I would have thought that the inlet manifold port is machined to size.
It is...and it's larger than you can get the TB casting, so no need for concern.
Just to remind people...opening up the TB will only give 1-2 BHP if you are lucky, on a standard engine...and go too far, and it'll kangaroo in traffic. That's from experience.
The ramps are there for a reason - to speed up airflow and make it more progressive at small openings...remove them and you lose the smooth transition from closed to part open throttle.
Just removing the ramps is usually OK with little by way of negative effects...but re-profile the casting and you can get kangarooing, with absolutely no gain in power.
I'll say that again: there is NO gain over simply removing the ramps, and that's on a 195+ BHP 16v.
So, by all means do it...just understand the downsides, and don't go expecting miracles.
If anyone is opening it up in a lathe, you'll need a 4 jaw, as the casting is offset.
As I said earlier best on a face plate over a 4 jaw as you will probably need to shim it to get it running true and its easier to hold, done it loads f**ked a few up in the process
You are right it is has a an offset
Not so sure on the purpose of the ramp, I will say that the step enables an easier tidy shut off between the two cores in the mould, its how I would build it.
You are right in saying it would speed the air up so I. am sitting on the fence.
Guys to just inject a little bit of realism to the thread,
Surely you need to mark the porting on your own throttle bodies because there could well be casting differences and if you pull too much material out then you merely create a step again in the other direction?
To get a good match they need to be marked up for you to shave...
As I mentioned if you get it wrong on a lathe you will create an undercut opposite the original step, need to clock the bore and mark the cutting surface so you can see where its cutting.
Bore is pretty good but flanges run out a little hence face plate and shim mentioned above.
Some types need an angle plate so you can get in on the compound slide from the back
I have a shelf full of TB's and MAF housings which I have mullered over the years, I used to do a practice one before I took on paying work....
Butterfly must come out when working it on a lathe, also the mechanism and wheel off the side.
Also be aware that you may hit some porosity, also cutting speed will need to be right as you will get a rough finish.....
By all means have a go, the 8v and VR are about the easiest to do and KR the hardest on golfs.
I made a fortune on Fiesta Zetec's as they are pretty restrictive and the Mazda large body TB's are like gold dust and twice the price.
There is a hole in the ceiling tiles above my old workshop where one did a flyer
