ITB port size in relation to engine size and bhp

What size ports are in the head.

If you compare them to a pair of 45 webers, you would probably want 36 or 38mm chokes in them so I'd say go for it!

I built a 1.6 k series using 33mm bike carbs and it made more power than stick and ran very well.

Cool thanks for the info.

The twincam has square shaped inlet ports, measuring about 42x42mm across and up/down.



Honest question mate, how does the length of the manifold make a difference? I plan to make it as short as possible TBH, the injection twincam head has the injectors and fuel rail mounted in the head itself. Like this...

Runner length calculator put 3 or 4 as number of induction waves into calculator and you will need to google the cam duration (the final measurment is from inlet valve to inlet opening)

you want it as long as possible. usually there isn't enough space under a bonnet to get it the length required.

different length runners tested

makes for interesting reading.

I hate to be that guy, but wouldn't a zetec swap be a better option?
A zetec on itb's would be quite a few horses more, and miles better in reliability. Loads more aftermarket support and potential for more power.
Most stock parts are cheaper too.

I have some (R6?) TBs that might suit quite well - are you coming to A52/the beach this month? Cheap to you.

inlet runner length is from valve to opening of runner. so you can have the carbs close to the engine and have very long trumpets to get the overall length or have a long manifold and short trumpets with exactly the same runner length. i also read that the further away the butterflies the larger thay need to be but you also need the velocity. i also read that the higher the red line of the engine the further away the butterfly needs to be.

with carbs or injectors further away from the head gives the fuel more time to atomize and will help with power. there is always a compromise in which configuration to go for whether it is drivability or all out power or somewhere inbetween.

all i can say is very short runners will not help with power. from there it is either loads of testing of different configurations of length, size and position or build a manifold that should be somewhere in the middle and hope it works (that is what iv'e done)

I appreciate a Zetec option would be better in the long run for tuning, but I quite like the DOHC they are good on fuel and I'm not really up for having to fabricate and mess around loads.

My plans are ultimately to build a 2.3 8v DOHC engine (using the 2.3 bottom end from a Scorpio mated my original head) with a lightened flywheel, throttle bodies and a 4 branch exhaust manifold. There a guy on FSOC who's got a similar setup minus the ITB's but with some piper cams and his made 168bhp. I don't want loads of power just enough to give the Sierra a bit more poke, but keep the reliability of a fairly unstressed NA engine.

Probably won't happen, but you never know