you'd be doing a fair amount of fabrication regardless of what route you go. but if you do alter the pivot bar to make it smaller, you might as well bore out the throttle body, swap out the flap for a larger one (to fit the larger bore), and fabricate a thinner (yet still strong) pivot bar that fits where the existing bar is now - which means the ends of the bar would be thicker than the middle.

the bigger bore would give you more airflow, the smaller pivot bar would give you less restriction, and the new flap would make sure everything still works.

boring out the throttle body should be less than $100 (see my previous post with the link). fabricating a new flap is cheap and easy. it's just a flat circle with some holes in it. but creating the new pivot bar will be more expensive since it will have to be milled.

this... this might actually be a fun project... i'll take some measurements later today to sate my curiosity.

 

I pinged Evolve out of the UK who does BMW and Audi. I told them they should look into this and they said they might take a gander. I will keep you posted

 

Took some quick measurements:
TB diameter at opening: 84mm
TB diameter at butterfly flap: 82 mm
Pivot bar width: 9mm
IM diameter at opening: 86mm
TB wall width at opening: 2mm

The opening to the intake manifold is 2mm wider than the throttle body, meaning enlarging the TB bore will not lead to another bottleneck at the IM.

Please note, I hate math so my numbers could be wrong. I used the above numbers to make the following calculations:

Area of TB opening: 5542 sq mm
Area of TB at flap: 5281 sq mm
Area of pivot bar: 738 sq mm
Area of IM opening: 5809 sq mm

Based on this, the TB constitutes a 22% reduction in area at the flap.
(area of IM opening) - [(area of TB at flap)] - [(area of pivot bar)] = (area at most restricted point in TB)
(area at most restricted point in TB) / (area of IM opening) = (percentage difference in areas of largest and smallest points)

If we bore out the TB to be consistent straight through (84mm without the factory reduction to 82mm at the flap), and keeping all else the same, using the math above the 22% reduction in area drops to a 17.3% reduction in area. The bottleneck would therefore be reduced by 21.4%, and the area of the TB at its most restricted would increase by 6%. This is without modifying the pivot bar or reducing the wall thickness of the TB (aside from boring out the step, the minimum thickness of the TB's walls is not reduced). It does, of course, require a new butterfly flap to fit the larger bore.

Opening the TB up even more, which would require reducing the TB wall thickness below 2mm, would provide even more airflow. But then you've got to worry about component strength.

 

Isn't the taper there to increase air speed. By boring it you will reduce the air speed effect.

 

Yes, I was just about to say that. My above post was about opening up the area of the TB. As for airflow speed, you might have an issue. You could keep the current butterfly flap and do a knife-edge port (the walls of the TB are blunt, so air hits them and it causes turbulence that lowers air speed. knife-edging sharpens the wall of TB so air flows in much more smoothly).

About the taper itself... The reduction in diameter at the butterfly flap isn't so much a taper as it is a step. it isn't a smooth reduction in area from opening to flap. It's a step that reduces the area from 84mm to 82mm. Having a shop port the TB *should* keep the 82mm diameter in place, while opening the diameter at the openings by knife-edging them, and turn the step into a true taper.

Only way to really find out is to send a TB to a shop! (Yes, I'm still considering it!) But from what I've heard about TBs, generally it won't pick up more than one or two HP, if anything, but it should give a little bit better throttle response. The only way it'd be giving more power is if it's truly the bottleneck that's keeping our power down. I think, since we don't have access to AM's R&D, we'd just have to test this out ourselves.

 

Im sold.. I want to do this.... there must be some potential this route. Im also thinking taking the head off and milling that down as well.

We all know that the Vantage was designed not to out do the DB9. ( No disrespect or offense meant to DB9 owners )

 

The Ferrari 458 has a redesigned airbox on new models .... are you telling me with there F1 expertise they could not of put this new airbox in the car in the first place. Pleeeeaase...

But 80% of people that have a 458 are brand happy and not so fussed on power etc...