hey people have recently been playing round with my ca18det while its apart i thought id fully remove the rods from the stock manifold butterflies and port match the two piece manifolds, and i found that between the two manifolds there was up to 5-6mm mismatch in places has anyone else done this? im thinking with that and a bigger throttle body,chasing one now... i should come up with some sort of gain??? also people who have done it, do i need to plug the rod-holes between ports? i am thinking because the injectors are downstream of the holes it wont matter?

Yes I'd say it would matter. I too have pondered if it's possible to mill out the land between the two portrs to create a "monster" single intake port like the UKDM ones had.....

yes i have a ca18 head with the plenum and runners all match ported i havnt had it flow tested but it must be alot better than standard



this picture shows how much needed to be taken out




the left is stock and the right is ported

dont need to block holes between ports. they may create a little turbulence but you woundnt notice.anything used to block holes could dislodge and suck through engine.
must block holes to outside to prevent air leak.
have you run the car with all this working?
i am interested to hear what difference removing it makes.
the most benefit you will get from porting is the area closest to the valve seat.

I remember looking into this recently....you end up losing a bit of torque down low without the butterflies and overall hp doesn't change much.

The port matching would up ultimate hp though - so it's probably a net gain over 3500rpm and a little bit of a loss below.

dattodude dynoed before and after so can tell you the difference the butterfly removal makes.

dazza i havent run the car yet but on the manifolds i removed up to 6mm of mismatch which i think is huge... that was on plenum and up to 2mm on intake ports bolting to the head.... surely that much will do something will find out when i rebuild the engine i suppose.

I didn't get into match porting with my engine. But I did notice the exhaust manifold gasket was hanging down 4mm into one of my exhaust runners. So I be careful when installing the exhaust manifold too.

But the butterflies are important for torque below 4500rpms. If you are running after market ECU, and not programming the butterfly function in, then you may as well remove them.

If you are running a light flywheel and are only interested in power between 5000-8000rpm, then pulling out the butterflies is a good idea.

Engines are not all about flow. They are about gas speed too, and a turbo engine is quite different to an atmo engine.

ford barra NA has butterflys
turbo does not (same manifold)
i would have thought they would have less affect on a turbo motor
6mm mismatch? thats huge, yeah fix it
with a ca you could make a spacer plate between manifolds to lengthen the runner
guys will spend days on the flow bench trying to find that last bit and when they bolt the manifolds back on it is no better
you must work on the bottleneck in the system

that would work IF you have done the bowls, seats and chambers as well