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post #37 of (permalink) Old 11-04-2007, 16:07
Scarlet Fever
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Join Date: Jul 2002
Location: Near Stansted Airport
Car: MGF
Posts: 5,476
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Throttle bodies.

Standard F comes with a 48mm diameter throttle body, This means that when the maximum acceleration is applied, 48mm cross sectional area of air is delivered to the engine.

There are larger throttle bodies available out there, the normal route is to fit the one developed for the Trophy 160, known as the Trophy Throttle Body, or Trophy TB. This has a 52mm internal diameter butterfly, meaning that under the same circumstances outlined above, 52mm cross sectional area of air is delivered to the engine.

Doesn't sound like much, but we are talking area here, the real difference is around 17% more air in for a given depression of the loud pedal.

What does this do for the car? Well, surprisingly little in measurable terms. You will actually loose a bit of low down torque, but gain it top end, and in bhp terms we are talking only a +2bhp(ish) gain. Where it does score though is the immediacy of the throttle response.

I have said above that for a given throttle response you are getting up to +17% more air in, this equates to an engine that revs more quickly, making the car feel more responsive. In real terms it is probably only marginally quicker - there is an argument that the quicker you reach the max power/torque point in the rev range the quicker the car will be, but the difference isn't marked enough for this to be considered a good power modification from a real performance vs s spent point of view.

So why do it then? Well, there is a reliability argument for ditching the plastic 48mm throttle body in favour of an aluminium 52mm one, but the real reason for doing it is the size of the grin on the driver's face. A freer reving engine makes the car feel a lot faster, this is subjective but produces a real feel good factor for the driver.

I have mentioned that a lot of this is down to the adjustment of the throttle cable, inherrant to the fitting of the new TB and it is true that your grin an be widened just by doing this simple adjustment on the old TB, but the 52mm one maximises this benefit.

On a track, your lap times will be marginally quicker with a 52mm TB, but you will have more fun getting there as the car feels that much more urgent.
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