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Difference Between E12 And E21 Heads


NullZwei
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I'm guessing it may relate to combustion chamber and valve size but I'm not exactly.sure.  If anyone can elaborate on the exact differences, that information would be greatly appreciate and may be helpful to others as well.  Thanks for your assistance.

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Valves are the same size, 

The combustion chamber is different, but the performance differences between the two isn't worth going into on a street hot-rod engine.  Deck height is going to be a more important consideration.  For reference the pictured IE cast pistons are both rated at 9.5:1 compression.

E12PANORAMA_zps2b002eff.jpg

E21PANORAMA_zps970fe46d.jpg
 

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The combustion chambers are completely different shapes, using a piston designed for one head on the other is going to have contact issues and even if you do a bit of work on them the compression ratio and squish area will be all screwed up. Flat top pistons fit with any of the heads, if you want a domed piston and some compression ration increase, get the right piston for the head!

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how does this compare to a 121 head?

 

The 121 cumbustion chamber is quite a bit different.  Valve sizes were the same however.  Obviously you have the dowel port open for the mechanical fuel pump as well.

 

43c6e002-035d-4db9-8e63-654c8ca79e0b_zps

 

 

For giggles, this is a 121 head period-prepped by BMW MOTORSPORT.  These were often used on different Alpina setups including the A4S.  Note the Hemi'd cumbustion chamber and the extensive porting.

 

121MShead_zps466d02bd.jpg

 

Since the head was hemi'd as you can imagine a similar piston was used.

http://www.alpinabmw2002.com/2011/05/alpina-mahle-bmw-m10-schmiedekolben.html

Edited by AceAndrew
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Andrew, just out of curiousity, what models/years used the E21 head?  I have a brand new E21 head with an 86 casting mark but is drilled for the fuel pump dowel pin.  Does Ireland carry any other compression rations for this head?

 

E21 heads were original equipment from mid '75 to late '79 (changed when they went from 2.0L down to 1.8L).

 

 That being said, BMW did do later casting runs on the earlier heads which were sold through the dealer parts network (and were never equipped on a newer car).  According to Jeff/Jeremy the last heads available new from the dealer sold out in the early 90's (before my time).   I've got a replacement M10 running an '84 casting of the 121 head.

 

EDIT: Yes, can do other compressions but it is not a time efficient ordeal, which is why its not on the web.  A higher or lower custom compression would be done along with a regular production run (which is about every 3 months).  If you're not in a rush (and wont be the guy calling "is it ready, is it ready?") then sure.  Also keep in mind a cast piston is a fair amount heavier than a forged piston, especially if you're retaining more material on the top (to increase compression).  Also 9.5:1 seems to be the friendliest to tune on California 91 octane.

 

Joe in the UK is running 10.5:1 versions of the cast pistons

http://www.iemotorsport.com/gallery/v/car-of-month/December+2012+-+Joe+Reynolds+-+1600-2+Alpina/

Edited by AceAndrew
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On 5/21/2013 at 7:18 PM, AceAndrew said:

E21 heads were original equipment from mid '75 to late '79 (changed when they went from 2.0L down to 1.8L).


Andrew,

 

I'll certainly defer to you on this topic -- and maybe we're saying the same thing -- but my impression was that the E21 head was developed along with the new e21 cars (introduced ca. May '75 in Europe) and was first installed in U.S. 2002s for the 1976 model year (all production after August '75), but only on 49-state versions. The E21 head, I understood, is what permitted '76 49-state versions to meet EPA standards without the thermal reactor that had been required in (a.) all '75 models and (b.) the CA-only versions of the '76 models.

 

Separately, and this thread helps to un-wind the myth, I've heard multiple knowledgeable people express a belief that E21 heads can only accommodate flat-top pistons. I suspect this belief is rooted in the flat-top 8.0:1 pistons that were standard on all '76 2002s with the E21 head. The low compression ratio facilitated lower emissions and the use of regular gas, but was not dictated by the E21 head. I'm embarrassed to say I don't know the source of the 9.5:1 E21-head pistons Korman installed in my car, but they appear to work just fine.

 

Regards,
 

Steve

 

EDIT: For what it's worth -- and it's not much -- later U.S. sales brochures refer to the E12 head as having "triple-hemispherical combustion chambers" while the E21 head has "dual-hemispherical combustion chambers." An early, ca. 1968, brochure -- possibly referring to a 121 head, advertises "hemispherical swirl-action combustion chambers."

 

post-41123-0-85638600-1369181964_thumb.j

Edited by Conserv
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I'll certainly differ to you on this topic -- and maybe we're saying the same thing -- but my impression was that the E21 head was developed along with the new e21 cars (introduced ca. May '75 in Europe) and was first installed in U.S. 2002s for the 1976 model year (all production after August '75). The E21 head, I understood, is what permitted '76 49-state versions to meet EPA standards without the thermal reactor required in all '75 models and the CA version of the '76 models.

 

I think we're on the same page here, but you've definitely elaborated on it much more than I.

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If I'm reading this thread correctly, this setup that I had in this motor should NOT have worked.

This is a BMW M10 head from a 1978 320i. However, the pistons were not matched to the new cylinder head. They are piano top..,

This setup lasted me almost 5 years, until approximately 1 month ago. .?????

I guess I was just LUCKY!! Halfway across the country in May.

The debate rages on..,,

null-3.jpg

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Its not that it should "not have worked" but rather someone made it "work" like a back-road Afrikaner making the alternator belt from a VW Bug work on a desperate Land Rover.  Worked, but very poorly.  Me thinks you'll be enjoying the incoming Korman engine that much more based on your previous setup.

 

I've learned never to underestimate someones ability to "make it work", but most of the time the next owner spends more time "making it right".

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Its not that it should "not have worked" but rather someone made it "work" like a back-road Afrikaner making the alternator belt from a VW Bug work on a desperate Land Rover.  Worked, but very poorly.  Me thinks you'll be enjoying the incoming Korman engine that much more based on your previous setup.

 

I've learned never to underestimate someones ability to "make it work", but most of the time the next owner spends more time "making it right".

Thanks. Makes total sense now! You are so right. Man, I can hardly wait for that Korman "Done Right" Motor.

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