so this comment got me thinking:
VWVortex.com - FrankenTurbo F23 Project: FrankenTT is go!
now Issam is quite a respected fella in the vag tuning world, esp 1.8t, and is responsible for the following thread:
VWVortex.com - TECH : TEST 1 OF 3 | Throttle Body Sizing
which although quite an old test, still has some credibility.
so what am i getting at.
Well MOST people on here and all over the tuning world run 63mm or 2.5 inch pipe work for their boost hoses.
and there is lots of ummmming and arrrring about inlet manifolds and throttle bodies and the benefits that can be had.
If you havnt already read tufftys thread, he and bill recorded some considerable gains through a large plenum/runners alone, promising for alot of people pushing respectable power.
so what about the Throttle body. Well apart from Issams tests over in the US quite some years ago there is much more speculation to the benefits of a larger one. After tufftys recent update it seems he will be doing some testing on a larger one soon-ish, although i dont knwo what tb it is and the sizing. hopefully he can share.
so my thoughts on this,
63mm boost piping, as used by myself, has a wall thickness between 0.5-1mm, lets say 0.5mm for now, 1mm seems thick to me.
The pipe has 62mm internal diameter, and an area of 3019mm^2.
so now lets take our standard 60mm ID throttle body as found on our S3.
Area of 2827mm^2. Already some way off the boost pipe size.
Now if we apply Issams theory of 80% useable area in the throttle body (due to the butterfly and the pin on which it rotates), we have a useable area of 2261mm^2.
2261 Vs 3019
quite a difference im sure you'l agree.
now as we all know and have come to learn, 'its all about the flow' TM
so if we are going to have the 'ideal' setup in our boost/inlet system, we need a throttle body, that at 80% of its internal area, matches the area of our boost pipes. Afterall, we are moving a HUGE volume of air.
So if we spec a 70mm Throttle body, which has a 3848mm^2 internal area, and 3078mm^2 80% useable area, we have a much better match.
3078 Vs 3019
so in theory, a 70mm throttle body, based on Issams 80% comment, would be ideal.
Now if we refer back to his tests in the above thread, 70mm seems the best option to me. Backing all this crap up? I think so.
If however Issams 80% is a little high, and tbh im thinking it might be. And we apply a 90% (10% restriction from butterfly assembly) Then a 65mm TB might cut it.
65mm has 3318mm^2 area. 90% = 2986mm^2
2986 Vs 3019. A tad better.
i started thinking about this for my own build, and the fact il hopefully be using a large plenum/runner inlet. And i want a TB that will 'match' the flow of my pipe setup. Then Issams comment on vortex got me thinking basically.
so this is some food for thought when you are spec'ing your build, and whilst the standard TB will work, and will be fine, we all want cheap gains, and a TB isnt all that expensive, and on big turbo builds, may yield some worthwhile horsepower.
Next step, find a suitable Tb.
list of TB and internal diameters
standard = 60mm
2.7TT S4 = 65mm???
VR6 = 65mm
NA S4 = 70mm
R32 = 75mm
RS4 = 75mm
Hemi = 80mm
the above may be edited. subject to measurement