What to do to the head performance wise?

[scaraveos]

Hello, I will soon remove the head from the engine. What can be done to it and the intake performance wise while its out?

Thanks!

[E30_fiend]

port match the intake. Port and polish the head. Bigger intake and exhaust valves. Aluminum rocker arms. High performance valve springs. and an aftermarket higher duration cam shaft.

[Madhatter]

dont even say what head/engine it is.

[mattdk318i]

bigger valves actually dont help flow at all, Per Metric mechanic. They found that the stock valves flow just fine

[Madhatter]

I would tend to disagree with you. Larger valves and bowl work saw a 40cfm increase on my head, didnt even touch the ports other than the guides.

[scaraveos]

dont even say what head/engine it is.

M20B25 325i

So where do you get bigger valves and how much bigger? How much do they cost?

How about extrude hone intake and big bor throttle body?

[TS87325IS]

I would tend to disagree with you. Larger valves and bowl work saw a 40cfm increase on my head, didnt even touch the ports other than the guides.

Did you try just increasing the bowl with stock valves before you flow tested it? just curios. I belive Metric Mechanic has tried several combinations and said they flow better with stock valves . just my two cents.

[digger]

Madhatter is not telling you the whole story about his situation;)

[NC325iC]

add 12 valves, if you cant do that, you should just valve job port and polish, new cam and rockers

[CorvallisBMW]

Get a good 3-angle valve grind with a backseat. There was an article posted on here a few months back that showed a big increase in flow from a simple backseat grind. I think it was called backseat....i dunno. Maybe someone can find that article. Other than that, port-match, extrude-hone, bigger TB, rockers, aggresive cam, stiffer valve springs.

[z31maniac]

dont even say what head/engine it is.

Being in the M20 section and all...................

[digger]

Being in the M20 section and all...................

there are 3 different M20 heads available and the modifications will vary significantly depending on which you have

[Madhatter]

Madhatter is not telling you the whole story about his situation;)

Its a 731 head for sure (which is why i asked what motor it is), but the peak flow figures occured well before you got into the large lift amounts the new cam could produce. It actually peaked fairly early.

Being in the M20 section and all...................

See digger's post above. 885 for example, id advise not to open up the inlet port at all, dont increase the diameter. Work on the guide area and the transitions in and out of the bowls. Larger bore of the 2.5L motor could take larger valves though and I think they would see some gains. However look at replacing the seats to do so rather than having existing ones cut. Clean up the bowls, working the backside then make sure your short side transitions and the bowl to seat transition is smooth and free.

The flow in and out of the bowl area is where you need to concentrate most of the work, flow figures have shown the velocities are lower on the larger port heads than probably expected, so opening up the port could actually result in a loss of torque as they begin to drop.