Ported inlet manifold (M20 325i)

[garyp_E30_325i]

I'm thinking of porting my inlet manifold (M20 325i), does anyone know what over bore I should be looking at?

[Cloggy Saint]

For a larger throttle body?

[E30BeemerLad]

all that is involved in the "porting" is making sure the port from the manifold matches upto the ports on the side of the head, so that there is a clear flow for the gases to enter, so there is no ridge os say a smaller hole for the inlet on the head compared to a larger diameter hole on the manifold.

Best thing to do is get some markers blue ink and paint the side of the head and mate the manifold up to it, you can then see where the ports match or don't match and know where to remove metal.

You will probably end up taking metal out of the head rather than the inlet manifold but I have not done this so am speaking theoretically/ bull shit mate

probably best to wait for one of the heros to arrive and correctly advise you. I have a spare head and manifold on the way, so may look at doing this myself too

[garyp_E30_325i]

For a larger throttle body?

BBTB fitted about two weeks ago.

[Cloggy Saint]

i'm confused, which end of the manifold do you want to port?

[garyp_E30_325i]

i'm confused, which end of the manifold do you want to port?

Both.

I've fitted the larger throttle body (but I'm not sure how much larger it is, it was just available to me at cost so I took it), so increasing the bore at the inlet to match the TB should be beneficial - I would think.

I haven't ported the heads, yet, but if there was a benefit from porting the inlet manifold by e.g. 1mm and then porting the heads to match, then I would certainly be keen to do that. It's just that I have the 'spare' inlet manifold off the car, so it would be easy for me to get that done first (I'm using my E30 on a daily basis at the moment) then do the rest later (when I fit the inlet manifold).

I just wanted to know if anyone had experience of what a suitable / good increase in bore would be.

Sorry if I didn't word my original question very well.

I suppose if I port both ends it would be good to get them gas flowed too...?

[E30BeemerLad]

pic here is of the ports being opened out on a 320 head, you can just see what is being removed if you look at the port which is being ground, you can just make out the blue circle around it. This was done by mating up the inlet gasket to the head and then drawing around the inside of the gasket where metal was showing, the same principle applies to your inlet manifold.

I think you will discover if you mate a gasket up to the spare manifold you have that there is not much spare metal there, more likely to be some spare on the head itself, but I would not recommend attempting anything like this with the head still bolted on as you will never get away without getting some metal swarf into places you shouldn't.