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MG MGF Technical - throttle bodies

the accelerator response on my 97 f is just starting to hold up as the revs go down to idle and have read about this on dieters site however is there any point in putting on a 52mm tb if the inlet manifold is only 48mm? or is it actually larger?, if not can it be ground out to match? i am contemplating a pod filter+ a throttle body. thanks bruce
b dix

Hi Bruce,

the 48mm and 52mm throttle bodies are dimensionally the same: they share the same 57mm ID outlet diameter, so there is no step problem with the manifold inlet (although if you've got a VVC style cast alloy inlet plenum, then as Mike Satur has noted, casting irregularities can cause a significant mismatch between the TB and plenum, so this is an area worth checking). The key difference is the size of the butterfly and choke: the 48mm being 48mm and the 52mm ... well, you get the picture! LOL

Hope this helps
Rob Bell

Rob, I have recently seen references to Rover 56mm Tbs on fee-bay. Do you know anythng about them?
Steve Ratledge

not good apparently, according to DVA on the lotus board they rob power.
Will Munns

Nothing to add other than what Will's written Steve. Depending on who you ask, you either get the 'bigger must be better' answer - but little in the way of supportive evidence. On experience with the 52mm throttle body, I can't believe that they'd be any better than the standard throttle body. If DVA says it is worse than standard, then I am sure that he has evidence to support this belief.

It is just possible, depending on the state of tune of a particular engine, that a 56mm TB could be of use - but IMO, if you are wanting more than a 52mm TB can offer, then you are looking at MTBs.
Rob Bell

many thanks for your info i have the non vvc engine with plastic tb,so possibly staying with alloy replacement would be ok if no benefits are to be had with 52mm tb, cheers bruce
b dix

Bruce, I saw a 1 bhp gain on the rolling road with the 52mm on my car (standard 1.8i) - hardly enough to write home about. But the throttle response is much more eager (probably because of the larger aperture opening for any given movement of the throttle pedal) - which for some is justification enough to take this route. :o)
Rob Bell

Sorry, no BHP benifits are to be had from 52mm, but it will give you a snappier throttle response. BHP _losses_ are to be had with 56mm
Will Munns

This thread was discussed between 14/03/2005 and 15/03/2005

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