School me on the 731 head

[der affe]

i have a set of euro ETA 525e (11.2:1) pistons that i will be putting up for sale soon alsong with lightened ETA rods that i will be putting up for sale soon.
use those with the 885 head and you end up with a 10.2:1 2.7i stroker and less recipricating weight because of the lightened rods (43 grams lighter per rod).

just throwing that out there as an option.........

[ForcedFirebird]

You won't be disappointed, click the vid link in my signature to see how my 2.7 runs after the 885 head and Motronic 1.3 ecu upgrades. Still has the stock 2.93 rear gears to boot ;)

[acolella76]

Looks like I'll be going with the 885 head :)

Seems like it leaves me more options.. If i want more power I can easily boost it :D

[ForcedFirebird]

885 is a superior head than the 731, cop the small CR difference for a better flowing head

This.

I would buy the 885 head and call it a day.

This.

the compression really won't be a huge deal - a few % loss. it's not like the stock B25 is a high-CR screamer. it will certainly wake up your eta motor either way.

...and...this.

Losing .7:1 compression and gaining the flow and cam of the 885 head is definitely worth it, and not too bad on the wallet. ;)

[nando]

It would probably be a lot cheaper for me to just do that on my current head.. would it not?

And yeah I'm probably going to just slap the 885 head on. Maybe use a thinner head gasket to help with compression?

the compression really won't be a huge deal - a few % loss. it's not like the stock B25 is a high-CR screamer. it will certainly wake up your eta motor either way.

[Faviolosky]

tell you what tell me where you are going to get it, and ill get it, then your left with one option, :-D:-D

no seriously

[hotballs]

It would probably be a lot cheaper for me to just do that on my current head.. would it not?

The 200 head is yes basically the same as the 731 head, minus the intake ports and the 7 oil journals vs. 4. So you would have to hog out the intake ports of the 200 head and drill the extra holes to lube the 7 bearing cam to make is a 731 head. Honestly not worth it if you can just start with a 731 head. Plus the 323i cam is "hotter" than the 885 cam.

The 731 valves and 200 valves are exactly the same. You can put i exhaust valves in the 731 head. There is enough room to grind the stock seat to add +2mm valves on the exhaust side, but only enough room to do +1mm on the intake side. After that you need to put in new seats. (You get a machinist to grind down the i intake valve 1mm and grind out the intake seat 1mm.) And port it. And $1000 later you'll still have a NA m20.

[acolella76]

I would personally use the 731 head and port it to use 885 valves and manifolds

It would probably be a lot cheaper for me to just do that on my current head.. would it not?

And yeah I'm probably going to just slap the 885 head on. Maybe use a thinner head gasket to help with compression?

[nando]

I would buy the 885 head and call it a day.

[SpecM]

I would personally use the 731 head and port it to use 885 valves and manifolds

[acolella76]

So basically, me spending the $275 for a 731 wouldn't really be worth it when I can get a rebuild 885 head for half that?

I know the 731 won't work with the seta pistons. If i had them, or the money/time to put some in, I wouldn't have posted this thread

[nando]

what digger says, also 731 heads have 80mm bore so only works with ETA not seta

hmm? you talking about the combustion chamber size? M20B27 (eta and seta) and M20B25 are all 84mm bore, not 80mm. the combustion chamber of the 731 is the same as the 200, but of course you're still right that it won't work with seta pistons.

[Gruelius]

what digger says, also 731 heads have 80mm bore so only works with ETA not seta

[digger]

885 is a superior head than the 731, cop the small CR difference for a better flowing head

[blueapplesoda]

you get higher compression with a 731 head than with 885, and the valves are near 885 size. This would be a proper "2.7i" utilizing higher compression. if you were to boost the motor than 885 would be a better choice, as it lowers the compression ratio.