Question about oversized valves and reaming.

[Mucci]

I saw IE sells +1mm oversized valves that work with the stock valve seats, they just needed to be reamed out. 

 

On the M10 heads, do the seats overhang the intake/exhaust tracts? I'm curious how much of a difference reaming out the stock seats would make, especially if the seats are flush with the air tract. 

 

Pic to better describe:

 

I have a million other things to buy for this car that are higher priority. I'm really just curious

[avoirdupois]

Your question is loaded with variables.  To the best of my knowledge, as originally installed, valve seats sat flush and were easily cut and resurfaced to accommodate later produced 46 mm valves.  However, newer installed seats might not necessarily be identical to the original seats and therefore could, not surprisingly, slightly protrude into intake plenums.

 

 

 

 

Edited October 8, 2019 by avoirdupois

[tzei]

Flush. +1 mm valves are used in n/a race engines (if rules allow). And to make use of them you'll need cam, comp and yadda yadda... but this you already knew right.

[Mucci]

Does seat reaming for oversized valves also include boring out the aluminum its set in? Wouldn't the bottleneck still be the air tract?

[Mucci]

* double post.

Edited October 8, 2019 by Mucci

[xr4tic]

There are a few threads about larger valves not being worth it because of valve shrouding, although I'm sure you could fix that with even more head work ($$$).

 

I had to buy new valves for my head and went with stock size (E21 head), the cost increase wasn't worth it for me.

[xr4tic]

Double post, appears the system is still glitched

Edited October 8, 2019 by xr4tic

[oldguy]

You keep saying reaming which is usually related to the guide.  You're talking about throat blending or cutting.   That step is shown here.  

  The problem is port work is usually required to take advantage of the valve being larger and throat being cut out.  A 121 and 121ti head will not support a +1 valve without new seats cut in.  a e12 and e21 head will support a +1 valve due to larger seat installed factory.  

[Einspritz]

A reality if you are going to replace the seats in an oversize size, is that you will have to have them made as I bought supposedly the last 3 exhaust from BMW for a turbo and had to have one made, which isn't a big problem but you will have to provide the proper specifications.