BMW vs AMC head

[Cabriolet]

many people ask the quest of what is the difference between the crappy AMC head vs the bmw head. well some say the ports are different sizes and such.

when i pulled my head off my mtech i found that it was an AMC head so i replaced it with a 87 bmw b25 head. i was very surprised to find very little difference. the AMC head is very poorly cast. many rough spots and the top side of the head is ~3-4 mm shorter and makes it difficult to fit the seals in.
as for the intake and exhaust ports. they are both the same size. though there is about 1mm deviation between the ports on the AMC head. meaning they arent all the same size. the intake side of the AMC head was cut smaller to fit an ETA engine, the bored for an "I" head. the chamber was also rebored to "I" specs. the BMW head has a better design on the intake ports, being a smoother line into the valve.

please see the pics bellow to see the differences.













thx, any questions? ill try to answer as i can.

[digger]

thats pretty terrible detail where they machine the roof of the port entry........the floor of the BMW head looks flatter which is good for flow around the short side

[MR 325]

Glad somebody finally took the time to compare the two. I would personally never use the AMC head whether it be in stock form or modified like the ones I sell.

[YAN-3]

Oh wow I never knew about these AMC heads. Gonna do some searching now. Thanks for this.


Learneded somfen new today!

[Mr.SWISS]

The cooling ports appear larger on the AMC head but with all the other epicfailz I would run away from this casting.

[Northern]

any particular way to tell which cars have the amc heads?

[SkiFree]

^ The big AMC letters cast into the head where you'll normally find '885'.

[Cabriolet]

any particular way to tell which cars have the amc heads?

BMW head: right over the exhaust port #2 you will see 2.5 in raised number.

the AMC and 885 are hard to see when its on the car, because the intake manifold blocks the view.

[nebulous123]

this is only for the B25 right? Noticed you didn't mention the B27.

[Northern]

and this is only a replacement head, not some loopy factory part, correct?

[bernzpeed]

i found an AMC head on the 89 325i vert that we parted out.

[Cabriolet]

and this is only a replacement head, not some loopy factory part, correct?

im thinking it was a factory item, maybe bmw couldn't meet the demand and had AMC make them for them. there is just too many around to conclude that people changed heads.

[Mr.SWISS]

im thinking it was a factory item, maybe bmw couldn't meet the demand and had AMC make them for them. there is just too many around to conclude that people changed heads.

Interesting....

So far these have all came from M20B25's right?

[bastianshaw]

im thinking it was a factory item, maybe bmw couldn't meet the demand and had AMC make them for them. there is just too many around to conclude that people changed heads.

Agreed.

[Sagaris]

You would expect the Spec E30 guys to have gone through and dynoed each one to see which is superior in stock form.