Installed this CNG venturi yesterday.
Its almost the same size as the previous one but the advantage it has over that one is tapered ends. The diameter difference versus the original air intake manifold is around 40%.
I can live with it, provided it doesn't need any more holes to be covered with tape.
Installed it myself, wasn't easy. Needed a lot of squeezing and pushing. Cost me 350 Rs and two hours time.
Hopefully my car will be a happier machine on CNG from now on.