# Increasing Throttlebody size for more power



## shortysclimbin (Sep 27, 2005)

Old practices for increasing HP output was to increase the Throttlebody size after other air mods where done to increase engine HP. Has anyone looked into increasing the size of ours slightly to show some more gains? Granted this should be more important for NA guys. I really think 250whp NA is possible with this engine. Looking for discussions on size, increases and info on what others have done. I don't have the car handy to look up other sizes, but I know we should be able to find some.


----------



## thygreyt (Jun 7, 2009)

lol. 250 whp IS possible, but not right now.

we have done research... read around.

we CAM not do it right now. :laugh:

btw, increasing the tb size wont help much.


----------



## shortysclimbin (Sep 27, 2005)

thygreyt,

For the record... All that has been discussed is its doable and here are some places that might do it. And other said it will screw up your A/F ratios and the ecu will not like it. All of which are true... BUT no real research has been done! Who has installed one? Who has tuned the ecu to correct the TB size? Who has also port matched there MAF housing and intake to compensate? :banghead:

Now, I own tuning tools and own a full machine shop. I was looking for info on who has done it, and or size info of oem. What results they had or things they noticed? Pictures of issues? There might be a direct drop in that will work WITH tuning to compensate for the tables. This could net some easy power all said and done after Intake, exhaust, and cams have been done.


----------



## Jefnes3 (Aug 17, 2001)

1. Increasing the TB size does NOT affect AFR.

2. Increasing the TB size on the 2.5L motor has NO measurable gains in peak power.

3. Changing the TB size without software simply throws off the TB control loop a bit at part throttle, this is what the ecu complains about. This does not 'hurt' anything.


-Jeffrrey Atwood


----------



## thygreyt (Jun 7, 2009)

thank you jeff.


----------



## shortysclimbin (Sep 27, 2005)

Jeff,

I disagree on a few things, but see what you may be saying. Please enlighten me with more details so I understand a little better. 

This is what I know, i am going to assume that ecu tuning is part of these changes and that our key focus on tuning the engine is power output not emissions based.

The ECU controls fueling dependent on the MAF sensor, TB positioning, knock sensor, and emissions controls. If you break an engine down to its very basics (suck, bang, blow) by changing the amount of air an engine is able to intake or scavenge will directly effect how much fuel can be put into it. Many aftermarket bolt on modifications increase an engines ability to scavenge waste out off or ingest air into it. If the throttle body valve is to small for an engine it will limit the amount of air and fuel that it will be able to combust. This can usually be seen at higher rpm levels when demand for max air is present. The only way I know how to tell if the TB valve is to small would be to actually see what amount of vacuum the engine draws at full loads. Comparing this to a non modified engine might give you an idea on how much you can increase you TB size to have comparable to stock operations. 

Jeff first point: states that a TB change will not affect AFRs in an engine. This would only be true if the TB is not the limiting factor in the amount of air getting into an engine during any condition. You might see this by an engine having the ability to go lean during wide open throttle runs.

Jeff on your second point I have no ability or knowledge to state you are right or wrong. How did you come to these conclusions? Is the amount of air flow drastically larger than what is used in the engine? During wide open runs does the engine have a tendency to become rich? Do you have data you would be willing to share showing us the AFR and flow of the 2.5l engine you tested this on? What do you feel is the limiting portion of the engine from allowing us to inject more fuel for combustion and why?

On your third point Jeff I would like to point out an example: 

Say we have a TB that is 70mm in Diameter Or ruffly 385mm2 Area A mere 5% increase (3.5mm) in Diameter would net us an area of 424mm2 or a change of 10.2%. This change will allow a 10.2% increase of air in comparison to stock at any given throttle position. That change would then allow more air to flow into the engine if the TB was the limiting factor on the engine.


----------



## VWShocker (Mar 19, 2010)

Find an MKIV R32 TB and be my guest. Wasn't worth my time, money and effort since I trust Jeff with my car's life and he's my walking VW Bible. 

-E


----------



## thygreyt (Jun 7, 2009)

do you even get whom are you talking to?
Jeff atwood is THE guy. one of the few Key characters when talking about the 2.5 engine.

jeff (former C2 owner), Josh (NLS), Eurojet (all 3), Andre (audi4u)... all of em are some of all the key people on the 2.5 platform... 

-Jeff was 50% owner of C2, he helped tune and develop the 2.5 turbo kit available, prototype cams, prototype SRI, and more.
- [email protected] did THE mk1 engine swap and has intimately worked with C2 in the past.
- Eurojet, well all their prods and now the turbo kit
- Andre did the DIY turbo kit.

all i am trying to say.... i believe em. i think whole heartedly that you are wrong, just because one of the mentioned people is saying so. (on top of ALL the research done)

so, i dont want the thread closed, or people getting offended. But you must realize that if someone like him is saying something, then to the very least, pay atention.
or just grab a pile of cash, and start playing, until you come with the same results given.


----------



## KulturKampf (Nov 30, 2009)

greyt is right you have to realize that saying that jeff and josh are wrong is like saying hurst cant tune a challenger. i understand that larger TBs do indeed let more air in BUT without a larger intake mani and larger air intake tubing (cai or otherwise) then the gains would be so minimal that it wouldnt be worth spending the money and this is on any type of engine not just vw, with the exception of the honda k20 or alot of older domestics. if you think that they are wrong or that no one knows what they are talking about go ahead and try it..but dont you think other people who have tried it? not every single dubber is on vortex and alot of companies are trying to get power out of the 2.5 so dont you think other people have tried? and if it was worth it they would have said something or made something. not be be a **** but its the truth


----------

