WOT? If so, I definitely see the value of a larger bore for a street car, and why improved throttle response would be desirable on the track.

Good stuff.!

Thanks also for posting the old thread with Steve’s responses.

Now provide an actual test (dyno) to prove it! Let's avoid the hyperbole posted earlier in the this thread.

I'm not sure your interpretation is quite right. I think before you are limited by the AFM the larger throttle body makes a difference, only because it allows more flow for a specific throttle angle setting. 1/4 open throttle on a big throttle body flows more air that 1/4 open small throttle body. that doesn't mean the engine capability changes, just that you would need to move your foot further to achieve that same output.

think of it this way, the stock throttle body is 63mm, so assuming full cross section when at WOT, that gives you ~3120 mm^2. now assume you enlarge your throttle body to say 90mm for a total of 6240 mm^2. we've already established that you will not get any significant gains at WOT since the AFM is the limiter, but lets look at part throttle. at 1/4 open on the 90mm body you will effectively have 1560 mm^2 area for flow. you can achieve that same are with the smaller TB but you have to move the throttle to 1/2 open. so does this mean the larger throttle body will outperform the smaller one? No, it simply means you need to move your foot further, however you will likely feel greater throttle response with the larger TB. the trade off comes with diminishing return with greater throttle positions. with the larger TB once you have reached 1/2 throttle you have achieved the same area as the small TB at WOT and as assumed earlier you cant flow any more air the WOT on the small TB so anything past 1/2 throttle on the large TB does not provide any additional power.

Perhaps I am not understanding this very well then. I thought that Steve W was essentially saying that at lower RPM's, when the flapper opening is not the limiting factor, if you go to WOT, there will be a increase in air flow (over the stock diameter throttle body) until the flapper restriction takes over, and that the benefit is not limited to only partial throttle openings.

Irregardless, I do think that it would take multiple dyno runs at various combinations of RPMs and throttle openings to illustrate what the differences are after installation of a larger bore really are. Obviously, certain effects have been felt by drivers in the seat of the pants with these larger bores- I'm just not sure yet whether those effects are something that will benefit me with the way that I will drive this particular car....

After looking at this little guy, I better understand why some builders ditch the factory induction system for something better:

http://forums.pelicanparts.com/uploa...1751985062.jpg

If you pull a WOT run on a dyno you need to also monitor intake vacuum during the pull, the real good tuners know this :)
If you have vacuum in the intake during WOT pull you have a restriction somewhere in the intake.

A 3.4L upgrade will often cause a -2PSI vacuum reading in the intake, I know because we have measured this. The main cause is the air meter, when I replace these meters with my wide open 76mm MAF system that pressure drop is nearly eliminated to under -0.7PSI

The Air meter is the issue.

You can achieve exactly the same effect (ie increased volumetric efficiency at less than WOT) with the standard sized throttle body just by moving your right foot quicker. It costs nothing.

Sure, Dave doesn't have sunny disposition, but I appreciate that he is someone that only posts factually correct information and is willing to ask the difficult questions of those posters who are either mistaken or have a self-interest to protect. I'm sure I'm not the only one who has learnt from his insights.

Sal,
Your comments regarding intake vacuum made me investigate the effect of the standard 3.2 airbox since I had already eliminated my air flow meter.

I found from datalogging my MAP sensor that there was a measurable difference between different setups.

In fact, I couldn't detect a difference between no cover but with filter and no filter or cover at all. This led me to keep the paper filter but bore some large but discrete holes in the cover. The results were, to quote my old post: " showed the pressure drop to be between 5.1kPa (Standard airbox lid and filter) to 3.8kPa (No lid/no filter and surprisingly Lid with extra holes with filter) at WOT at around 6100 to 6300rpm".

Have you done any testing of air filters?

I didn't consider a K&N filter as I've seen too many dusty inlet tracts from their (mis)use.

It's worth 12 Dynojet rwhp according to Steve Wong:

http://forums.pelicanparts.com/porsche-911-technical-forum/636516-3-2-dyno-tests-airboxes-mufflers.html

I'd really like to know the difference between a standard 3.2 intake and a ported one. Do you have any data on this Sal?