What size throttle bodies??

[Brooky]

What size induvidual throttle bodies should i use on a 1242cc 16v Fiat engine, i know of some one that use hayabusa ITB's and there 40+mm, but that was on a race engine, my engine will be used for fast road/track days etc.

thank you Tom

[RedLexus]

Well 40's are way too big , we run CBR900s on a 2.0l Zetec Ford , in an Escort and they're "only" 38s... I would say 32-34 should be fine . There are loads of Honda CBR 400/600s carbs for sale on the 2nd hand market.

I should add , these are Carbs , not throttle bodies , but the size should remain much the same .

[Guy Croft]

A throttle body can be sized readily by comparing with the equivalent max choke size for that spec engine if you were using carbs, so on your engine I'd be say on 40DCOE with 34 choke. A handy comparison because there are far more engines 'out there' still running carbs. The throttle body diameter (it has no choke of course, it's just a parallel bore) should be around that choke size, 34mm and certainly no bigger than 36mm I suggest.

On a 2liter-ish 4 cylinder unit 45 DCOEs with 40mm choke would equate to a 40 throttle bodies, that's going to suit up to about 225 bhp, over that one might perhaps be on 48 carbs with 42mm chokes and 225-300 bhp and using a 42 or 45mm throttle body.

From tests - there seems actually little to choose between say a 40 and 45 throttle body on a given engine (that came from a Vauxhall Nova tarmac rally 1600 back-to-back test, but certainly make them too big and you could expect a significant loss of torque due to the high velocity drop. So in your case anything from 32-36mm throttle body should be fine.

GC

[LanciaDan]

Looks promising,

How hard would it be to fit TB to a LC TC 2.0? Would it require a lot of fabrication? Im actually quite interested in doing this to my Thema, yet I am unsure how much mechanical work it would take to fit? Wouldnt it also require a retune of the ECU?

Thanks
Dan

[Brooky]

Thanks for the replys peolple. some other people have said i shouldnt go over 30mm....but Guy, ill take your word for it.

Throttle bodies under 30mm have proved hard to find,but i have found a set of 34mm tb's so ill email him again and check.

Ill be making the manifold myself as i have a few machines in my shed and i'll be able to get ally parts welded at work. And ill be running with Megasquirt so all will be good hopefully.

Thanks alot guys

[Julian]

Most throttle bodies for cars are built to use the old Weber DCOE pattern for fixings so the hard part of fitting them to the car is a bit of a doddle if you can get a twin cam manifold. Getting it to work is a bit harder...

[Brooky]

The weber DCOE's are carbs, ill be using throttle bodies of a motorbike, these use silicone joiners to mount to the inlet manifold and i'll be able top make an inlet manifold no probs.

#Getting it to work.....well ill be using MS so it'll just be trail and error untill i get it right

[smckeown]

On the subject of TB size but with the addition of chokes...

Guy,

I made the mistake of buying 45mm TBs ages ago, and have 45mm spacers too so changing them is not really an option.

I have played with placing chokes into the TBs previously to try and resolve a nasty mid range dip. Subsequently a new exhaust manifold with unes lengths has been purchased and expected to be the real solution.

So going forward, would you advise playing with chokes in the TBs to gain more mid range without sacrificing top end (say 40mm chokes in 45mm TBs) or just take the chokes out.

I have a peugeot 205 GTI (xu9ja) 1.9 8v race engine (peak power between 190-205bhp)

thank you
sean

[SteveninNI]

IN my experience with the MASS hot rod 205 engines- they needed a 42mm choke size (in a 48SP carb) to make 210bhp or so.
less compromised the top end. It depends on the engines useage really doesnt it?

[Brooky]

i think ill be going for 34mm TB's as Guy and a few others suggest.