25i what head
Moderator: martauto
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frenchi
- E30 Zone Newbie
- Posts: 92
- Joined: Sat Feb 23, 2013 11:00 pm
building up 25i from an 1989 all bottom is ok and tight what head will go on for more wow in the rip dept
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Brianmoooore
- E30 Zone Team Member
- Posts: 49360
- Joined: Mon Jan 10, 2005 11:00 pm
Strangely enough, the best head for a 2.5i is the one that BMW fitted; the 885. Minor improvements can be made to it, but nothing that you'd notice in the real world to justify the expense.
The limiting factor is that it only has two valves, so to make any real gains in head performance you need to go to a four valve head. A few four valve heads have been made for the M20, IIRC, but it'll be a lot cheaper and easier to use a M5x complete.
The main improvement you can do to a M20 when building one up is to increase the compression ratio with appropriate pistons, such as the pre facelift version.
The limiting factor is that it only has two valves, so to make any real gains in head performance you need to go to a four valve head. A few four valve heads have been made for the M20, IIRC, but it'll be a lot cheaper and easier to use a M5x complete.
The main improvement you can do to a M20 when building one up is to increase the compression ratio with appropriate pistons, such as the pre facelift version.