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Throttle body comparo --> stock/Weber/Audi

 
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emoore924  



Joined: 13 Apr 2004
Posts: 2788

PostPosted: Sat Jan 05, 2008 1:56 am    Post subject: Throttle body comparo --> stock/Weber/Audi Reply with quote

First off, I'm no fluid dynamics engineer, so if you are and this seems simplistic, apologies, and corrections welcome. That being said, use this at arm's length, YMMV, yadda...

Ive been calculating some flow numbers and ended up with the following as a residual of that effort. What I'm working through is a determination of the most appropriate diameter of i/c tubing for my application and wanted to know which TB has the potential for the highest flow rate -- so I went after the area of the holes in the stock TB, a Weber "big throat", and an Audi 5000 TB as a proxy for their ability to flow better or worse than the others.

The last two numbers in each set of numbers are the most interesting to me as they list the total net area for each TB and the equivalent diameter of an unobstructed pipe -- the absolute minimum I would want to use for i/c piping.

Interesting to note that there's not a lot of difference in area between the Audi with two smaller throats and the Weber with one large one.

I suppose you could flow bench them to find out essentially the same thing as I have here, but I don't have one of those...

All numbers are in inches or square inches. Here ya go...

TB Stock N/A
secondary diameter / 1.0000
area of secondary / 0.7854
area of secondary pivot (deduct from area) / 0.3125
net area of secondary / 0.4729
primary diameter / 1.8125
area of primary / 2.5801
area of primary pivot (deduct from area) / 0.5664
net area of primary / 2.0137
Total TB area / 2.4865
unobstructed equivalent pipe diameter / 1.779

TB Weber
secondary diameter / 0.0000
area of secondary / 0.0000
area of secondary pivot (deduct from area) / 0.0000
net area of secondary / 0.0000
primary diameter / 2.3750
area of primary / 4.4300
area of primary pivot (deduct from area) / 0.7422
net area of primary / 3.6878
Total TB area / 3.6878
unobstructed equivalent pipe diameter / 2.167

TB Audi 5000
secondary diameter / 1.3750
area of secondary / 1.4848
area of secondary pivot (deduct from area) / 0.4297
net area of secondary / 1.0552
primary diameter / 2.0625
area of primary / 3.3409
area of primary pivot (deduct from area) / 0.6445
net area of primary / 2.6964
Total TB area / 3.7515
unobstructed equivalent pipe diameter / 2.186
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endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Sat Jan 05, 2008 2:15 am    Post subject: Reply with quote

Hmm, it is interesting the weber and the audi units are so close. I think IC plumbing diameter should be based on total flow or HP figures rather than TB size. Corky Bell has some pretty good formulas for this.

Todd
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"simsport" said....superchargers are better than turbos its official!....
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Rich H  



Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK

PostPosted: Sat Jan 05, 2008 2:24 am    Post subject: Reply with quote

No Fluid Dynamacist but worked on aircraft for 6 years, correct me if I'm wrong but as I see it I wouldn't be too worried about the individual areas. The boudary layers on all of the surfaces would be of much more importance than the actual area. And a smaller area will just mean a faster air flow (Good for cylinder fill and torque at mid-range)

They need flow benching really to get something useful. Even doing things like filing the butterfly pivot bar oval (Reduce x-section) and making sure all the screws are flush will make a big difference.

Rich
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gegge  



Joined: 27 Jul 2007
Posts: 994
Location: Sweden

PostPosted: Mon Apr 21, 2008 8:43 pm    Post subject: Reply with quote

Noticed the header on the Weber Redline Throttlebody:



"All except turbo"
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT clone LSD Coilovers
924 -85 DP kit, BBS RS, M030 and tuned engine
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emoore924  



Joined: 13 Apr 2004
Posts: 2788

PostPosted: Tue Apr 22, 2008 12:37 pm    Post subject: Reply with quote

Ya know, I dunno why it says that. It bolts right up to my 1980 and it is bigger than the stock TB... Maybe the comment relates to the 81-82 with the idle and WOT switches, which the Weber doesn't seem to have provision for...
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flosho  



Joined: 01 Jul 2004
Posts: 3158
Location: Eau Claire, Wisconsin

PostPosted: Tue Apr 22, 2008 1:10 pm    Post subject: Reply with quote

I wanna know what the hell intake that is in the picture? With a north/south mounted throttle body!!?
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moone924  



Joined: 05 Feb 2003
Posts: 865
Location: Southwest Littleton Colorado

PostPosted: Tue Apr 22, 2008 2:24 pm    Post subject: Reply with quote

flosho wrote:
I wanna know what the hell intake that is in the picture? With a north/south mounted throttle body!!?


A intake manifold for a front drive VW - read the top of the instructions
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gegge  



Joined: 27 Jul 2007
Posts: 994
Location: Sweden

PostPosted: Tue Apr 22, 2008 4:20 pm    Post subject: Reply with quote

emoore924 wrote:
Ya know, I dunno why it says that. It bolts right up to my 1980 and it is bigger than the stock TB... Maybe the comment relates to the 81-82 with the idle and WOT switches, which the Weber doesn't seem to have provision for...


I guess thtat you are right, but Iīve seen Weber TBīs with the additional switches. Ok, so no bolting issues then? Is it airtight and can withstand positive boost?

Did you use the adapter/mounting plate to convert the square boltpattern into rectangular?
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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT clone LSD Coilovers
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black with low ET "Phonies"
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gegge  



Joined: 27 Jul 2007
Posts: 994
Location: Sweden

PostPosted: Tue Apr 22, 2008 4:58 pm    Post subject: Reply with quote

A comparison betweeen Audi to the left and stock to the right:


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Carl Fredrik Torkildsen

924 turbo -81 Carrera GT clone LSD Coilovers
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924s -86 Black on black with low ET "Phonies"
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emoore924  



Joined: 13 Apr 2004
Posts: 2788

PostPosted: Wed Apr 23, 2008 1:01 pm    Post subject: Reply with quote

I have the audi TB on my turbo now. It was essentially a direct swap. I had to grind down the manifold opening just a little to accommodate the larger throats, but there were really no other mods required. Works fine. Works great in fact.

I also have a single throat Weber with the adapter for the oval TB manifold. I've not tried it other than test fit and it seems to fit right up. However, I would think this would be a better fit for the later style Manifold (the one that uses the round factory TB...)

Either way, I would expect no problem with + pressure if you gasket it properly.

Also either way, I would expect that either the audi or the weber to be a better performing TB than the stock units.

Just a point of information, ALL of the difference between the audi TB and the stock TB is in the secondary. See my other thread comparing the diameters of the throats in the various TBs.
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ideola  



Joined: 01 Oct 2004
Posts: 15426
Location: Woodstock IL

PostPosted: Sat Jul 11, 2015 2:56 pm    Post subject: Reply with quote

"Big bore" throttle body cross reference:
Neuspeed 3-65.10.xx
Audi 5000 85, 86 non turbo
VW Fox 91 -93
VW Cabrolet 91 -93
VW Golf MK2 8v
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