+1 valves in a 731 head

[Gruelius]

Hi all,
I got told 325i inlet (42mm) in a 731 head (40mm) is a very expensive task for machining, how about a 41mm valve? or do they not really exist?

Thanks

[jlevie]

Seems to me that increasing valve size is going to mean increasing seat size, which requires some expensive machine work. So I don't see where there'd be an advantage to 41mm vs 42mm valves.

[nando]

Pretty sure they can be reamed +1mm, at least the 885 can be.

[Gruelius]

yeah, i know for a fact 325i vavles need the combustion chamber modded, just looking to not have that drop off in flow for higher lift.

Also 855 heads cost ~$700-1k here so thats why im sticking with 731

[SpecM]

$700 to 1000? whaaaaaaa?

they're like $50 here

[nando]

$700 to 1000? whaaaaaaa?

they're like $50 here

where?

[SpecM]

where?

ok ok... I meant a buddy-buddy deal for a head that may need freshened up

but good heads swap hands for $200-300 easy

[Gruelius]

yeah we had no super eta's and most bmw owners were tightasses getting 318i's so rarity of the head has bumped its value lol.

[lennon]

the rarity of the 731 head has somewhat bumped it's value here, for people with eta's. i wouldn't bother installing plus size valves in that head. it would be wiser to save that money and get an 885 head/m20b25 if you don't have one. even at 700-1000 you would probably come out on top for cheaper than doing all that work to a lesser head. and why not buy one on here from the states or elsewhere?

[Gruelius]

complete motor looking ~$ 1500

I bought a m50 from usa once and gto fucked completely on it. ended up losing about $700 aud. shippings a pain and if the head had a crack develop from shipping id be effed

i also have a good nick 731 head in my parts pile.

may just have it ported but i feel like its going to choke the 2.7.

[BMC227]

but i feel like its going to choke the 2.7.

lol, little do you know.

[digger]

use B25 valves and ream the seats and deshroud if neccesary. If you do a half assed job you get half assed results

[wakdog]

Would it really be worth the effort of fitting the larger valves?

I have a 2.7 ETA block with 10.2:1 euro pistons and a AMC 731 head (after my last one cracked) My 731 head is ported to essentially the same size intake ports as a 885 head (probably a little bit larger) and we just have to match this to a 325i intake mani and i should be good to go. Would I gain much in this setup from a +1 valve setup...?

[digger]

Would it really be worth the effort of fitting the larger valves?

I have a 2.7 ETA block with 10.2:1 euro pistons and a AMC 731 head (after my last one cracked) My 731 head is ported to essentially the same size intake ports as a 885 head (probably a little bit larger) and we just have to match this to a 325i intake mani and i should be good to go. Would I gain much in this setup from a +1 valve setup...?

a 731 head with B25 valves and ported mildly flows same as a 885 head but without as much volume in the ports. Why would you go larger ports than the 885? the 885 is already a little large. I hope this was decided based on flow numbers otherwise you might have killed port velocity.

[wakdog]

spoke to the guy who did the porting and hes told me its the same size ports as a 885 head, and jsut a general cleanup inside as the AMC casting is pretty average as it comes from the factory